Protein Synthesis

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शिक्षकों के लिए: Protein Synthesis (Biology, HL) 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

Transcription: DNA to mRNA

Transcription is the first stage of protein synthesis, occurring in the nucleus; it produces an mRNA molecule from a gene.
The DNA double helix unwinds and hydrogen bonds between complementary bases break, exposing the gene to be transcribed.
Free RNA nucleotides pair with complementary bases on the template strand of DNA.
RNA polymerase bonds the sugar-phosphate groups of RNA nucleotides to form the mRNA backbone.
The mRNA strand separates from DNA, and the DNA double helix re-forms.
mRNA leaves the nucleus through a nuclear pore; DNA is too large to leave.
In RNA, uracil replaces thymine and pairs with adenine; cytosine pairs with guanine.

Protein synthesis

The Genetic Code

The genetic code is a triplet code: each sequence of three DNA bases (a triplet) codes for one amino acid.
There are 20 different amino acids used to build proteins.
The code is degenerate (redundant): multiple codons can code for the same amino acid, which can limit the effect of mutations.
The code is non-overlapping: each base is read only once as part of a codon.
The code is universal: almost all organisms use the same triplet codes for the same amino acids, enabling genetic engineering.
Some triplets code for start (TAC – methionine) and stop signals, marking where genes begin and end.
A codon is a sequence of three mRNA bases that codes for a specific amino acid; a triplet is the corresponding three DNA bases.

Translation: mRNA to Polypeptide

Translation occurs in the cytoplasm on ribosomes and synthesises a polypeptide from the mRNA code.
Ribosomes are made of proteins and ribosomal RNA (rRNA) and consist of a large and a small subunit.
The small subunit binds mRNA; two tRNA molecules can bind to the large subunit at once.
tRNA molecules carry specific amino acids to the ribosome; their anticodon pairs with a complementary codon on mRNA.
A peptide bond forms by condensation between adjacent amino acids; this is an anabolic reaction requiring ATP.
The ribosome moves along the mRNA one codon at a time until a stop codon is reached, releasing the polypeptide.

Mechanism of Transcription

Transcription occurs in three stages: initiation, elongation and termination.
During initiation, RNA polymerase binds near the promoter, causing DNA strands to separate.
During elongation, RNA polymerase moves along the template strand and adds the 5' end of free RNA nucleotides to the 3' end of the growing mRNA.
RNA is synthesised in a 5' to 3' direction; mRNA is also read 5' to 3' during translation.
Termination occurs when RNA polymerase reaches a terminator sequence, detaching the enzyme and mRNA.
Transcription factors bind to specific DNA sequences to regulate transcription, ensuring correct genes are expressed at the right time.

Post-Transcriptional Modification

In eukaryotes, the initial mRNA transcript is pre-mRNA, which must be modified to form mature mRNA.
A methylated cap is added to the 5' end to protect against degradation by exonucleases.
A poly-A tail (long chain of adenine nucleotides) is added to the 3' end for protection and to help the transcript exit the nucleus.
Introns (non-coding sequences) are removed and exons (coding sequences) are joined together in a process called splicing.
Alternative splicing allows different mature mRNAs to be produced from the same gene, increasing the size of the proteome compared to the genome.
Prokaryotic mRNA does not require significant post-transcriptional modification; translation can occur immediately.

Protein Structure & Mutations

A gene mutation is a change in the DNA base sequence; it may result in a new allele.
Mutations occur randomly, often as copying errors during DNA replication in S phase of interphase.
Point mutations alter a single base and can change one amino acid in the polypeptide.
Sickle cell disease is caused by a point mutation: DNA triplet GAG changes to GTG on the coding strand, leading to mRNA codon GUG instead of GAG.
This results in valine replacing glutamic acid at position 6 of the β-globin polypeptide, altering haemoglobin structure and function.
Sickle-shaped red blood cells have reduced oxygen-carrying capacity and can block capillaries, causing pain, fatigue and anaemia.
Mutations in gametes can be inherited; mutations in body cells are not inherited.

The sickle cell mutation

Translation & the Proteome

Translation is divided into initiation, elongation and termination.
Initiation: the small ribosomal subunit binds the 5' end of mRNA; initiator tRNA carrying methionine binds at the P site; the ribosome moves to a start codon (AUG); the large subunit joins.
Ribosomes have three tRNA binding sites: A (aminoacyl), P (peptidyl) and E (exit).
Elongation: tRNAs bring amino acids; peptide bonds form between amino acids; the ribosome moves along mRNA one codon at a time.
tRNA molecules are single-stranded, fold into a clover shape via hydrogen bonds, and are about 80 nucleotides long; there are 20 types, one for each amino acid.
After translation, polypeptides often require modification (e.g., folding, disulfide bond formation) to become functional proteins.
Proteasomes recycle unneeded, damaged or misfolded proteins; ubiquitin tags proteins for breakdown.

