L02

Question 1

what are the features of post translational modification PMT

Answer 1

covalent addition to or cleavage of proteins

After protein biosynthesis

important component of cell signalling

occurs on the amino-acid chain or at a terminal

extending the 21 aa’s available

Question 2

PMT can be reversible or irreversible

Answer 2

True

Question 3

what are the types of PMTs

Answer 3

cleavage

methylation

acetylation

disulfide bond

glycosylation

phosphorylation

Question 4

when would cleavage take place

Answer 4

secondary structure or beyond

Question 5

what protein is an example for PMT cleavage

Answer 5

insulin

Question 6

what peptide is removed from insulin

Answer 6

C

Question 7

what produces mature insulin

Answer 7

carboxypeptidase E

Question 8

what are the features of phosphorylation

Answer 8

One of the most common/well studied

1/3 of cellular proteins thought to be phosphorylated at any given time

reversibly add/remove phosphate

causes conformational change in the protein

activate or deactivate an enzyme (phosphate has 2 neg charges so causes conformational change)

activation forms a site recognised by other proteins

deactivation can mask a binding site preventing protein -protein interaction

Question 9

what are protein kinases

Answer 9

Enzymes that catalyse the transfer of a phosphate group from a high energy donor molecule to a specific substrate- phosphorylation

Question 10

how many protein kinases are characterised so far

Answer 10

513

Question 11

how many protein kinases have a homologous catalytic domain

Answer 11

478

Question 12

phosphorylation is unidirectional

Answer 12

true

Question 13

what are phosphatases

Answer 13

enzyme catalyse the removal of a phosphate group from a substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group (dephosphorylation

Question 14

protein phosphatases are often in a chain

Answer 14

True

Question 15

what is glycosylation

Answer 15

a carbohydrate (monosaccharide to complex) is covalently bound to a functional group (e.g. hydroxyl) on a protein, via a glycosidic bond

Question 16

how many glycosylation disorders

Answer 16

40

Question 17

glycosylation is Built on Dolichol- which ‘anchors’ to the membrane

Answer 17

true

Question 18

what are the types of glycosylation

Answer 18

N-linked

O-linked

Glypiation

C-linked

Phosphogly-cosylation

Question 19

what are the features of N-linked glycosylation

Answer 19

Glycan bind to the amino group of asparagine

happens in the ER

examples: insulin receptor, ECM, regulation

Question 20

what are the features of O-linked glycosylation

Answer 20

Monosaccharides bind to the hydroxyl group serine or threonine

happens in ER, Golgi, cystosol and nucleus

example: collagen, a number of pathogenic bacteria (e.g. clostridium toxins)

Question 21

what are the features of glypiation glycosylation

Answer 21

Glycan core links a phospholipid and a protein

example: anchors cell surface proteins

Question 22

what are the features of C-linked glycosylation

Answer 22

Mannose binds to the indole ring of tryptophan

Example: only mammalian cells, ECM

Question 23

what are the features of Phosphogly-cosylation glycosylation

Answer 23

Glycan binds to serine via phosphodiester bond

Question 24

what are the features of Acetylation

Answer 24

1. addition or removal of an acetyl group
2. donated by acetyl co-enzyme A
3. Can be enzymatic or non-enzymatic
4. enyzmes involve Acetylase or Deacetylase
5. co- or post-translational modification

-80-90% of human proteins are co-trans acetylated at the Nα-termini of the nascent polypeptide chains

-co- = modification of an amino acid as the translation occurs

6. particular proteins are chromosome related and this indicates its importance in gene expression

Question 25

what are the types of acetylation

Answer 25

N-terminal Lysine acetylatio

Question 26

what are the features of N-terminal acetylation

Answer 26

1. most common co-transational modification in eukaryotes 2. synthesis localisation stability 3. 80-90% of human proteins

Question 27

what are the features of Lysine acetylation

Answer 27

1. often acetylation and deacetylation cycle is linked to transcription factors (e.g. p53) 2. activation of gene expression

Question 28

features of acetylation in histones

Answer 28

Histone acetyltransferase/deacetylase (HDAC or HAT, now KDAC and KAT) Located in cytoplasm or nucleus Acetylation removes the +ve charge from the histone meaning the DNA wraps less tightly acetylation of histones encourages binding of effector proteins, relaxation of chromatin conformation, and an increase in transcription also in the synthesis, stability and localization of other proteins. High level acetylation associated with transcriptional hyperactivity

Question 29

which amino acids undergo methylation

Answer 29

lysine (once, twice or three times) arginine (once or twice)

Question 30

which enzyme reverses methylation

Answer 30

demethylase

Question 31

what is an example of a molecule that donates a methyl group

Answer 31

S-adenosylmethionine

Question 32

compare carbonyl methylation to nitrogen methylation

Answer 32

carbonyl methylation is generally reversible and used to modulate a reaction nitrogen methylation however are generally irreversible creating new amino acids

Question 33

compare lysine methylation and arginine methylation

Answer 33

arginine methylation 1. regulation of RNA processing 2. Gene transcription 3. DNA damage repair 4. protein translocation 5. signal transduction lysine methylation 1. histone function regulation 2. epigenetic regulation of transcription 3. Lysine Methyltrasferase (KMT)