12.3

Question 1

translation

Answer 1

-process of protein synthesis
-basics same in prokaryotes and eukaryotes
-occurs in 3 stages: initiation, elongation, termination
-mRNA provides template
-tRNAs read template and deliver specified amino acids (AAs)
-rRNAs and proteins form translation machinery (ribosome)
-protein synthesis is N-terminus to C-terminus

Question 2

prokaryotic mRNA

Answer 2

contains multiple coding sequences (due to operons)

Question 3

Eukaryotic mRNA

Answer 3

contains a single coding sequence

Question 4

genetic code

Answer 4

-each amino acid is specified by a sequence of 3 nucleotides, the codon
-64 possible codons but only 20 encode amino acids

Question 5

tRNA

Answer 5

-single stranded RNA of 70-80 nucleotides, self folds into ‘cloverleaf’
-AA loaded onto 3’ acceptor end by aminoacyl tRNA synthetase
-anticodon loop recognizes and binds to complementary codon in mRNA

Question 6

tRNA-mRNA base pairing

Answer 6

-cells often express fewer tRNAs than the number of possible codons (61)
some tRNAs can recognize more than 1 codon by wobble

Question 7

wobble

Answer 7

wobble pairing involves less stringent base pairing between 3’ base of codon and 5’ base of the anticodon

Question 8

ribosome

Answer 8

2 subunits
small: decode the mRNA
large: catalyzes peptide bond formation

3 tRNA binding sites
E-site
P- site
A-site

Question 9

E site

Answer 9

(exit) -binds tRNA of previous amino acid

Question 10

P site

Answer 10

(peptidyl)- binds tRNA attached to growing peptide chain

Question 11

A site

Answer 11

(aminoacyl)- holds tRNA attached to the next amino acid

Question 12

initiation: recognition of translation start site (prokaryotes)

Answer 12

1. small subunit binds ribosome binding site (RBS) on mRNA to determine translation start site
2. initator tRNA-N-formyl-Met binds to start codon in the P- site
3. large subunit binds
4. A site open accept next tRNA-AA
5. switch to elongation

Question 13

initiation: recognition of translation start site (eukaryotes)

Answer 13

1. small subunit binds to 5’ cap to determine translation start site
2. tRNA-met binds to start codon in the P- site
3. large subunit binds
4. A site open accept next tRNA-AA
5. switch to elongation

Question 14

termination of translation

Answer 14

-elongation continues untul stop codon (UAA, UAG, UGA) is reached
-release factor recognizes stop codon
triggers release of new polypeptide from P-site tRNA