Week 28 / Translation Flashcards
1
Q
Q: What is transcription in gene expression?
A
A: Transcription is the enzymatic synthesis of RNA from a DNA template, forming the first step in gene expression.
2
Q
Q: What is the product of transcription?
A
A: Transcription generates a messenger RNA (mRNA) molecule.
3
Q
Q: What is translation in gene expression?
A
A: Translation is the enzymatic synthesis of protein from a transcribed gene sequence into a functional RNA molecule (mRNA).
4
Q
Q: What is the primary structure of a protein?
A
A: The primary structure is the sequence of amino acids in a polypeptide chain.
5
Q
Q: What is the secondary structure of a protein?
A
A: The secondary structure refers to local folded structures within a polypeptide due to interactions between atoms of the backbone.
6
Q
Q: What is the tertiary structure of a protein?
A
A: The tertiary structure is the overall three-dimensional shape of a polypeptide, primarily determined by interactions between the R groups of amino acids.
7
Q
Q: What is the quaternary structure of a protein?
A
A: The quaternary structure occurs when multiple polypeptide chains (subunits) come together to form a functional protein.
8
Q
Q: What is translation in gene expression?
A
A: Translation is the process where ribosomes read the transcribed mRNA and generate a protein.
9
Q
Q: How does translation occur in prokaryotes?
[whats special about translation in prokaryotes ?]
A
A: In prokaryotes, translation is co-transcriptional, meaning it happens at the same time as transcription.
10
Q
Q: How does translation occur in eukaryotes?
A
A: In eukaryotes, translation occurs after transcription, though some elements of the process are co-transcriptional.
11
Q
Q: Where does translation occur in the cell?
A
A: Translation happens in the cytoplasm.
12
Q
Q: What is the function of ribosomes? [2]
A
A: Ribosomes read the mRNA sequence and assemble the protein based on the message.
13
Q
Q: What is the composition of ribosomes?
A
A: Ribosomes are composed of approximately 65% ribosomal RNA (rRNA) and 35% ribosomal proteins.
14
Q
Q: What is the approximate diameter of a ribosome?
A
A: Ribosomes have a diameter of approximately 10 nm.
15
Q
Q: How are ribosomal subunits characterized?
A
A: Ribosomal subunits are characterized based on their sedimentation rate, measured in Svedberg units (S).
16
Q
Q: How do ribosomes assemble under optimal conditions?
A
A: rRNAs and ribosomal proteins self-assemble into a ribosome, as the structural information is inherent in the sub-components.
17
Q
Q: What roles do rRNAs play in ribosomes?
A
A: rRNAs have both structural and catalytic activity, contributing to ribosome function.
18
Q
Q: What is the function of the small ribosomal subunit?
A
A: The small ribosomal subunit contains the decoding center, which is essential for reading the mRNA.
19
Q
Q: What is the function of the large ribosomal subunit?
A
A: The large ribosomal subunit contains the peptidyl transferase center, a catalytic RNA responsible for peptide bond formation.
20
Q
Q: What is a polyribosome?
A
A: A polyribosome is formed when multiple ribosomes are loaded onto a single mRNA strand.
21
Q
Q: What is the role of transfer RNAs (tRNAs) in the ribosome? [2]
A
A: tRNAs carry amino acids and occupy the A-, P-, and E-sites during translation.
22
Q
Q: What happens at the A-site of the ribosome?
A
A: The A-site (acceptor site) is where the aminoacyl-tRNA lands with its amino acid.
23
Q
Q: What happens at the P-site of the ribosome?
A
A: The P-site (peptidyl-tRNA site) is occupied by the last amino acid added to the growing polypeptide chain.
24
Q
Q: What happens at the E-site of the ribosome?
A
A: The E-site (exit site) is where the tRNA, after transferring its amino acid, leaves the ribosome.
25
Q: How are the A-, P-, and E-sites structurally formed in the ribosome?
[where do these sites lie?]
[they are completely formed when?]
A: Although
the bulk of these sites lies in the large ribosomal subunit,
they are completed only when the small subunit is present.
26
Q: What is the function of transfer RNAs (tRNAs)?
[2]
A: tRNAs are adapter molecules that deliver amino acids to the ribosome during translation.
27
Q: What is unique about tRNA bases?
A: tRNA contains many (>20%) post-transcriptionally modified bases.
28
Q: What is the secondary structure of tRNA called?
