Translation

Question 1

What is Transfer RNA?

Answer 1

A transfer RNA is a small RNA molecule that:

• binds a specific amino acid
• recognises the corresponding codon in messenger RNA by base pairing (anticodon)

Question 2

What is the start codon? (Bases)

Answer 2

AUG

Question 3

What does the start codon do?

Answer 3

Specified the beginning of translation. Codes for methionine.

Question 4

What are the 3 stop codons?

Answer 4

UAG, UGA, UAA

Question 5

What do the stop codons do?

Answer 5

Specify the end of translation

Question 6

Which directions do anticodons go?

Answer 6

5’ to 3’

Question 7

Which direction do codons go?

Answer 7

3’ to 5’

Question 8

What is the secondary shape of tRNA?

Answer 8

Clover leaf- in reality an L-shape molecule- 3 loops folded on top of each other with a stem (loop because they do not base pair to one another

Question 9

What does aminoacyl-tRNA synthetase do?

Answer 9

Joins the correct amino acid to the tRNA

Question 10

Why can some tRNAs recognise more than one codon?

Answer 10

Because of imperfect “wobble” base pairing

Question 11

Where does the imperfect “wobble” occur?

Answer 11

At the third position of the codon

Question 12

How are T & C, and A & G similar?

Answer 12

Are chemically similar

Question 13

Where does protein synthesis take place?

Answer 13

Ribosomes.

Question 14

What are ribosomes?

Answer 14

Complex structures containing RNA and protein

Question 15

What are ribosomes made up of?

Answer 15

Has two subunits- 1 large and 1 small. Has binding sites for mRNA and for tRNA (E,P,A sites)

Question 16

What is the difference in colour between the large and small subunits of a ribosome?

Answer 16

The large is lighter green

Question 17

Describe protein synthesis (the basics)?

Answer 17

. Messenger RNA binds to ribosome
. Aminoacyl-tRNAs recognise and bind to base triplets in mRNA
. The ribosome transfers the growing polypeptide to the new amino acid
. Protein is extended from amino terminus to carboxy terminus
. Initiation, elongation and release factor proteins assist the process

Question 18

What is the initiation mechanism?

Answer 18

Process involves initiation factor proteins:

1. Methionyl-tRNA (in eukaryotes) or formylmethionyl-tRNA (in bacteria) binds to P site in small subunit of ribosome
2. mRNA binds to the small subunit; start codon binds to tRNA anticodon
3. Large subunit of ribosome binds
4. Aminoacyl-tRNA for second amino acid binds A site on ribosome
5. Protein synthesis proceeds as for elongation

Question 19

Describe the elongation mechanism

Answer 19

1. Messenger RNA is bound to the small subunit of the ribosome. The growing polypeptide is attached to tRNA in the P site of the ribosome
   Aminoacyl-tRNA for the next amino acid recognises and binds to the mRNA bade triplet in the A site of the ribosome
2. The ribosome transfers the growing polypeptide from the peptidyl-tRNA in the P site to the new aminoacyl-tRNA
3. The large subunit moves relative to the small subunit
4. The ribosome is “reset” so that the next tRNA can bind
5. The “spent” tRNA is ejected from the E site and the next aminoacyl-tRNA binds

(If the wrong tRNA comes along it will be rejected)

Question 20

What is the P site?

Answer 20

Where the growing polypeptide chain is

Question 21

Where does the energy for protein synthesis come from?

Answer 21

The hydrolysis of GTP

Question 22

Describe how GTP is used to provide energy in protein synthesis

Answer 22

1. EF-Tu (in bacteria; called EF1 I’m eukaryotes) carries aminoacyl-tRNA to the ribosome. EF-Tu also binds GTP. If bade pairing is correct, EF-Tu releases aminoacyk-tRNA and hydrolyses GTP to GDP and phosphate
2. EF-G (I’m bacteria;called EF2 in eukaryotes) with bound GTP binds to the A site. It hydrolyses GTP and resets the ribosome ready for the next aminoacyl-tRNA

Question 23

Describe the termination mechanism of translation

Answer 23

Translation ends at the first in-frame stop codon (UAA or UAG or UGA).

1. Release factor protein binds to A side instead of tRNA
2. Peptidyl-tRNA bond is hydrolysed, releasing newly synthesised protein
3. Ribosome dissociates into large and small subunits (so that the process can start again)

Question 24

Give examples of model organisms

Answer 24

. Escherichia coli (bacteria)
. Saccharinyces cerevisiae (yeast)
. Fruit flies
. Mice
. Humans

Question 25

Cells only rise from pre-existing cells. What are the requirements for this?

Answer 25

. Raw materials . Energy source . Information- this is what the genes provide, along with the structure

Question 26

What is responsible for the differences between organisms?

