Lecture 31

Question 1

Translation: Initiation

Answer 1

small subunit binds mRNA
first codon (AUG) on mRNA moves to P site on ribosome
large subunit binds, forming E,P,A sites for translation

Question 2

translation

Answer 2

components: mRNA, tRNA, ribosome
stages: initiation, elongation, termination

Question 3

Translation: Elongation

Answer 3

• elongation factor (EF-Tu) binds to charged tRNA and to GTP and brings them to A site of ribosome
• peptide bond forms between AA in P site and AA in A (peptide = bond between AA) catalyzed by peptidyl transferase on ribosome
• tRNA in P site is empty and tRNa in A site has growing AA chain
• ribosome translocates(moves to next codon on mRNA)
• empty tRNA moves to e site, tRna with AA chain –> P site, A site ready to accept next charged tRNA: cycle repeats until the end
• eventually tRNAs in the E site are ejected

Question 4

Translation: termination

Answer 4

• stop codon enters A site (UAA, UGA, UAG)
• stop codons do not bind tRNA, bind release factors
• dissociate entire complex, releases new protein

Question 5

Messenger RNA (mRNA)

Answer 5

made up of codons, uses bases U, A, C, G

Question 6

codon

Answer 6

• a block of information on mRNA, made of a set of 3 bases; specifies an amino acid
• 64 possible codons for only 20 amino acids

Question 7

Transfer RNA (tRNA)

Answer 7

• 2D structure: clover leaf
• 3D structure: L-shape
• 2 functional ends: acceptor stem that binds amino acid (3’) and anti-codon loop of 3 sequential nucleotides that are complimentary to 1 codon on mRNA

Question 8

initiator tRNA

Answer 8

charged with special amino acid (formylmethionine aka fmet)

Question 9

ribosome

Answer 9

site of protein synthesis (where translation occurs) composed of protiens, enzymes (peptidyl transferase), ribosomal RNA (rRNA) when large and small subunits come together, they form 3 binding sites (P, A, and E)

Question 10

stop codons

Answer 10

UAA, UGA, UAG

Question 11

start codon

Answer 11

AUG

Question 12

formylmethionine

Answer 12

charges initiator tRNA

Question 13

elongation factor (EF-Tu)

Answer 13

binds to charged tRNA and GTP and brings them to A site of ribosome

Question 14

genetic code

Answer 14

sequences of nucleotides that make each strand of DNA unique

Question 15

Degenerate

Answer 15

some amino acids are specified by multiple codons

Question 16

peptide bond

Answer 16

forms between amino acid in P site and amino acid in A site catalyzed by peptidyl transferase on ribosome

Question 17

cloverleaf

Answer 17

2D structure due to complementary binding in molecule

Question 18

acceptor stem

Answer 18

3’ end binds amino acid (one end of the 3D structure)

Question 19

release factor

Answer 19

stop codons bind with these in step 2 of termination, then in step 3 they dissociate the entire complex, releasing new proteins

Question 20

anticodon loop

Answer 20

on tRNA is amino acid, tRNA binds to mRNA at the UUU codon

Question 21

charging reaction

Answer 21

• happens on enzyme called aminoacyl tRNA synthase active site, specific amino acid will react with ATP and attach AMP to carboxyl end of amino acid
• specific tRNA with appropriate anticodon binds to ezyme
• amino acid transferred to acceptor stem of tRNA with energy from AMP (energy from AMP is used to drive reaction)
• charged tRNA leaves enzyme and goes to ribosome

Question 22

aminoacyl tRNA synthease

Answer 22

where the charging reactions occur

Question 23

anticodon

Answer 23

on tRNA is AAA it binds to the UUU codon on mRNA

Question 24

ribosomal small subunit

Answer 24

binds mRNA

Question 25

ribosomal large subunit

Answer 25

binds after AUG codon binds in P site forming the E P and A sites for translation

Question 26

Peptidyl transferase

Answer 26

enzyme catalyzing translation

Question 27

P site (peptidyl)

Answer 27

binds tRNA attached to amino acid chain

Question 28

A site (aminoacyl

Answer 28

binds charged tRNA

Question 29

E site (exit)

Answer 29

binds empty tRNA (no AA attached)

Question 30

GTP

Answer 30

gets bound to charged tRNA and brought to the site A of the ribosome

Question 31

amino acids

Answer 31

translated from DNA strand, the codons all code for a certain amino acid and they make a protein

Question 32

translocation

Answer 32

fourth step of elongation: ribosome moves to the next codon on mRNA, empty tRNA is moved to E site, tRNA with AA chain to the P site, and A site is ready to accept next charged tRNA

Question 33

L-shaped

Answer 33

3D structure of tRNA, clover leaf folds in on itself forming L-shaped structure has 2 functional ends: acceptor stem and anti-codon loop