Regulation Of Gene Expression (A Level Only)

Aprenda jogando

Responda a estas perguntas para ganhar energia, depois pesque e explore. Sem precisar de conta.

Para educadores: slides de aula, resumos de revisão prontos para usar de Regulation Of Gene Expression (A Level Only) (Biology, AQA) — use na sua aula ou rode o tópico como atividade interativa de turma que seus aprendizes jogam como um jogo ao vivo.

Notas de aula

Totipotent Cells

A stem cell is a cell that can divide by mitosis an unlimited number of times.
Each new cell produced can either remain a stem cell or differentiate into a specialised cell, such as a blood or muscle cell.
The ability of stem cells to differentiate into specialised cell types is called potency.
Totipotent cells can divide and produce any body cell, including extra-embryonic cells that make up the placenta.
Totipotent cells exist for a limited time in early mammalian embryos; the zygote and cells up to the 16-cell morula stage are totipotent.
During development, totipotent cells begin to translate only part of their DNA, leading to cell specialisation.
No totipotent cells are present in later stages of development, as cells lose the ability to differentiate into any cell type.

Stem Cells: Potency and Types

Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo, but not into extra-embryonic cells (placenta).
Pluripotent stem cells can divide an unlimited number of times and keep replacing themselves, and can be used in treating human disorders.
Induced pluripotent stem cells (iPS cells) are artificially created from adult somatic cells using appropriate protein transcription factors.
The transcription factors cause specific genes to be expressed, genetically reprogramming the cell to behave like an embryonic stem cell, capable of self-renewal and pluripotency.
Multipotent stem cells can differentiate into a limited range of cell types, all within a specific tissue or organ system (e.g. bone marrow, skin, gut, heart, brain).
Multipotent cells are important in tissue maintenance and repair, and are more specialised than pluripotent cells but still retain the ability to self-renew.
Unipotent cells can only differentiate into their own lineage (one specific cell type) but still retain the ability to self-renew; most cells in animal bodies are unipotent.
An example of unipotent cells is cardiomyocyte (heart muscle cell) formation, where cells only become more cardiomyocytes.

The Use of Stem Cells

Embryonic stem cells are very versatile as they can become any tissue type, offering long-term potential for curative treatments.
Disadvantages of embryonic stem cells include ethical concerns (destruction of embryos), immune rejection risk, and the possibility of forming tumours if cell division is not controlled.
Uses of embryonic stem cells include replacing lost dopamine-producing neurons in Parkinson’s disease, generating insulin-producing β cells in Type 1 diabetes, replacing damaged retinal cells in macular degeneration, and rebuilding nerve connections in spinal cord injury.
Adult stem cells (multipotent) can divide by mitosis but produce a limited range of cell types; they are found in bone marrow (blood cells) and brain (neural and glial cells).
Uses of adult stem cells include bone marrow transplants for leukaemia, skin grafts for burns, and cartilage/bone repair.
Advantages of adult stem cells: no embryo destruction (fewer ethical issues) and lower risk of immune rejection if from the same patient.
Disadvantages of adult stem cells: limited differentiation potential, harder to isolate and grow in large quantities, and may have accumulated mutations over time.
iPS cells offer advantages of no embryo destruction and no risk of immune rejection (made from patient’s own cells), but disadvantages include low efficiency, high cost, and the need for specialised transcription factors and careful culture conditions.

Producing Tissue Cultures of Explants

Creating clones of cauliflowers demonstrates totipotency through the production of tissue culture.
Cauliflower is used because it is mostly actively dividing cells and can withstand being handled.
Many plant cells are totipotent, unlike animal cells, so an entire plant can be reproduced from any of these cells.
A small piece of plant cut for culturing is called an explant, which is grown into a new clone of the original plant.
The technique is used by scientists to reproduce endangered species of plants.
Method: wipe surfaces with disinfectant, soak apparatus in sterilant, cut a thin section of cauliflower floret (about 1 cm) as the explant.
Sterilise the explant by soaking in sterilising solution for 15 minutes, swirling every couple of minutes, to ensure only cauliflower cells are present.
Place explant on agar growth medium containing nutrients and a sterilant, leave on a sunny windowsill for three weeks; growth shows the cells are totipotent.

Regulation of Transcription

Eukaryotes use transcription factors to control gene expression; these are proteins that help control the process of transcription.
Transcription factors either activate or repress the transcription of a particular gene.
Transcription factors enter the nucleus from the cytoplasm through nuclear pores and bind to the promoter region at the start of a gene.
The promoter is a section of DNA upstream of the coding region that is the binding site for proteins that control gene expression.
Binding of transcription factors can either assist or prevent RNA polymerase binding, thus increasing or decreasing the rate of transcription.
Oestrogen is a steroid hormone that functions as a transcription factor; it is small, hydrophobic, and can diffuse through the cell membrane and nuclear pores.
Oestrogen controls up to 100 different genes and is involved in the female fertility cycle and stimulating sperm production in males.
Oestrogen pathway: diffuses into cytoplasm, then nucleus, binds to ERα oestrogen receptor causing conformational change, detaches from protein complex, binds to cofactor, and binds to promoter region to stimulate RNA polymerase and gene transcription.

