Chapter 30 (Amino Acids, Proteins and DNA)

Question 1

What is the R group for Glycine?

Answer 1

H

Question 2

What is an alpha amino acid?

Answer 2

The NH2 and COOH groups are attached to the same C

Question 3

Why are amino acids optically active (except glycine)?

Answer 3

They have a chiral carbon as there are four different groups on the central C so they rotate plane polarised light.

Question 4

What is a zwitterion?

Answer 4

The dipolar form an amino acid takes in neutral conditions with [NH3]+ group and [COO]- group.

Question 5

Why do amino acids have a high melting point?

Answer 5

Ionic interaction between zwitterions

Question 6

What happens to an amino acid in a high pH?

Answer 6

COOH loses H and forms COO-

Question 7

What happens to an amino acid in a low pH?

Answer 7

NH2 gains a H and forms NH3+

Question 8

What are dipeptides?

Answer 8

Combination of two amino acids with one amide (peptide) link

Question 9

How are amino acids split?

Answer 9

Heated with concentrated hydrochloric acid or concentrated strong alkali and then salt into 2 amino acids

Question 10

How are amino acids separated?

Answer 10

Chromatography

Question 11

Describe the method for thin layer chromatography?

Answer 11

1) Wearing gloves, draw a pencil line 1cm above bottom of TLC plate and mark spots for each sample, equally spaced along line.
2) Use a capillary tube to add a tiny drop of each solution to a different spot to allow the plate to air dry.
3) Add solvent to a chamber or large beaker with a lid so that is not more than 1 cm in depth.
4) Place the TLC plate in the chamber, make sure that the level of solvent is below the pencil line. Replace the lid to get a tight seal.
5) When the level of the solvent reaches about 1cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard.
6) Spray paper with ninhydrin/shine UV light to see spots.
7) Calculate Rf values of the observed spots.

Question 12

Why id the line drawn in pencil in TLC`?

Answer 12

Will not dissolve into solvent

Question 13

Why is only a small drop of amine acid used in TLC?

Answer 13

Big drops could merge together

Question 14

Why is the solvent below the pencil line in TLC?

Answer 14

If above then the samples from the plate will dissolves into the solvent.

Question 15

Why is a lid put on the experiment in TLC?

Answer 15

Prevents evaporation of a toxic solvent.

Question 16

Why is the plate dried in a fume cupboard in TLC?

Answer 16

The solvent fumes are toxic.

Question 17

How do you increase the accuracy of the Rf value in TLC?

Answer 17

Allow the solvent to rise to near the top of the plate.

Question 18

What is the equation for Rf value?

Answer 18

Distance moved by amino acid/distance moved by solvent

Question 19

Describe the primary structure of proteins

Answer 19

Sequence of amino acids joined together by condensation reactions to form peptide links.

Question 20

Describe the secondary structure of proteins

Answer 20

Hydrogen bonding between N-H and C=O groups of the peptide links along the polypeptide chains.

Question 21

Describe the structure of a beta-pleated sheet protein

Answer 21

Parallel regions of proteins lined up with hydrogen bonds between them leading to a slat, sheet-like structure.

Question 22

Describe the structure of an alpha-helix protein

Answer 22

Hydrogen bonds are formed every four amino acids, forcing the chain in a cylindrical formation. The structure is elastic and flexible e.g. keratin.

Question 23

Describe the tertiary structure of proteins

Answer 23

The 3D shape of the protein held together by H hydrogen bonding, ionic interactions and disulphide bonds between the R-groups of the amino acids.

Question 24

How are disulphide bonds broken?

Answer 24

Heat, reduction or a reaction with a base

Question 25

What type of reaction is the digestion of proteins?

Answer 25

Hydrolysis

Question 26

What is the function of enzymes?

Answer 26

Act as biological catalyst, providing an alternative reaction with a lower activation energy.

Question 27

Describe the lock and key hypothesis

Answer 27

Substrates must have the right shape to fit into the active site.

Question 28

What is the isoelectric point of an amino acid?

Answer 28

The pH at which it has no overall charge.

The point midway between the two pKa values of its two functional groups.

Question 29

What is a fibrous protein?

Answer 29

Long chains of polypeptides found in bundles and insoluble in water.

Question 30

What are globular proteins?

Answer 30

Polypeptide chains folded into roughly spherical shapes that are soluble in water.

Question 31

What is a stereo specific active site?

Answer 31

An active site that binds one enantiomer of a racemate

Question 32

How do some drugs act as enzyme inhibitors?

Answer 32

Block the active site to prevent the substrate from binding so no E-S complexes can form.

Question 33

What are the key molecules in a DNA nucleotide?

Answer 33

Phosphate
Deoxyribose sugar
Nitrogenous base

Question 34

How many hydrogen bonds are between each base pair?

Answer 34

AT = 2
CG = 3

Question 35

How does cisplatin work?

Answer 35

1) The two chloride ions are displaced by water molecules.

2) The N lone pair on guanine form dative covalent bonds with Pt which is a ligand replacement reaction.