Amino Acids

Question 1

How are the 20 amino acids classified?

Answer 1

by their R group properties

Question 2

Which amino acids are hydrophobic??

Answer 2

Gly
Ala
Val
Leu 
Ile
Pro 
Met
Phe
Trp

Question 3

Why can prolines affect structural flexibility of polypeptides?

Answer 3

b/c it has. distinctive amino group NH2 group which forms a cyclic structure making it rigid

Question 4

Is cysteine hydrophilic or hydrophobic?

Answer 4

hydrophobic even though it is classified as a polar amino acid

Question 5

Which amino acids has a secondary amino group or imino group?

Answer 5

proline since its imino group forms a cyclic structure

Question 6

When transferring an amino acid from a non-polar solvent to water and we get delta G < 0, what does this telll us about the reaction?

Answer 6

that the transfer is favorable and the reaction is hydrophilic

Question 7

When transferring an amino acid from a non-polar solvent to water and we get delta G > 0, what does this telll us about the reaction?

Answer 7

the transfer is unfavorable and the amino acid is hydrophobic

Question 8

The hydropathy index is directly proportional to what?

Answer 8

Gibbs free energe (delta G of the transfer).

Question 9

If we have a large positive hydropathy index number, what would this tell us about our amino acid?

Answer 9

this would reflect higher hydrophobicity

Question 10

Base on hydropathy index, which amino acid is more hydrophobic?

Isoleucine: 4.5 or alanine with 1.8 hydropathy index

Answer 10

They’re both hydrophobic since the number is positive, but isoleucine is higher thus more hydrophobic

Question 11

What are the two ionizable groups in amino acids and what is their pka?

Answer 11

COOH to COO- + H+ has pka of 2.2

NH2 + H+ = NH3+ has a pka 9.4

Question 12

You have a carboxyl group and it is placed in a pH of 4 is will it be protonated or deprotonated

Answer 12

deprotonated b/c anything above 3.5 is negative charge

Question 13

What does it mean when an amino acid is amphoteric at physiological pH?

Answer 13

that the amino acid posses both acid and base properties

Question 14

what does it mean when an amino acid is zwitterionic?

Answer 14

both positive and negative charges in the same molecule (their charge cancels out)

Question 15

the isoelectric point is what?

Answer 15

the pH at which the amino acid has neutroa charge or net zero charge (zwitterionic)

Question 16

What are enantiomers?

Answer 16

they are stereoisomers that are mirror images of each other. they are non-superimposable and each stereoisomer has a unique configuration

Question 17

Do all amin acids have a chiral center?

Answer 17

no, glycine does not b/c it has 2 hydogen bonds aka it is not optically active

Question 18

What does it mean to be optically active?

Answer 18

amino acids w/chiral centers can rotate polarized light

Question 19

What is stereochemistry?

Answer 19

the spatial arrangement of the atoms in the molecule - aka the arrangements of the different groups around the alpha carbon

Question 20

Trying to superimpose stereisomers that are mirror images of each other is impossible without doing what?

Answer 20

breaking a bond or bonds and rearranging them

Question 21

Different molecules are in different…

Answer 21

configurations

Question 22

If enantiomers rotate polarized light clockwise they are called?

Answer 22

positive dextrorotatory or D configuration amino acids

Question 23

If enantiomers rotate polarized light anti-clockwise they are called?

Answer 23

negative Levorotatory or L configuration

Question 24

The R and S configuration systems is used to characterize what?

Answer 24

molecules with multiple chiral centers

Question 25

Are amino acids in the L or D form?

Answer 25

they are almost all in the L form. The D form is rarely found but do occur in bacteria and the human brain

Question 26

What is stereospecificity?

Answer 26

the ability to distinguish between stereoisomers

-example our sensory receptors can distinguish between aspartame (sweet and its D configuration which is bitter

Question 27

What is the difference between conformation and configuration

Answer 27

conformation to another conformation requires rotation and configuration to another configuration requires breaking one or more bonds.