Evaluating Data about Genetic Expression

Gene expression is the process by which genetic information is used to synthesise proteins or functional RNA molecules.
Investigations often measure mRNA (using RT-PCR or microarrays) or protein levels (using ELISA) under different conditions; higher levels usually indicate increased gene expression.
RNA analysis can identify which genes are expressed in a specific cell, helping determine cell function and differences between healthy and diseased cells.
For example, genes responsible for tumour formation can be detected by analysing over-expressed genes in cancer cells, leading to drugs that block their expression.
A phenotype is the observable characteristic resulting from the interaction between genotype and environment.
Twin studies: monozygotic twins share identical genotypes; differences in phenotype suggest environmental influence.
Adoption studies: comparisons between adopted children and biological vs adoptive families help isolate genetic and environmental contributions.
When evaluating data, consider the strength and direction of correlations, whether results suggest causation or merely association, and the extent to which confounding variables have been controlled.

Epigenetics

Epigenetics involves changes in gene function without changes to the base sequence of DNA.
The epigenome is all of the chemical modifications to all histone proteins and DNA (except base changes) in an organism.
In eukaryotic cells, DNA is wrapped around proteins called histones; histones can be chemically modified by adding acetyl groups, and DNA can be modified by adding methyl groups.
The epigenome is heritable but can undergo change; identical twins become more distinguishable with age because their epigenomes change independently.
Changes to the epigenome are caused by environmental factors such as smoking, stress, exercise and diet, and by internal signalling from the body’s cells.
Chemical modification of histones and DNA controls how tightly DNA is wound; tighter winding ‘switches off’ genes as promoter regions are hidden from transcription factors and RNA polymerase.
Histone modification is reversible and can differ between cell types and vary with age.
Acetylation of histones: acetyl groups (COCH₃) are added to lysine amino acids, removing the positive charge and the ionic bond with DNA’s negative phosphate backbone, so DNA wraps less tightly, allowing RNA polymerase and transcription factors to bind more easily and switching gene expression on.
Methylation of DNA: methyl groups (CH₃) are added to cytosine bases within sequences containing multiple cytosine and guanine bases; this suppresses transcription because methylated bases attract proteins that bind to DNA and inhibit transcription.

Epigenetics & Disease

Epigenetic therapies aim to reverse epigenetic changes to restore normal gene expression; they are promising because epigenetic changes are reversible, unlike mutations.
Epigenetic therapies are being explored for neurological diseases (e.g. Alzheimer’s, schizophrenia), autoimmune diseases, metabolic conditions (e.g. diabetes), infertility and developmental disorders.
Cancer arises from uncontrolled cell division, often caused by mutations or incorrect expression of genes.
DNA in human tumour cells has changes in DNA methylation and histone acetylation, causing tumour suppressor genes to be silenced and oncogenes to be activated, leading to deregulation of the cell cycle and tumour formation.
Cancer treatments can involve drugs that reverse epigenetic changes: removal of methyl groups from tumour suppressor genes enables their expression, so proteins can regulate the cell cycle and stop tumours forming.
Removal of acetyl groups from histones attached to oncogenes causes DNA to wrap more tightly, silencing these genes; reducing oncogene expression stops cancer as faulty cells can die through apoptosis.
DNA demethylating agents (e.g. azacitidine) inhibit DNA methyltransferases to reactivate silenced tumour suppressor genes.
Histone deacetylase (HDAC) inhibitors prevent histone deacetylation, maintaining acetylation so chromatin remains open, increasing expression of beneficial genes like those inducing apoptosis.

RNA Interference

RNA interference (RNAi) is a form of post-transcriptional modification which occurs in the cytoplasm.
RNAi is sequence-specific silencing of gene expression and can be very precise in silencing certain genes.
Small interfering RNAs (siRNAs) are small, double-stranded RNA molecules that bind to mRNA transcribed from target genes because their base sequence is complementary.
Each siRNA is attached to a protein complex which can break down the mRNA, so it cannot be translated into proteins.
RNAi pathway: double-stranded RNA (dsRNA) is produced by RNA-dependent RNA polymerases (RDRs), then hydrolysed into smaller fragments (~23 nucleotides) called siRNAs.
In the cytoplasm, siRNAs bind to protein complexes which use energy from ATP to separate the two strands, exposing bases for complementary base pairing with mRNA.
Once target mRNA leaves the nucleus and enters the cytoplasm, single-stranded siRNA binds to it through complementary base pairing; the mRNA is cut into fragments by the enzyme/protein complex.
Cut mRNA cannot be translated and is broken down into RNA nucleotides by enzymes.
Therapeutic applications: siRNAs against viral genetic material signal its degradation, stopping viral replication; siRNAs can target overexpressed oncogenes in cancer treatment.

