Translation

Question 1

1. mRNA (messenger RNA) 3.5%

Answer 1

• Varies in length (100,000 kinds, few copies of each)
• Acts as the intermediary between DNA and the ribosomes
• Translated into protein by ribosomes
• RNA version of the gene encoded by DNA

Question 2

2. rRNA(ribosomal RNA) ~80%

Answer 2

• There are few kinds with many copies of each
• Binds with proteins to form the ribosomes
  rRNAs are processed and assembled into ribosome subunits in the nucleolus – the main site of ribosome biogenesis

Question 3

3. tRNA (transfer RNA) 15%

Answer 3

• Very short: 70-90 bp (~40 kinds, many copies of each)
• Functions as the delivery system of amino acids to ribosomes

Question 4

Codons:

Answer 4

triplets of nucleotides ; U,A, G, C

Question 5

how many codons and stop codons

Answer 5

64 codons
-> 61 code for an amino acid
-> 3 stop codons -> UGA, UAA, UAG

e.g. codon: AUG
Anticodon: UAC

Question 6

TRNA role

Answer 6

they read codons on messenger RNAs (mRNAs) and deliver the appropriate amino acid to the ribosome for protein synthesis.

Question 7

TRNA charging -> how do we get the amino acid to bind to the 3’ end?

Answer 7

Amino acids needs ATP and then releases PP to create an amino acid with AMP.

The AA-AMP and tRNA meet at the Amino Acyl tRNA Synthetase Enzyme. Then the AMP is released resulted in a charged tRNA.

Question 8

Ribosomes subunit sizes

Answer 8

large: 60s
small: 40s

Question 9

what do ribosomes consist of

Answer 9

rRNA and proteins

Question 10

Initiation

Answer 10

Eukaryotic initiation factor type 4 identifies the mRNA

Small ribosomal subunit binds to mRNA with imitation factors.

Eukaryotic initiation factor type 2 binds tRNA – that contains anticodons that are complementary to those in mRNA. e.g. start codon : AUG

GTP bound to Eukaryotic initiation factor type 2 gets broken down to GDP + Pi

Then the APE site (large ribosomal subunit) binds to mRNA. -> GDP is release along with Pi and EIFs

Question 11

do flash cards when finished video on elongation and termination

Question 12

Proteins Are Made on Polyribosomes

Answer 12

The synthesis of most protein molecules takes - 20 seconds and several minutes (2 aa/sec!)

The mRNA molecules being translated are usually found in the form of polyribosomes
(or polysomes): large cytoplasmic assemblies made up of several ribosomes spaced as close as 80 nucleotides apart along a single mRNA molecule

Question 13

RNA and Ribosomes:

Answer 13

RNAs, and not proteins, are responsible for the ribosome’s overall structure, its ability to position tRNAs on the mRNA, and its catalytic activity in forming covalent peptide bonds

Question 14

Characteristics of the genetic code:

Answer 14

Comma less exception: viruses
Non overlapping exception: viruses
Redundant / degenerate -> wobble hypothesis

Question 15

Wobble hypothesis:

Answer 15

Codon–anticodon base pairing is less stringent than the standard A-U and G-C base pairing and this is the base of the redundancy of the genetic code (most amino acids are specified by more than one mRNA codon)

Some tRNAs are constructed so that they require accurate base- pairing only at the first two positions of the codon and can tolerate a mismatch (or “wobble”) at the third position

5’ base of anticodon and hence 3’ base of codon is in the “wobble” position, allowing a single tRNA species to recognise more than one codon *inosine in tRNAs is formed from the deamination of adenosine, a chemical modification that takes place after the tRNA has been synthesized.

Question 16

Frameshift mutations:

Answer 16

A frameshift mutation is a type of mutation involving the insertion or deletion of a nucleotide that shifts the grouping and changes the reading frame.

-> Crohn’s disease, cystic fibrosis, sickle cell anaemia, Tay-Sachs disease and certain types of cancer can be caused by frameshift mutations.

Question 17

Activation of K-Ras proto-oncogene by mutation

Answer 17

The most frequent K-Ras mutation in human cancers is K-RasG12V

K-Ras mutations are observed in 17%–25% of all cancers; most frequently in pancreatic (80% - 90%), lung (~30%) and colorectal (30% - 40%) cancers

Question 18

Activation of TERT oncogene by mutation

Answer 18

TERT gene promoter mutations generate de novo consensus binding motif for ETS/TCF transcription factors resulting in increased expression of TERT gene

TERT gene promoter mutations are observed in ~ 30% of primary melanomas