3. Enzymes & Protein Synthesis

Question 1

What is the lock and key theory?

Answer 1

A substrate is complementary to the enzyme’s active site.
The substrates form temporary bonds with the amino acids in the active site to form an enzyme-substrate complex.
After the reaction has been carried out the products are released and the enzyme is unchanged

Question 2

What is the induced-fit theory?

Answer 2

The enzyme’s active site will change to slightly to fit more closely around the substrate. Only specific substrate’s will induce this change in shape however

Question 3

How do enzymes lower the activation energy?

Answer 3

Charged sites on the substrate and active site interact and the oppositely charged groups distort the substrate to assist in bond making or bond breaking.

Question 4

Why is it important for the activation energy to be lowered?

Answer 4

The normal energy required for the reaction to start would damage the cell and it also speeds up the rate at which reactions happen.

Question 5

What happens in a catabolic reaction?

Answer 5

Larger substrates are broken down

Question 6

What happens in an anabolic reaction?

Answer 6

Product is built up

Question 7

What is the effect of enzyme concentration on the rate of a reaction assuming substrate is always in excess?

Answer 7

The initial rate will be directly proportional to the enzyme concentration as there are a greater number of active sites to form enzyme substrate complexes.

Question 8

What effect does substrate concentration have on the rate of reaction?

Answer 8

Initially substrate conc. produces more successful enzyme-substrate collisions so rate increases.
As the conc continues to be increased the enzymes become a limiting factor as all active sites are full so there is no overall effect on the rate

Question 9

What is the structure of a DNA nucleotide?

Answer 9

phosphate group, deoxyribose sugar and an organic base e.g A, T, C, G

Question 10

What type of bond holds adjacent nucleotides together?

Answer 10

phosphodiester

Question 11

How many hydrogen bonds does the AT pairing form?

Answer 11

2

Question 12

How many hydrogen bonds does the CG pairing form?

Answer 12

3

Question 13

What type of reaction joins mononucleotides together to form a polynucleotide?

Answer 13

condensation reaction

Question 14

What term is used to describe the pairs of bases?

Answer 14

complementary

Question 15

Where does transcription take place?

Answer 15

Nucleus

Question 16

Describe the process of transcription.

Answer 16

1. Hydrogen bonds break and the double helix unwinds
2. Free RNA nucleotides line up against their complementary base on the template strand
3. Once a stop code is reached the mRNA molecule detaches from the DNA and leaves the nucleus into the cytoplasm

Question 17

What is the structure of an RNA nucleotide?

Answer 17

Phosphate group, ribose sugar, organic base e.g. A, U, C, G

Question 18

Which organic base is replaced by uracil in RNA?

Answer 18

Thymine

Question 19

Which enzyme is involved in transcription?

Answer 19

RNA polymerase

Question 20

Describe the process of translation.

Answer 20

1. mRNA molecule binds to a ribosome where the process takes palce
2. tRNA molecule carrying an amino acid binding site pairs with the codon on the mRNA that is complementary to its anticodon
3. The amino acids are brought close together so join in condensation reactions to form peptide bonds

Question 21

What are two differences between an mRNA and a tRNA molecule?

Answer 21

1. tRNA has an amino acid binding site and mRNA does not

2. mRNA is a single strand where as tRNA is folded and held in place by hydrogen bonds