Two Types of Tumours

Tumours are groups of abnormal cells that form lumps or growths and can start in any cell in the body.
All tumours may cause harm by damaging the organ in which they are located, causing blockages or obstructions, or damaging other organs by exerting pressure.
Malignant tumours are cancerous; they grow rapidly, invade and destroy surrounding tissues.
Cells within malignant tumours secrete chemicals that cause formation of blood vessels to supply the tumour with nutrients, growth factors and oxygen.
Cells can break off malignant tumours and spread to other parts of the body via the bloodstream or lymphatic system, called metastasis.
Malignant tumours can grow back after surgery; their formation can be initiated by carcinogens such as UV or X-ray exposure, tobacco from cigarettes, asbestos, and processed meat.
Benign tumours are not cancerous; they grow slowly, do not invade other tissues, and do not metastasise.
Benign tumours can cause damage by blockages or pressure, but do not usually grow back after removal; they can be initiated by inflammation, infection, injury, diet, genetics, toxins and radiation.
Examples of benign tumours include polyps in the nose, colon and ovaries, non-cancerous brain tumours, and warts caused by viral infection.

Tumour Development

Cancer arises from uncontrolled mitosis due to mutations in genes regulating the cell cycle; cancerous cells divide uncontrollably, forming a tumour.
Mutations in genes that regulate cell division can lead to cancer; these genes may become oncogenes.
Most mutations either result in early cell death or the cell being destroyed by the immune system, so they usually have no harmful effect.
Harmful mutations that escape these mechanisms can be passed to all descendant cells; carcinogens (e.g. UV, tobacco tar, X-rays) increase mutation risk.
Tumour suppressor genes are normal genes encoding proteins that repair DNA, slow the cell cycle at checkpoints, and signal apoptosis if damage is irreparable.
Mutations or epigenetic silencing of tumour suppressor genes can lead to tumour formation; BRCA-1 is a tumour suppressor gene mainly expressed in breast tissue, and reduced expression leads to breast cancer.
Proto-oncogenes code for proteins that stimulate cell growth and differentiation; mutation can convert them into oncogenes, causing constant activation of proteins that stimulate cell growth and division, speeding up the cell cycle.
Oncogene activation can occur via inversion or translocation mutations on a proto-oncogene, leading to increased gene expression or protein production that cannot be switched off.
Abnormal methylation: increased methylation of tumour suppressor genes silences them (transcription factors cannot bind), so tumour suppressor proteins are not synthesised; reduced methylation of proto-oncogenes increases expression, making the gene behave like an oncogene even without mutation.
Oestrogen-dependent breast tumours: high oestrogen concentrations can lead to breast cancer; ~70% of breast tumours are oestrogen receptor-positive. The drug tamoxifen is a competitive inhibitor of oestrogen, binding ERα receptor and preventing gene activation, inhibiting tumour growth.

Slides

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

CADASTRE-SE — GRÁTIS ENTRAR

Questões de prática

Prévia grátis — 8 de 55 perguntas. Cadastre-se para ver todas.

1.Which row correctly describes totipotent cells?
Medium
- AThey can divide and produce any body cell, including the cells that make up the placenta
- BThey can differentiate into any cell type found in an embryo but not into extra-embryonic cells
- CThey can differentiate into a limited range of cell types within one tissue or organ system
- DThey can differentiate into only one specific cell type but can still self-renew
2.Pluripotent stem cells can differentiate into any cell type found in an embryo, but they cannot differentiate into which cells?
Medium
- AExtra-embryonic cells that make up the placenta
- BNerve cells
- CMuscle cells
- DSkin cells
3.Totipotent cells are present throughout the later stages of human development.
Easy
True or false?
4.Which of the following are advantages of using induced pluripotent stem (iPS) cells rather than embryonic stem cells? (select all that apply)
Medium
- ANo embryos are destroyed, so there are fewer ethical issues
- BThey can be made from the patient's own cells, so there is no risk of immune rejection
- CConverting adult somatic cells into iPS cells is very efficient
- DThey are cheap to produce because no specialised transcription factors are needed
- EThey are tailored to the individual, which supports personalised medicine
5.Match each type of stem cell to the range of cell types it can differentiate into.
Medium
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
- Any body cell, including the cells of the placenta
- Any cell type found in an embryo, but not extra-embryonic cells
- A limited range of cell types within a specific tissue or organ system
- Only one specific cell type, but the cell can still self-renew
6.Most cells in an animal's body are unipotent.
Easy
True or false?
7.A transcription factor is best described as which of the following?
Medium
- AA protein that binds to the promoter region of a gene and controls the rate of transcription
- BA section of DNA upstream of the coding region that is the binding site for regulatory proteins
- CA small, hydrophobic steroid hormone that diffuses through the cell surface membrane
- DAn enzyme that joins nucleotides together during the process of translation
8.Transcription factors can only increase the rate of transcription of a gene.
Easy
True or false?

