Amino Acid's And Proteins

Question 1

Give the meaning of each of the three terms used to describe the levels of protein structure (3)

Answer 1

– Primary structure describes sequence of amino acid’s via peptide bonds

– Second airy structure describes shape taken up by protein chain such as alpha helix structure or beta pleated sheets

– Tertiary structure describes the further folding to give overall shape due to extra bonds

Question 2

Describe how paper chromatography can be used to identify an unknown amino acid (6)

Answer 2

-pencil line on paper (bottom) put spot of mixture on the line

– Place in beaker containing solvent (ensure solvent below of spot)

– Cover with watch glass

– When solvent nearly reaches top, Markwest solvent is

– Identify position of spots and allow to dry then Spray with ninhydrin solution

– Workout RF values or if done understand the conditions you standard RF tables

Question 3

What is the equation for Rf value?

Answer 3

Distance travelled by spot/distance travelled by solvent

Question 4

What is another word for amino acid monomers?

Answer 4

Amino acid residues

Question 5

What is the name of the link between Amy and group and a carboxylic acid group?

Answer 5

Peptide link

Question 6

Describe the process of making a dipeptide(2)

Answer 6

–Amine group of one amino acid reacts with carboxylic acid group of another amino acid

– in a condensation reaction

Question 7

Describe the process of breaking down a protein into its individual amino acid’s(5)

Answer 7

– In a hydrolysis reaction

– Add hot aqueous 6 mol dm^-3 HCl

– Keep it under reflux for 24 hours

– This produces ammonium salt of amino acid

– Final mixture neutralised using a base

Question 8

Explain why spots travel different distances in paper chromatography(2)

Answer 8

– Different substances have different solubilities

– Therefore as solvent spreads up paper different chemicals in mixture move with it but at different rates

Question 9

Define amphoteric

Answer 9

Contains both acidic and basic properties

Question 10

What is a zwitterion?

Answer 10

Overall neutral molecule with both positive and negative charge in different parts of molecule

Question 11

And amino acid can only exist as a zwitterion near its isoelectric point.what is an isoelectric point?

Answer 11

The pH where overall charge on amino acid is zero

Question 12

Is isoelectric point the same for all amino acid’s?

Answer 12

Depends on R group

Question 13

Describe what happens when amino acid is placedo in more acidic conditions than isoelectric point(2)

Answer 13

– Amine group becomes protonated to NH3 +

– COO- group become COOH

Question 14

Describe what happens when amino acid is placed in more basic conditions than isoelectric point (2)

Answer 14

– COOH group loses protons to become COO-

– NH3+ becomes NH2

Question 15

What happens when amino acid is exposed to isoelectric point?

Answer 15

Both carboxyl group and amino group likely to be ionised forming zwitterion

Question 16

Why does tertiary structure occur?

Answer 16

Different forces occur due to the R groups of the amino acid to keep it stable

Question 17

Name the forces that can hold a tertiary structure (4)

Answer 17

– Instantaneous dipole -induced dipole

– Ionic interactions

– Hydrogen bonds

– Disulphide bonds