Post-Translational Processing of Proteins and Genetic Code

Question 1

What are the 4 types of post-translational modifications?

Answer 1

protein folding
proteolytic cleavage
chemical modification
protein degradation

Question 2

Why do polypeptides fold?

Answer 2

to adopt its correct tertiary structure

Question 3

protein folding is aided by:

Answer 3

molecular chaperones

Question 4

what are the chaperones in E. coli?

Answer 4

Hsp70 and chaperonins

Question 5

What is the role of chaperones?

Answer 5

they bind to the hydrophobic regions of the proteins to prevent aggregation by holding the protein in an open conformation until it is ready to fold

Question 6

What are the two functions of proteolytic cleavage?

Answer 6

trimming and cutting polyproteins into segments of active proteins

Question 7

describe trimming in terms of proteolytic cleavage

Answer 7

used to remove short pieces from the N and/or C-terminal regions, leaving a single shortened molecule that folds into active proteins

Question 8

where is proteolytic cleavage common?

Answer 8

in eukaryotes in secreted polypeptides

Question 9

describe proteolytic cleavage involving insulin

Answer 9

-synthesized as preproinsulin (105)
-1st 24 aa are removed to give proinsulin
-2 additional cuts leaving A & B chains
-A & B link by disulfide bonds to form mature insulin

Question 10

addition of a small chemical group to the amino or carboxyl groups in a polypeptide

Answer 10

chemical modification

Question 11

what accounts for diversity of a protein?

Answer 11

chemical modification

Question 12

What is the most common chemical modification?

Answer 12

phosphorylation-one or more phosphate groups are added

Question 13

attachment of large carbohydrate side chains

Answer 13

glycolysation

Question 14

involves the regulated post translational modification of substrate proteins via the addition of ubiquitin

Answer 14

protein degradation

Question 15

misfolded or proteins destined for rapid turnover undergo breakdown involving _________________

Answer 15

ubiquitin and the proteasome

Question 16

ubiquitination of substrate proteins signals the protein for ____________

Answer 16

degradation by the proteasome

Question 17

describe the ubiquitination pathway

Answer 17

-protein tagged with ubiquitin
-recognized for degradation
-proteasome degrades protein into peptide subunits

Question 18

triplets of bases corresponding to the amino acids

Answer 18

genetic code

Question 19

how many possible trinucleotide sequences are there

Answer 19

64 possible
61 codons represent amino acids and 3 represent stop codons

Question 20

codons that encode the same amino acid are said to be ____________

Answer 20

synonymous

Question 21

polypeptides are translated from mRNA so the genetic code is usually ______________

Answer 21

RNA bases

Question 22

How do codons reduce the effect of mutation?

Answer 22

since similar amino acids are coded by similar codons, a single base substitution wont cause an entirely different amino acid to be made

Question 23

the base in the 3rd position is not significant because the 4 codons differing only in the 3rd base represent the same aa

Answer 23

third-base degeneracy

Question 24

codon in mRNA must first pair with the anticodon of the corresponding

Answer 24

aminoacyl-tRNA

Question 25

all codons that a particular tRNA recognizes must be identical at which base positions?

Answer 25

the 1st two

Question 26

what is the wobble hypothesis

Answer 26

-accounts for the existence of multiple codons for a single aa
-suggested by crick
-the first two bases of a codon pair according to the normal base pairing rules with the last two bases of the anitcodon

Question 27

why does wobbling occur

Answer 27

the structure of the ribosomal A site permits increased flexibility at the first base of the anticodon