protein synthesis

Question 1

What tRNA is used?

Answer 1

Aminoacyl-tRNA synthetases govern the correct translation of genetic code through loading of tRNAs with correct amino acid

Question 2

What are ribosomes?

Answer 2

-70S ribonucleoprotein particles made of a small 30S and large 50S subunits

Question 3

How is triplet code redundant?

Answer 3

-there are 20 amino acids that make up most portiens
-64 possible triplet codons to encode for those (64 possibilities with 4 bases)-so several diff triplet codon sequences can encode from same amino acid

Question 4

how is triplet code unambiguous?

Answer 4

-each codon can only encode 1 specific amino acid

Question 5

How does protein synthesis start?

Answer 5

-with initiation of codon AUG which codes for amino acid methionine

Question 6

What are reading frames?

Answer 6

-specified by the start codon and strength of ribosome binding site
-3 reading frames are possible within a 4 letter encoded triplet decoded sequence

Question 7

What is aminoacyl-tRNA?

Answer 7

-anticodon is template-recognition site
-amino acid attached to 3’ end

Question 8

which end is amino acid attached to

Answer 8

3’ end

Question 9

What is loading/amino-acylation?

Answer 9

-Amino-acylation of tRNA is the process of attachment of amino acids to their corresponding tRNA molecules

Question 10

How does amino acid attach

Answer 10

It is esterified to the 3’ hydroxyl group of the terminal adenosine of tRNA

Question 11

What is structure of tRNA

Answer 11

-amino acid attachment site
-extra arm
-anticodon loop
-phosphorylated 5’ terminus

Question 12

What do tRNAs contain?

Answer 12

-several modified nucleosides
E.g.
* Methylinosine (ml)
* Dihydrouridine (UH2)
* Ribothymidine (T)
* Psuedouridine ()
* Methlguanosine (mG)
* Dimethylguanosine (m2G)
Inosine (I) – part of anticodon

Question 13

L shaped structure

Answer 13

-This is referred to as the L-shaped structure of tRNA.
-The end of one arm is the anticodon, the other is the CCA stem.
-Intramolecular base-pairing in tRNA assists with its 3-D structure in terms of formation and stability.

Question 14

Ribosome structure

Answer 14

-RNA/protein hybrid structures
-site of peptide bond formation contains only RNA (yellow) with no protein (red) within

Question 15

What is aminoacyl tRNA synthesise

Answer 15

-enzymes that attach the amino acids to tRNAs
-highly specific for each amino acid
-need to read anticodon to be able to differentiate between amino acids with similar structures
-have proofreading function to hydrolyse wrongly charged tRNAs

Question 16

how does amino acid attach to trna

Answer 16

flexible cya arm can move the amino acid between the activation site and the editing site of aminoacyl trna
-if amino acid fits into editing site, it will be removed via hydrolysis

Question 17

How big is rRNA

Answer 17

-70S

Question 18

What is it made up of

Answer 18

-50S subunit, 30S subunit

Question 19

What is secondary structure of rRNA

Answer 19

16s

Question 20

How is tertiary structure of rRNA determined

Answer 20

-by X-ray crystallography

Question 21

What is polycistronic mRNA

Answer 21

-an mRNA corresponding to multiple genes whose expression is also controlled by a single promoter and a single terminator.
-occurs in prok
-has multiple translation start sites / ribosome binding sites
-happens in prokaryotic mRNA
-produces several proteins

Question 22

What is monocistonic mRNA

Answer 22

monocistronic mRNA produces a single protein while polycistronic mRNA produces several proteins that are functionally-related.
-Occurs in euk mRNA
-has single translation start site
-can produce 1 protein

Question 23

what is polysome

Answer 23

transcription of a segment of E. coli DNA generates mRNA molecules that are immediately translated by multiple ribosomes. a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”. It consists of a complex of an mRNA molecule and two or more ribosomes that act to translate mRNA instructions into polypeptides.

Question 24

How is translation initiated?

Answer 24

-there is translation initiation site and a region on mRNA which is responsible for binding to ribosomes via interaction of 16S rRNA

Question 25

What are elongation factors?

Answer 25

-Elongation factors e.g. EF-Tu are proteins that deliver aminoacyl-tRNA to the ribosome in the cytosol.

Question 26

How many tRNA binding sites are there in ribosome and why

Answer 26

-3 that bridge the 30S and 50S subunits
-E site, P site, A site

Question 27

What is polypeptide escape path

Answer 27

-a tunnel passes through 50S subunit
-the growing polypeptide chain is extruded through this tunnel

Question 28

Role of protein factors in protein synthesis

Answer 28

-translation initiation in prokaryotes requires initiation factors to aid assembly of 30S initiation and then assembly of 70S initiation complex

Question 29

What happens at P site

Answer 29

peptidyl tRNA in P site

Question 30

What happens inn A site

Answer 30

aminoacyl-tRNA binds in A site]

Question 31

What happens due to this

Answer 31

with both sites occupied, a new peptide bond is formed
-translocation occurs freeing up A site
-allows deacylated tRNA to dissociate

Question 32

What is the wobble hypothesis?

Answer 32

-tRNA molecules can recognise more than one codon – enabling redundancy in the genetic code as one tRNA recognises several codons. There can also be several tRNAs with the same amino acid for different anticodons. inosine can be anticodon for U/C/A in pork, but only U and C in elk

Question 33

Translation Fidelity:

Answer 33

• Translation of long proteins requires a low error frequency
  Probability of synthesising an error free protein

Question 34

How many amino acids translated epr second in ecoli?

Answer 34

40 amino acids

Question 35

What is the error rate?

Answer 35

The error rate is approximately 10-4 or 1 in 10,000