CH 3

Question 1

How do amino acids react to water

Answer 1

In pH 7 water, amino acids IONIZE
- it causes the amino group to act as a base & attracts a proton to form NH3+
- the carboxyl group then acts as an acid

Question 2

why are the charges on the function groups of amino acids important

Answer 2

(1) They help amino acids stay in solution, where they can interact with one another and with other solutes,
(2) they affect the amino acid’s chemical reactivity.

Question 3

Function of amino acids with side chains that have no functional groups

Answer 3

• they consist solely of carbon & hydrogen atoms
• rarely participate in chemical reactions
• influence primarily depends on size & shape rather than reactivity

Question 4

Hydrophilic R-groups

Answer 4

polar & electrically charged

Question 5

Hydrophobic R-groups

Answer 5

nonpolar lacking charge & highly electronegative atoms capable of forming hydrogen bonds with water

Question 6

acidic r-groups

Answer 6

• has a negative charge & lost a proton
• e.g. aspartate

Question 7

basic r-groups

Answer 7

• positive charge & picked up a proton
• e.g. lysine

Question 8

uncharged polar r-group

Answer 8

• has highly electronegative oxygen that will form a polar covalent bond in the r group
• e.g. serine

Question 9

Why are peptide bonds unusually stable

Answer 9

the nitrogen can intermittently donate its pair of unshared valence electrons to the carbon in the C-N bond

Question 10

How do R-groups affect each amino acid

Answer 10

size, shape, chemical reactivity, & solubility
- properties & function

Question 11

secondary structures

Answer 11

• H bonding occurs btwn oxygen on carbonyl (- charge) of one amino acid residue & the H (+ charge) on the amino group of another

Question 12

dimer

Answer 12

proteins with 2 polypeptide subunits

Question 13

macromolecular machines

Answer 13

a group of proteins, & possibly other nonprotein macromolecules, that assemble to carry out a particular function

Question 14

does protein folding tend to be spontaneous

Answer 14

yes
- this occurs when a chain is placed in an aqueous solution

Question 15

hydrophobic interactions with proteins

Answer 15

drive proteins to fold such that their nonpolar R-groups coalesce (join) in the interior
- increases entropy of the surrounding water
- folded molecule has less potential energy = more stable

Question 16

molecular chaperones

Answer 16

a protein that facilitates the folding or refolding of a protein into its correct 3D shape
- heat-shock proteins
- attach to hydrophobic patches before aggregates can form

Question 17

prions

Answer 17

• proteinaceous infectious particles
• infectious particle that consists entirely of protein
• adopt a normally folded shape & an infectious, often disease-causing shape
• can bind normally folded prion proteins & cause them to adopt infectious shape