Maintenance And Use Of Genetic Information

Question 1

SSB function

Answer 1

Helicase unwinds DNA, ssb prevents reformation of double helix

Question 2

Topoisemerase function

Answer 2

Breaks phosphodiester bond ahead of replication fork-> prevents positive supercoiling

Question 3

How does DNA replication take place in the same direction

Answer 3

Lagging strand loop

Question 4

What’s end replication paradox

Answer 4

Small amount of DNA lost from end of chromosome each time because no space for rna primer

Question 5

How is loss of DNA prevented

Answer 5

Telomerase forms telomeres (TTAGGG)
Template rna anneals to DNA-> telomerase adds nucleotides-> telomerase translocates further along DNA adding more nucleotides

Question 6

Types of mutation

Answer 6

Missense
Silent 
Nonsense
Small scale deletion/insertion: multiple of 3(eg cystic fibrosis)/ not multiple of 3 (frameshifts) 
Inversion
Deletion
Duplication
Translocation

Question 7

Examples of gross mutations

Answer 7

Deletion: cri du chat (chromosome 5)
Translocation: chronic myelogeneous leukaemia (pieces of 9 and 22 swap)

Question 8

Spontaneous mutation causes

Answer 8

DNA replication error
Replication slippage (gain/loss of repeats)
Deamination (eg when c is deaminated to u-> pairs with A; when A is deaminated to hypoxanthine-> pairs with C )

Question 9

Physical and chemical induced mutation

Answer 9

Physical— ionising radiation/UV RAdiation (thymine dimers)

Chemical— free radicals/nitrous acid/ alkylating agents

Question 10

How’s DNA repaired

Answer 10

Directly (dealkylation by enzymes— guanine mutated to 06 methylguanine; fixed by MTase)

Removal of mistake and resynthesis

Question 11

How’s DNA exposed

Answer 11

Nucleosome sliding

DNA pulled away