Biochem

Question 1

What is the difference between a nucleotide and a nucleoside?

Answer 1

Nucleotide = base + sugar + phosphate
Nucleoside = base + sugar

Question 2

What end are new nucleotides added on to and what direction is DNA read in?

Answer 2

New nucleotides added to 3’ end

Read from 5’ - 3’

Question 3

What type of bond is between A and T and C and G?

Answer 3

A=T (double bond)

C=-G (triple bond)

Question 4

What enzyme catalyses DNA replication?

Answer 4

DNA polymerase (can only build onto an RNA primer - primase)

Question 5

Where does DNA transcription start and which side does it read?

Answer 5

Origins or replication (there are multiple points)

Bidirectional

Question 6

What are the 2 strands called in DNA replication?

Answer 6

Leading strand (has a free 3' end)
Lagging strand (okazaki fragments)

Question 7

What enzyme unwinds DNA?

Answer 7

Helicase

Question 8

What enzyme checks the transcribed DNA strand for mutations?

Answer 8

DNA polymerase

Question 9

Where on DNA is the initiation site for RNA transcription?

Answer 9

Promotors - TATA box

Question 10

Where are steroid receptors active?

Answer 10

Only in the nucleus (inactive in the cytoplasm)

Question 11

What are the 3 tRNA binding sites on a ribosome?

Answer 11

EPA
E = exit
P = peptidyl
A = aminoacyl

Question 12

What are the types of chomosomal mutation?

Answer 12

Deletion,
Duplication,
Translocation,
Inversion

Question 13

What are the types of DNA mutation?

Answer 13

Point, frameshift

Question 14

What is the difference between lock-and-key enzyme binding and induced fit?

Answer 14

Lock and key: active site of substrate is complementary to that of the enzyme
Induced fit: partial binding of the enzyme initiates a conformational change which increases binding of the enzyme to the substrate

Question 15

What enzyme phosphorylates and what dephosphorylates a molecule?

Answer 15

Phosphatase: dephosphorylates
Kinase: phosphorylates

Question 16

What is Km?

Answer 16

The concentration of substrate and which the reaction is progressing at half of Vmax

Question 17

On a line weaver-Burk plot which point indicates Km and which indicates Vmax?

Answer 17

Km: intersection with X axis (1/[S])
Vmax: intersection with y axis (1/v)

Question 18

What does a low Km indicate?

Answer 18

Higher affinity for the substrate (needs a lower conc to progress at a high rate)

Question 19

What is the difference between competitive and non-competitive inhibition and are they reversible?

Answer 19

Competitive: inhibitor binds to same site as substrate to stop it binding
Non-competitive: inhibitor binds to site other than substrate and changes the conformation of the active site to prevent binding
Both are reversible

Question 20

In competitive and non-competitive inhibition which factor remains constant?

Answer 20

Competitive: Vmax remains constant (Km varies)

Non-competitive: Km remains constant (Vmax varies)