Mais perguntas

9.Which statement correctly describes epigenetics?
Medium
- AHeritable changes in gene function without any change to the base sequence of DNA
- BChanges to the base sequence of DNA that alter the protein produced
- CThe removal of introns from mRNA before translation
- DThe random alignment of chromosomes during meiosis
10.Which of the following environmental factors can cause epigenetic changes? (select all that apply)
Medium
- ASmoking
- BDiet
- CExercise
- DStress
- ERandom alignment of chromosomes at meiosis
11.Acetylation of histones increases gene expression. Which statement explains why?
Medium
- AAdding acetyl groups removes positive charges on lysine, so the DNA wraps less tightly and RNA polymerase can bind more easily
- BAdding acetyl groups increases the positive charge on lysine, so the DNA wraps more tightly around the histones
- CAdding acetyl groups to cytosine bases attracts proteins that inhibit transcription
- DAdding acetyl groups cuts the mRNA into fragments so it cannot be translated
12.What is the effect of DNA methylation on gene expression?
Medium
- AIt suppresses transcription because methylated bases attract proteins that bind to the DNA and inhibit transcription
- BIt increases transcription because the DNA wraps less tightly around the histones
- CIt has no effect because the base sequence of the DNA is unchanged
- DIt increases transcription because RNA polymerase binds more easily to the promoter
13.Identical twins become more distinguishable with age because their epigenomes change independently even though their DNA is the same.
Easy
True or false?
14.At which point in protein synthesis does RNA interference take effect?
Medium
- AAfter transcription, in the cytoplasm, before translation
- BDuring transcription, in the nucleus
- CDuring translation, at the ribosome
- DBefore transcription, at the promoter region
15.Why do siRNAs only affect specific genes or parts of genes?
Medium
- AThe siRNA base sequence is complementary to the mRNA of the target gene, so it can only bind to that mRNA
- BThe siRNA binds to the promoter region of the target gene
- CThe siRNA is complementary to the DNA coding strand of the target gene
- DThe siRNA is complementary to the protein produced by the target gene
16.Which of the following is a mutagenic agent that could cause a mutation leading to tumour development?
Medium
- AUltraviolet radiation
- BATP
- CAmylase
- DWater
17.Which row correctly pairs a type of tumour with a characteristic?
Medium
- AMalignant — cells can break off and spread to other parts of the body through the bloodstream or lymphatic system
- BMalignant — grows slowly and does not invade other tissues
- CBenign — cells metastasise to other organs
- DBenign — always grows back after surgical removal
18.Which statements about tumour suppressor genes are correct? (select all that apply)
Medium
- AThey are normal genes that encode proteins which repair DNA
- BThey encode proteins that slow the cell cycle at checkpoints
- CThey encode proteins that signal apoptosis if damage is irreparable
- DIncreased methylation of tumour suppressor genes increases their expression
- EBRCA-1 is an example of a tumour suppressor gene mainly expressed in breast tissue
19.A mutation occurs in a gene that codes for a transcription factor which activates a tumour suppressor gene. How could this mutation lead to tumour growth?
Hard
- AThe transcription factor is no longer functional, so the tumour suppressor gene is not transcribed, the cell cycle is not slowed and cells divide uncontrollably
- BThe transcription factor becomes permanently active, so the tumour suppressor gene is over-expressed and the cell cycle stops
- CThe transcription factor is converted into an oncogene, which directly repairs damaged DNA
- DThe transcription factor binds to the promoter of an oncogene and prevents its expression
20.Benign tumours are cancerous and can metastasise to other parts of the body.
Easy
True or false?
21.Mutations in proto-oncogenes can convert them into oncogenes. What is the effect of this?
Medium
- AConstant activation of proteins that stimulate cell growth and division, speeding up the cell cycle
- BSilencing of the gene so cell division is slowed
- CRepair of damaged DNA and triggering of apoptosis
- DIncreased methylation of the gene so transcription factors cannot bind
22.Increased methylation of a tumour suppressor gene can lead to cancer. Which statement best explains how?
Hard
- AThe gene is silenced because transcription factors cannot bind, so the tumour suppressor protein is not synthesised
- BThe gene is activated because transcription factors bind more easily, so too much tumour suppressor protein is made
- CThe base sequence of the gene is changed, producing a faulty tumour suppressor protein
- DThe gene is converted into an oncogene, which stimulates cell division
23.Place the steps of the RNA interference pathway in the correct order, starting with the production of double-stranded RNA.
Medium
- Double-stranded RNA is produced by RNA-dependent RNA polymerases
- dsRNA is hydrolysed into smaller fragments called siRNAs
- siRNAs bind to protein complexes which use ATP to separate the two strands
