Translation

Question 1

translation

Answer 1

uses the sequence data carried by mature mRNAs as a blueprint for a polypeptide

Question 2

ribosomes

Answer 2

complex of rRNA and proteins that catalyze translation
rRNA is catalysis agent
large subunit (3 rRNAs and 40 proteins) and small subunit (1 rRNA and 33 proteins) join together during translation

Question 3

initiation (prokaryotes)

Answer 3

small subunit binds to the recognition sequence on mRNA, the Shine-Dalgarno sequence
lines up such that binding to the small ribosomal subunit lines up the start codon in the P site

Question 4

initiation (eukaryotes)

Answer 4

recognition sequence is not the same as the start codon - where translation actually begins
small ribosomal subunit binds to the 5’ cap of the mRNA and moves along until the start codon is reached

Question 5

aminoacyl tRNA synthetase

Answer 5

catalyzes the reaction that binds the amino acid to the tRNA
unique tRNA-synthetase for each amino acid

Question 6

tRNA

Answer 6

each tRNA uniquely binds to one of the 20 amino acids
has an anticodon that complements the codon on the mRNA
third position of the anticodon is not always complementary - wobble base pairing

Question 7

initiation complex

Answer 7

small subunit + mRNA + tRNA
small subunit travels along mRNA from the 5’ cap until the start codon is reached
first tRNA will bind to start codon
large ribosomal subunit joins onto the initiation complex
P site of large subunit lines up with tRNA of the initiation complex

Question 8

heuristic

Answer 8

during elongation, tRNAs are tested in the A site for a match to the mRNA codon
match cannot be determined outside of the A site, so random charged tRNAs are passed through until a match is found

Question 9

A site

Answer 9

a charged tRNA enters the A (aminocacyl site), anti-codon and codon bind
large ribosomal subunit acts as a peptidyl transferase to create a peptidyl bond between the A and P amino acid

Question 10

P site

Answer 10

peptidyl-tRNA
where the new amino acid is added to the growing polypeptide
refers to the peptide bond that is formed

Question 11

ribosome movement

Answer 11

ribosomes move in the 5’->3’ direction, moving the first amino acid into the E site where it leaves the ribosome
second tRNA is now in the P site, holding the growing polypeptide chain

Question 12

dehydration reaction

Answer 12

a dehydration reaction forms a peptide bond and the newly added amino acid becomes the C terminus
polypeptides grown in the N -> C direction

Question 13

E site

Answer 13

exit site
where the empty tRNA sits before being ejected
ribosome moves one more codon in the 3’ direction of mRNA - the uncharged tRNA moves to the exit site

Question 14

release factors

Answer 14

cause translation termination
protein that acts to detach the polypeptide in the P site, binds to the stop codon in the A site
ribosome subunits dissociate when release factor binds to A

Question 15

polysomes

Answer 15

enable rapid translation
many ribosomes attached to one mRNA
stage of translation depends on ribosomes position relative to the mRNA
polysome can have ribosomes in all three stages

Question 16

protein longetvity

Answer 16

mechanism for post-translation regulation
protein content is a function of synthesis and degradation
protein targeted for destruction when ubiquitin is added, attracts other ubiquitin, and forms a polyubiquitin chain

Question 17

proteosome

Answer 17

proteins are digested in a proteosome
protein-polyubiquitin complex binds to a proteosome, a large complex where the ubiquitin is removed and the protein is digested by proteases

Question 18

downregulation

Answer 18

if degradation takes place faster than synthesis, the gene is downregulated