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NSF > Proteins > Flashcards

Proteins Flashcards

1
Q

anabolic

A

building up

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2
Q

catabolic

A

breaking down

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3
Q

sequence to get a prot

A
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4
Q

roles of prots

A
  1. stryctural - collagen, keratin, fibroin
  2. movement - muscle fibres actin + myosin
  3. immune sys - antibodies
  4. endocrine sys - hormones + receptors
  5. transport - Hb, transferrin (Fe carrier)
  6. biological catalysis - enzs
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5
Q

general structure alpha aas

A
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6
Q

zwitterions

A

dipolar ion = no net charge unless R grp charged

aas in sol at normal physiological pH normally zwitterions

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7
Q

isomers alpha aas

A

asymmetric mols so 2 diff forms - optical isomers/enantiomers
* mirror images but can’t be superimposed onto each other

in biology prots only contain L form
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8
Q

Types aas

A
  1. electrically charged side chains
  2. polar uncharged side chains
  3. hydrophobic side chains
  4. special cases
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9
Q

polar meaning

A

has pos + neg ends as charge not evenly distributed throughout

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10
Q

which aa tends to be found in coils

A

proline

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11
Q

prot primary structure

A

sequence aas joined peptide bonds bet carboxyl grp 1 aa + amino grp next

occur by condensation reaction where H20 mol removed

by convention: N-terminal on left

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12
Q

prot secondary structure

A

determined + maintained by H bonds bet O + H
* w/in prot backbone, not bet R grps

  1. alpha helix = folded into spiral w outer surface covered R grps to interact other prots etc
    * CO grp residue n bonded NH grp residue (n+4)
  2. beta-pleated sheets in parallel (sequences same direction) or anti-parallel (opp)
    * can be diff peptide chains or 1 chain folded (therefore antiparallel)
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13
Q

prot tertiary structure

A

arrangement in space of aas, held together by diff interactions determined by sequence aas:
* disulphide bond
* side chain H bonding
* electrostatic attraction
* hydrophobic interactions - hydrophobic R grps sit together to avoid contact w water
* metal ion coordination

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14
Q

prot quaternary structure

A

interactions bet diff peptide chains by same side chain interactions:
* disulphide bond
* side chain H bonding
* electrostatic attraction
* hydrophobic interactions
* metal ion coordination

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15
Q

3 main types prot

A
  1. globular
  2. fibrous
  3. membrane
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16
Q

globular prots

A
  • fold into compact structures - often w cleft for small mol
  • usually hydrophobic side chains inside, hydrophillic outside to interact w aqueous environ = soluble
  • majority prots
  • e.g. enzs, antibodies
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17
Q

fibrous prots

A
  • multiple strands held together strong bonding
  • usually insoluble + structural
  • e.g. collagen (skin, bone, tendon), keratin (hair, nails, horn), fibroin (silk)
18
Q

mem prots

A
  • hydrophobic regions sit in cell mem
  • transmit mols + signals in/out cells
  • e.g. channels + receptors
19
Q

prion disease

A

disease starting from prot malformation:
genetic switch flipped + prot gradually to mainly beta sheets = sticky + aggregate , causing neuronal cell death

prions = infectious prots

20
Q

bovine spongiform encephalopathy (BSE)

mad cow disease

A

neurodegenerative prion disease brain + spinal cord
* 2.5-8yr incubation
* transmissable to humans if you eat infected meat

21
Q

role of enz

A

act as biological catalyst by increasing RoR w/o being changed themselves
* decrease activation E by:
1. bringing substrates together
2. excluding water
3. stabilising transition state
4. transferring chem grps

22
Q

enz active site

A

3D region of enz that performs catalytic reaction, usually involving making/breaking bonds by binding substrate + converting it to product

binds specific aa side chains by weak forces:
* electrostatic interactions
* H bonds
* Van der Waals forces
* hydrophobic interactions
* sometimes reversible covalent bonds

forms predominantly non-polar environ

23
Q

how are enzs made specific

A

properties + spatial arrangement relatively few aas at AS determine which mols can bind + so substrates