- Single-stranded siRNA binds to the target mRNA by complementary base pairing
- The mRNA is cut into fragments and broken down into RNA nucleotides
24.The drug tamoxifen is used in the treatment of oestrogen-dependent breast tumours. How does tamoxifen work?
Medium
- AIt acts as a competitive inhibitor of oestrogen by binding the ERα receptor and preventing gene activation
- BIt increases the concentration of oestrogen so that more cell cycle genes are expressed
- CIt adds methyl groups to the DNA of tumour suppressor genes
- DIt cuts the mRNA of oncogenes into fragments in the cytoplasm
25.Which of the following are ways in which all tumours may cause harm to the body? (select all that apply)
Medium
- ADamaging the organ in which the tumour is located
- BCausing blockages or obstructions
- CDamaging other organs by exerting pressure
- DRepairing damaged DNA in surrounding cells
- ETriggering apoptosis of the tumour cells
26.Which of the following is the best definition of a stem cell?
Medium
- AA cell that can divide by mitosis an unlimited number of times, whose new cells can remain stem cells or differentiate
- BA cell that has lost the ability to divide and carries out one specialised function
- CA cell produced by meiosis that is genetically different from its parent cell
- DA cell that can only differentiate into one specific cell type and cannot self-renew
27.The zygote formed when a sperm cell fertilises an egg cell is totipotent.
Easy
True or false?
28.Which statement about epigenetic cancer therapies is correct?
Hard
- ARemoval of methyl groups from the DNA of tumour suppressor genes enables the genes to be expressed so the proteins can regulate the cell cycle
- BRemoval of acetyl groups from histones attached to oncogenes causes the DNA to wrap less tightly, increasing oncogene expression
- CDNA demethylating agents add methyl groups to reactivate silenced tumour suppressor genes
- DHistone deacetylase inhibitors prevent acetylation so that chromatin remains open
29.Which of the following explains why cauliflower is used to demonstrate totipotency in tissue culture?
Medium
- AIt is comprised mostly of actively dividing cells and can withstand being handled
- BIt contains no DNA in its cells so it cannot be contaminated
- CIts cells are unipotent and can only form more cauliflower cells
- DIt is an animal tissue that can be grown in agar
30.Why are all apparatus and surfaces sterilised when producing a tissue culture from a cauliflower explant?
Medium
- ATo ensure no fungi contaminate the experiment, which would result in fungal growth rather than explant growth
- BTo speed up the rate at which the explant cells divide
- CTo remove the DNA from the cauliflower cells
- DTo increase the concentration of nutrients in the agar
31.In an investigation, mRNA concentrations for a particular gene were measured in two cell types. Cell type P had a much higher mRNA concentration than cell type Q. Which conclusion is best supported?
Hard
- AThe gene is expressed at a higher level in cell type P than in cell type Q
- BThe gene is mutated in cell type P
- CCell type P contains more DNA than cell type Q
- DThe protein produced by the gene is inactive in cell type P
32.Which of the following are advantages of using adult stem cells rather than embryonic stem cells? (select all that apply)
Medium
- ANo embryo destruction, so there are fewer ethical issues
- BLower risk of immune rejection if the cells come from the same patient
- CThey have unlimited differentiation potential and can form any cell type
- DThey are easy to isolate and grow in large quantities
- EThey are already used successfully in a variety of treatments
33.The modification of histones is reversible and can therefore be different in different cell types and can vary with age.
Medium
True or false?
34.Which of the following correctly describes metastasis?
Medium
- ACells break off a malignant tumour and spread to other parts of the body through the bloodstream or lymphatic system
- BA benign tumour grows slowly and exerts pressure on surrounding organs
- CA tumour suppressor gene is silenced by increased methylation
- DA proto-oncogene is converted into an oncogene by a carcinogen
35.In an experiment, genetically identical plants were grown at two different temperatures and showed different phenotypes. Which conclusion is best supported by this result?
Hard
- AThe environment contributes to the phenotype, since genetically identical organisms show phenotypic variation
- BThe phenotype is determined entirely by the genotype
- CThe differences are caused by mutations in the DNA base sequence
- DThe differences are caused by meiosis producing genetic variation
36.A gene is heavily methylated in a patient's tumour cells but not in their healthy cells. Which statement best explains how this could contribute to tumour formation?
Hard
- AMethylation of a tumour suppressor gene silences it, so the protein that slows the cell cycle is not produced and cells divide uncontrollably
- BMethylation of a proto-oncogene increases its expression, so more protein that slows the cell cycle is produced
- CMethylation changes the base sequence of the gene, producing a faulty protein
