DNA & Protein Synthesis

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शिक्षकों के लिए: DNA & Protein Synthesis (Biology, AQA) के लिए इस्तेमाल के लिए तैयार लेसन स्लाइड्स, रिवीज़न नोट्स — इन्हें अपने लेसन में इस्तेमाल करें, या टॉपिक को एक इंटरैक्टिव क्लास एक्टिविटी की तरह चलाएं जिसे आपके शिक्षार्थी लाइव गेम की तरह खेलें।

लेसन नोट्स

The Genome and Proteome

The genome is the complete set of genes present in a cell.
The full genome is present in every cell of an organism, but not every gene is expressed; the genes expressed depend on the cell type.
The proteome is the full range of proteins that a cell can produce.
The proteome is usually larger than the genome due to post-translational modification of proteins (often in the Golgi apparatus).
Each gene can produce multiple different proteins via alternative splicing.
Processes such as alternative splicing and protein modification increase the complexity of the proteome from the genome.

Structure of RNA

RNA is a polynucleotide made of many nucleotides linked in a long chain.
RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose) and the bases adenine, guanine, cytosine and uracil (never thymine).
RNA molecules are single-stranded; each strand has a sugar-phosphate backbone and exposed unpaired bases.
mRNA is a transcript copy of a gene that encodes a specific polypeptide; it carries the genetic code from DNA in the nucleus to ribosomes.
tRNA has a folded shape and is single-stranded, but hydrogen bonds between some complementary bases hold the strand together in certain regions.
tRNA has an anticodon complementary to a specific triplet (codon) on mRNA, and a site for a specific amino acid.

Transcription

Protein synthesis occurs in two stages: transcription (DNA is transcribed to produce mRNA) and translation (mRNA is translated to produce an amino acid sequence).
Transcription occurs in the nucleus; a section of DNA unwinds and hydrogen bonds break, catalysed by helicase, exposing the gene.
Free activated RNA nucleotides pair with complementary bases on the template strand via hydrogen bonds.
The non-template (non-transcribed) strand has the same base sequence as the mRNA transcript, but with uracil replacing thymine.
RNA polymerase bonds the sugar-phosphate groups of RNA nucleotides to form the sugar-phosphate backbone of mRNA.
RNA polymerase moves along the template strand in the 3' to 5' direction, so mRNA grows in the 5' to 3' direction.
When transcription is complete, hydrogen bonds between mRNA and DNA break, the DNA re-forms its double helix, and mRNA leaves the nucleus via a nuclear pore.

Eukaryotic and Prokaryotic Transcription

Eukaryotic genomes contain non-coding DNA: non-coding multiple repeats between genes and introns within genes.
Eukaryotic transcription produces pre-mRNA, which contains both introns and exons.
Splicing removes non-coding sections (introns) and joins coding sections (exons) before the pre-mRNA exits the nucleus.
The resulting mature mRNA contains only exons and exits the nucleus to join a ribosome for translation.
Alternative splicing joins different combinations of exons from the same pre-mRNA, so a single eukaryotic gene can code for more than one polypeptide.
In prokaryotes, transcription produces mRNA directly from the DNA template because prokaryotic genes do not contain introns; there is no pre-mRNA stage.
In prokaryotes, transcription and translation are coupled because both occur in the cytoplasm, allowing rapid protein synthesis.

Translation

Translation occurs in the cytoplasm; mRNA attaches to a ribosome after leaving the nucleus.
Free tRNA molecules in the cytoplasm bind with their specific amino acids and bring them to the mRNA on the ribosome.
The anticodon on each tRNA pairs with a complementary codon on the mRNA molecule.
Two tRNA molecules fit onto the ribosome at any one time, bringing their amino acids side by side.
A peptide bond forms between the two amino acids; this requires energy in the form of ATP, provided by mitochondria.
Translation continues until a stop codon on mRNA is reached, signalling termination; the completed amino acid chain forms the final polypeptide.

The Genetic Code and Amino Acid Sequences

The four RNA bases (A, U, C, G) can form 64 different codons, but only 20 amino acids are coded for, so the genetic code is degenerate.
Multiple mRNA codons can encode the same amino acid (e.g., UGU and UGC both code for cysteine), so a change in the genetic code does not necessarily change the amino acid sequence.
The START codon (AUG, coding for methionine in eukaryotic cells) initiates translation at the correct location.
STOP codons (e.g., UAA) terminate translation and do not code for any amino acid.
The genetic code is non-overlapping: each base is read only once in the codon it is part of.
Each amino acid is coded for by a triplet (codon) of 3 nucleotides; the last codon is a STOP codon that does not code for an amino acid.
To calculate the number of amino acids from coding mRNA nucleotides: divide by 3, then subtract 1 for the STOP codon.
To derive an amino acid sequence, convert the DNA template sequence into mRNA codons using complementary base pairing, then use a codon table to translate each codon.

