Amino Acids, Proteins and DNA

Question 1

Do amino acids have acidic or basic properties?

Answer 1

Acidic and Basic properties

Question 2

What happens to an amino acid in acidic solution?

Answer 2

The zwitterion’s NH2 group will be protonated to NH3+

Question 3

What happens to an amino acid in basic solution?

Answer 3

The zwitterion’s COOH group will be deprotonated to COO-

Question 4

What do amino acids exist as? What does this mean?

Answer 4

Zwitterions - They have a permanent positive and negative charge

Question 5

What are proteins?

Answer 5

Sequences of amino acids joined by peptide bonds.

Question 6

What types of bonding are important in a protein? Why?

Answer 6

Hydrogen bonding, Sulfur-Sulfur bonds
Disulphide bridges are stronger than Hydrogen bonds

Question 7

Primary, Secondary, Tertiary structure of Proteins

Answer 7

Primary: The sequence of amino acids along the protein chain. Bonded by covalent bonds
Secondary: The shape of the protein chain - Alpha helix/ beta pleated sheets
Tertiary: Alpha-helix or beta-pleated sheet is folded into a complex 3D shape - Ionic, disulphide bridges, VDW’s

Question 8

What does hydrolysis of a peptide link produce

Answer 8

Its constituent amino acids

Question 9

How can amino acids be separated and identified

Answer 9

Thin layer chromatography
Located using developing agents like ninhydrin or UV light
Identified by RF value

Question 10

What is a TLC plate made of

Answer 10

Plastic sheet coated with silica

Question 11

How do you carry out Thin Layer Chromatography

Answer 11

Spot the samples onto a pencil line a few cm above the base of the TLC plate.
Place this in a beaker or tank, with solvent level below the pencil line. Ensure there is a lid on the beaker to keep the inside saturated with solvent vapour.
Wait until the solvent front is almost at the top of the TLC plate;
Then remove from the beaker and analyse.

Question 12

Why does TLC separate amino acids

Answer 12

Solvent carries amino acids up the TLC plate. The rate of movement depends on the balance between that amino acid’s affinity for the solvent (solubility in it) and affinity for the stationary phase (attraction to the silicon with hydrogen bonding).

Question 13

How do you find the primary structure of a protein.

Answer 13

Reflux with HCl for 24 hours.
Do TLC

Question 14

What type of proteins are enzymes?

Answer 14

Globular

Question 15

What are enzymes?

Answer 15

Biological catalysts

Question 16

What does the stereospecificity of enzymes mean

Answer 16

Only 1 enantiomer is catalysed

Question 17

How are enzymes inhibited?

Answer 17

A molecule with a very similar shape and structure to the substrate is devised. Binds to the enzyme’s active site. Blocks the active site (does not desorb easily). Substrate cannot adsorb to the active site, so reaction cannot be catalysed

Question 18

How are molecules modelled on computed

Answer 18

Now we understand factors that affect the shapes of
extremely complex proteins, we can model drugs that haven’t even been synthesised, predict their properties and design drugs that will treat a range of medical conditions

Question 19

What is a nucleotide made up of?

Answer 19

A phosphate ion, 2-deoxyribose, a nitrogenous base

Question 20

Why is DNA a polymer

Answer 20

nucleotides are monomers linked by covalent bonds between the phosphate and sugar

Question 21

In what form does DNA exist

Answer 21

As 2 complementary strands in a double helix

Question 22

What is the main anti-cancer drug

Answer 22

Cisplatin

Question 23

How does cisplatin work?

Answer 23

It prevents DNA replication by ligand replacement.
The cl –> H20 –> N on guanine

Question 24

Why is N a better ligand than Cl-

Answer 24

N atoms have a lone pair that can datively bond to the Pt so are better ligand

Question 25

Cons of Cisplatin

Answer 25

Affects healthy cells that replicate quickly e.g. hair
Damages kidneys

Question 26

State the meaning of the term complementary when it is used to refer to DNA strands.

Answer 26

(Complementary means the two strands must have base sequences) that match (all) A to T and C to G