The Genetic Code, Translation & Roles of RNA

Question 1

Crick, Brenner et al experiment to crack genetic code

Answer 1

bacteriophage T4 used that infects E.coli
generated mutants in eII gene of bacteriophage

can see how mutations affect the wild type by shifts in the rest of the sequence

Question 2

how is genetic code of mRNA read?

Answer 2

read in 3 nucleotides
to create codons

some a.a. have more than one tRNA (degenerate)
some tRNA can tolerate mismatch at 3rd codon

Question 3

what is the genetic code?

Answer 3

universal
many variations are known in mitochondria & some nuclear genomes

Question 4

what ate the roles of tRNA in translation?

Answer 4

mRNA: codes for proteins
rRNA: (ribosomal RNA) form basic structure of ribosome & catalyse protein synthesis
tRNA: adaptors between mRNA and amino acids

Question 5

RNA in translation

Answer 5

1. mRNA carries genetic info
2. tRNA deciphers codons of mRNA
3. rRNA makes up the ribosome

Question 6

1. how does tRNA deciphers codons in mRNA?

Answer 6

1. enzymes couple correct amino acids to tRNA
2. anticodon tRNA pairs with mRNA codon
   delivering correct amino acid to mRNA

Question 7

what is the structure of a ribosome?

Answer 7

large complex of 4 RNAs & >80 proteins

large and small subunit of ribosome
3 sites: A, P, E
enters via A site and leaves via E

Question 8

what are the three stages of translation?

Answer 8

Initiation
Elongation
Termination

Question 9

what are the steps in initiation?

Answer 9

1. initiator tRNA binds to small subunit at the start codon
2. allows large subunit to then bind to small subunit & ribosome to assemble
3. P- site in ribosome filled with initiator tRNA

Question 10

what are the steps in elongation?

Answer 10

1. correct tRNA bind to the mRNA codon in A site
2. tRNA amino acid then transferred to the initiator tRNA amino acid
3. empty tRNA can then move through exit site & be released
4. ribosome slides down mRNA leaving a space for a corresponding tRNA in the A site

Question 11

what are the steps in termination?

Answer 11

1. reach the STOP codon
2. tRNA that binds to STOP has a termination factor attached
3. translation ends
4. ribosomal subunits disassemble & released the newly synthesised protein