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BMS2002 > L02 > Flashcards

L02 Flashcards

1
Q

what is post translational modification PMT

A

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

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2
Q

PMT can be reversible or irreversible

A

True

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3
Q

what are the types of PMTs

A

cleavage

methylation

acetylation

disulfide bond

glycosylation

phosphorylation

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4
Q

when would cleavage take place

A

secondary structure or beyond

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5
Q

what protein is an example for PMT cleavage

A

insulin

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6
Q

what peptide is removed from insulin

A

C

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7
Q

what produces mature insulin

A

carboxypeptidase E

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8
Q

what are the features of phosphorylation

A

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

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9
Q

what are protein kinases

A

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

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10
Q

how many protein kinases are characterised so far

A

513

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11
Q

how many protein kinases have a homologous catalytic domain

A

478

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12
Q

phosphorylation is unidirectional

A

true

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13
Q

what are phosphatases

A

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

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14
Q

protein phosphatases are often in a chain

A

True

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15
Q

what is glycosylation

A

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

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16
Q

how many glycosylation disorders

A

40

17
Q

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

A

true

18
Q

what are the types of glycosylation

A

N-linked

O-linked

Glypiation

C-linked

Phosphogly-cosylation

19
Q

what are the features of N-linked glycosylation

A

Glycan bind to the amino group of asparagine

happens in the ER

examples: insulin receptor, ECM, regulation

20
Q

what are the features of O-linked glycosylation

A

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)

21
Q

what are the features of glypiation glycosylation

A

Glycan core links a phospholipid and a protein

example: anchors cell surface proteins

22
Q

what are the features of C-linked glycosylation

A

Mannose binds to the indole ring of tryptophan

Example: only mammalian cells, ECM

23
Q

what are the features of Phosphogly-cosylation glycosylation

A

Glycan binds to serine via phosphodiester bond

24
Q

what are the features of Acetylation

A
  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

  1. particular proteins are chromosome related and this indicates its importance in gene expression
25
Q

what are the types of acetylation

A

N-terminal

Lysine acetylatio

26
Q

what are the features of N-terminal acetylation

A
  1. most common co-transational modification in eukaryotes
  2. synthesis
    localisation
    stability
  3. 80-90% of human proteins
27
Q

what are the features of Lysine acetylation acetylation

A
  1. often acetylation and deacetylation cycle is linked to transcription factors (e.g. p53)
  2. activation of gene expression
28
Q

features of acetylation in histones

A

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

29
Q

which amino acids undergo methylation

A

lysine (once, twice or three times)

arginine (once or twice)

30
Q

which enzyme reverses methylation

A

demethylase

31
Q

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

A

S-adenosylmethionine

32
Q

compare carbonyl methylation to nitrogen methylation

A

carbonyl methylation is generally reversible and used to modulate a reaction

nitrogen methylation however are generally irreversible creating new amino acids

33
Q

compare lysine methylation and arginine methylation

A

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)

BMS2002 (14 decks)

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