A: The secondary structure of tRNA is called a clover-leaf structure.
29
Q: How long is the primary structure of a tRNA molecule?
A: The primary structure of tRNA is between 60 and 95 nucleotides long, most commonly around 75 nucleotides.
30
Q: What stabilizes the secondary structure of tRNA?
A: The secondary structure is stabilized by significant levels of intra-tRNA hydrogen bonding.
31
What are the key differences between 70S and 80S ribosomes in terms of structure and function?
Answer:
70S Ribosomes: Found in prokaryotes (bacteria and archaea) and in mitochondria and chloroplasts of eukaryotic cells. Composed of a 50S large subunit and a 30S small subunit.
80S Ribosomes: Found in the cytoplasm of eukaryotic cells. Composed of a 60S large subunit and a 40S small subunit.
Function: Both types are involved in protein synthesis, but 70S ribosomes are generally smaller and more sensitive to antibiotics like tetracycline and chloramphenicol, whereas 80S ribosomes are larger and more complex.
32
Q: How is genetic information carried in mRNA?
A: The mRNA sequence carries its message in a code of 3-letter “words” called codons.
33
Q: What are codons?
A: Codons are continuous sequences of three nucleotide triplets that encode amino acids.
34
Q: What happens during translation?
A: During translation, codons are read, and the information is used to insert amino acids into a growing polypeptide chain.
35
Q: Why is the genetic code considered redundant?
A: Virtually every amino acid is encoded by more than one codon, providing a built-in redundancy to the code.
36
Q: What components are required for translation in prokaryotes? [4]
A: mRNA, tRNA, ribosome, GTP, initiation factors, and elongation factors.
37
Q: What are the three stages of translation in prokaryotes?
A: Initiation, elongation, and termination.
38
Q: What is translocation in translation?
A: Translocation is the movement of the ribosome along the mRNA during translation.
39
Q: What is the purpose of the initiation step in translation?
A: The purpose of initiation is to assemble the translation "machinery" at the translation start site.
40
Q: What forms the initiation complex in translation?
[3]
A: The initiation complex is formed from the ribosome, mRNA, and initiator tRNA (formylated methionine tRNA) that specifically recognizes the AUG codon.
41
Q: Where does the initiator tRNA enter during translation initiation?
A: The initiator tRNA enters the P-site, while all subsequent tRNAs enter the A-site.
42
Q: What additional components are required for translation initiation?
A: Three initiation factors and a molecule of GTP are required.
43
What are the steps to Translation Initiation? [5]
R — Ribosome assembly
Ribosome + mRNA + initiator tRNA (fMet-tRNA) come together at the start codon (AUG).
I — Initiator complex forms
These components form the initiation complex at the AUG codon.
P — P-site entry
The initiator tRNA enters the P-site (first and only tRNA to do this initially).
E — Entry of other tRNAs
All other tRNAs enter the A-site, not the P-site.
G — GTP & initiation factors
3 initiation factors (IF1, IF2, IF3) + GTP are needed to complete the process.
-----------------------------
Assembly of Machinery: The ribosome, mRNA, and initiator tRNA (formylated methionine tRNA) come together at the translation start site.
Formation of Initiation Complex: The ribosome, mRNA, and initiator tRNA form the initiation complex, with the initiator tRNA specifically recognizing the AUG codon.
Entry of Initiator tRNA: The initiator tRNA enters the P-site of the ribosome.
Entry of Subsequent tRNAs: All subsequent tRNAs enter the A-site.
Requirement of Initiation Factors and GTP: Three initiation factors and a molecule of GTP are required to complete the initiation process.
44
Q: What is involved in the elongation step of translation?
A: The elongation step involves aminoacyl-tRNA delivery, peptide bond formation, and translocation (movement).
45
Q: What is the state of the ribosome after initiation?
A: After initiation, the P-site is occupied, and the A-site is empty.
46
Q: How many elongation factors are recruited to the initiation complex?
A: Three elongation factors are recruited to the initiation complex.
47
Q: What is the role of elongation factors in translation?
A: Elongation factors help deliver aminoacyl-tRNAs to the ribosome, and GTP hydrolysis causes the release of EF-Tu.
48
Q: What does the translocase do during elongation?
A: Translocase uses energy from GTP hydrolysis to eject the tRNA from the P-site and move the peptidyl-tRNA into the P-site from the A-site.
49
Q: How does the ribosome prevent frameshifting during elongation?