स्लाइड्स

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साइन अप करें — फ्री लॉग इन

प्रैक्टिस सवाल

फ्री प्रीव्यू — 61 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.Which molecule carries the genetic code from the nucleus to the cytoplasm?
Easy
- ADNA
- BmRNA
- CtRNA
- DrRNA
2.The genetic code is non-overlapping, meaning each base is read only once as part of a codon.
Easy
True or false?
3.Which enzyme is responsible for catalysing transcription?
Easy
- ADNA polymerase
- BRNA polymerase
- CHelicase
- DLigase
4.Which of the following correctly describes a codon?
Medium
- AA sequence of three DNA bases that codes for an amino acid
- BA sequence of three mRNA bases that codes for an amino acid
- CA sequence of three tRNA bases that are complementary to a codon
- DA sequence of three amino acids that forms a polypeptide
5.Which of the following are features of the genetic code? (Select all that apply.)
Medium
- AIt is degenerate.
- BIt is universal.
- CIt is overlapping.
- DIt is non-overlapping.
- EIt is read in the 5' to 3' direction.
6.Match each molecule with its correct description.
Medium
- mRNA
- tRNA
- rRNA
- DNA
- Carries the genetic code from the nucleus to the cytoplasm
- Carries amino acids to the ribosome
- Forms part of the ribosome structure
- Stores the genetic code in the nucleus
7.In eukaryotes, translation occurs in the nucleus and transcription occurs in the cytoplasm.
Medium
True or false?
8.Which enzyme catalyses the formation of bonds between the sugar-phosphate groups of RNA nucleotides during transcription?
Medium
- ARNA polymerase
- BDNA polymerase
- CDNA ligase
- DATP synthase