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प्रैक्टिस सवाल

फ्री प्रीव्यू — 56 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.What is meant by the term genome?
Easy
- AThe full range of proteins that a cell can produce
- BThe complete set of genes present in a cell
- CAll the mRNA molecules present in a cell at a given time
- DThe complete set of enzymes coded for by a cell
2.Which statement about the proteome is correct?
Easy
- AThe proteome is usually smaller than the genome
- BThe proteome is always identical in every cell of an organism
- CThe proteome is usually larger than the genome because of post-translational modification and alternative splicing
- DThe proteome contains only proteins coded for by exons
3.Which of the following are true of RNA nucleotides? (select all that apply)
Medium
- AThey contain the pentose sugar ribose
- BThey contain the nitrogenous base thymine
- CThey contain the nitrogenous base uracil
- DThey contain the nitrogenous base adenine
- EThey are always double-stranded
4.tRNA is a single-stranded molecule that is folded into a shape held together by hydrogen bonds between some complementary bases.
Easy
True or false?
5.The proteome of a cell is always smaller than its genome.
Easy
True or false?
6.Which enzyme is responsible for forming the sugar-phosphate backbone of mRNA during transcription?
Easy
- ADNA polymerase
- BHelicase
- CRNA polymerase
- DLigase
7.What is the role of RNA polymerase in transcription?
Medium
- AIt breaks hydrogen bonds between DNA strands
- BIt joins RNA nucleotides together to form the sugar-phosphate backbone of mRNA
- CIt joins amino acids together to form a polypeptide
- DIt removes introns from pre-mRNA
8.Which of the following correctly describes a difference between transcription in prokaryotic and eukaryotic cells?
Medium
- AProkaryotic transcription produces pre-mRNA that requires splicing
- BEukaryotic transcription produces mRNA directly without a pre-mRNA stage
- CProkaryotic transcription produces mRNA directly because prokaryotic genes do not contain introns
- DEukaryotic transcription occurs in the cytoplasm