A: The ribosome maintains a 6 base-pair contact with the mRNA to prevent frameshifting.
50
Q: When does elongation stop?
A: Elongation proceeds until a termination codon appears in the A-site.
51
What are the steps to Translation Elongation? [7]
🧩 A — Aminoacyl-tRNA Delivery
Delivered to the A-site by elongation factors (like EF-Tu + GTP).
🧷 P — Peptide Bond Formation
A peptide bond forms between the amino acid in the A-site and the growing chain in the P-site.
🔀 E — Elongation: Translocation
Ribosome shifts:
Peptidyl-tRNA: A-site → P-site
Empty tRNA: P-site → E-site → ejected
Powered by GTP hydrolysis
⚙️ T — Three Elongation Factors
EF-Tu, EF-Ts, EF-G
Help with delivery, positioning, and translocation
GTP hydrolysis releases EF-Tu
🔄 T — Translocase Action
EF-G (translocase) uses GTP to shift tRNAs during ribosome movement
🧬 P — Prevention of Frameshifting
Ribosome maintains a 6 base-pair contact with mRNA to stay in frame
⛔ T — Termination Codon
Elongation stops when a stop codon (UAA, UAG, UGA) enters the A-site
-----------------------------------------
Aminoacyl-tRNA Delivery: Aminoacyl-tRNAs are delivered to the ribosome, with the help of elongation factors.
Peptide Bond Formation: The ribosome catalyzes the formation of a peptide bond between the amino acid of the incoming tRNA and the growing polypeptide chain in the P-site.
Translocation: The ribosome moves along the mRNA, shifting the peptidyl-tRNA from the A-site to the P-site, and ejecting the empty tRNA from the P-site. This movement is driven by GTP hydrolysis.
Elongation Factors and GTP Hydrolysis: Three elongation factors are recruited to the initiation complex. They help deliver the aminoacyl-tRNAs, and GTP hydrolysis results in the release of EF-Tu.
Translocase Action: Translocase uses the energy from GTP hydrolysis to eject the tRNA from the P-site and move the peptidyl-tRNA into the P-site from the A-site.
Prevention of Frameshifting: The ribosome maintains a 6 base-pair contact with the mRNA, preventing frameshifting.
Termination Codon: Elongation proceeds until a termination codon appears in the A-site.
52
Q: What happens during translation termination?
A: Termination is the process where the ribosome is dissociated from the mRNA.
53
Q: Why do tRNAs not recognize a STOP codon?
A: There are no tRNAs that recognize a STOP codon.
54
Q: What is the role of protein release factors in termination?
A: Protein release factors interact with STOP codons and cause the release of the polypeptide chain.
55
Q: What STOP codons are recognized by Release Factor 1 (RF1)?
A: RF1 recognizes UAA and UAG STOP codons.
56
Q: What STOP codons are recognized by Release Factor 2 (RF2)?
A: RF2 recognizes UAA and UGA STOP codons.
57
Q: How does Release Factor 3 (RF3) assist in termination?
A: RF3 helps RF1 and RF2 to carry out their role in termination.
58
Q: What happens to the polypeptide chain during termination?
A: The release factor causes the peptidyl transferase to transfer the polypeptide to water instead of the next tRNA, leading to protein release.
59
Q: What is required for the dissociation of the ribosome complex from the mRNA?
A: EF-G and a release factor (RF) are required for dissociation and removal of the uncharged tRNA from the P-site.
60
What are the steps to Translation Termination?
🅂 — STOP Codon Recognition
UAA, UAG, or UGA enters the A-site → triggers termination.
🆁 — Release Factor Recognition
RF1: Recognizes UAA & UAG
RF2: Recognizes UAA & UGA
RF3: Assists RF1 and RF2
🅿 — Polypeptide Release
Peptidyl transferase adds water instead of an amino acid → releases the polypeptide
🅓 — Disassembly of Ribosome
EF-G + RF3 help dismantle the ribosome and remove uncharged tRNA
----------------------------------------------------------
Recognition of STOP Codons: Termination begins when a STOP codon (UAA, UAG, or UGA) is encountered in the A-site of the ribosome.
Interaction with Release Factors: Protein release factors (RFs) recognize the STOP codons.
RF1 recognizes UAA and UAG.
RF2 recognizes UAA and UGA.
RF3 helps RF1 and RF2 in their role.
