lecture 1 & 2: review; AA structure and properties

Question 1

ΔG < 0 :
ΔG > 0 :
ΔG = 0 :

Answer 1

ΔG < 0 : spontaneous fwd rxn [exergonic]
ΔG > 0 : non- spontaneous [endergonic]
ΔG = 0 : system at equilibrium

Question 2

diffusion is driven by _____

Answer 2

diffusion is driven by enthalpy

Question 3

what between water molecules contribute to favorable/ unfavorable ΔH?

Answer 3

H-bonding between water molecules contribute to favorable ΔH

Question 4

hydrophobic effect

Answer 4

tendency of non-polar molecules to self-associate in water

Question 5

driving force of the hydrophobic effect

Answer 5

increased solvent entropy

Question 6

fixed charges are present in ___ and ___

Answer 6

fixed charges are present in proteins and membranes

Question 7

charged groups essential for (3)

Answer 7

• stabilizing protein and membrane structure
• solubilizing proteins in water
• recognition of substrates by enzymes

Question 8

____ acids completely dissociate in water while ___ acids only partially dissociate

Answer 8

strong acids completely dissociate in water while weak acids only partially dissociate

Question 9

pH = pKa :
pH&raquo_space; pKa :
pH &laquo_space;pKa :

Answer 9

pH = pKa : [A-] = [HA]
pH&raquo_space; pKa : [A-]&raquo_space; [HA]
pH &laquo_space;pKa : [A-] &laquo_space;[HA]

Question 10

HH equation relates pH to ____ through the ___ term to its _____ through the ____

Answer 10

HH equation relates pH to the intrinsic strength of the acid through the pKa term to its fractional ionization through the [A-]/[HA] term

Question 11

when pH is far from pKa, the buffer solution will be ____ and can’t act as a buffer

Answer 11

when pH is far from pKa, the buffer solution will be fully protonated and can’t act as a buffer

Question 12

zwitterion

Answer 12

both (+) and (-) charges at neutral pH

Question 13

only (L/ D) stereoisomers of amino acids are found in protiens

Answer 13

only L stereoisomers of amino acids are found in protiens

Question 14

non-polar [hydrophobic] amino acids (5)

Answer 14

• glycine
• alanine
• valine
• leucine
• isoleucine

Question 15

amino acids often found in the hydrophobic core of proteins [inside/ not exposed to water] (3)

Answer 15

• leucine
• isoleucine
• valine

Question 16

amino acids that may be found either inside or outside proteins [more able to tolerate water] (2)

Answer 16

• alanine

- glycine

Question 17

as side chains of aliphatic amino acids increase, they become more/ less hydrophobic

Answer 17

as the side chains increase they become more hydrophobic

Question 18

which amino acids can be used to calculate the concentration of protiens? (4)

Answer 18

• aromatic amino acids
• phenylalanine
• tyrosine
• tryptophan

Question 19

phenylalanine is (highly/ not) hydrophobic

Answer 19

phenylalanine is highly hydrophobic

Question 20

polar amino acids usually found on proteins surface (3)

Answer 20

• serine
• cysteine
• threonine

Question 21

non-polar amino acid usually buried in the protein (1)

Answer 21

• methionine

Question 22

proline (is/is not) hydrophobic and is found ____

Answer 22

proline is hydrophobic but is found near the proteins surface

Question 23

cysteine undergoes a ___ rxn to form a disulfide bond with another cysteine

Answer 23

cysteine undergoes an oxidation rxn to form a disulfide bond with another cysteine

Question 24

purpose of the disulfide bonds between cysteines

Answer 24

the disulfide bonds between cysteines stabilize the 3D structure of some proteins

Question 25

all ____ amino acids can form H-bonds and are usually found ____

Answer 25

all polar amino acids can form H-bonds and are usually found on the protein surface

Question 26

basic amino acids (3) are usually (+/-)

Answer 26

• histidine
• lysine
• argenine
• usually positively charged

Question 27

acidic amino acids (4) are usually (+/-)

Answer 27

• aspartic acid
• glutamic acid
• asparagine
• glutamine
• usually negatively charged

Question 28

histidine can act as a proton donor and acceptor because ____

Answer 28

histidine can act as a proton donor and acceptor because of a side chain pKa near physiological pH