Answer 26

. Differences between gene products (sequence of amino acids in proteins) . Differences in patterns of gene expression (under what circumstances genes get turned on and off)

Question 27

Compared to ribose what does deoxyribose lack?

Answer 27

An O on the 2’ carbon

Question 28

How many hydrogen bonds are between A and T?

Answer 28

2

Question 29

How many hydrogen bonds are between G and C?

Answer 29

3

Question 30

DNA and RNA are chemically similar but RNA has...

Answer 30

. Ribose (extra O to DNA) instead of deoxyribose . U instead of T. Only difference between the two is the presence of a methyl group makes no difference to the base pairing

Question 31

How are the amino acids in proteins joined together?

Answer 31

By peptide bonds- the carboxylate group of one amino acid and the amino group of the next in the chain (results in the loss of water)

Question 32

What is transfer RNA?

Answer 32

A small RNA molecule that: - binds a specific amino acid - recognises the corresponding codon in messenger RNA by base pairing anticodon if the transfer RNA

Question 33

Describe Aminoacyl-tRNA synthase**

Answer 33

Group of enzymes that decides which amino acid to put into the transfer RNA). Joins the correct amino acid to the tRNA at its terminus which requires energy from ATL hydrolysis, but in the case below it requires a lot of energy so it actually hydrolyses ATO-ADP and then to adenosinemonophosphate, releasing 2 phosphates and therefore getting more energy than if you only went from ATP-ADP

Question 34

Describe the structure of ribosomes

Answer 34

Contains RNA and protein. Rach ribosome has two subunits-a small one and a large one. The ribosome has bonding sires for mRNA and for tRNAs (E, P, A sites)

Question 35

Describe the basics of protein synthesis

Answer 35

. Messenger RNA binds to ribosome . Aminoacyl-tRNAs recognise and bind to base triplets in mRNA (transfers polypeptide to the amino acids) . The ribosome transfers the growing polypeptide to the new amino acid (is transferring the polypeptide to the amino acid) . Protein is extended from amino terminus to carboxyl terminus . Ribosomes get help from a additional proteins called the: initiation, elongation and release factor proteins assist the process

Question 36

Describe the first step of the initiation mechanism

Answer 36

. Methionyl-tRNA (in eukaryotes) or formylmethionyl-tRNA (in bacteria) binds to P surge in small subunit of ribosome. First codon is AYG however, I’m bacteria the methylene group is chemically modified by the addition of the formyl group. So bacteria start with cornel-methylene

Question 37

Describe the second step of the initiation mechanism

Answer 37

MRNA binds to the small subunit:start codon binds to tRNA anticodon (which would be CAU) this positions the messenger RNA in the right place to start protein synthesis

Question 38

What happens in stages 3,4 and 5 in the initiation process?

Answer 38

3. Large subunits of ribosome binds 4. Aminoacyl-tRNA for second amino acid binds to A dire on ribosome 5. Protein synthesis proceeds as for elongation

Question 39

What happens in the first rage of the elongation process?

Answer 39

mRNA is bound to the small subunit of the ribosome. The growing polypeptide is attached to the tRNA in the P site of the ribosome. Have the large subunit attached. Amino acid-tRNA for the next amino acid recognises and binds to the mRNA bade triplet in the A-sure if the ribosome m. If the tRNA does not match the codon then it is rejected so, the tRNA will not bind until it is the right one. The tRNA is ejected so, the E-sure stands for ejected

Question 40

What happens in the second stage of elongation?

Answer 40

The ribosome transfers the growing polypeptide from the peptidyl-tRNA in the P-sure to the new aminoacyl-tRNA (if the wrong tRNA comes along it will be rejected). So the polypeptide chain has grown by A single amino acid in length.

Question 41

What stages in stages 3,4 and 5 of the elongation process?

Answer 41

3. Large subunit moves relativ to the small subunit. So, the small subunit stays where it was 4. The ribosome is reset, by sliding in 2 steps, so that the next tRNA can bind. So opposite 5. The “spent” tRNA is ejected from the E site and the next aminocyl-tRNA binds

Question 42

What are he roles of elongation factors?

Answer 42

1. EF-Tub(in bacteria; called EF1 in eukaryote) carries aminoacyl-tRNA to the ribosome. EF-Tu also binds GTP. If base pairing is correct, EF-Th releases aminoacyl-tRNA and hydrolyes GTP to GDP and phosphate (EF-Tu and EF1 are pretty much the same thing) 2. EF-G (calmed EF2 in eukaryotes) with bound GTP binds to the A sure. It hydrolyses GTP and resets the ribosome ready for the next amino acid-tRNA

Question 43

What happens in the termination mechanism?

Answer 43

1. Release factor protein binds to A site instead of tRNA. This is shown with AUG as it has no tRNA 2. Peptidyl-tRNA bond is hydrolysed, releasing newly synthesised protein 3. Ribosome dissociates into large and small subunits (process can start again)