Translation

Question 1

Where does transcription and translation occur in eukaryotes?

Answer 1

Transcription occurs in the nucleus and mRNA translation occurs in the cytoplasm and eukaryotes, and because of this, mRNA generally last longer in eukaryotes

Question 2

What does colinear refer to in translation?

Answer 2

The sequence of bases pair triplets in the coding region of a gene specifically a Cole linear sequence of amino acids, and it’s polypeptide product
one gene, one colinear polypeptide

Question 3

Who discovered that one gene is one colinear peptide

Answer 3

Bradley and Tatum through the genetic analysis of nutritional mutants

Charles Yanofsky and colleagues

Question 4

Who and How did they discover which codes of nucleotides encode specific protein

Answer 4

Marshall Nuremberg and Johann Matthaei broke the genetic code for amino acid organization
When they added a homopolymer (polyU mRNA) contained 1 radioactively labelled amino acid and 19 unlabelled amino acid. The dude was incubated at 37° in translation took place. The protein was filtered and the procedure was repeated in the 22 each to containing a different labelled amino acid the tube in which the protein with radioactively labelled contains know we synthesize protein with the amino acid specified by the homopolymer so in this case UUU encoded phenylalanine

Basically they broke the genetic code for amino acids

Question 5

Features of the genetic code

Answer 5

Composed of nucleotide triplets called codons
It is degenerate, and some amino acids are specified by more than one codon
It is comma free/ uninterrupted
It is nearly universal

Question 6

Why is there degeneracy in the genetic code? Why is there more than one codon for some amino acids?

Answer 6

There is flexibility in binding at the third position or first anticodon position, known as the wobble position and usually this doesn’t affect what amino acid codes for both codon specified the same amino acid
Often times the base in the third coat on decision can be changed and still specifies the same amino acid
this feature of the genetic code explains degeneracy

Question 7

Inosine

Answer 7

Inosine is an adenine/guanine derivative caused by deamanation of adenine

Second base pair with c, u or a, giving the tRNA a lot more flexibility in terms of pairing partners

It is often on the anticodon wobble position

Question 8

Wobble hypothesis

Answer 8

Non-standard bearings could take place at the third place of a codon

Question 9

What are the macromolecules of translation?

Answer 9

1. Ribosomes - made up of many proteins (>50) and ribosomal rRNA molecules (3-4)
2. Amino acid activating enzymes
3. tRNA molecules
4. Soluble proteins (translation factors) involved in polypeptide chain initiation, elongation and termination

Question 10

Ribosomes

Answer 10

Composed of proteins into several different RNAs
Composed of both a large and small subunit that assemble
A ribosome is an RNA machine with a key roles in protein synthesis, including the formation of peptide bonds between amino acids

Question 11

Prokaryotic ribosome

Answer 11

50S + 30S
= 70S ribosome
30 S subunit contains a 16 S ribosomal RNA that contains the shine dalgarno sequence
Contains 3 rRNAs

Question 12

Eukaryotic ribosome

Answer 12

60S + 40S = 80S
Contains 4 rRNA components

Question 13

Aminoacyl, tRNA synthetase

Answer 13

Each amino acid has its own aminoacyl tRNA synthetase
this enzyme charges the tRNA with its specific amino acid

Question 14

What are the steps of charging a tRNA?

Answer 14

An amino acid becomes attached to the appropriate tRNA by the aminoacyl tRNA synthetase in two-step reaction involving 1. the addition of AMP
2. the addition of tRNA

Question 15

tRNA

Answer 15

Transfer RNAs
The amino acid is covalently attached to the three prime end of the tRNA
tRNAs are adaptors between amino acids, anticodon and mRNA
the anti-codon of the tRNA base pairs with the codon of mRNA

Question 16

Components of the Initiation complex in prokaryotes

Answer 16

mRNA, large and small ribosomal subunits, initiation factors IF 1 to IF 3 and GTP are all required to form the initiation complex

Question 17

Binding of the initiation factors and formation of the initiation complex in prokaryotes

Answer 17

IF3 binds to the small ribosomal subunit, preventing the large one from binding

part of the small ribosomal subunit (16S component) recognizes the Shine-Dalgarno sequence and binds there
tRNA charged with in formal methionine forms a complex with IF2 and GTP, and binds to the initiation codon
while I F1 joins the small ribosomal subunit
All initiation factors, dissociate, and GTP is hydrolyzed to GDP
the large subunit the joins to create a 70 S initiation complex

Question 18

What are the differences between initiation of translation in eukaryotes vs. prokaryotes

Answer 18

The amino group of methionine is not formulated (fMET), so it’s just MET
The initiation complex forms at the five prime terminus of the mRNA at the 7 MG 5’ cap structure. There is no Shine-Dalgarno sequence.
The ribosome initiation complex scans inward for the first AUG
The Kozak sequence is there
The poly A tail of eukaryotic mRNA interacts with the mRNA 5’ 7-MG cap structure via a cap binding protein complex to promote translation initiation

Question 19

Draw initiation in eukaryotes with the cap binding proteins

Question 20

Elongation

Answer 20

I charged tRNA, binds to the A side of the ribosome (requires complex formation of EF Tu plus GTP)
Once in the A site, GTP is hydrolyzed to GDP and is released along with EF-Tu
rRNA in large subunit catalyzes the formation of the peptide bond between the two in amino acids
Polypeptide chain is transferred to the amino acid in a site
Then EFGNGTP are needed to move the ribosome along the mRNA sequence. The tRNA does not move with the ribosome because it is bound by complementary base pairing. The second amino tRNA is now in the P site.
A new amino SLT only again binds to the A site and the cycle is repeated

Question 21

EF-Tu

Answer 21

Helps with the binding of the tRNA to the A site
Forms a complex with GTP which is then hydrolyzed to GDP + Pi once tRNA is bound to A site

Question 22

EF-G

Answer 22

Helps move the ribosome down the mRNA

Question 23

What direction does the ribosome move along the mRNA?

Answer 23

5’ to 3’

Question 24

Termination

Answer 24

Polypeptide chain termination occurs when a chain termination codon also known as a stop codon enters a site of the ribosome
There are no tRNAs that bind to stop codons
When a stop codon, is encountered a release factor binds to the A site
The release factor 1 & 2 binding promotes the cleavage of the polypeptide chain from the tRNA, releasing the chain and leading to termination the binding of release factor three and GTP to the ribosome assist in the dismantling of the entire complex

Question 25

RF 1

Answer 25

Release factor one
Recognizes UAG and UAA stop codons
Binding promotes the cleavage of the polypeptide chain from tRNA

Question 26

RF2

Answer 26

Recognizes UAA and UGA stop codons
Binding promotes the cleavage of the polypeptide chain from tRNA, releasing the chain and leading to termination