Mod 7- From RNA To Protein

Question 1

What is the genetic code composed of?

Answer 1

20 amino acids but only 4 nucleotides in messenger RNA

So a group of nucleotide is required to code for 20 amino acids

Question 2

What is a codon?

Answer 2

A 3 nucleotide or triplet code used to specify the amino acids

Question 3

How many possible codons are there?

Answer 3

64 possible codons

Question 4

How many codons specify amino acids?

Answer 4

61 codons

Question 5

How many codons are stop codons?

Answer 5

3 codons

Question 6

What does the term ‘degeneracy’ refer to in the genetic code?

Answer 6

Many amino acids have more than one codon

Question 7

What is an open reading frame?

Answer 7

The sequence of codons that runs from a specific start codon to a specific stop codon

There are 3 reading points

Question 8

What is the start codon for almost every protein chain?

Answer 8

AUG (codes for Methionine)

Question 9

What are the three stop codons?

Answer 9

UAA, UGA, UAG

Question 10

What is the function of tRNA?

Answer 10

To link to a specific amino acid and to recognize a codon in mRNA

Ensures amino acid-codon match

Question 11

What is the role of aminoacyl-tRNA synthetases?

Answer 11

Each tRNA is recognized by only one of 20 aminoacyl-tRNA synthetases

aminoacyl-tRNA = tRNA joined to an amino acid

Question 12

True or False: Each aminoacyl-tRNA synthetase is specific for both an amino acid and a tRNA.

Answer 12

True

Question 13

What is the paradox regarding tRNAs and codons?

Answer 13

> 20 tRNAs but < 61 codons

So some tRNAs recognise more than 1 codon

Question 14

What is ‘wobble’ in the context of tRNA?

Answer 14

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

Question 15

What does the wobble mechanism permit?

Answer 15

Degeneracy in the genetic code

Question 16

Fill in the blank: The genetic code is primarily specified by _______ interactions.

Answer 16

amino acid-tRNA

Question 17

What is the significance of modified nucleotides in tRNA?

Answer 17

They are especially present in the anticodon loop

Question 18

What are the implications of degeneracy in the genetic code?

Answer 18

61 codons for 20 amino acids and >1 tRNA species for certain amino acids

Question 19

What does the term ‘anticodon’ refer to?

Answer 19

The part of tRNA that interacts with the codon

Question 20

What is the amino-acid acceptor arm?

Answer 20

The part of tRNA where the amino acid binds

Question 21

What are the three stages of translation?

Answer 21

Initiation, Elongation, Termination

Question 22

What is the role of the ribosome in translation?

Answer 22

The ribosome facilitates the assembly of amino acids into polypeptide chains.

It is where protein synthesis occurs

Question 23

What are the two subunits of the ribosome?

Answer 23

Small subunit and Large subunit

Question 24

What does the term ‘Svedberg’ (S) refer to?

Answer 24

A measure of the sedimentation rate of suspended particles centrifuged under standard conditions.

Question 25

What is the significance of the Shine-Dalgarno sequence?

Answer 25

It interacts with 16S rRNA of the 30S small subunit to identify the site of initiation of protein synthesis.

Question 26

What is the function of initiation factors in translation?

Answer 26

They assist in the assembly of the initiation complex and ensure the accuracy of tRNA binding.

Question 27

Which amino acid is used for initiation in prokaryotes?

Answer 27

Formylmethionine (fMet)

Question 28

Fill in the blank: The process of attaching amino acids to tRNA is known as _______.

Answer 28

Amino acid activation

Question 29

What are the roles of EF-Tu and EF-G during elongation?

Answer 29

* EF-Tu: mediates aminoacyl-tRNA entry to ribosome * EF-G: mediates translocation

Question 30

What happens during the termination stage of translation?

Answer 30

Release factors bind to the A site, hydrolyzing the polypeptide chain from tRNA.

Question 31

True or False: GTP is involved in all stages of protein synthesis.

Answer 31

True

Question 32

What are the three prokaryotic release factors?

Answer 32

* RF1: UAA/UAG * RF2: UAA/UGA * RF3: assists RF1 or 2 binding to ribosome

Question 33

What energy sources are required for protein synthesis?

Answer 33

* ATP * GTP

Question 34

What does the P site of the ribosome do?

Answer 34

It is the peptidyl-tRNA site where peptide bonds form.

Question 35

What does the A site of the ribosome do?

Answer 35

It is the aminoacyl-tRNA site where incoming aminoacyl-tRNA binds.

Question 36

What is the role of GTP in translation?

Answer 36

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**

Question 37

What is the role of tRNA in translation?

Answer 37

tRNA transports amino acids to the ribosome for incorporation into polypeptides.

Question 38

What does the term 'ternary complex' refer to in translation?

Answer 38

The association of aminoacyl-tRNA, EF-Tu, and GTP.

Question 39

Fill in the blank: The mRNA is read in the _______ direction during translation.

Answer 39

5' to 3'

Question 40

What is the function of the large subunit of the ribosome?

Answer 40

It catalyzes peptide bond formation between amino acids.

Question 41

What are the key components required for protein synthesis?

Answer 41

* Ribosomes * tRNA * mRNA * Accessory factors * Energy (ATP and GTP)

Question 42

What is the primary role of ribosomal RNA (rRNA) in the ribosome?

Answer 42

It forms the structural and functional core of the ribosome.

Question 43

What is a key feature of the secondary structure of rRNA?

Answer 43

It is made up of 40 or more stem loops.

Question 44

Describe amino acid activation

Answer 44

- 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

Question 45

Name the initiation factors in translation

Answer 45

- 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

Question 46

Describe the initiation of translation

Answer 46

- 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

Question 47

Describe elongation in translation

Answer 47

- 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

Question 48

What are the 3 prokaryotic release factors in translational termination?

Answer 48

RF1 = UAA/UAG RF2 = UAA/UGA RF3 = helps RF1 or 2 to bind to ribosome-GTPase

Question 49

Describe termination in translation

Answer 49

- 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