lecture 21 - translation

Question 1

cellular messengers

Answer 1

receptor proteins stud the outside of your cells and transmit signals to partner proteins on the inside of the cells

Question 2

muscles

Answer 2

muscle protein called actin and myosin enable all muscular movememt. from blinking to breathing to rollerblading

Question 3

hair and nails

Answer 3

protein called alpha-keratin froms your hair, fingernals and also is the major component of feathers, wool, claws, scales, horns, hooves

Question 4

brain and nerves

Answer 4

ion channel proteins control brain signaling by allowing small molecules into and out of nerve cells

Question 5

enzymes

Answer 5

in you saliva, stomach, and small intestine are proteins that help you digest food

Question 6

cellular construction workers

Answer 6

huge clusters of proteins form molecular machines that do your cells heavy work such as copying genes during cell division and making new proteins

Question 7

The genetic code

Answer 7

1. the DNA sequence encoding a protein is read in triplets, or codons
2. 61/64 codons are sense codons
3. three stop codons, signal termination of translation
4. the code is degenerate (redudant): a single AA can be encoded by more than one codon (20 common aa)
5. AUG codes for methionine, usually start of translation

Question 8

ORF (open reading frame)

Answer 8

a run of sense codons before a stop codon is encountered

Question 9

translation requires 4 primary components

Answer 9

• ribosomes - site of translation
• mRNA template
• tRNAs - adaptors
• aminoacyl-tRNA synthetases

Synthesis of a single polypeptide chain requires a coordinated action of atleast 100 proteins and RNAs

Question 10

transfer RNA (tRNA) as adaptor

Answer 10

Adaptor molecules recognize codons in mRNA and carry specific amino acids

Question 11

tRNA 2D structure

Answer 11

the structure of the tRNA molecyke reveals how it is capable of functioning as an adaptor
- a small molecule, single stranded, 73-93 nt
- each tRNA represents a single aa which it can covalently bind (3’ terminal A residue)

• coverleaf - secondary structure, held together by H-bonds

Question 12

amino acid attachment site on tRNA

Answer 12

3’-OH end

Question 13

T loop

Answer 13

ribothymidine and pseudoridine

Question 14

D loop

Answer 14

dihydrouridine

Question 15

each tRNA contains anticodon

Answer 15

complementary to the codon, representing its aa

Question 16

3D structure of tRNA

Answer 16

3D (twisted) L shaped structure
- formed by 2 extended helices perpendicular to each other
- D and (TpsiC) T loops come “together”
- the shape must be the same for each tRNA so it can “fit into ribosome”
- anticodon and the acceotir arm are at opposite ends of the L structure

Question 17

each tRNA has an anticodon sequence

Answer 17

that will base pair with a codon in mRNA (antiparallel)

Question 18

2 first nucleotides of each codon

Answer 18

are the primary determinants of specificity, and the difference between cofons usually lies at the third position

Question 19

wobble enables one tRNA to recognize two or more codons

Answer 19

a min. of 32 tRNAs are required to recognize a;; the amino acid codons

31 tRNAs for the amino acids and one for initiation

Question 20

watson crick base pairing

Answer 20

61 different tRNAs would be required

Question 21

wobble base pairing

Answer 21

the 3rd base of codon and 1st of anticodon can form “unusual” base pairing - the rules are more relaxed because of the “geometry”.

The wobble hypothesus was formalized by F. Crick

the 5’ nucleotide in the anticodon is in the wobble position

the wobble bases allow a single tRNA anticodon to bind more than one mRNA codon

Question 22

in the wobble position ..

Answer 22

• G can pair with U
• I (inosine) can pair with U,C,A

Question 23

charging of rRNAs

Answer 23

aminoacyl-tRNA synthetases charge tRNAs (attach correct aa)

Question 24

tRNA(ala)

Answer 24

is an uncharged tRNA specific for alanine

Question 25

Ala-tRNA(ala)

Answer 25

is a tRNA specific for alanine that is charged with alanine

Question 26

aminoacyl-tRNA synthetases:

Answer 26

amino acids are activated and linked to specific tRNAs

• two step process that uses ATP
• takes place in the cytoosol (the enzymes active site)

steps:
1. Adenylylation step = the AA is linked to adenylate, forming aminoacyl-AMP
2. tRNA charging step

Question 27

amino acyl mechanism

Question 28

aminoacyl-tRNA synthetases attach the correct amino acids to their tRNAs

Answer 28

• 20 different aminoacyl-tRNA synthetases: one per amino acid
• each enzyme is specific for one amino acid but can recognize ALL tRNAs for that amino acid (isoaccepting or cognate)
• recognition of tRNAs
  1. anticodon arm
  2. acceptor arm