O2: 30 Amino acids, proteins, and DNA

Question 1

What properties do amino acids have?

Answer 1

Both acidic and basic.

Question 2

How do you draw a zwitterion?

Answer 2

NH2 -> NH3+
COOH -> COO-

Question 3

How do you draw an amino acid in acidic conditions?

Answer 3

NH2 -> NH3+

Question 4

How do you draw an amino acid in alkaline conditions?

Answer 4

COOH -> COO-

Question 5

What are proteins?

Answer 5

Sequences of amino acids joined by peptide links.

Question 6

Explain the importance of hydrogen bonding and sulfur-sulfur bonds in proteins.

Answer 6

Hydrogen bonds exist between polar groups, stabilising the secondary and tertiary structures of proteins.
Disulfide bonds link together and stabilise the tertiary structure.

Question 7

What is the primary structure of proteins?

Answer 7

The sequence of amino acids.

Question 8

What is the secondary structure of proteins?

Answer 8

Hydrogen bonds form between peptide links, folding the protein into either an a-helix or B-pleated sheet.

Question 9

What is the tertiary structure of proteins?

Answer 9

More bonds form between groups in the protein.
e.g. hydrogen bonds, disulfide bridges, ionic bonds.

Question 10

What does hydrolysis of the peptide link of a protein produce?

Answer 10

The constituent amino acids.

Question 11

How can amino acids be seperated and identified?

Answer 11

By thin-layer chromatography.

Question 12

How can amino acids be located on a chromatogram?

Answer 12

Using developing agents like ninhydrin or UV light.

Question 13

How can amino acids be identified on a chromatogram?

Answer 13

By their Rf values.

Question 14

Draw a peptide bond.

Answer 14

H-N=C-O

Question 15

What is the formula for Rf values?

Answer 15

Rf value = distance travelled by spot / distance travelled by solvent

Question 16

What are enzymes?

Answer 16

Proteins.

Question 17

Explain the ‘lock and key’ model for enzymes.

Answer 17

Enzymes’ active sites are highly specific so the substrate needs to have a complementary shape in order for the reaction to be catalysed.

Question 18

Explain stereospecificity in enzymes.

Answer 18

Because enzymes’ active sites are so highly specific, only one enantiomer of the substrate will work. Enzymes are proteins so also contain chiral centres.

Question 19

How can drugs work as enzyme inhibitors?

Answer 19

The drugs have a similar shape to the substrate so they bind to the active site, blocking it from substrate molecules.

Question 20

How are drugs designed now?

Answer 20

With the help of computers to model enzymes’ active sites and predict how drugs will interact with them.

Question 21

What is a nucleotide made up from?

Answer 21

A phosphate ion bonded to 2-deoxyribose which is bonded to a base.

Question 22

What is the structure of a single strand of DNA?

Answer 22

A polymer of nucleotides linked by covalent bonds between the phosphate group of one nucleotide and the 2-deoxyribose of another.
This results in a sugar-phosphate polymer chain with bases attached to the sugars.

Question 23

What does DNA exist as?

Answer 23

Two complementary strands arranged in the form of a double helix.

Question 24

What is cisplatin used as?

Answer 24

An anticancer drug.

Question 25

How does cisplatin work?

Answer 25

It prevents DNA replication in cancer cells by a ligand replacement reaction with DNA.
A bond is formed between platinum and a nitrogen atom on guanine.

Question 26

What does society need to do when it comes to cisplatin?

Answer 26

Assess the balance between the benefits and the adverse effects of drugs, like cisplatin.

Question 27

How can you counter the adverse effects of cisplatin?

Answer 27

Use very small amounts or target the drug specifically to cancer cells.

Question 28

Why does cisplatin have adverse effects?

Answer 28

It can kill healthy, normal cells by binding to the DNA in those cells and stopping replication.

Question 29

How does cisplatin prevent DNA replication?

Answer 29

The N atoms on guanine form co-ordinate bonds with cisplatin’s platinum, replacing the chlorine ligands in a ligand substitution reaction.
This causes the DNA strands to kink so they can’t unwind and replicate properly.