और सवाल

9.During splicing, what happens to the pre-mRNA molecule?
Medium
- AIntrons are removed and exons are joined together
- BExons are removed and introns are joined together
- CThe entire pre-mRNA molecule is broken down
- DUracil bases are replaced by thymine bases
10.Which of the following is a difference between mRNA and tRNA?
Medium
- AmRNA contains uracil, while tRNA contains thymine
- BmRNA is double-stranded, while tRNA is single-stranded
- CmRNA is a straight molecule, while tRNA has a folded shape
- DmRNA contains ribose, while tRNA contains deoxyribose
11.Which of the following statements about the genetic code is correct?
Medium
- AThe genetic code is degenerate because multiple codons can code for the same amino acid
- BThe genetic code is overlapping because each base is read more than once
- CEach amino acid is coded for by a single codon only
- DThe genetic code is made up of 20 codons
12.A segment of mRNA contains 303 coding nucleotides. How many amino acids will be in the polypeptide produced?
Medium
- A100
- B101
- C102
- D303
13.Which of the following is the correct mRNA sequence coded for by the DNA template strand TAC CCG AAA ACT?
Medium
- AAUG GGC UUU UGA
- BATG GCC TTT TGA
- CTAC CCG AAA ACT
- DUAC CCG AAA ACU
14.During translation, what is the role of the anticodon on a tRNA molecule?
Medium
- AIt carries the genetic code from the nucleus to the ribosome
- BIt pairs with a complementary codon on the mRNA molecule
- CIt catalyses the formation of peptide bonds between amino acids
- DIt signals the start of transcription
15.Which molecule provides the energy required for the formation of a peptide bond during translation?
Medium
- AATP
- BDNA
- CmRNA
- DtRNA
16.Which of the following correctly describes the role of the ribosome in protein synthesis?
Medium
- AIt transcribes DNA into mRNA
- BIt is the site where translation occurs and peptide bonds form
- CIt contains the anticodons that bring amino acids to the mRNA
- DIt splices pre-mRNA to form mature mRNA
17.Which of the following is a correct difference between DNA and RNA?
Medium
- ADNA contains ribose, RNA contains deoxyribose
- BDNA contains thymine, RNA contains uracil
- CDNA is single-stranded, RNA is double-stranded
- DDNA contains uracil, RNA contains thymine
18.The anticodons of two tRNA molecules are UGC and AAC. What is the corresponding sequence of bases on the coding DNA strand?
Medium
- ATGC AAC
- BACG TTG
- CUGC AAC
- DTGC TTG
19.A section of DNA has the sequence TAC GCG TCA ATG ATA CTG on the template strand. What is the sequence of anticodons on the tRNA molecules that would synthesise the polypeptide?
Medium
- AUAC GCG UCA AUG AUA CUG
- BAUG CGC AGU UAC UAU GAC
- CATG CGC AGT TAC TAT GAC
20.Which of the following is the correct order of events during protein synthesis?
Medium
- ATranscription → splicing → translation
- BTranslation → transcription → splicing
- CSplicing → translation → transcription
- DTranscription → translation → splicing
21.Which of the following features apply to transcription but not to replication? (select all that apply)
Medium
- AA double-stranded molecule is produced
- BOnly one strand of DNA acts as a template
- CRNA polymerase is used
- DHydrogen bonds are broken
- EPhosphodiester bonds are formed
22.Which of the following statements about the genome and proteome are correct? (select all that apply)
Medium
- AThe genome is the complete set of genes in a cell
- BThe proteome is the full range of proteins a cell can produce
- CThe genome is usually larger than the proteome
- DAlternative splicing can increase the number of proteins produced from one gene
- EEvery gene is expressed in every cell
23.Which of the following are differences between mRNA and tRNA? (select all that apply)
Medium
- AmRNA is a straight molecule, tRNA is folded
- BmRNA contains uracil, tRNA contains thymine
- CmRNA contains codons, tRNA contains anticodons
- DmRNA is single-stranded, tRNA is double-stranded
- EmRNA is found in the nucleus and cytoplasm, tRNA is found in the cytoplasm
24.The non-template strand of DNA has the same base sequence as the mRNA transcript, except that uracil replaces thymine.
Easy
True or false?
25.In eukaryotic cells, splicing occurs in the cytoplasm after the pre-mRNA leaves the nucleus.
Easy
True or false?
26.The START codon AUG codes for the amino acid methionine in eukaryotic cells.
Easy
True or false?
27.The genetic code is non-overlapping, meaning each base is only read once in the codon that it is part of.
Easy
True or false?
28.RNA polymerase moves along the template strand in the 5' to 3' direction.
Easy
True or false?
29.Match each molecule or structure to its correct description.
Medium
- mRNA
- tRNA
- Ribosome
- RNA polymerase
- Contains codons and carries the genetic code from the nucleus to the ribosome
- Contains an anticodon and brings specific amino acids to the mRNA
- The site where translation occurs and peptide bonds form
- Joins RNA nucleotides together during transcription
30.Place the following events of protein synthesis in the correct order, starting with the earliest.
