Amino acids, proteins and DNA

Question 1

Why are amino acids amphoteric?

Answer 1

They contain a basic amino group and an acidic carboxylic group

Question 2

What other property do amino acids have?

Answer 2

They are chiral molecules and so a solution of a single amino acid enantiomer will rotate plane polarised light.
An exception is glycine as the side chain is a hydrogen

Question 3

What is a zwitterion?

Answer 3

It is a dipolar ion

Question 4

Where do zwitterions exist in amino acids?

Answer 4

They only exist near an amino acid’s isoelectric point. This is the pH where the average overall charge on the amino acid is zero.

Question 5

What technique can be used to identify unknown amino acids?

Answer 5

Thin-layer chromatography

Question 6

Why is thin layer chromatography used to identify amino acids?

Answer 6

Different amino acids have different R groups and therefore have different solubilities in the same solvent.

Question 7

What are proteins?

Answer 7

They are condensation polymers of amino acids joined together by peptide links.

Question 8

Describe the primary structure of proteins

Answer 8

it is a sequence of amino acids in the long chain that makes up the protein

Question 9

Describe the secondary structure of proteins

Answer 9

The peptide links can form hydrogen bonds with each other meaning the chain is not a straight line. The most common secondary structures are an alpha helix and a B-pleated sheet.

Question 10

Describe the tertiary structure of proteins

Answer 10

The chain of amino acids is itself often coiled and folded in a characteristic way that identifies the protein. Extra bonds can form between different parts of the polypeptide chain which gives the protein a kind of three-dimensional shape.

Question 11

How are the secondary and tertiary structures of protein formed?

Answer 11

They are formed by intermolecular forces causing the amino acid chains to fold or twist.

Question 12

What are the two main types of bonds that hold proteins in shape?

Answer 12

Hydrogen bonding

Disulfide bonds

Question 13

Which factors affect hydrogen bonding and the formation of disulfide bonds?

Answer 13

Temperature

pH

Question 14

What are enzymes?

Answer 14

They are proteins that act as biological catalysts

Question 15

How do enzymes work?

Answer 15

They only work with specific substrates because the substrate has to fit into the active site. ‘Lock and key’ model

Question 16

What makes the active sites stereospecific?

Answer 16

Enzymes are made up of amino acids and therefore contain chiral centres. This means that only one of the enantiomers of a substrate will properly fit into the active site.

Question 17

What are inhibitors?

Answer 17

They are molecules that have a similar shape to the substrate

Question 18

What factors affect the amount of inhibition that occurs?

Answer 18

relative concentrations of inhibitor and substrate

how strongly the inhibitor bonds to the active site

Question 19

How do some drugs work?

Answer 19

They work as inhibitors by blocking the active site of an enzyme and stops it from working.

Question 20

How are scientists using technology to develop new drugs?

Answer 20

Computers are used to model the shape of an enzyme’s active site and predict how well potential drug molecules will interact with it. They can quickly examine hundreds of molecules looking for ones with the right shape before they start synthesising and testing things in the lab.

Question 21

What is DNA?

Answer 21

It is a polymer of nucleotides which contains all the genetic information of an organism

Question 22

What is nucleotide?

Answer 22

It is made up from a phosphate ion bonded to 2-deoxyribose which is in turn bonded to one of the 4 bases.

Question 23

How is the sugar-phosphate backbone made?

Answer 23

Nucleotides join together to form a polynucleotide chain. covalent bonds form between the phosphate group of one nucleotide and the sugar of another.

Question 24

What is the structure of DNA?

Answer 24

DNA is made up of two polynucleotide strands that spiral together to form a double helix structure which is held together by hydrogen bonds between the bases.

Question 25

Explain how hydrogen bonding between base pairs leads to the two complementary strands of DNA

Answer 25

Adenine always pairs with thymine and guanine always pairs with cytosine.
This leads to the complementary strands because whenever there is an adenine base on one strand, there will be thymine on the other and whenever there is a guanine base on one strand, there will be a cytosine base on the other, and vice versa.

Question 26

Cisplatin is used as an anticancer drug. How does cisplatin prevent DNA replication in cancer cells?

Answer 26

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

Question 27

What problems can be caused by cisplatin?

Answer 27

It can bind to DNA in normal cells. This can be a problem for healthy cells that replicate frequently such as hair cells and blood cells. This can cause hair loss and suppress the immune system and also cause kidney damage.

Question 28

How can the problems caused by cisplatin be reduced?

Answer 28

• giving patients very low doses of cisplatin

- target the humor

Question 29

Why is cisplatin still used as a chemotherapy drug?

Answer 29

The balance of the long-term positive effects outweigh the negative short-term effects.