Proteins

Question 1

What are proteins?

Answer 1

Proteins are heteropolymers of alpha amino acids, most functionally diverse and abundant molecules in living systems.

Question 2

How many amino acids in Mammalian systems and how are they found?

Answer 2

20 Amino acids in the body, some made in body, essential amino acids are gained from food.

Question 3

Why are proteins so complex?

Answer 3

Proteins can exist as a single polypeptide, others have same polypeptide (Homomeric) or different polypeptides (heteromeric)

Question 4

What non protein factors can be added onto proteins?

Answer 4

Lipids, carbs, and metal ions
Also amino acids can be modified

Question 5

The structure for all Alpha amino acids are the same but one? Which one?

Answer 5

Proline

Question 6

How are proteins named?

Answer 6

From the central carbon down the R group in the Greek alphabet

Question 7

How are AAs classified?

Answer 7

AAs are classified by their R group.

R group can be as simple as H (Glycine) to a carbon skeleton with various functional groups.

Question 8

R groups have four categories of what can affect an amino acid, what are they?

Answer 8

1.Non-charged polar side chains (aliphatic-aromatic)
2.Uncharged polar side chains
3.Acidic
4.Basic

Question 9

Why can Glycine be hydrophobic and hydrophilic?

Answer 9

Glycine can be polar or non-polar

Question 10

Why are non polar side chains hydrophobic?

Answer 10

Because hydrogen and carbons make the hydrophobic

Question 11

Give two points about Proline that makes it different

Answer 11

1.Proline R group is bonded to the amine making its amine group secondary
2.Cyclic structure allows bends within resulting polypeptide

Question 12

Give two facts about uncharged polar side chains

Answer 12

1. They are hydrophilic (good for being on the surface of proteins for aqueous solution)
2. They can make H bonds as some have hydroxyl groups, or amide and carbonyl groups (glutamine)

Question 13

What can Two Cysteines do?

Answer 13

Two Cysteines have -SH groups which can form a disulphide bond to stabilise many extracellular proteins (albumin)

Question 14

Four main points about acidic side chains

Answer 14

1.Extra COO- group
2.polar
3.Negative charge
4.Hydrophilic

Question 15

What are aspartate and glutamate (pH 7)

Answer 15

They are amides of asparagine and glutamine

Question 16

Three main points about basic side chains

Answer 16

1. Polar
2. Hydrophilic
3. Positive charge

Question 17

3 facts about Histidine (basic)

Answer 17

1. Switches between neutral and positive charge and physiological pH
2. Found at enzyme active sites
3. Helps catalyse making and breaking bonds

Question 18

Name three amino acids with special properties

Answer 18

Glycine (Adds flexibility and is amphipathic), Proline (ring structure adds kinks), Cysteine (Two can form a disulphide bond within)

Question 19

Give a couple optical properties about AAs

Answer 19

1.Bonded to four groups (except gly)
2.Chiral Centre
3.Enantiomers of Alpha AAs are labelled either as D- or L-
4.Most in humans are L- configuration
5.D- are rare can be found in bacterial cell walls.

Question 20

Give a couple spectral properties about AAs

Answer 20

1. Do not absorb light so colourless
2. Aromatic side chains absorb UV (Phe,Trytophan,Tyrosine 280 nm) allowing spectroscopy of protein concentration.

Question 21

Post transitional modification of AAs allow addition of:

Answer 21

1. Hydroxyl -OH
2. Phosphoryl -PO4^3-
3. Methyl -CH3
4. Acetyl -COCH3
5. Carboxylation - COOH

Question 22

Give 2 points about hydroxylation

Answer 22

1.Added -OH stabilises collagen fibres via H bonds
2.Vitamin C deficiency stops hydroxylation of collagen leading to scurvy.

Question 23

Give 3 points about methylation

Answer 23

1.Lysine can be methylated up to 3 times at its amino group
2.Histone methylation regulates gene expression
3.N-Methyllysine is found in myosin, a contractile component of muscle.