FCELL- DNA structure

Question 1

describe the main structural features of the DNA helix

Answer 1

double helix - complementary polynucleotide chains

minor and major grooves - provide access to proteins that want to read DNA

cellular DNA is supercoiled, present as chromatin in the nucleus

can be damaged by radiation / chemicals - importance of DNA repair - cancer therapy

A and B form = right hand helices
Z form = left hand helices

Question 2

how is DNA supercoiling achieved

Answer 2

DNA gyrase uses ATP to supercoil the DNA -

other enzymes - Topo IV, Topo I - release supercoiling forming relaxed DNA

Question 3

what are some features of supercoiling

Answer 3

energy sealed within it - facilitate unwinding of helix DNA replication

reduces the size of the DNA

Question 4

what is a tetraplex DNA

Answer 4

four stranded DNA helix formed at telomeres - required G- rich DNA sequences

Question 5

what is a holiday junction

Answer 5

4 stranded junction - arise naturally in living cells through DNA strand exchange between two homologous chromosomes - important role in DNA repair - can open the helices and exchange a strand of DNA - results in linking of chromosomes

Question 6

what are the levels of DNA structure

Answer 6

primary - sequence of bases
secondary - helical structure
tertiary - DNA supercoiling
Quaternary - interlocked chromosomes

Question 7

what is the process of sanger sequencing

Answer 7

DNA strand is copied with DNA polymerase in the presence of inhibitors that arrest DNA synthesis specifically at A,C,T,G

DNA strands are separated by length on gel

incorporation of inhibitor is radioactive

DNA bands can be visualised

Question 8

describe how chemicals and other environmental ages can result in DNA damage

Answer 8

spontaneous - loss of bases, hydrolysis of C to U

chemical and radicals - generated by oxidative metabolism (change in base structure, insert between bases)

radiation - UV light produces thymine dimers, ionising radiation (break chromosomes)

Question 9

describe DNA repair reasons

Answer 9

maintains genome stability
more than 100 different proteins involved

important - defects in DNA repair mechanisms = prone to cancer

Question 10

which anticancer therapies rely on DNA damaging agents

Answer 10

Cyclophosphamide
doxorubicin
overcome DNA repair in cells so cancer cells cannot replicated and are therefore killed