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MCAT Biochem > 1 - Amino Acids, Peptides, Proteins > Flashcards

1 - Amino Acids, Peptides, Proteins Flashcards

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MCAT flashcards
1
Q

What groups make up amino acid

A

Amine (-NH2), carboxyl (COOH), H, R group

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2
Q

Name for 20 amino acids

A

Proteinogenic amino acids

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3
Q

The alpha carbon is generally ____ meaning they are optically ___

A

Chiral, active

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4
Q

Which amino acid is not optically active

A

Glycine - R group is hydrogen

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5
Q

Why are amino acids L-amino acids

A

NH2 is drawn on left of Fischer projection for S configuration in eukaryotes

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6
Q

Which amino acid does not have S-sterochemistry

A

Cysteine - R stereo bring L-amino acid

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7
Q

Which amino acids have a chiral carbon in R group

A

Threonine (T) and isoleucine (I)

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8
Q

Nonpolar, nonaromatic amino acids

A

IVGLAMP
Isoleucine, valine, glycine, leucine, alanine, methionine, proline

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9
Q

Which 2 amino acids have S in it

A

Methionine (—S—), cysteine (HS—)

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10
Q

Why is proline unique

A

Has cyclic R group - limits flexibility, found at start of alpha helixes or folds of ß-sheets

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11
Q

Uncharged aromatic amino acids

A

FWY
Phenylalanine, tryptophan, tyrosine

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12
Q

Nonpolar, aromatic amino acids

A

FW
Phenylalanine, tryptophan

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13
Q

Polar, aromatic amino acids

A

Y
Tyrosine

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14
Q

Why is the thiol group in cysteine important

A

Prone to oxidation (disulfide bridges)

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15
Q

Polar, nonaromatic amino acids

A

STNQC
Serine, threonine, asparagine, glutamine, cysteine

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16
Q

Acidic (negative) amino acids

A

DE
Aspartame (aspartic acid), glutamate (glutamic acid)

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17
Q

Basic (positive) amino acids

A

KRH
Lysine, arginine, histidine

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18
Q

Hydrophobic amino acids

A

ALIVF
Alanine, leucine, isoleucine, valine, phenylalanine

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19
Q

Hydrophilic amino acids

A

HQDRENK
Histidine, glutamine, aspartate, arginine, glutamate, asparagine, lysine

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20
Q

Why are amino acids amphoteric

A

Can become positive or negative (accept or donate proton)

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21
Q

What does the first pKa refer to

A

COOH

22
Q

What does the second pKa refer to

A

NH2

23
Q

What does zwitterion mean

A

Hybrid ion - both positive and negative charged ends

24
Q

What does the titration curve look like when pH is close to pKa

A

Slope becomes flat - implies same amount of intermediates
[NH2—COO-] equals [NH3+—COO-]

25
Q

What does pI mean

A

Isoelectric point - the pH where the molecule is electrically neutral

26
Q

How do you calculate pI

A

Take average of the pKa
If basic, average the 2 amino pKa
If acidic, average the 2 carboxyl pKa

27
Q

What are peptides made of

A

Amino acids, residues

28
Q

Oligopeptide vs polypeptide

A

Oligo: 4-20 amino acid chain
Poly: 21+ amino acid chain

29
Q

How are peptide bonds formed

A

Electrophilic carbonyl is attacked by NH3+

30
Q

What type of reaction is peptide bond formation

A

Condensation or dehydration (remove water)

31
Q

Where is there limited rotation in backbone of peptide chain

A

Between the N-C=O bond due to resonance
It can become N=C-O

32
Q

What catalyzes hydrolysis

A

Hydrolytic enzymes - add H to amino side, add OH to carbonyl side

33
Q

Functions of proteins (4)

A

Enzymes, hormones, membrane pores and receptors, elements of cell structure

34
Q

What bond is involved in primary structure

A

Peptide bond (covalent)

35
Q

What bond is important in secondary structure

A

H-bonds

36
Q

Describe alpha helixes

A

Turn clockwise, stabilized by intramolecular H-bonds, R groups face out

37
Q

Describe beta sheets

A

Held together by H-bonds, R groups face up/down the plane, makes a chain

38
Q

Fibrous proteins

A

Long strands/sheets like collagen

39
Q

Globular proteins

A

Globe-like, spherical like myoglobin

40
Q

How is tertiary structure controlled

A

Hydrophobic ends go inside stabilizing protein
Hydrophilic ends form electrostatic interactions outside

41
Q

What structure are disulfide bridges important in, what does it do

A

Tertiary structure, it creates loops - can determine curliness of hair

42
Q

What are intermediate steps in protein folding called

A

Molten globules

43
Q

What makes up quaternary structure

A

Aggregate of globular peptides, subunits

44
Q

4 reasons why quaternary structure is advantageous

A

Increase stability by decreasing surface area
Reduce amount of DNA needed to code for that protein
Bring catalytic sites closer together
Cooperativity/allosteric effects - one conformational change in subunit can enhance/reduce activity of other subunits

45
Q

Conjugated vs simple proteins

A

Simple - only made of the 20 amino acids
Conjugated - functions by interacting with prosthetic groups

46
Q

Examples of prosthetic groups

A

Organic molecules (vitamins) or metals (iron)

47
Q

3 different prosthetic groups attached to protein

A

Lipid - lipoprotein
Carbohydrate - glycoprotein
Nuclei acid - nucleoprotein

48
Q

Function of prosthetic group

A

Deliver protein to a specific location (nucleus, membrane, lysosome, ER)

49
Q

What happens during denaturation, what causes it

A

Tertiary structure is broken by heat or solutes

50
Q

How does heat denature protein

A

Overcome hydrophobic interactions and cause protein to unfold

51
Q

How do solutes denature protein

A

Urea - break disulfide bridges, overcome H-bonds in secondary structure
Detergent - solubilize protein by destroying any bond (noncovalent) and promote denaturation

MCAT Biochem (2 decks)

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