Week 6 lecture material

Question 1

Is genetic code the same as gene sequence?

Answer 1

NO

Question 2

What are the reading frames for aa sequence?

Answer 2

Start reading from 5’ AUG and go towards 3’.

Question 3

Do translation and transcription start from the same site?

Answer 3

No, transcription has promoters and the start later on, translation has a start codon AUG and immediately start from there.

Question 4

What are the 3 types of mutations that can occur when you have nucleotide base pair substitution?

Answer 4

1. Silent mutation: change in single base pair yet codes for the same aa
2. Missense: New amino acid code
3. Nonsense: Codes for stop.

Question 5

What do TRNA’s do?

Answer 5

1. They recognise codons on mRNA nad bring the proper aa
2. TRNA’s are about 80 nucleotides long
3. Has 5’ end and 3’ end transcribed as usual
4. It base paris with itself in regions (double helical regions)
5. Aa gets attached to 3’ end
6. ANticode binds to the mRNa anti parallel and complementart
7. There are modified bases

Question 6

Which position is flexible in TRNA?

Answer 6

The 3’ on the mRNA and 5’ on the TRA are the flexible positions.

Question 7

How is redudency managed for translation?

Answer 7

There are two strategies:
1) More than 1 tRNA for many aa
2) Some tRNAs can recognise and base pair with more than 1 codon

Question 8

Do eukaryotes have more flexibility than bacteria in codon and anticodon?

Answer 8

No, bacteria has more flexibility than eukaryotes and I = inosine often in 5’ antiwobble position

Question 9

How do you make sure right aa is made on TRNA?

Answer 9

we relie on base pairing and aminoacetyl-tRNA synthetases.

Aminoaceltyl synthases take the right aa and use ATP to attach the right aa on the TRNA. there are 20 aminoacetly synthases, 1 for each aa

Question 10

If mistakes happen with aminoacetyl-tRNA how is it fixed?

Answer 10

By hydrolytic editing

Question 11

Which end on the TRNA is the acceptor arm?

Answer 11

The 3’ end, it recognises the right aa

Question 12

How is recognishion achieved in TRNA?

Answer 12

1. Identify the tRNA anticodon nucleotides, this is done by glutamine aminoactlyl-trna synthase
2. Regognise the nucleotide sequence (at the acceting arm 3’ end)
3. Reading the nucleotide at additional places.

Question 13

How many sub units does ribosome have?

Answer 13

2 subunits, large (many proteins many ribosomal RNA) and small (many proteins 1 ribosomal rna).

Question 14

How many sites does ribosome have and what are they?

Answer 14

A: aminoacyl site
P: peptidyl site
E: exit site

Question 15

Where are the ribosomes located in eukaryotes?

Answer 15

In the endoplasmic reticulum and in the cytosol

Question 16

Where is peptide bond formed in the ribosome?

Answer 16

It is formed in the peptidyl transferase activity in the rRNA in the large subunit

Question 17

What are ribozime?

Answer 17

RNA molecule that posses catalytic activity

Question 18

For quality control and check what does EF-tu do in eukaryotic cell?

Answer 18

EF-Tu doesnt exsist in eukaryotic cell, this is in bacterial cell it checks the amino acyl trna. Humans have EF-1

Then it goes with it at the A site, it also checks if the base pariing is correct, if it is nit EF-Tu wont release and peptide bond wont form.

If it is correct, GTP gets hydrolysed and EF-tu is released.

There is a slight delay before the polypeptide bond is formed as there is one last checking

Question 19

After the checking and attaching onto the Psite how is it moved into the A site?

Answer 19

EF-G (in prokaryotes) and EF2 in humans helps the ribosome to move the mRNA forward one codon and helps to speed up the elongation of the polypeptide chain.

Question 20

Can ribosomes perform protein synthesis without the aid of elongation factor?

Answer 20

ye but its slower and inefficient

Question 21

What is the role of elongation factors?

Answer 21

Improve speed and efficiency and error checking funtion

Question 22

What is the elongation mediated by?

Answer 22

GTP hydrolysis and release of EF-Tu (bacteria), EF-G (bacteria)

EF-Tu binds aminoacyl-TRNA (EF1 in humans)
EF-G: helps ribosome move mRNA 1 codon (EF2 in humans)

Question 23

Do bacteria have poly A tail and caps?

Answer 23

NO

Question 24

What is polycistronic mRNA?

Answer 24

Multiple proteins coding for one mRNA in PROKARYOTES

Question 25

What are ribosome binding sequence also called in prokaryotes?

Answer 25

Shine Dalgaro Sequences

Question 26

What basepairs in ribosomal subunits in bacteria or prokarytoes?

Answer 26

Shine Dalgano Sequences or ribosome binding sites

Question 27

How does initian of translation take place in prokaryotes or bacteria?

Answer 27

Ribosome binding sites or Shine -Dalgarno sequences on mRNA base paris with rRNA in small ribosomal subunits

Positioning of small subunits to initiating AUG codons on mRNA also requires Inition factors

fMethionine aminoacyl trna binds to inititor codon

Large ribosomal subunit binds.

Question 28

How does translation termination occur?

Answer 28

Human release fator or proteins (not TRNA) are used.

Question 29

What do both eukaryotes and prokaryotes have?

Answer 29

Polyribosomes or polysomes. They are ribsomes essentially one after the other. It is relatively slow. The gap is about 80nt.

Question 30

How is protein folded?

Answer 30

These are proteins that help in the protein folding as they emerge after translation.

Question 31

what are post translation modifications to the proteins?

Answer 31

1. Phosphorylation and Glycosylation is required for most proteins.

Some need covalent modifications to make proteins active and recruit protein to correct membrance or organelle.

Question 32

How are old proteins destroyed in cells?

Answer 32

a target protein called polyubiquitin chain is attached to the protein and taken to proteasome, proteases sees this and degregates it.

Question 33

What are antibiotics?

Answer 33

Many inhibitors that hurt bacteria by screwing up bacterial translations