और सवाल

9.Which of the following statements about the genetic code are correct? (Select all that apply.)
Medium
- AThe genetic code is non-overlapping.
- BThe genetic code is degenerate, meaning multiple codons can code for the same amino acid.
- CThe genetic code is universal, meaning almost every organism uses the same code.
- DEach base is read multiple times in different codons.
- EThere are 64 different possible codons.
10.The genetic code is degenerate because multiple codons can code for the same amino acid.
Easy
True or false?
11.Place the following steps of translation initiation in the correct order.
Medium
- Small ribosomal subunit attaches to the 5' end of mRNA
- Initiator tRNA carrying methionine binds to the small ribosomal subunit
- Ribosome moves along the mRNA until it locates a start codon (AUG)
- Large ribosomal subunit binds to the small subunit
12.During transcription, which DNA strand is transcribed to produce mRNA?
Easy
- AThe template strand
- BThe coding strand
- CBoth strands simultaneously
- DNeither strand; mRNA is synthesised from scratch
13.Which of the following are functions of post-transcriptional modification in eukaryotes? (Select all that apply.)
Hard
- AAddition of a methylated cap to the 5' end
- BAddition of a poly-A tail to the 3' end
- CRemoval of introns and joining of exons
- DTranslation of the mRNA before it leaves the nucleus
- EProtection against degradation by exonucleases
14.A DNA coding strand has the sequence TTC GAG CAT TAC GCC. Which mRNA codon sequence is transcribed from the template strand?
Medium
- AUUC GAG CAU UAC GCC
- BAAG CUC GUA AUG CGG
- CTTC GAG CAT TAC GCC
- DAAG CTC GTA ATG CGG
15.An mRNA molecule is 180 nucleotides long. How many amino acids does it code for?
Medium
- A60
- B90
- C180
- D540
16.The DNA coding strand triplet GAG is mutated to GTG. What is the resulting change in the polypeptide?
Hard
- AGlutamic acid is replaced by valine
- BValine is replaced by glutamic acid
- CA stop codon is introduced
- DNo change occurs
17.A student wants to observe the site of translation in a eukaryotic cell using an electron microscope. Which cellular structure should they look for?
Medium
- ARibosome
- BNucleus
- CGolgi apparatus
- DMitochondrion
18.A researcher adds a drug that blocks the binding of RNA polymerase to the promoter region of a gene. Which process will be directly affected?
Medium
- ATranscription
- BTranslation
- CDNA replication
- DPost-transcriptional modification
19.During an experiment, a cell is treated with a chemical that prevents the addition of a poly-A tail to mRNA. Which of the following is the most likely immediate consequence?
Hard
- AThe mRNA will be less stable and may be degraded more quickly.
- BThe mRNA will not be able to bind to ribosomes.
- CThe mRNA will not be able to exit the nucleus.
- DThe mRNA will not undergo splicing.
20.Which of the following are required for transcription to occur in a eukaryotic cell? (Select all that apply.)
Medium
- ARNA polymerase
- BDNA template strand
- CRibosomes
- DFree RNA nucleotides
- EtRNA molecules
21.In eukaryotes, post-transcriptional modification of mRNA includes the removal of introns and joining of exons.
Easy
True or false?
22.Match each molecule or structure with its correct role in protein synthesis.
Medium
- RNA polymerase
- Ribosome
- tRNA
- Promoter
- Binds to DNA and catalyses transcription
- Site of translation
- Carries amino acids to the ribosome
- Binding site for RNA polymerase
23.Place the following steps of transcription in the correct order.
Medium
- RNA polymerase binds to the promoter
- DNA strands separate to form an open complex
- RNA polymerase moves along the template strand, adding RNA nucleotides
- RNA polymerase reaches a terminator sequence
- mRNA strand detaches and DNA re-forms
24.A mutation changes a codon from GAG to GUG in the mRNA for the β-globin chain of haemoglobin. What is the effect on the polypeptide?
Hard
- AGlutamic acid is replaced by valine at position 6.
- BValine is replaced by glutamic acid at position 6.
- CThe polypeptide is shortened.
- DThe polypeptide is unchanged due to degeneracy.
25.Which of the following correctly describes the direction of transcription and translation?
Medium
- ABoth occur in the 5' to 3' direction.
- BTranscription occurs 5' to 3', translation occurs 3' to 5'.
- CTranscription occurs 3' to 5', translation occurs 5' to 3'.
- DBoth occur in the 3' to 5' direction.
26.During translation, the ribosome moves along the mRNA in the 3' to 5' direction.
Medium
True or false?
27.Which of the following correctly describes a triplet?
Easy
- AA sequence of three DNA bases that codes for a specific amino acid
- BA sequence of three mRNA bases that codes for a specific amino acid
- CA sequence of three tRNA bases complementary to a codon
- DA sequence of three amino acids coded for by one gene
28.If an mRNA codon has the sequence CAG, what is the sequence of the complementary tRNA anticodon?
Medium
- AGUC
- BGTC
- CCAG
- DCUG
29.Which RNA molecule is the shortest, being around 80 nucleotides in length?
Easy
- AtRNA
- BmRNA
- CrRNA
- Dpre-mRNA
30.A ribosome has three tRNA binding sites. Which site does the initiator tRNA occupy when translation begins?
Medium
- AThe P site
- BThe A site
- CThe E site
- DThe promoter
31.Which of the following correctly describes the direction in which mRNA is synthesised during elongation?
Medium
- A5' to 3', with the 5' end of the free RNA nucleotide added to the 3' end of the growing strand
- B3' to 5', with the 3' end of the free RNA nucleotide added to the 5' end of the growing strand
- C5' to 3', with the 3' end of the free RNA nucleotide added to the 5' end of the growing strand
- D3' to 5', with the 5' end of the free RNA nucleotide added to the 3' end of the growing strand
32.Which of the following are true of the promoter? (Select all that apply.)
Medium