Medium
- The two strands of a DNA molecule separate
- mRNA nucleotides join with exposed DNA bases to form pre-mRNA
- The introns are spliced from the pre-mRNA to produce mRNA
- The mRNA molecule leaves the nucleus
- A ribosome attaches to the mRNA molecule
- tRNA molecules bring specific amino acids to the mRNA molecule
- Peptide bonds form between the amino acids
31.Match each feature to the process it applies to during protein synthesis or DNA replication.
Medium
- A double-stranded molecule is produced
- Only one strand of DNA acts as a template
- RNA polymerase is used
- Hydrogen bonds between complementary bases are broken
- Replication only
- Transcription only
- Both replication and transcription
32.Which of the following features apply to transcription but not to DNA replication? (select all that apply)
Medium
- AA double-stranded molecule is produced
- BOnly one strand of DNA acts as a template
- CRNA polymerase is used
- DThe product contains uracil instead of thymine
- EHydrogen bonds between complementary bases are broken
33.Which of the following correctly describes the role of RNA polymerase in transcription?
Medium
- AIt joins RNA nucleotides together to form the sugar-phosphate backbone.
- BIt joins DNA nucleotides together to form the sugar-phosphate backbone.
- CIt breaks hydrogen bonds between complementary DNA bases.
- DIt catalyses the formation of peptide bonds between amino acids.
34.A section of DNA has the sequence TAC GCG TCA ATG ATA CTG on the template strand. What is the sequence of anticodons on the tRNA molecules that would synthesise the corresponding polypeptide?
Medium
- AAUG CGC AGU UAC UAU GAC
- BUAC GCG UCA AUG AUA CUG
- CTAC GCG TCA ATG ATA CTG
35.Which of the following statements about the genetic code are correct? (select all that apply)
Medium
- AThe genetic code is degenerate, meaning multiple codons can code for the same amino acid.
- BThe genetic code is overlapping, meaning each base is read more than once.
- CThe START codon AUG codes for methionine.
- DSTOP codons code for amino acids.
- EThe genetic code is non-overlapping.
36.A DNA template strand has the sequence TAC GGG TTC. Which mRNA sequence is transcribed from it?
Medium
- AAUG CCC AAG
- BATG GGG TTC
- CUAC GGG UUC
- DTAC CCC AAG
37.A section of mRNA has 303 coding nucleotides. How many amino acids are in the polypeptide produced?
Medium
- A100
- B101
- C102
- D303
38.Two tRNA anticodons are UAU and GAC. What is the sequence of bases on the corresponding section of the coding DNA strand?
Medium
- ATAT GAC
- BATA CTG
- CUAU GAC
- DTAC GAC
39.A student is asked to write the mRNA sequence for the first five amino acids of lactase: Met, Glu, Leu, Ser, Tyr. They write AUG GAG CCU AGC UAA. Using the genetic code, which of the student's codons do not code for the amino acid they are meant to?
Hard
- AThe codons for Leu and Tyr
- BThe codons for Glu and Leu
- CThe codons for Ser and Tyr
- DThe codon for Tyr only
40.Which of the following features apply to transcription but not to DNA replication?
Medium
- ARNA polymerase is used
- BA double-stranded molecule is produced
- CHydrogen bonds are broken
- DPhosphodiester bonds are formed
41.Name the organelle involved in translation.
Easy
42.Name the process that removes base sequences from pre-mRNA to form mRNA.
Easy
43.Complete the sentence about the genome and proteome.
Easy
The genome is the complete set of ____ present in a cell, while the proteome is the full range of ____ that a cell can produce.
44.Complete the sentence about RNA structure.
Medium
RNA nucleotides contain the pentose sugar ____ instead of deoxyribose, and the nitrogenous base ____ instead of thymine.
45.Complete the sentence about transcription.
Medium
During transcription, the enzyme ____ breaks hydrogen bonds between DNA strands, and the enzyme ____ joins RNA nucleotides together.
46.Complete the sentence about splicing.
Medium
During splicing, the non-coding sections called ____ are removed, and the coding sections called ____ are joined together.
47.Complete the sentence about translation.
Medium
During translation, the ____ on tRNA pairs with a complementary ____ on mRNA.
48.Name the process that removes introns from pre-mRNA to form mRNA.
Easy
49.A polypeptide has 50 amino acids. How many coding nucleotides are in the mRNA that codes for it?
Medium
50.Complete the sentence about the genetic code.
Medium
The genetic code is described as ____ because multiple codons can code for the same amino acid.
51.State the role of RNA polymerase in transcription.
Easy
52.Describe how the process of translation leads to the production of a polypeptide.
Hard
53.Describe how mRNA is produced in the nucleus of a cell.
Hard
54.Give two differences between the structure of mRNA and the structure of tRNA.
Hard
55.Compare the structure of DNA with RNA.
Hard
56.A polypeptide has 50 amino acids. How many coding nucleotides are in the mRNA that codes for it?
Medium
- A168 nucleotides
- B138 nucleotides
- C183 nucleotides
- D153 nucleotides

