Protein Notes

Question 0

What is the amino acid structure made up of ?

Answer 0

A carboxyl group, an amino group, a proton and an R side chain
- r side chain alters the properties of the amino acid because they can differ in size, charge, polarity and hydrophobicity

Question 1

What is the basic structure of a protein ?

Answer 1

It is made up of amino acid residues - 20 different naturally occurring ones

Question 2

What is an alpha- carbon ?

Answer 2

The alpha- carbon of an amino acid is when there is 4 different groups attached to the carbon so as long as the r side chain is different from the other 3 groups then the carbon is the known as the alpha carbon in the chiral centre

Question 3

What does the alpha-carbon in the chiral centre allow ?

Answer 3

It allows 2 forms of each amino acid, an L form and a D form
In biology proteins are made from the L form

Question 4

What joins amino acids together to make a protein ?

Answer 4

Peptide bond - between the carbonyl group of he first residue and the alpha amino group of the next

Question 5

What is the primary sequence of a protein ?

Answer 5

It is the linear sequence of amino acids
Dictates the folding of the protein and therefor its function
It starts with the N terminus at the left and ends with the C terminus at the right

Question 6

What enzyme is used in transcription ?

Answer 6

RNA polymerase

Makes mRNA in the 5’ to 3’ orientation using the template strand of DNA as a template

Question 7

Once RNA polymerase has copied the template strand to produce the mRNA strand what happens to it ?

Answer 7

It is modified by the addition of a 5’ UTR cap (untranslated region) and a 3’ UTR poly-adenylate on sequence and it is also further modified by splicing out introns and annealing appropriate exons together

Question 8

Why are caps added to each end of the mRNA strand ?

Answer 8

For protection and to help it leave the nucleus

It is the 5’ cap which is recognised by a nuclear pore complex enabling it to leave the nucleus

Question 9

How can a number of variants be produced for proteins ?

Answer 9

1- either by separate genes that are closely related

2- or by alternative splicing of a single gene

Question 10

What is alternative splicing ?

Answer 10

It is the process in which exons of the pre-mRNA are reconnected in multiple ways during RNA splicing

Question 11

What are 2 control modes of protein function ?

Answer 11

1- sequence of the protein and its concentration at steady state
2- post translational modifications which is better suited to acute environmental changes

Question 12

What are post translational modifications ?

Answer 12

Covalent modifications of certain amino acids at certain points in the sequence

Question 13

What are some examples of stable and long lasting post translational modifications ?

Answer 13

N-glycosylation

N-myristoylation

Question 14

What are examples of short lived post translational modification ?

Answer 14

Phosphorylation
O-glycosylation
Oxidation

Question 15

What is glycosylation and what are he 2 major classes of it ?

Answer 15

Covalent attachment of sugars to the side chain of certain residues in a protein
N-glycosylation = covalent bond between a nitrogen atom in asparagine or arginine with a sugar molacule
O-glycosylation= attaches a sugar molecule to an oxygen atom of serine, threonine or tyrosine

Question 16

Where does N-glycosylation and O-glycosylation occur ?

Answer 16

N- occurs in ER and Golgi

O- occurs in the cytosol

Question 17

What is phosphorylation ?

Answer 17

Transient modification

Can involve attachment of a phosphate group to the oxygen atom serine, threonine or tyrosine

Question 18

What is myristoylation ?

Answer 18

Attachment of a 14 carbon fatty acid to the N terminus of a protein
Attachment is at the alpha amino group
Helps the protein to interact with membranes

Question 19

What causes sickle cell anaemia ?

Answer 19

A point mutation in the beta-globin chain of haemoglobin causing hydrophilic amino acid glutamic acid to be replaced by hydrophobic amino acid valine at the 6th position

Question 20

What forms haemoglobin S (HbS) ?

Answer 20

2 wild type alpha globin subunits

2 mutant beta globin subunits

Question 21

What happens at the mutant beta-globin subunit at low oxygen levels ?

Answer 21

The absence of the polar amino acid in the 6th position promotes non covalent polymerisation of hb
This distorts the red blood cells into a sickle shape and decreases their elasticity
Impairs their ability to move through capillaries causing ischaemia tissue
The blood cells are also prone to haemolytic which release Hb into the blood stream producing anaemia