1-amino acids Flashcards

1
Q

which C is C1

A

the C=O one

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2
Q

which C is C2

A

alpha carbon

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3
Q

do all amino acids have beta carbon

A

all but glycine

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4
Q

which aa have branced beta carbons

A

valine and isoleucine

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5
Q

which aa have branched gamma (4) carbons

A

leucine

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6
Q

what is the weight of free aa (average)

A

128Da

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7
Q

what is the weight of aa residue (average)

A

110Da

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8
Q

what makes the difference in average weight of free aa and residue

A

the mass of water from peptide bond formation

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9
Q

how many H bonds can histidine donate

A

2 when protonated

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10
Q

how many H bonds can histidine accept

A

none when protonated

1 if non protonated

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11
Q

how many H bonds can amides donate

A

2 (from NH2)

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12
Q

how many H bonds can amides accept

A

2 (2 lone pairs on C=)

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13
Q

how many H bonds can arginine donate (just the R group)

A

5

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14
Q

rate
Phe, Tyr, His, Trp
in order of decreasing polarity

A

His, tyr, Trp, Phe

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15
Q

where do tyrosine and tryptophan absorb strongly in ultraviolet

A

280nm

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16
Q

when does cysteine become cystine

A

oxidizing environments - extracellular/lumen

17
Q

what is lost in the reaction to make cystine

A

2H+ and 2e-

18
Q

is cysteine polar or non polar

A

polar

19
Q

is cystine polar or non polar

A

non-polar

20
Q

how are some uncommon amino acids made

A

modification of amino acids after incorporation into a polypeptide chain (PTM)

21
Q

is L or D more common

A

L

22
Q

what is the pKa of a functional group at the pH

A

when base and acid forms are equal

23
Q

does the acid or base form predominate below the pKa

A

acid

24
Q

does the acid or base form predominate above the pKa

A

base

25
Q

what is a zwitterion

A

net charge at zero, has x amount of negative and x amount of positive

26
Q

what does diprotic mean

A

there are two titratable groups (COOH and HN3+)

27
Q

is it generally negative or positive above the pI

A

negative

28
Q

is it generally negative or positive below the pI

A

positive

29
Q

how do you find the net average charge on the moledule

A

add the net average charge on each potentially charged functional group

30
Q

what is the isoelectric point of a moledule

A

pH at which the overall/net charge on a molecule is zero (equivalent negative and positive)

31
Q

how do you calculate pI for diprotic amino acids

A

average of pK1 and pK2

32
Q

how do you calculate pI for triprotic amino acids

A

average pK values bounding species with net 0 charge

33
Q

how many buffering regions in triprotic amino acids

A

3

34
Q

what can change the pKa for functional groups

A

presence of electron withdrawing groups or other charged groups

35
Q

what does a +ve charge generally do to pKa

A

lower

(pulls e from groups that may be deprotonated, makes it easier)

36
Q

what does a -ve charge generally do to pKa

A

raise

charges not as cancelled out so not as strong acid so higher pKa

37
Q

if pKR of Sec is 5.43 and Cys has pKR of 8

what is pI of Sec compared to Cys

A

lower (pH7 cys=0 and Sec=-1, pI lower

also the average in the calculation will be lower)