Amino acids and Peptides

Question 1

Role of proteins

Answer 1

Catalysis (glycogen synthase, DNA polymerase)
Transport (hemoglobin, lactose permease)
Structure (collagen, keratin)
Immunity (Antibodies, cytokines, chemokines)
Communication (hormones, neurotransmitters)
Motion (myosin, actin)

Question 2

Describe the structure of an amino acid

Answer 2

-An acidic carboxyl group connected to the alpha carbon
-a basic amino group connected to the alpha carbon
-an alpha hydrogen connected to the alpha carbon
-a R group

Question 3

Which is the only amino acid that isnt chiral?

Answer 3

Glycine

Question 4

What kind of amino acids do proteins contain?

Answer 4

L-amino acids only

Question 5

What are amino acids classified by?

Answer 5

The basis of R - group, nutrition, catabolism

Question 6

How to tell if an amino acid is hydrophobic (non-polar)?

Answer 6

-If the R side chain is only made up of hydrocarbons - side chains don`t lose or gain protons or participate in hydrogen or ionic bonds
-Methionine is exception as contains sulfur
-If side chain is aromatic

Question 7

Examples of hydrophobic amino acids

Answer 7

Alanine, Valine, Leucine, Isoleucine, Methionine, Proline, Glycine, Phenylalanine, Tryptophan, Tyrosine

Question 8

How to tell if an amino acid is hydrophyllic (polar)?

Answer 8

-Side chains are not just hydrocarbons - have charges - reactive with h2o
-Acidic if 2 carboxyl groups and 1 amino group
-Basic if 2 amino groups and 1 carboxyl group

Question 9

Examples of hydrophyllic amino acids

Answer 9

Neutral - Serine, Threonine, Cysteine, Glutamine, Asparagine
Acidic - Glutamic acid, aspartic acid
Basic- Lysine, Histidine, Arginine

Question 10

What are the 3 special amino acids?

Answer 10

Cysteine, Glycine, Proline

Question 11

Why is Cysteine a special amino acid?

Answer 11

Sulfhydryl(thiol) group (-SH) of 2 cysteines can be oxidised to form a covalent cross link called a disulphide bond.

Question 12

Why is glycine a special amino acid?

Answer 12

Simple side chain (R group) - JUST A HYDROGEN

Question 13

Why is proline a special amino acid?

Answer 13

Its side chain and alpha - amino N form a rigid ring structure - contributes to the formation of protein collagen - often nfound at a bend or turn in a protein

Question 14

At a low pH amino acids exist in a….

Answer 14

Positively charged form (cation) - amino group hasn´t been protonated yet so still holds its positive charge

Question 15

At a high pH amino acids exist in a….

Answer 15

Negatively charged form (anion) - carboxyl group hasnt been protonated but amino group has so carboxyl group holds its negative charge

Question 16

Between the pka for each group, the amino acid exists in a ……….

Answer 16

Zwitterion form - has both a pos and neg charge

Question 17

At the amino acid isoelectric point (PI)

Answer 17

The net charge is zero - amino acid is lest soluble in water and does not migrate in an electric field

Question 18

Amino acids withz uncharged side chains have how many pka values?

Answer 18

2 - the pka of the carboxyl group and the pka of the amino group

Question 19

What do buffers do?

Answer 19

Prevent changes in pH close to the pKa

Question 20

What are the 7 amino acids with ionizable side groups?

Answer 20

Terminal carboxyl group - aspartic acid/glutamic acid, histidine
Terminal amino group - Cysteine, tyrosine, lysine, arginine

Question 21

How many pkas do amino acids that have ionisable side chains have?

Answer 21

3

Question 22

Condensation / Dehydrolysis Rxn with respect to amino acids fusing

Answer 22

Carboxyl and amino groups from 2 adjacent amino acids fuse together

Question 23

How are amino acids read?

Answer 23

From the amino terminal to the carboxyl terminal

Question 24

What differences can be used to separate proteins?

Answer 24

Charge, size, affinity for a ligand, solubility, hydrophobicity, thermal stability