2.2 - Protein Structure Flashcards

1
Q

amino acid group at acid pH

A

protonated

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2
Q

carboxyl group at basic pH

A

ionised

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3
Q

amino acid group and carboxyl group at neutral pH (2)

A
  1. amino acid group = protonated
  2. carboxyl group = ionised

(total charge = 0)

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4
Q

amino acid ion state at physiological pH

A

zwitterions

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5
Q

zwitterions

A

molecules that contain both positively and negatively charged functional groups with an overall charge of 0

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6
Q

amino acid shape

A

chiral

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7
Q

chiral

A

asymmetric in such a way that the structure and its mirror image are not superimposable

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8
Q

amino acid form in biological systems

A

L form

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9
Q

peptide bonds

A

linkage of carboxyl group of one amino acid to amine group of another, with elimination of a water molecule

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10
Q

why are peptide bonds planar?

A

due to sharing of electrons

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11
Q

Trans-peptide group

A

R groups at opposite ends

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12
Q

Cis-peptide group

A

R groups next to each other

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13
Q

why is the core amino acid chiral in 19/20 amino acids?

A

because it has 4 different groups

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14
Q

stereoisomers

A

same molecular formula and atomic connectivity, but their atomic arrangement in space is different

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15
Q

which amino acid cant exist as a stereoisomer?

A

glycine-R=hydrogen atom

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16
Q

Enantiomers (2)

A

amino acids can be:
1. L (left)
2. D (right)

17
Q

amino acid enantiomers found in proteins in living organisms

A

L amino acids

18
Q

enantiomers

A

two stereoisomers related to each other by a reflection (mirror images of each other, which are non-superimposable)

19
Q

number of amino acid combinations for a 100 residue protein

20
Q

amino acid classes (5)

A
  1. non-polar
  2. polar
  3. acidic
  4. basic
  5. generic
21
Q

how are amino acids abbreviated?

A

three letter and one letter abbreviations

e.g. Alanine, Ala, A

22
Q

unique properties of glycine (

A
  1. side chain is - H
  2. glycines occur in tightly packed protein regions
23
Q

unique properties of proline (3)

A
  1. introduces “kink” in chain
  2. can form ‘cis’ backbone
  3. difficult to fit into category, shares many properties with aliphatic amino acids
24
Q

what increases the hydrophobicity of amino acids?

25
Q

amino acids with aromatic R groups (3)

A
  1. Phe
  2. Tyr
  3. Trp
26
Q

feature of aromatic amino acids

A

absorb UV light

27
Q

wavelength of light absorbed by Trp and Tyr at neutral Ph

28
Q

wavelength of light absorbed by Phe at neutral pH

29
Q

how are disulfide bonds formed? (2)

A
  1. side chains d cysteine contain highly reactive thiol group
  2. two thiol groups form disulfide bond
30
Q

effect of oxidising/reducing environments on disulfide bonds (2)

A
  1. formed in oxidising environments
  2. broken in reducing environments
31
Q

purpose of disulfide bridge

A

link distant amino acids

32
Q

cytochrome c

A

protein found in all aerobic organisms and protein sequences from distantly related species such as mammals and bacteria (similar enough to conclude proteins are homologous)

33
Q

what does the globin gene encode for?

A

haemoglobin

34
Q

haemoglobin in adults

A

iron containing heme molecule surrounded by 4 globin proteins (2 a-globins and 2 B-globins)

35
Q

how does sickle cell anaemia result from defective haemoglobin? (2)

A
  1. haemoglobins stick together
  2. RBCs damaged
36
Q

what causes sickle cell anaemia?

A

single mutation (significant change to protein structure and RBC structure as a result)