Amino Acid - Structure And Function

Question 1

Amino acid with non-polar side chains

Answer 1

No acid/base chemistry (R-group does not bind or give protons )
Do not form hydrogen bonds
Have hydrophobic interactions

Question 2

When does Cys and Tyr donate protons

Answer 2

When at alkaline pH

Question 3

Can Ser,Thr,Tyr form hydrogen bonds and how ?

Answer 3

Yes they can ,they contains OH or SH

Question 4

What do you need to form a disulfide bridge or a cystine dimer

Answer 4

2-SH groups

Question 5

What can we consider about -CONH2 of Asn

Answer 5

May serve as the sight of attachment of oligosaccharide chains in glycoproteins (N-link gylcosyation )

Question 6

True or false , Asp and Glu are proton acceptors

Answer 6

False , they are proton donors .

Question 7

What is the state of Asp and Glu at a neutral PH

Answer 7

The side chains are almost fully ionized or dissociated (COO-) and carry a negative charge

Question 8

Finish the statement : Lys and Arg are (a)_______ ionized and carry a (b)_________ charge

(a) fully | partially
(b) positive/ negative

Answer 8

Fully

Positive

Question 9

Why is a histidine a good buffer ?

Answer 9

Histidine is weakly basic and partially positively charged at a physiological pH .In proteins histidine can be positive or uncharged .

Question 10

3 letter abbreviation for Asparagine

Answer 10

Asn

Question 11

What is Gln and how is different to Glu

Answer 11

Glutamine , it’s different to glutamate because it’s the major carrier of NH3

Question 12

Difference between phenylalanine and Tyrosine in terms of structure

Answer 12

Tyrosine : has an OH

Phenylalanine: has no OH

Question 13

Why do we say the alpha c is a choice, or optically active

Answer 13

It has four different groups attached (except Gly)

Question 14

Which of the following acids will have the highest pKa?
A.Nitric acid
B.Sulfuric acid
C.Hydrocholoric acid
D.Pyruvic acid

Answer 14

Pyruvic acid is the only acid on this list which is not strong.
•The higher the pKa the weaker the acid
•The lower the Ka, the weaker the acid: because  pKa = -log(Ka)

Question 15

What is the Kw(ion-product ) of water (the value)

Answer 15

10^14

Question 16

The water dissociation equation

Answer 16

pH =[H+][OH-]

Question 17

Which of the following amino acids will be most close to its zwitterionic form at neutral pH?
A.Alanine
B.Glutamate
C.Aspartate
D.Lysine
E.Argnine

Answer 17

Answer is alanine
•The charges available to alanine come from its amino functional group, and its carboxylic acid functional group. Its zwitterionic form occurs when both of these functional groups are charged, resulting in a net zero charge on the entire molecule (+1 – 1 = 0)
•The other amino acids listed have additional ionizable functional groups on the R-group, so the pH where they are zwitterions will be either higher or lower than for alanine.
•Identify other amino acids that also form there zwitter ion at near neutral pH

Question 18

Explain the difference between D and L isomers (amino acids )

Answer 18

L amino acids are those with the alpha amino group on the left and the D amino acids have alpha amino group on the right

Question 19

What is the location of non polar amino acids in soluble proteins

Answer 19

Interior of proteins (shielded from environment )

Question 20

What is the location of non polar amino acids in membranes or other hydrophobic environments

Answer 20

Found on Protein surfaces

Question 21

What is the Henderson -Hasselbach equation

Answer 21

PH= pKa +log [[A-]/[HA]]

Question 22

When titrating alanine what are the 3 forms in solution
Alanine in acid sol .
Alanine in neutral sol .
Alanine in basic sol.

Answer 22

Acid - +H3N and COOH
Neutral - +H3N and COO-
Base - 2HN and COO-

Question 23

What is the isoelectric point

Answer 23

It is the pH at which net charge is zero

Question 24

How do I calculate the pI

Answer 24

PI is pk1 + pk2 divided by 2

Question 25

What are the 3 ionizable groups on histidine

Answer 25

COOH ,NH+ , NH3+

Question 26

How do I calculate the pI of histidine

Answer 26

Pk2 + pk3 / 2

Question 27

What are the corresponding pHs of the 3 pks of histidine pk1= COOH Pk2 = R group Pk3 = NH3

Answer 27

1-1.8 2-6 3-9.3

Question 28

Name 3 blood buffers

Answer 28

``` Bicarbonate Phosphate Proteins Hemoglobin NH3 /NH4+ ```

Question 29

Name two strong acids that dissociate completely

Answer 29

Sulfuric acid and hydrochloric acid

Question 30

Name 4 weak acids

Answer 30

Carbonic acid ,lactic acid , pyruvic acid | Citric acid

Question 31

True or false : uncharged drugs don’t cross the intestinal lumen compared to charged drugs

Answer 31

False , they cross much more readily

Question 32

What happens when water self dissociates

Answer 32

Hydrogen bonds occur between the hydrogen of one atom and the oxygen of another . Forming hydroium ion (H30+ ) hydroxide (OH -)

Question 33

Increasing acidity means more ______ and less _______ | [H+] or [OH-]

Answer 33

1.[H+] and 2.[OH-]

Question 34

Does sulfuric acid completely dissociate in water

Answer 34

Sulfuric acid is a weak acid and doesn’t dissociate completely in water (only the first dissociation is considered strong )

Question 35

Name some strong acids

Answer 35

HCl ,HBr ,HNO3 ,perchloric acid

Question 36

Name some strong bases

Answer 36

LiOH , NaOH , potassium hydroxide ,Ba(OH) 2 , Mg(OH )2

Question 37

How can Mg(OH)2 be ingested if it’s a strong base

Answer 37

It is a laxative , it has very low solubility in water.

Question 38

Describe the titration curve of a strong acid by a strong base

Answer 38

It has a sharp change where the equivalence point is the 1/2 of the region

Question 39

The higher the ka the ________ the acid

Answer 39

Stronger

Question 40

The lower the pKa the ____________ the acid

Answer 40

The stronger acid

Question 41

What is the difference between the strength of an acid and concentration of the acid

Answer 41

Strength - the extent of the proton dissociation | Concentration of the acid is the amount of dissolved substance

Question 42

What does it mean when the pH is equal to the pKa

Answer 42

There is equal amounts of the weak acid and it’s conjugate base (50% dissociated )

Question 43

The buffering region

Answer 43

This is the region on the curve which is demonstrated when the pH changes slowly

Question 44

Acetic acid has a pKa of 4.75. a 0.1 M acetic acid solution from pH 4.75 and slowly add strong acid (HCl) , what predominates

Answer 44

The conjugate form Protonated form Neutral form

Question 45

Acetic acid has a pKa of 4.75. a 0.1 M acetic acid solution from pH 4.75 and slowly add strong base (NaOH) , what predominates

Answer 45

Conjugate base form Deprotonated form Ionized form

Question 46

When is. Buffer formed

Answer 46

When a weak acid and a similar amount of its conjugate base are mixed