Amino Acids

Question 1

What are proteins?

Answer 1

Proteins are long polymers of amino acids

Question 2

What is the general structure of an amino acid?

Answer 2

An amino acid has an amine group on the left bonded to a central carbon on the right and a side chain R group

Question 3

What is an alphas carbon and what is an alpha amino acid?

Answer 3

The alpha carbon is the central carbon, it is the 1st carbon next to the COOH group

• amino acids are alpha amino acids in proteins as the amine is bonded to the carbon

Question 4

What type of bonds form between amino acids?

Answer 4

amide (peptide bonds) form

Question 5

How do amino acids form a zwitterion?

Answer 5

As all amino acids contain an acidic and a basic group they are able to undergo an acid base reaction to form a zwitterion

Question 6

What occurs at a low pH, a neutral pH and a high pH for an amino acid?

Answer 6

low pH= the amino acid becomes NH3+

neutral pH= The NH2 becomes NH3+ and the carboxyl becomes COO-

High pH= the COOH becomes COO-

Question 7

What is a result of the ability of amino acids to form zwitterions?

Answer 7

Amino acids often act like salts , and have high melting points and high solubility in H2O

Question 8

Are all amino acids chiral?

Answer 8

Yes, all amino acids are chiral in the L form (NH2 is on the left of the molecule)

Question 9

How many amino acids are essential and how are they described in shortcode?

Answer 9

8/20 amino acids are essential

- 3 letter shorthand codes describe each amino acid

Question 10

What type of amino acids can exist?

Answer 10

• polar
• non polar
• acidic
• basic

Question 11

Describe non polar vs polar amino acids?

Answer 11

Whilst both forms of amino acids have neutral side chains (no charge), non polar refers to molecules who’s side chain is hydrophobic, whereas polar amino acids have hydrophilic side chains which can form hydrogen bonds

Question 12

Describe and distinct between acidic and basic amino acids:

Answer 12

Acidic/basic amino acids have charged side chains, however acidic amino acids are proton donors (they have a + charge or an extra H), whilst basic amino acids are proton acceptors (they have a - charge or less H than normal)

• both interact strongly in different peptides/proteins however remain ionic in their R group

Question 13

What occurs to zwitterions in acidic/basic solutions?

Answer 13

acidic solutions: zwitterions accept protons to their basic COO- group to leave only NH3+

basic solutions: zwitterions lose protons from their basic NH3+ to leave only COO-

Question 14

What is an isoelectric point and how is it calculated?

Answer 14

It describes the pH at which a sample of an amino acid has equal numbers of positive and negative charges (the net charge will be 0)

equation: PI = 1/2 X (pKa of COOH + pKa of NH2)

Question 15

Why do amylose and glycogen have different structures?

Answer 15

• glycogen’s glucose monomers are joined by a 1,6 bonds whereas amylose’s glucose monomers are joined by a 1,4 bonds

Question 16

Can RNA and DNA both form a double helix?

Answer 16

Yes, uracil in RNA can base pair with adenine

Question 17

What are some features of disulfide bonds?

Answer 17

• it is a covalent bond
• it can be both inter and intramolecular
• two S atoms must be adjacent for it to bond
• It is a stronger bond than a hydrogen bond
• Disulfide bonds confer structural stability upon the molecules in which they form

Question 18

What are B turns and which amino acids are most likely to form them?

Answer 18

A secondary structure also called a reverse turn where the chain is made to double back on itself , this causes two adjacent strands which can then be stabilised to form the b sheet structure

Question 19

Two alpha sheets are joined by a structure of what name?

Answer 19

An a turn