Protein Synthesis

Question 1

translation

Answer 1

polypetide synthesis as directed by mRNA

Question 2

ribosome

Answer 2

catalyst for translation

• made of small and large subunits (composed of proteins and rRNA) which only join for translation
• large subunit contains A, P and E sites

Question 3

tRNA

Answer 3

small RNA molecules with intramolecular base pairing

• 2D structure has 3 loops (picture a clover sorta)
• anticodon is a three nucleotide sequence in the middle loop
• interprets the mRNA by complementary base pairing and translates in into protein

Question 4

anticodon

Answer 4

the tree base sequence on tRNA that pairs to the codon on mRNA

Question 5

amino acid

Answer 5

the monomeric subunit or a polypeptide

Question 6

open reading frame

Answer 6

also called protein coding region

-everything between the start and stop codons

Question 7

codon

Answer 7

a series of 3 adjacent nucleotides that code a specific amino acid

Question 8

start codon

Answer 8

first codon of an open reading frame
always 5’-AUG-3’
codes for protein Met

Question 9

stop codon

Answer 9

last codon of an open reading frame

indicates that no more amino acids should be inserted

Question 10

5’ untranslated region

Answer 10

the region in front of (on the 5’ side) of the open reading frame, is not translated

Question 11

3’ untranslated region

Answer 11

the region behind (on the 3’ side) of the open reading frame, is not translated

Question 12

aminoacyl-tRNA synthetase

Answer 12

enzyme that catalyzes formation of covalent bond between tRNA and an amino acid
-recognizes one specific amino acid and all it’s associated tRNA anticodons

Question 13

A site

Answer 13

aminoacyl-tRNA binding site

entry point for aminoacyl-tRNA into the ribosome

Question 14

P site

Answer 14

peptidyl chain-tRNA binding site (also has an exit tunnel for the growing polypeptide)
site occupied by tRNA molecule covalently attached to the growing peptidyl chain

Question 15

E site

Answer 15

exit site for tRNA molecule out of the ribosome

Question 16

mRNA binding site

Answer 16

a sequence in the 5’ untranslated region of bacterial mRNA that aligns the bacterial ribosome to the correct AUG (start) codon

Question 17

reading frame

Answer 17

refers to the three possible ways to translate a protein coding region, depending on where the ribosome starts to decode the 3-nucleotide codons
-the correct reading frame is established by aligning the ribosome to the start codon

Question 18

peptidyl transferase

Answer 18

when the ribosome (acting as an enzyme) forms the peptide bond between the C-terminus of the growing peptide chain and the N-terminus of the new amino acid
-the peptide chain is transferred from the tRNA in the P-site to the amino acid covalently bonded to the tRNA in the A-site

Question 19

polygenic

Answer 19

an mRNA that codes for more than one protein (occurs in prokaryotes but not eukaryotes, ex trp E,D,C,B,A genes all encoded on the same strand of E. coli mRNA)

Question 20

trp operon

Answer 20

series of open reading frames in E. coli cells that encode the enzymes required to synthesize amino acid tryptophan

Question 21

trpO

Answer 21

operator

• specific DNA sequence where trp repressor protein can bind if active
• regulates trp synthesis
• lies between trp promoter and trp operon

Question 22

trpR

Answer 22

repressor protein

• changes shape in response to [trp] in cell
• when [trp] high, trp binds to the repressor, which binds to the operator and prevents RNA polymerase from binding to the promoter
• otherwise, it stays inactive and free in the cytosol

Question 23

constitutive expression

Answer 23

gene expression that is always active because it isn’t regulated

Question 24

stages of translation

Answer 24

initiation (assemble ribosomal subunits and mRNA, find the start codon)
elongation (adding amino acids to the growing polypeptide chain)
termination (disassemble ribosomal subunits and mRNA at stop codon)

Question 25

heterochromatin

Answer 25

DNA packed super tightly (around histone?) such that transcription machinery cannot bind
-the gene is effectively “off”

Question 26

euchromatin

Answer 26

more dispersed form of DNA that transcription machinery is able to bind to