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31

What is pK(a)?

The pH at which 50% of the HA (acid) has ionised

32

What is the Henderson-Hasselbalch equation?

pH = pK + log[A-]/[HA]

33

What is the relationship between pH, pKa and ionisation?

If the pKa is higher than pH, acid is less likely to be ionised

34

What is critical pH?

pH at which tooth becomes unsaturated with respect to Ca and PO43- allowing hydroxyapatite in enamel to dissolve
Region of pH 5.2-5.5

35

How does saliva protect teeth from decay?

Produces many buffers (principally bicarbonate) which prevent resting pH falling much lower than pH 6.3

36

What are the main buffers in saliva and how effective are they?

Proteins - not effective as nearly all charged groups from peptide bonds
Phosphate - good but not in high enough conc. to be effective
Bicarbonate - good

37

What is the role of bicarbonate in plaque?

Acts to neutralise acid rather than buffer acid
Produces H+ pushing reaction to right producing CO2 and H2O - CO2 released as mouth open system

38

What conc. does carbonic acid stay at in the mouth and what changes?

About 1.3mMol/L
pH and [HCO3-] change, bicarbonate varies with flow rate

39

What must all AAs have?

Amino (NH2), carboxyl (COOH), H and R group
a-carbon is C atom amino and carboxyl groups are attached

40

What is the role of side chains?

Are the functional groups
Determine structure, function and charge of AAs
Charged, polar or hydrophilic R groups exposed on surface
Non-polar, hydrophobic R groups buried in interior

41

What confers an AAs' optical activity?

An asymmetric C atom - C attached to 4 different groups
All AAs except GLYCINE (R group = H) are asymmetric

42

What does being asymmetric mean?

Means compound has spatially distinct but chemically identical isomers that are mirror images of each other (enamtiomers)
Both are optically active (rotate plane polarised light) to right (Dextro) or to left (Levo - majority of AAs)

43

What is a zwitterion?

A molecule that bears groups of opposite polarity
As amino and carboxylic acid groups readily ionise AAs are dipolar/zwitterions

44

How does the charge of AAs change with increasing pH?

Low pH - amino protonated, carboxyl normal
pH 7 - amino protonated, carboxyl ionised
High pH - amino normal, carboxyl ionised

45

Define AMPHOTERIC

Molecules that have both acidic and basic groups
AAs are amphoteric

46

Define anion

A negative ions from gain of e-

47

Define cations

+ve charged molecule

48

Name the aliphatic AAs? (Hydrophobic/non-polar)
VIGAL

V - valine
I - isoleucine
G - glycine
A - alanine
L - leucine

49

Name the aromatic AAs
Y+T

Phenylalanine (phenol - aromatic)
Tryptophan (Y + T = aromatic)
Both non-polar
Tyrosine (Y + T)

50

Name the sulphur containing AAs
MC Sulphur

M - methionine
C - cysteine (can from S-S, stabilise proteins)
MC Sulphure

51

Name the neutral polar AAs

Hydroxy-Soft Towel
Serine
Threonine

Amide derivates of Acids
Asparagine
Glutamine

52

What is the ImIno acid?

Proline - causes bends in polypeptides

53

Name acidic AAs

Aspartic acid
Glutamic acid

COOH R group - ionised at pH 7

54

Name the basic AAs
Larry is basic

L - lysine
Ar - arginine
His - histidine
LArHis - extra +ve charge

55

What formula is used to calculate the isoelectric point? How is this calculated for amino acids with 2 carboxyl/amino groups?

pI = (pKa + pKb)/2
a (acidic) = COOH b (basic) = NH2
For 2 carboxyl groups the (pKa1 + pKa2)/2 is used

56

What is a dalton?

Da is a unit of molecular weight equivalent to 1 H atom
Compares how heavy something is to H

57

Describe the primary structure of a protein

Unique sequence of AAs held by peptide bonds
Compare structure to find common sequences suggesting members of a multigene family

58

Describe the secondary structure of proteins

H bonding determines secondary structure either a-helix or B-pleated sheet

59

Describe boding in and structure of an a-helix

N atom in peptide bond shares H atom with CO group 4 residues upstream
Polypeptide twists around in a spiral, each turn takes 3.6 AAs residues

60

Describe B-pleated sheets

B strands laterally connected by 2/3 H bonds
Typically 3-10 AAs long