- DMethylation of the gene increases the binding of transcription factors, so the gene is over-expressed
37.Match each type of stem cell with its correct level of potency.
Medium
- Totipotent
- Pluripotent
- Multipotent
- Unipotent
- Can differentiate into any body cell type
- Can differentiate into any cell type found in an embryo, but not extra-embryonic cells
- Can differentiate into a limited range of cell types within a specific tissue
- Can differentiate into only one specific cell type
38.Place the stages of the oestrogen stimulation pathway in the correct order.
Medium
- Oestrogen diffuses through the cell surface membrane into the cytoplasm
- Oestrogen diffuses through a nuclear pore into the nucleus
- Oestrogen attaches to an ERα oestrogen receptor held within a protein complex, causing a conformational change
- The ERα oestrogen receptor detaches from the protein complex and diffuses towards the gene
- The ERα oestrogen receptor binds to a cofactor and then to the promoter region, stimulating RNA polymerase binding and transcription
39.Which of the following statements about the epigenome are correct? (select all that apply)
Medium
- AIt includes all chemical modifications to histones and DNA, excluding changes to the base sequence
- BIt is heritable but can undergo change
- CIt is fixed at birth and remains identical throughout life
- DIdentical twins can become more distinguishable with age due to independent changes in their epigenomes
- EIt only involves methylation of DNA, not histone modifications
40.Which of the following are roles of proteins encoded by tumour suppressor genes? (select all that apply)
Hard
- ARepairing DNA
- BSlowing the cell cycle at checkpoints
- CSignalling apoptosis if DNA damage is irreparable
- DStimulating cell growth and division
- EActivating oncogenes
41.Give the term for a cell that can divide by mitosis an unlimited number of times and whose daughter cells can remain stem cells or differentiate into specialised cells.
Easy
42.Complete the table entries describing types of stem cell by filling in each gap.
Easy
Embryonic stem cells taken from an embryo after the first few cell divisions are ____. Cells taken from an embryo that can become any type of cell apart from the cells of the placenta are ____. Adult stem cells found in bone marrow are ____. Heart muscle cells that can only become more heart muscle cells are ____.
43.Give the term for a type of artificially created stem cell produced from adult somatic cells using appropriate protein transcription factors.
Easy
44.Complete the description of the oestrogen stimulation pathway by filling in each gap.
Medium
Oestrogen diffuses through the cell surface membrane into the cytoplasm and then through a ____ into the nucleus. In the nucleus it attaches to an ____ receptor held within a protein complex, causing the receptor to undergo a ____ change. The receptor then detaches, binds a cofactor and binds to the ____ region of the gene, stimulating RNA polymerase binding and gene transcription.
45.Complete the description of the RNA interference pathway by filling in each gap.
Medium
Double-stranded RNA is hydrolysed into smaller fragments roughly 23 nucleotides long called small interfering RNAs (siRNAs). In the cytoplasm, siRNAs bind to protein complexes which use energy from ____ to separate the two strands of the siRNA. Single-stranded siRNA then binds to the target ____ through complementary base pairing, and the mRNA is cut into fragments so it cannot be ____.
46.Complete the table showing how bases pair between mRNA and siRNA by filling in each gap.
Medium
Adenine in mRNA pairs with ____ in siRNA. Cytosine in mRNA pairs with ____ in siRNA. Adenine in mRNA is complementary to ____ on the original DNA nucleotide in the gene.
47.Small interfering RNAs (siRNAs) are produced when double-stranded RNA is hydrolysed into smaller fragments. Give the approximate length of these fragments, in nucleotides.
Medium
48.Give the term for the section of DNA upstream of the coding region that is the binding site for proteins controlling the expression of a gene.
Easy
49.Complete the sentence about the epigenome by filling in each gap.
Easy
All of the chemical modifications to all ____ proteins and DNA (except base changes) in an organism are called the ____.
50.Explain what is meant by the term epigenetic in the context of gene expression.
Medium
51.Some substances found in red meat could potentially lead to genetic mutation. Describe and explain how these substances might increase the chance of getting colon cancer.
Hard
52.Explain how a transcription factor might function as a repressor rather than an activator.
Hard
53.Explain why the use of embryonic stem cells is more controversial than the use of adult stem cells.
Hard
54.Describe what is meant by siRNAs and explain how they can silence the genes involved in the replication of a virus.
Medium
55.Small interfering RNAs (siRNAs) are produced when double-stranded RNA is hydrolysed into smaller fragments. Give the approximate length of these fragments, in nucleotides.
Medium
- A25 nucleotides
- B27 nucleotides
- C23 nucleotides
- D21 nucleotides

