L2&3 Amino Acids and pH

Question 1

Chiral

Answer 1

C atom with four different substituents

All alpha Cs of AA are chiral except glycine

Question 2

Nonpolar

Answer 2

Uncharged
Hydrophobic
Aggregate in aqueous solitons

Question 3

Polar

Answer 3

Hydrophilic
Posses electronegative O, N, or S atom
Can form H, ionic, or covalent bonds
Charged or uncharged

Question 4

Hydrophobic

Answer 4

Water fearing

Question 5

Hydrophilic

Answer 5

Water loving

Question 6

Electronegative atom

Answer 6

Measure of tendency of an atom to attract a bonding pair of electrons

O, N, S have strong pull on electrons

Question 7

Hydrophobic effect/interaction

Answer 7

When AA side chains are uncharged and repel water

Question 8

Covalent bond

Answer 8

Shared electrons

Peptide bonds, disulfide bonds

Much stronger than noncovalent

Used to make polymers from monomers

Requires enzyme to break bond

Polar or nonpolar

Question 9

Polar covalent

Answer 9

Electrons shared by atoms of differing electro negativity

Creates partial pos and partial neg which creates permanent dipole

Basis of H bond

Question 10

Permanent dipole

Answer 10

Partial neg and pos charge that occurs when electrons are not shared equally

Allows molecules to interact through electrostatic forces

Question 11

Peptide bond

Answer 11

Bond between amino and carboxyl group of AA

forms protein backbone but also between side chains in special cases

Covalent

Question 12

Disulfide bond

Answer 12

Joins 2 sulfhydryl groups

Covalent

Question 13

H-bond

Answer 13

Sharing of H atom between 2 electronegative groups

Weaker than ionic because a full charge is not shared

Question 14

Ionic bond

Answer 14

Transfer of electrons

Attractive forces gold two ions together

Question 15

Van der Waals interactions

Answer 15

Weak forces between molecules in close contact

Arise from transient dipole interactions

Question 16

pH

Answer 16

Negative log of hydrogen ion concentration

pH=-log[H+]

Inversely related to [H+]

Small changes in pH = large changes in [H+]

2pH changes = 100 fold changes in [H+]

Question 17

pKa

Answer 17

pH at which a weak acid will be 50% dissociated

Proportional to affinity of weak acid for its proton

Low pKa = H+ easily dissociable, strong weak acid

High pKa= H+ bound more tightly, weak weak acid

Question 18

pI

Answer 18

Isoelectric point

At pH=pI one group completely dissociated and one is completely associated

Question 19

Amino group and pKa

Answer 19

+NH3

pka > 7

Termed basic

Question 20

Carboxyl group and pKa

Answer 20

-COOH

pKa < 7

Termed acidic

Question 21

R-group

Answer 21

Variable group for AA

Question 22

Conjugate base

Answer 22

Dissociated form of a weak acid

Question 23

Weak acid

Answer 23

Molecule that contain dissociable hydrogen ion

Question 24

Noncovalent

Answer 24

Determines shape polymer will assume within cell and how it interacts with other biomolecuels

Weaker but more quantity

Hydrophobic interactions
Ionic
H bonds
Van der Waals

Question 25

Basic AA structure

Answer 25

Alpha C bonded to an amino group, a carboxyl group, a hydrogen atom and a variable side group

Question 26

Nonpolar AA interactions

Answer 26

Side chains uncharged and only contain hydrocarbons except tryptophan and methionine Tryptophan- 1N among 9Cs acts hydrophobic Methionine- S sandwiched btw hydrocarbon masks electronegativity Participate in hydrophobic interactions, exclude water NOT a bond

Question 27

Polar uncharged AA side chain interactions

Answer 27

Contain electronegative atom Participate in H bonds Noncovalent interaction which H is shared by 2 electronegative atoms

Question 28

Cysteine interactions

Answer 28

Only AA with sulfhydryl group Polar and uncharged Forms ionic and disulfide bonds

Question 29

Polar charged AA with acidic side chains interactions between

Answer 29

Contain COOH that dissociated and negatively charged at physiological pH Proton donors Participate in H bonds and ionic bonds

Question 30

Polar charged AA with basic side chains

Answer 30

Side chains positively charged at physiological pH Accept protons Participate in H bonds and ionic bonds

Question 31

Ka

Answer 31

Ka=[H+][A-]/[HA] Products/reactants Measure of the extent of the reaction ( how much product produced) at equilibrium Measure of strength of acid a lot of products=a lot of dissociation=high Ka= stronger acid

Question 32

Henderson-Hasselbalch equation

Answer 32

Estimates extent of dissociation (balance btw [HA] and [A-]) pH=pKa + log [A-]/[HA] pka is -log of Ka

Question 33

What happens when [A-] = [HA]

Answer 33

pH=pKa Acid is 50% dissociated

Question 34

pka

Answer 34

Low pKa=high ka=easily dissociable=strong weak acid High pKa=low ka=more tightly bound= weak weak acid

Question 35

Henderson-hasselbalch rule of thumb

Answer 35

pH is 1 pH unit above pKa the acid is 91% dissociated pH is 1 pH unit below pKa the acid is 9.1% dissociated

Question 36

Buffers

Answer 36

Weak/acid conjugate base pairs that release or absorb H+ according to the pKa and laws of mass action to minimize changes in pH

Question 37

Maximum buffering range

Answer 37

Runs from one pH unit below to one pH unit about the pKa of the weak acid/conjugate base pair

Question 38

Buffering capacity

Answer 38

Measure of efficiency in resisting pH changes Amount of base that must be added to solution to change pH by one unit

Question 39

Best buffering region is

Answer 39

50/50 mix of protons and conjugate base

Question 40

When looking at titration curve

Answer 40

Look at where a lot of base was added and where there was a little change in pH