रिवीज़न नोट्स

## The Genome & Proteome - **Genome** = the complete set of genes present in a cell. The full genome is present in every cell, but not every gene is expressed — which genes are expressed depends on cell type. - **Proteome** = the full range of proteins a cell can produce. It is usually **larger than the genome** because of post-translational modification (often in the Golgi apparatus) and because each gene can produce multiple proteins via **alternative splicing**. ## The Structure of RNA - RNA is a **polynucleotide** — many nucleotides linked in a long chain. - RNA nucleotides contain the bases **A, G, C and uracil (U)** — never thymine (T) — and the pentose sugar **ribose** (not deoxyribose). - RNA molecules are **single-stranded**: a sugar-phosphate backbone with exposed unpaired bases projecting sideways. - **mRNA** is a transcript copy of a gene that encodes a specific polypeptide; it carries the genetic code from DNA in the nucleus to the ribosomes. - **tRNA** has a folded shape; despite looking double-stranded it is single-stranded, held together in regions by hydrogen bonds between complementary bases. It has an **anticodon** (triplet of unpaired bases) at one end and a site for a specific amino acid at the other. There are at least 20 types. ## Transcription - Occurs in the **nucleus**. A section of DNA unwinds — hydrogen bonds between complementary base pairs break ('unzipping'), catalysed by **helicase**. - Free activated RNA nucleotides pair (via hydrogen bonds) with complementary DNA bases on the **template strand**. The other strand is the **non-template (non-transcribed) strand**; its base sequence is the same as the mRNA transcript, but with uracil replacing thymine. - **RNA polymerase** bonds the sugar-phosphate groups together to form the mRNA backbone. It moves along the template strand **3' to 5'**, so mRNA grows **5' to 3'**. - mRNA leaves the nucleus via a pore in the nuclear envelope. ## Eukaryotic & Prokaryotic Transcription - Eukaryotic genomes contain non-coding DNA: **multiple repeats** between genes and **introns** within genes. - Eukaryotes transcribe the whole gene to make **pre-mRNA** (introns + exons). Before leaving the nucleus, **splicing** removes non-coding sections and joins coding sections (exons) — this mature mRNA carries only exons. - **Alternative splicing**: exons can be spliced in different combinations from the same pre-mRNA, so one gene can code for more than one polypeptide. - Prokaryotes: **no pre-mRNA stage** (genes have no introns, so no splicing); transcription produces mRNA directly. Transcription and translation are **coupled** — translation can begin while transcription is in progress (both occur in the cytoplasm), allowing rapid protein synthesis. ## Translation - Occurs in the **cytoplasm** at the **ribosome**. - tRNA molecules bind their specific amino acids and bring them to the mRNA. The anticodon pairs with a complementary **codon** on mRNA. - Two tRNA molecules fit on the ribosome at once, bringing amino acids side by side; a **peptide bond** forms between them (requires **ATP**, provided by mitochondria). - Continues until a **stop codon** is reached; the amino acid chain then forms the final polypeptide. ## Nucleic Acid & Amino Acid Sequence Comparison - 4 bases form **64 codons** but only **20 amino acids** — so the genetic code is **degenerate** (e.g. UGU and UGC both code for cysteine). - **START codon** = AUG, codes for methionine in eukaryotic cells, initiates translation. **STOP codons** (e.g. UAA) terminate translation and code for no amino acid. - The code is **non-overlapping** — each base is read once. - Each amino acid is coded for by a triplet of 3 nucleotides; the last codon is a STOP codon. - **Number of amino acids** = (coding nucleotides ÷ 3) − 1. - To derive an amino acid sequence: convert DNA to mRNA codons by complementary base pairing, then read the codon table left to right.

Genome: The complete set of genes present in a cell.
Proteome: The full range of proteins that a cell can produce.
Transcription: DNA is transcribed, and an mRNA molecule is produced.
Translation: mRNA is translated, and an amino acid sequence is produced.
Template strand: The strand of the DNA molecule that is transcribed.
Non-template (non-transcribed) strand: The strand of the DNA molecule that is not transcribed; its base sequence is the same as the mRNA transcript, but with uracil replacing thymine.
RNA polymerase: The enzyme that bonds the sugar-phosphate groups of RNA nucleotides together to form the sugar-phosphate backbone of the mRNA molecule.
Pre-mRNA: The molecule produced during transcription in eukaryotic cells; it contains the introns and exons of a certain gene.
Splicing: The non-coding sections are removed and the coding sections are joined together.
Alternative splicing: Different combinations of exons are joined together from the same pre-mRNA transcript, meaning a single eukaryotic gene can code for more than one polypeptide chain.
mRNA: A transcript copy of a gene that encodes a specific polypeptide; it carries the genetic code from DNA in the nucleus to the ribosomes.
tRNA: A folded, single-stranded RNA molecule with an anticodon at one end and a site for a specific amino acid at the other; it brings amino acids to the mRNA during translation.
Anticodon: A triplet of unpaired bases on a tRNA molecule, complementary to a specific triplet of bases on an mRNA molecule.
Codon: A triplet of bases on an mRNA molecule that codes for an amino acid.
Degenerate (genetic code): Multiple mRNA codons can encode the same amino acid; e.g. UGU and UGC both code for the amino acid cysteine.
START codon: Marks the start of the protein and initiates translation from the right location; always the amino acid methionine in eukaryotic cells, coded for by the codon AUG.
STOP codons: Cause translation to terminate at the end of the protein and do not code for any amino acids, e.g. UAA.
Non-overlapping (genetic code): Each base is only read once in the codon that it is part of.

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