24
Q

induced fit model for enz-substrate binding

A

as binds, aas move slightly to pull substrate in, change its structure slightly - for closer fit

so AS shape changes slightly

most enzs have this model

25
Q

types enz-substrate binding

A

isosteric + allosteric

26
Q

describe isosteric enz-substrate binding

A

RoR incrreases w substrate conc until enz saturated

parameters defining enz activity from ‘Michaelis-Menten’ plot initial rate + substrate conc, showing how quickly substrate converted product

most enzs

hyperbolic curve then plot
27
Q

allosteric enz-substrate binding

A

enz changes to increase rate if substrate and/or effectors present
* e.g. multiple ASs - substrate binds 1, increasing activity others; or causes change in shape of all to fit (induced fit)
* each subunit own AS + allosteric sites where subunits join - something binds there + changes shape ASs so can accept substrate

allosteric site = anywhere other than AS where something can bind

don’t display Michaelis-Menten kinetics

sigmoidal curve

interaction of 1 triggers same conformational change in all subunits = cooperativity

28
Q

allosteric regulation

A

regulating effectors change enz’s shape + function by binding weakly allosteric site - inhibition or stimulation
* binding of activator stabilises conformation w functional AS
* binding of inhibitor stabilises inactive enz form

most have 2 or more polypeptide chains (subunits)

29
Q

enz feedback regulation

A

metabolic pathway w several enzs + series of reactions to end-product, producing intermediates
* end-product can act allosteric inhibitor early stage enz to save E + prevent build-up intermediates

30
Q

types enz inhibitor

A
  1. competitive - binds AS instead substrate
  2. non-competitive - binds allosteric site irrespective of whether substrate bound
  3. uncompetitive - only binds enz-subs complex
  4. allosteric - binds @ allosteric site; could be competitive if near AS, uncompetitive or non-competitive
31
Q

factors affecting enz activity

A
  1. substrate/enz conc
  2. pH
  3. temp - more can overcome ae
  4. post-translational modifications
  5. cofactors
32
Q

how post-translational modification affects enz activity

A

REVERSIBLE COVALENT ATTACHMENT
of small non-prot grp, most common phosphorylation-dephosphorylation as causes change 2/3 structure
* hydroxy side chains (serine, threonine, tyrosine) phophyd (OH grp to bind to)
* rapid reversible switch turn metabolic pathway on/off

PROTEOLYTIC ACTIVATION
enz synthed as larger, inactive precursor form (proenz/zymogen)

premature activation causes canine pancreatitis - autodigestion of pancreas
33
Q

how cofactors affect enz activity

A

many enzs require presence small non-prot unit to function
* inorganic ions
* complex organic mols (=conenzs) - sometimesreded/oxed during reaction

34
Q

what are proteinases

= proteases

A

enzs that cleave prots + may activate other enzs
e.g. blood clotting cascade where 1 removes prodomain enz + activates, does same for another + so on

35
Q

types proteases

A
  • serine
  • cysteine
  • aspartate
  • metalloproteinases
  • threonine proteinase
36
Q

serine proteinases

A

reactive serine residue at AS, e.g. trypsin

37
Q

cysteine proteases

A

cysteine at AS

38
Q

aspartyl proteinases

A

aspartate at AS

39
Q

metalloproteinases

A

metal ion (often Zn2+) at AS

40
Q

threonine proteases

A

threonine at AS, e.g. proteasome

41
Q

isoenzymes

= isozymes

A

diff forms of enz that cat same reaction, therefore similar AS
* usually derived diff genes + occur diff tissues

42
Q

what is a multi-enz complex

A

aggregation several enzs/coenzs into single functional unit usually to perform multi-step transformation

proximity enzs to each other:
* increases RoR
* minimises side reactions
* intermediates immediately available as susbtrates for next reaction

e.g. fatty acid synthase involved lipid biosynthesis

NSF (22 decks)

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