3.13 Amino acids, proteins and DNA

Question 1

What are the 2 functional groups of amino acids

Answer 1

NH2 and COOH (amine and carboxylic acid)

Question 2

Draw a general formula for alpha amino acids

Answer 2

google

Question 3

Are alpha amino acids chiral, why

Answer 3

Yes one carbon has 4 different substituents
Except glycine where R=H

Question 4

In what form do amino acids exist as solids
What consequence does this have

Answer 4

Zwitterions (ionic lattice) - high mtp and bpt

Question 5

What colour solids are most zwitterions at room temp

Answer 5

White solids

Question 6

Do zwitterions dissolve in water? Non polar solvents? Why?

Answer 6

Yes, but only in non polar solvents. Due to ionic nature/polar bonds

Question 7

Define a zwitterion

Answer 7

Ions which have both a permanent positive and negative charge, but are neutral overall

Question 8

How do zwitterions occur in amino acids? Draw a general structure of one

Answer 8

COOH is deprotonated –> COO-
NH2 is protonated –> NH3+

Question 9

What happens to amino acids in acidic conditions

Answer 9

Gains a proton on NH2 group

Question 10

What happens to amino acids in alkaline conditions

Answer 10

Loses a proton from COOH group

Question 11

What is the peptide linkage

Answer 11

-CONH-
The peptide linkage

Question 12

What is a dipeptide

Answer 12

2 amino acids bonded together

Question 13

What is a TLC plate made of

Answer 13

Plastic sheet coated with silica, SiO2
This is the stationary phase (the solvent is the mobile phase)

Question 14

Describe how you would carry out TLC

Answer 14

Spot the samples onto a pencil line a few cm above base of TLC plate
Place this in a beaker or tank, with solvent level below the pencil line. Ensure there is a lid of 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 15

Why does TLC separate amino acids (or other molecules)

Answer 15

Solvent carries amino acids up the TLC plate. The rate of movement depends on the balance between that amino acids solubility in the solvent and the affinity for the stationary phase

Question 16

What do you often have to do to enable the amino acids to be seen on the chromatogram

Answer 16

Spray with ninhydrin (aa are colourless, turns their spots purple)
Shine UV light

Question 17

How do you find the primary structure of a protein

Answer 17

Reflux with 6M HCl and reflux for 24 hours
Carry out TLC to find the number and type of amino acids present

Question 18

How do enzymes increase the rate of reaction

Answer 18

Reacting molecules form temporary bonds (via imf) to the enzyme. This weakens the bonds in the molecules, promotes electron movement and lowers EA

Question 19

What does the stereospecificity of enzymes mean

Answer 19

Active sites are so selective of the shape of substrates that only reactions involving one enantiomer are catalysed

Question 20

What does DNA stand form=

Answer 20

Deoxyribonucleic acid

Question 21

Draw a nucleotide

Answer 21

Google

Question 22

What forms between adjacent nucleotides

Answer 22

Hydrogen bonding

Question 23

What kind of polymer does the polymerisation of DNA lead to

Answer 23

Condensation polymer chain - backbone of phosphate and sugar molecules, with bases attached

Question 24

Draw the structure of cisplatin

Answer 24

google

Question 25

What is cisplatins function and how does it do this

Answer 25

Anti cancer drug
Bonds to strands of DNA to distort shape and prevent cell replication. It bonds to the N atoms on 2 adjacent G bases. The N atoms replace the Cl- ligands in a ligand substitution reaction

Question 26

Why are Cl- ions able to be replaced by N on the base

Answer 26

N atoms on the G base have lone pairs of electrons that can co-ordinately bond to the Pt ion; N atom are better ligands than Cl-; so replace them

Question 27

What are the drawbacks of using cisplatin

Answer 27

Affects healthy cells that are replicating quickly, eg hair follicles
Thought to damage kidneys