Resumos de revisão

## Totipotent Cells and Potency - **Stem cell**: a cell that can divide (by mitosis) an unlimited number of times; each new cell can remain a stem cell or differentiate into a specialised cell. - **Potency** = ability to differentiate into specialised cell types. Three types: - **Totipotent**: can divide and produce any body cell; also called embryonic stem cells. Exist for a limited time in early mammalian embryos and in extra-embryonic cells (placenta). The zygote and cells up to the 16-cell stage (morula) are totipotent. Initially unspecialised; during development they translate only part of their DNA, causing specialisation. No totipotent cells in later stages. - **Pluripotent**: embryonic stem cells that can differentiate into any cell type found in an embryo, but not extra-embryonic cells (placenta). Can divide unlimited times and self-renew. - **Multipotent**: can differentiate into a limited range of cell types within a specific tissue/organ system (e.g. bone marrow, skin, gut, heart, brain). Important in tissue maintenance and repair. - **Unipotent**: adult cells that can only differentiate into their own lineage (one specific cell type), but retain self-renewal. Most cells in animal bodies are unipotent. Example: cardiomyocytes (heart muscle cells). ## Induced Pluripotent Stem Cells (iPS) - Artificially created from adult somatic cells using appropriate protein transcription factors. - Transcription factors cause specific genes to be expressed, genetically reprogramming the cell to behave like embryonic stem cells. - Capable of self-renewal and pluripotency. Mimic embryonic stem cells without ethical concerns. ## Uses of Stem Cells - **Embryonic**: Parkinson’s (replace dopamine-producing neurons), Type 1 diabetes (insulin-producing beta cells), macular degeneration (retinal cells), spinal cord injury (nerve connections). Advantages: versatile, long-term curative potential. Disadvantages: ethical concerns (embryo destruction), immune rejection risk, can form tumours. - **Adult (multipotent)**: leukaemia (bone marrow transplants), burns/skin grafts, cartilage/bone repair. Advantages: no embryo destruction, lower rejection if same patient. Disadvantages: limited differentiation, harder to isolate/grow, may have accumulated mutations. - **iPS**: similar uses to embryonic; disease modelling, drug testing. Advantages: no embryo destruction, no immune rejection, personalised. Disadvantages: low efficiency, high cost. ## Producing Tissue Cultures of Explants - Cauliflower explants demonstrate totipotency. Many plant cells are totipotent. - Method: sterile conditions; cut thin section (explant) ~1cm; sterilise 15 min; place on agar growth medium with sterilant; leave on sunny windowsill 3 weeks. Result: clone of cauliflower. ## Regulation of Transcription - **Transcription factors**: proteins that help control transcription; activate or repress. - Enter nucleus via nuclear pores; bind to **promoter region** (DNA upstream of coding region) at start of gene. Binding allows or prevents RNA polymerase binding. - **Oestrogen** example: steroid hormone, hydrophobic, diffuses through cell membrane and nuclear pore. Binds ERα oestrogen receptor in protein complex → conformational change → detaches → binds cofactor → binds promoter → stimulates RNA polymerase binding and gene transcription. Controls up to 100 genes. ## Evaluating Data about Genetic Expression - **Gene expression**: process by which genetic information is used to synthesise proteins or functional RNA molecules. - Data types: mRNA concentrations (RT-PCR, microarrays), protein levels (ELISA), comparative data. Higher mRNA/protein usually = increased expression. - RNA analysis: match RNA to specific genes to determine which genes are expressed; can find cell function and differences between healthy and diseased cells. - **Phenotype** = observable characteristic resulting from interaction between genotype and environment. - Twin studies (monozygotic share identical genotypes; differences suggest environmental influence); adoption studies; environmental manipulation experiments. - Evaluate: strength/direction of correlations, causation vs association, confounding variables. ## Epigenetics - **Epigenetics**: changes in gene function, without changes to the base sequence of DNA. - **Epigenome**: all chemical modifications to all histone proteins and DNA (except base changes) in an organism. Heritable but can change. - DNA wrapped around **histones**. Chemical modification controls how tightly DNA is wound; tighter winding = genes 'switched off' (hidden from transcription factors and RNA polymerase). Reversible. - Environmental factors: smoking, stress, exercise, diet; internal signalling. - **Acetylation of histones**: acetyl groups (COCH₃) added to lysine amino acids. Lysine has positively charged R group forming ionic bonds with negatively charged phosphate backbone of DNA. Adding acetyl removes positive ion and bond → DNA wraps less tightly → RNA polymerase and transcription factors bind more easily → gene expression switched on. Deacetylation inhibits transcription. - **Methylation of DNA**: methyl groups (CH₃) added to cytosine bases within sequences with multiple cytosine and guanine bases. Suppresses transcription; methylated bases attract proteins that bind to DNA and inhibit transcription. ## Epigenetics & Disease - Epigenetic therapies aim to reverse epigenetic changes to restore normal gene expression; promising because reversible (unlike mutations). - Cancer: uncontrolled cell division; tumour cells have changes in DNA methylation and histone acetylation causing tumour suppressor genes silenced and oncogenes activated. - Treatments: drugs reversing epigenetic changes (removal of acetyl and methyl tags). Removal of methyl groups from tumour suppressor genes enables expression → proteins regulate cell cycle. Removal of acetyl groups from histones attached to oncogenes causes tighter wrapping, silencing them → faulty cells die by apoptosis. - DNA demethylating agents inhibit DNA methyltransferases (e.g. azacitidine). HDAC inhibitors prevent histone deacetylation, maintaining acetylation, chromatin open, increased expression of beneficial genes. ## RNA Interference (RNAi) - Post-transcriptional modification in cytoplasm; sequence-specific silencing. - **siRNA**: small, double-stranded RNA molecules (~23 nucleotides) that bind to mRNA via complementary base pairing. - Pathway: dsRNA produced by RDRs → hydrolysed into siRNAs → bind protein complexes using ATP to separate strands → single-stranded siRNA binds target mRNA in cytoplasm → mRNA cut into fragments by protein complex → cannot be translated → fragments broken down into RNA nucleotides. - Therapeutic: siRNAs against viral genetic material stop virus replication; target oncogenes in cancer treatment. ## Two Types of Tumours - **Malignant**: cancerous; grow rapidly, invade and destroy surrounding tissues; secrete chemicals causing blood vessel formation; cells can break off and spread via bloodstream/lymphatic system (**metastasis**); can grow back after surgery. Carcinogens: UV/X-ray, tobacco, asbestos, processed meat. - **Benign**: not cancerous; grow slowly; do not invade or metastasise; can cause damage by blockages or pressure; usually do not grow back. Causes: inflammation/infection, injury, diet, genetics, toxins/radiation. Examples: polyps, non-cancerous brain tumours, warts. ## Tumour Development - Cancer arises from uncontrolled mitosis due to mutations in genes regulating cell cycle. - **Tumour suppressor genes**: normal genes encoding proteins that repair DNA, slow cell cycle at checkpoints, signal apoptosis if damage irreparable. Mutations or epigenetic silencing → tumour formation. BRCA-1 repairs damaged DNA or triggers apoptosis; reduced expression → breast cancer. - **Proto-oncogenes**: code for proteins stimulating cell growth and differentiation. Mutation converts to **oncogenes** → constant activation → speeds up cell cycle. If apoptosis proteins affected, tumours form. Activation via inversion/translocation → increased gene expression or protein cannot be switched off. - **Abnormal methylation**: increased methylation of tumour suppressor genes silences them (transcription factors cannot bind) → no tumour suppressor proteins → tumour formation. Reduced methylation of proto-oncogenes increases expression → behaves like oncogene without mutation. - **Oestrogen-dependent breast tumours**: high oestrogen upregulates transcription via ERα receptor; ~70% of breast tumours are oestrogen receptor-positive. Tamoxifen is competitive inhibitor of oestrogen: binds ERα receptor, prevents gene activation, inhibits tumour growth.