Polypeptide Release: The release factor causes the peptidyl transferase to transfer the polypeptide chain to a water molecule rather than to the next tRNA, leading to the release of the protein.
Disassembly of the Ribosome Complex: EF-G and a release factor (RF) are required for the dissociation of the ribosome complex from the mRNA and the removal of the uncharged tRNA from the P-site.
61
Q: What is the purpose of co-translational control in the tryptophan operon?
A: Co-translational control is used as a control point for gene expression regulation in the tryptophan operon, coupling transcription and translation.
62
Q: What is the role of the trp operon in E. coli bacteria?
A: The trp operon encodes biosynthetic enzymes for the amino acid tryptophan, which is a rare amino acid.
63
Q: When is the trp operon expressed and repressed?
A: The trp operon is expressed when tryptophan levels are low and repressed when tryptophan levels are high.
64
Q: How is the trp operon regulated?
A: The trp operon is regulated by the trp repressor, which binds to tryptophan and blocks expression from the operon.
65
Q: What is attenuation in the context of the tryptophan operon?
A: Attenuation is a mechanism based on the coupling of transcription and translation to regulate tryptophan biosynthesis, especially when tryptophan levels are high.
66
Q: How does the ribosome control transcription in attenuation?
A: When tryptophan levels are low, the ribosome stalls, leading to the formation of an anti-terminator hairpin structure, allowing transcription and translation to continue.
67
Q: What happens when tryptophan levels are high in the tryptophan operon?
A: The ribosome moves quickly along the mRNA and stalls, causing the formation of a terminator hairpin structure, stopping transcription.
68
Q: What is the leader sequence in the tryptophan operon?
A: The leader sequence is located between the operator and the first gene of the operon, encoding a short polypeptide and containing an attenuator sequence.
69
Q: What role do hairpin structures play in attenuation?
A: The mRNA has sections that can self-associate to form hairpin structures, such as the anti-terminator and terminator hairpins, which regulate transcription.
70
Q: What are the sequences involved in hairpin formation for attenuation?
A: Sequences 2 and 3 form the anti-terminator hairpin, while sequences 3 and 4 form the terminator hairpin.
71
Q: What are the levels of protein structure?
A: The levels of protein structure are:
Primary: Sequence of amino acids
Secondary: Local folding into helices or sheets
Tertiary: Three-dimensional folding due to side chain interactions
Quaternary: Protein consisting of more than one amino acid chain
72
Q: What are the characteristics of the primary protein structure?
Q: What is the secondary protein structure?
Q: What is the tertiary protein structure?
Q: What is the quaternary protein structure?
A: The primary protein structure is the sequence of a chain of amino acids.
A: The secondary protein structure involves local folding of the polypeptide chain into structures like α-helices and β-pleated sheets.
A: The tertiary protein structure is the three-dimensional folding pattern of a protein due to side chain interactions.
A: The quaternary protein structure is a protein consisting of more than one amino acid chain.
73
Q: What are the basic properties of proteins?
A: Proteins contain carbon, hydrogen, oxygen, nitrogen, have a defined structure, mass, absorb UV light, and contain both charged and uncharged amino acids, as well as hydrophilic and hydrophobic amino acids.
74
Q: What is an α-helix in protein structure?
A: An α-helix is a secondary structure where the polypeptide chain coils into a spiral shape.
75
Q: What is a β-pleated sheet in protein structure?
A: A β-pleated sheet is a secondary structure where the polypeptide chain forms extended strands that align side by side.
76
Q: What is the mechanism of action of Chloramphenicol?
Flashcard 2
Q: How does Linezolid work?
Flashcard 3
Q: What do Macrolides, Clindamycin, and Streptogramins do?
Flashcard 4
Q: What is the mechanism of action of Tetracyclines?
Flashcard 5
Q: How do Aminoglycosides function?
A: Chloramphenicol binds to the 50S ribosomal subunit and inhibits the formation of peptide bonds between amino acids.
A: Linezolid binds to the 50S ribosomal subunit and prevents the formation of the 50/30S ribosomal complex.
A: These antibiotics block the polypeptide exit tunnel on the 50S subunit and prevent peptide chain elongation.
A: Tetracyclines bind to the 30S ribosomal subunit and interfere with the binding of tRNA to the ribosomal complex.
A: Aminoglycosides bind to the 30S ribosomal subunit and cause the mRNA codon to be misread. They also interfere with the initiation complex of the 30S and 50S subunits with mRNA.
