Mod 7- From RNA To Protein Flashcards
What is the genetic code composed of?
20 amino acids but only 4 nucleotides in messenger RNA
So a group of nucleotide is required to code for 20 amino acids
What is a codon?
A 3 nucleotide or triplet code used to specify the amino acids
How many possible codons are there?
64 possible codons
How many codons specify amino acids?
61 codons
How many codons are stop codons?
3 codons
What does the term ‘degeneracy’ refer to in the genetic code?
Many amino acids have more than one codon
What is an open reading frame?
The sequence of codons that runs from a specific start codon to a specific stop codon
There are 3 reading points
What is the start codon for almost every protein chain?
AUG (codes for Methionine)
What are the three stop codons?
UAA, UGA, UAG
What is the function of tRNA?
To link to a specific amino acid and to recognize a codon in mRNA
Ensures amino acid-codon match
What is the role of aminoacyl-tRNA synthetases?
Each tRNA is recognized by only one of 20 aminoacyl-tRNA synthetases
aminoacyl-tRNA = tRNA joined to an amino acid
True or False: Each aminoacyl-tRNA synthetase is specific for both an amino acid and a tRNA.
True
What is the paradox regarding tRNAs and codons?
> 20 tRNAs but < 61 codons
So some tRNAs recognise more than 1 codon
What is ‘wobble’ in the context of tRNA?
A mechanism that allows unconventional base pairing between the third base in codon and the first base in anticodon
This allows the tRNA to recognise more than 1 codon
What does the wobble mechanism permit?
Degeneracy in the genetic code
Fill in the blank: The genetic code is primarily specified by _______ interactions.
amino acid-tRNA
What is the significance of modified nucleotides in tRNA?
They are especially present in the anticodon loop
What are the implications of degeneracy in the genetic code?
61 codons for 20 amino acids and >1 tRNA species for certain amino acids
What does the term ‘anticodon’ refer to?
The part of tRNA that interacts with the codon
What is the amino-acid acceptor arm?
The part of tRNA where the amino acid binds
What are the three stages of translation?
Initiation, Elongation, Termination
What is the role of the ribosome in translation?
The ribosome facilitates the assembly of amino acids into polypeptide chains.
It is where protein synthesis occurs
What are the two subunits of the ribosome?
Small subunit and Large subunit
What does the term ‘Svedberg’ (S) refer to?
A measure of the sedimentation rate of suspended particles centrifuged under standard conditions.
What is the significance of the Shine-Dalgarno sequence?
It interacts with 16S rRNA of the 30S small subunit to identify the site of initiation of protein synthesis.
What is the function of initiation factors in translation?
They assist in the assembly of the initiation complex and ensure the accuracy of tRNA binding.
Which amino acid is used for initiation in prokaryotes?
Formylmethionine (fMet)
Fill in the blank: The process of attaching amino acids to tRNA is known as _______.
Amino acid activation
What are the roles of EF-Tu and EF-G during elongation?
- EF-Tu: mediates aminoacyl-tRNA entry to ribosome
- EF-G: mediates translocation
What happens during the termination stage of translation?
Release factors bind to the A site, hydrolyzing the polypeptide chain from tRNA.
True or False: GTP is involved in all stages of protein synthesis.
True
What are the three prokaryotic release factors?
- RF1: UAA/UAG
- RF2: UAA/UGA
- RF3: assists RF1 or 2 binding to ribosome
What energy sources are required for protein synthesis?
- ATP
- GTP
What does the P site of the ribosome do?
It is the peptidyl-tRNA site where peptide bonds form.
What does the A site of the ribosome do?
It is the aminoacyl-tRNA site where incoming aminoacyl-tRNA binds.
What is the role of GTP in translation?
GTP = Guanosine triphosphate
Provides energy through hydrolysis during:
initiation- addition of large subunit
elongation- addition of aminoacyl-tRNA by EF-Tu and EF-G, peptide synthesis and translocation
termination- release of peptide chain and dissociation of ribosome
GTP —> GDP + Pi
What is the role of tRNA in translation?
tRNA transports amino acids to the ribosome for incorporation into polypeptides.
What does the term ‘ternary complex’ refer to in translation?
The association of aminoacyl-tRNA, EF-Tu, and GTP.
Fill in the blank: The mRNA is read in the _______ direction during translation.
5’ to 3’
What is the function of the large subunit of the ribosome?
It catalyzes peptide bond formation between amino acids.
What are the key components required for protein synthesis?
- Ribosomes
- tRNA
- mRNA
- Accessory factors
- Energy (ATP and GTP)
What is the primary role of ribosomal RNA (rRNA) in the ribosome?
It forms the structural and functional core of the ribosome.
What is a key feature of the secondary structure of rRNA?
It is made up of 40 or more stem loops.
Describe amino acid activation
- attachment of amino acids to tRNA 3’ acceptor arm
- amino acid + ATP —> amino acid-AMP (AA-AMP) + PP (phosphate)
- AA-AMP + tRNA —> AA-tRNA + AMP
Name the initiation factors in translation
- IF1 = Blocks A (acceptor) site to tRNAi -met, inhibits premature 30S-50S interaction
- IF2 = tags tRNAi and regulates entry of tRNA into ribosome
- IF3 = inhibits premature 30S-50S interaction, stabilises free 30S, accuracy check for tRNAi-met binding
Describe the initiation of translation
- Initiation factors (active IF2)/ GTP interacts (binds to) with 30S ribosomal subunit
- Initiator tRNA (tRNAi) and mRNA join complex
- Start codon aligns with P-site where tRNAi-met binds to complete initiation complex
- IF2 becomes inactive and dissociates as well as IF3
- byproducts = ATP —>ADP and GTP —>GDP
Describe elongation in translation
- Starts at P site (peptide-tRNA site) where peptide bonds form
- tRNA-Meti is the only tRNA which can bind to the P site
- Elongation factors are necessary
- These bind to the ribosome A site
- A site (aminoacyl-tRNA site) = where incoming aminoacyl-tRNA binds
- Ternary complex formed = aminoacyl-tRNA-EFTu-GTP
- Causes peptide bonds formation
- Tu-GDP is ejected and recycled
- Association of EF-G-GTP and ejection of empty tRNA from the P site
- Ribosome translocates so peptidyl tRNA is now in P site, A site is free
What are the 3 prokaryotic release factors in translational termination?
RF1 = UAA/UAG
RF2 = UAA/UGA
RF3 = helps RF1 or 2 to bind to ribosome-GTPase
Describe termination in translation
- RF-GTP binds to A site when termination codon appears
- Release factor is recruited (a G-protein)
- Hydrolysis of polypeptide chain from tRNA
- This is released to be processed
- Dissociation of tRNA and RF