Stem cell: A cell that can divide (by mitosis) an unlimited number of times; each new cell has the potential to remain a stem cell or develop into a specialised cell.
Totipotent: Can divide and produce any body cell; also called embryonic stem cells; exist for a limited time in early mammalian embryos and in extra-embryonic cells (placenta).
Pluripotent: Embryonic stem cells that can differentiate into any cell type found in an embryo, but not extra-embryonic cells (placenta).
Multipotent: Stem cells that can differentiate into a limited range of cell types, all within a specific tissue or organ system.
Unipotent: Adult cells that can only differentiate into their own lineage (one specific cell type), but retain the ability to self-renew.
Induced pluripotent stem cells (iPS cells): Artificially created stem cells produced from adult somatic cells using appropriate protein transcription factors; capable of self-renewal and pluripotency.
Transcription factor: A protein that helps control the process of transcription; either activates or represses transcription of a particular gene.
Promoter: A section of DNA upstream of the coding region that is the binding site for proteins that control the expression of the gene.
Gene expression: The process by which genetic information is used to synthesise proteins or functional RNA molecules.
Epigenetics: Changes in gene function, without changes to the base sequence of DNA.
Epigenome: All of the chemical modifications to all histone proteins and DNA (except base changes) in an organism.
Acetylation of histones: Addition of acetyl groups (COCH₃) to lysine amino acids on histone proteins; removes positive charge and ionic bond with DNA, so DNA wraps less tightly, allowing RNA polymerase and transcription factors to bind more easily, switching gene expression on.
Methylation of DNA: Addition of methyl groups (CH₃) to cytosine bases within sequences containing multiple cytosine and guanine bases; suppresses transcription as methylated bases attract proteins that bind to DNA and inhibit transcription.
RNA interference (RNAi): A form of post-transcriptional modification which occurs in the cytoplasm; sequence-specific silencing of gene expression.
siRNA: Small, double-stranded RNA molecules (~23 nucleotides) that bind to mRNA via complementary base pairing, leading to mRNA breakdown and preventing translation.
Malignant tumour: A cancerous tumour that grows rapidly, invades and destroys surrounding tissues, can metastasise, and can grow back after surgery.
Benign tumour: A non-cancerous tumour that grows slowly, does not invade other tissues or metastasise, and usually does not grow back after removal.
Metastasis: The spread of cancer cells from a malignant tumour to other parts of the body through the bloodstream or lymphatic system.
Tumour suppressor genes: Normal genes which encode proteins that repair DNA, slow the cell cycle at checkpoints, and signal apoptosis if damage is irreparable.
Oncogenes: Genes formed by mutation of proto-oncogenes that cause constant activation of proteins stimulating cell growth and division, speeding up the cell cycle.
Proto-oncogenes: Genes that code for proteins that stimulate cell growth and differentiation; mutation can convert them into oncogenes.
Carcinogens: Agents that increase mutation risk, such as UV, tobacco tar, X-rays, asbestos, processed meat.

Unlock all 55 questions & more

Crie uma conta grátis para ver todas as perguntas, os slides, flashcards e resumos de revisão deste tópico.

CADASTRE-SE — GRÁTIS ENTRAR

Provas anteriores

A prática com provas anteriores deste tópico chega em breve.

Em breve