Amino acids, proteins and DNA

Question 1

What are zwitterions? Give an example of one

Answer 1

Ions that have both a permanent positive and a permanent negative charge, with the compound having an overall neutral charge

Amino acid (Amine group has a tendency to act as a base and accept a proton, Carboxlyic Acid group has a tendency to act as an acid and lose a proton)

Question 2

Amino acids are ionic. What properties this does this give them?

Answer 2

High melting and boiling points
Dissolve well in water
Dissolve poorly in non-polar solvents
Typically are white solids at room temp and behave similarly to an ionic salt

Question 3

Amino acids in strongly acidic and strongly alkaline conditions

Answer 3

Strongly acidic conditions

• Lone pair from the H2N group accepts a proton to form the positive ion
• The amine group has gained a hydrogen ion and is protonated

Strongly alkaline conditions

• The -OH from the carboxylic acid group loses a proton to form the negative ion
• The carboxylic acid group has lost a hydrogen ion and is deprotonated

Question 4

Draw a zwitterion

Answer 4

Draw an amino acid, but with a + on the N and instead of an OH group an O-

Question 5

What is it called when the amine group and carboxylic acid groups from different amino acids react?

Answer 5

Amide linkage

Question 6

Bonds between amino acids: type of bond and reaction and what is formed

Answer 6

Peptide bonds in a condensation reaction to form a dipeptide

Question 7

Hydrolysing a protein

Answer 7

Boiled in 6moldm-3 HCL for about 24 hours

+ H20 and H+ catalyst

Question 8

Structure of proteins

Answer 8

Primary structure - The sequence of amino acids in a polypeptide chain.

Secondary - Hydrogen bonds (or other IMF’S, or disulphide bridges) between amine and carboxyl groups twist and fold the structure into an alpha helix or a beta pleated sheet and hold the protein structure in place

Question 9

Why does wool stretch, and why does washing wool at high temperatures cause it to lose its shape?

Answer 9

Because when wool is gently stretched the hydrogen bods stretch, extending the fibres. When the tension is released the fibre returns to its original shape

High temperatures can permanently break the hydrogen bonds, and the garment may permanently lose its shape

Question 10

Thin layer chromatography

Answer 10

Book

Question 11

Rf value equatiom

Answer 11

Distance moved by spot/Distance moved by solvent

Question 12

Enzyme shape and bonding to active sites

Answer 12

Usually globular proteins

Temporary IMF’s

Question 13

Enzyme inhibition

Answer 13

Molecule of a similar shape to an enzymes substrate is create, and will bind to the active site, blocking it

Question 14

Cisplatin

Answer 14

Pt (left, 2x H3N, right, 2x Cl) - Square Planar
Bonds to adjacent guanine bases on a strand of DNA
This works because the nitrogen atoms on the guanine molecules have lone pairs, and so they displace the chlorine atoms

Question 15

What does cisplatin do?

Answer 15

Bonds to strands of DNA (guanine bases specifically), distorts the strands and preventing cell replication and division.

Question 16

Cell division

Answer 16

H bonds easily broken during cell division, unravelling the strands
Covalent bonds between the chains stay in place (chains remain intact and the sequence of bases is retained)
Complimentary bases line up, H bonds and phosphodiester bonds
Result: Two double helix molecules identical to the original molecule