Week 6: Translation

Question 1

Where does translation take place?

Answer 1

In the cytosol

Question 2

True or False: the genetic code is the sequence of DNA that makes up the organism

Answer 2

False

Question 3

What makes up the genetic code?

Answer 3

3 nucleotides and 1 amino acid (UGU codes for Cysteine)

Question 4

How are codons read?

Answer 4

mRNA triplets

Question 5

How does the genetic code account for the 64 codons but only 20 amino acids?

Answer 5

Redundancy - multiple codons code for the same amino acid (e.g. GUU, GUC, GUA, and GUG all code for Valine)

Question 6

How are reading frames determined?

Answer 6

They are determined by translation initiation bat the 5’ AUG

Question 7

How do reading frames with the same nucleotide sequence differ from each other?

Answer 7

Different reading frames may begin translation at different nucleotides and because nucleotides are read 3 at a time, different amino acids can be coded for

Question 8

Is the start site for translation the same at the start site for transcription?

Answer 8

No, there is UTR before the first AUG

Question 9

How are mutations classified?

Answer 9

They are classified by the effect on the nucleotide, the amino acid, and protein

Question 10

What are the three different types of nucleotide-pair substitutions?

Answer 10

Silent, missense, nonsense

Question 11

What is a silent mutation?

Answer 11

The nucleotide change does not affect the amino acid coded for

Question 12

What is a missense mutation?

Answer 12

The nucleotide change changes the amino acided coded

Question 13

What is a nonsense mutation?

Answer 13

The nucleotide change causes an early stop codon (no amino acid)

Question 14

What are the effects of nucleotide pair deletions/insertions

Answer 14

They can cause an immediate change to the frameshift (i.e. a missense or nonsense mutation)

Question 15

What makes a 3 nucleotide-pair deletion different from the rest?

Answer 15

Because 3 nucleotides are deleted, the frame shift does not go through any immediate changes, there is just one amino acid missing

Question 16

At which end is the Amino Acid attached to in tRNA?

Answer 16

the 3’ end

Question 17

In what direction is the genetic code read in?

Answer 17

5’-3’

Question 18

How do tRNAs translate mRNAs?

Answer 18

tRNA recognizes the codon on mRNA via its anticodon and brings the correct amino acid

Question 19

About how long are tRNAs?

Answer 19

80 nucleotides long

Question 20

How is codon redundancy in genetic code managed during translation?

Answer 20

• More than 1 tRNA for many amino acids
• Some tRNAs can recognize and base pair with more than 1 codon

Question 21

What is the wobble position?

Answer 21

The wobble position is where there’s a bit of flexible base pairing between the anticodon of the tRNA and the codon of the mRNA. It’s the 3’ position of the codon and the 5’ position of the anticodon.

Question 22

What is aminoacyl-tRNA synthease?

Answer 22

Aminoacyl-tRNA synthase is a key player in fidelity and error correction via hydrolytic editing. It gets the amino acid puts it on the correct tRNA.

Question 23

How is recognition achieved beteween a specific tRNA and its synthase?

Answer 23

• Identifying the tRNA anticodon nucleotides
• Recognizing the nucleotide sequence of the acceptorstem/arm
• Reading nucleotide sequences at additional positions on the tRNA

Question 24

What makes up a eukaryotic ribosome and what are they made of?

Answer 24

Large subunit: ~49 ribosomal proteins + 3 rRNA molecules
Small subunit: ~33 ribosomal proteins + 1 rRNA molecule

Question 25

Where are ribosomes located (in eukaryotes)?

Answer 25

In the endoplasmic reticulum and in the cytosol

Question 26

What do each of the sites on a ribosome stand for?

Answer 26

**A**= aminoacyl site **P**= peptidyl site **E** = exit site

Question 27

What makes peptide synthesis energetically favourable?

Answer 27

The energy stored in covalent bonds between the amino acid and tRNA in P site

Question 28

What catalyzes peptide bond formation in translation?

Answer 28

The peptidyl transferase activity of the rRNA in the large subunit

Question 29

Why is a ribosome a ribozyme?

Answer 29

Because of RNA molecules that posses catalytic activity

Question 30

In the elongation of the amino acid chain, what does EF-Tu (EF1 in euk.) check for in aminoactyl tRNA?

Answer 30

1. The right amino acid 2. the right anticodon-codon base pair

Question 31

What happens if the base-paring is not correct between an anticodon and codon?

Answer 31

EF-Tu/EF1 is not released, denying the formation of a peptide bond

Question 32

What happens if the base-pairing is correct between anticodon and codon?

Answer 32

GTP is hydrolyzed & EF-Tu/EF1 released

Question 33

Why is there a slight delay before formation of a peptide bond between amino acids?

Answer 33

It allos for one last check for accurate base-pairing

Question 34

What is EF-G/EF2's role in elongation?

Answer 34

It helps the ribosome to move the mRNA forward one codon and helps speed up elongation of the polypeptide chain

Question 35

Can protein synthesis happen without the use of elongation factors?

Answer 35

Yes but it would be much slower, inefficient, and would most likely have more mistakes

Question 36

What does it mean when bacteria has polycistronic mRNA?

Answer 36

There is more than one protein for one mRNA

Question 37

Describe the initiaiton of translation in **prokaryotes**

Answer 37

1. Shine-Dalgarno sequences on mRNA base pair with rRNA in small ribosomal subunits 2. Positioning of small subunits to initiating AUG codons on mRNA also requires Initiation Factors (IFs) 3. fMethionine aminoacyl tRNA binds to initiator coon 4. Large ribosomal subunit binds

Question 38

Describe the initiation of translation in **Eukaryotes**

Answer 38

1. tRNA conects to small ribsomal subunit (with initiation factors bound) without mRNA 2. both then connect to mRNA strand at 5' cap 3. once recognizing 5' most AUG, anticodon binds to AUG 4. translation initiation factors dissociate 5. large ribosomal subunit binds 6. tRNA binds to the second codon 7. first peptide bond is formed

Question 39

What terminates translation?

Answer 39

A translation release factor, which in humans is a protein, not tRNA. It recognizes and binds to the stop codon, releasing the newly synthesized polypeptide chain.

Question 40

What is a polyribosome/polysome?

Answer 40

It is when there are multiple ribosomes making the same protein simultaneously, which is relatively slow and about 80 nulcelotides apart

Question 41

What helps proteins fold?

Answer 41

Chaperone proteins (e.g. Hsp60, Hsp 70)

Question 42

What are examples of post-translational modifications?

Answer 42

* phosphorylation * glycosylation

Question 43

Why might covalent modifications be required in post-translational modifications?

Answer 43

It may be required to: - make protein active - recruit protein to correct membrane or organelle

Question 44

Proteins that are targeted for degredation have a small protein call ubiquitin covalently attached to them, which directs them to the ____________ where they are degraded by ____________, and the amino acids recycled into new proteins by the cell

Answer 44

proteasome; proteases

Question 45

What do many antibiotics target?

Answer 45

bacterial translation

Question 46

If chemicals are active on bacteria and eukaryotes or only eukaryotes, can they be considered antibiotics?

Answer 46

NO! They're poison and most likely used in the lab for experiments.