- AIt is a non-coding sequence located near to a gene
- BIt is itself transcribed into mRNA
- CIt acts as the binding site for RNA polymerase during initiation
- DIt is a coding sequence that determines the amino acid sequence
- EIts binding by RNA polymerase is controlled by regulatory proteins
33.Which of the following are examples of post-translational modification of a polypeptide? (Select all that apply.)
Medium
- AFolding into secondary, tertiary and quaternary structures
- BFormation of disulfide bonds
- CRemoval of a signal peptide from pre-proinsulin
- DAddition of a methylated cap to the 5' end
- EAddition of a poly-A tail to the 3' end
34.The genetic code is universal, meaning that almost every organism uses the same triplet codes for the same amino acids.
Easy
True or false?
35.Introns are the coding sequences that are joined together to form mature mRNA.
Easy
True or false?
36.The formation of a peptide bond between two amino acids is an anabolic reaction that requires ATP.
Easy
True or false?
37.Match each term with its correct definition.
Medium
- Triplet
- Codon
- Anticodon
- Stop codon
- Three DNA bases that code for a specific amino acid
- Three mRNA bases that code for a specific amino acid
- Three tRNA bases complementary to a codon
- A signal that ends translation when the polypeptide is complete
38.Match each cellular location or structure with the process that occurs there.
Medium
- Nucleus
- Cytoplasm at the ribosome
- Proteasome
- Golgi apparatus
- Transcription of DNA to mRNA
- Translation of mRNA into a polypeptide
- Proteolysis of tagged, damaged proteins
- Packaging and cleaving proinsulin into mature insulin
39.Place the stages of transcription in the correct sequence.
Medium
- RNA polymerase binds near the promoter and the DNA strands separate
- RNA polymerase moves along the template strand adding RNA nucleotides
- RNA polymerase reaches a terminator sequence
- RNA polymerase and the mRNA strand detach
40.Place the events of translation elongation in the correct order.
Medium
- A tRNA with the complementary anticodon binds to the exposed A site
- A peptide bond forms between the amino acids carried by the tRNAs
- The ribosome shifts along the mRNA by one codon
- The tRNA in the P site moves to the E site and is released
41.State the name of the part of the cell where polypeptide synthesis takes place.
Easy
42.Complete the sentence about the genetic code.
Easy
The genetic code is described as ____ because multiple codons can code for the same amino acid.
43.Name the enzyme that joins amino acids together during translation.
Medium
44.A gene contains 180 nucleotides in its mRNA. Calculate the number of amino acids that will be coded for by this gene. Show your working.
Medium
45.Myoglobin is a protein consisting of a single polypeptide chain of 153 amino acids. Calculate the minimum number of DNA bases needed to code for myoglobin.
Medium
46.Complete the sentences about the genetic code using the correct terms.
Medium
The genetic code is described as ____ because multiple codons can code for the same amino acid. It is described as ____ because almost every organism uses the same code.
47.A section of DNA contains 90 bases in its gene. Calculate the maximum number of amino acids that could be coded for by this section of DNA.
Easy
48.The protein insulin consists of two polypeptide chains: an A chain of 21 amino acids and a B chain of 30 amino acids. Calculate the minimum number of DNA bases required to code for the entire insulin protein.
Medium
49.Complete the sentence about the genetic code using the correct terms.
Easy
The genetic code is described as ____ because more than one codon can code for the same amino acid, and it is described as ____ because the same codons code for the same amino acids in almost all organisms.
50.Complete the sentences about post-transcriptional modification in eukaryotes.
Easy
In eukaryotes, the immediate product of transcription is called ____. During splicing, non-coding sequences called ____ are removed, and coding sequences called ____ are joined together.
51.Complete the sentences about the initiation of translation.
Easy
Translation is initiated when a small ribosomal subunit binds to the ____ end of the mRNA molecule. An initiator tRNA carrying the amino acid ____ binds to the start codon AUG.
52.State the name of the enzyme that catalyses the formation of bonds between the sugar-phosphate groups of RNA nucleotides during transcription.
Easy
53.Outline the process that allows the amino acids to be added to the polypeptide in the correct order.
Hard
54.Outline the process of transcription in eukaryotes.
Hard
55.Describe the role of transfer RNA (tRNA) in translation.
Medium
56.Describe the changes that occur between polypeptide synthesis and the formation of a functional protein.
Hard
57.Explain why the protein produced as a result of a point mutation may not function correctly.
Medium
58.A gene contains 180 nucleotides in its mRNA. Calculate the number of amino acids that will be coded for by this gene. Show your working.
Medium
- A60 amino acids
- B66 amino acids
- C72 amino acids
- D54 amino acids
59.Myoglobin is a protein consisting of a single polypeptide chain of 153 amino acids. Calculate the minimum number of DNA bases needed to code for myoglobin.
Medium
- A459 bases
- B505 bases
- C551 bases
- D413 bases
60.A section of DNA contains 90 bases in its gene. Calculate the maximum number of amino acids that could be coded for by this section of DNA.
Easy
- A36 amino acids
- B33 amino acids
- C27 amino acids
- D30 amino acids
61.The protein insulin consists of two polypeptide chains: an A chain of 21 amino acids and a B chain of 30 amino acids. Calculate the minimum number of DNA bases required to code for the entire insulin protein.
Medium
- A138 bases
- B183 bases
- C168 bases
- D153 bases

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