DNA replication

Question 1

The hiv virus infects lymphocytes explain why it’s only lymphs

Answer 1

Outside of the virus has proteins with complimentary shape to receptor in membrane of lymphocyte cells. This receptor will only be found on membrane lymphocyte cells

Question 2

The Rna in Hiv must be converted into DNA inside the cell for the virus to replicate, this DNA is inserted into the hosts genome and is transcribed like a normal gene. Describe the transcription of the HIV genetic material

Answer 2

Transcription is the conversion of DNA into RNA. A strand of DNA is read by RNA polymerase. This converts the DNA sequence into an RNA sequence complimentary to the strand being read. This MRNA leaves the nucleus and travels to a ribosome

Question 3

RNA polymerase transcribes at around 60 nucleotides per sound. The length of the HIV genome is 10.000 base pairs long. Calculate to the nearest whole number the ,ax no of HUV genomes that can be transcribed in a cell in one hour.

Answer 3

1 hour= 60 min 60 min= 60x 60 seconds = 3600s no. base pairs that can be transcribed in an hour= 3600 x 60=216000 no of genomes that can be replicated= 216000/ 10000=21.6 so roughly 22 genomes in an hour

Question 4

Use a labelled diagram to illustrate the process of DNA replication, referring to teh importancve of complementary base pairing and teh enzymes involved in the process

Answer 4

Question 5

Outline the process of DNA replication, explaining the importance of the enzymes DNA helicase and DNA polymerase

Answer 5

• The strands of DNA are separated by the enzyme DNA helicase which breaks the hydrogen bonds joining together the complimentary bases on each strand.
• As DNA helicase continues to separate teh two strands, free nucleotides bidn to their complimentary bases one each of the strands, forming hudrogen bonds
• These bound nucleotides are then joined togetehr by the enzyme DNA polymerase which forms phosphodiester bonds between each nucleotide
• Once all the nucleotides on each strand are joined together, two new identical molecules of DNA are formed

Question 6

• The data shows that teh level of radioactivity of DNA extracted from Ecoli taken from sample 2 has half the level pof radioactivity compared to sample 1.
• The DNA became radioactively labelled as the phosphorus-32 was incorporated into the phosphate groups in the DNA during DNA replication.
• The level of radioactivity halved in teh sample taken from phosphorus-31 because DNA replication is needed to form a new generation of bacteria
• and the new DNA synthesised would incorporate teh non-radioactive phosphorus-31 isotope.
• Therefore, only half of the DNA extracted from sample 2 will be radioactive so teh levels of radioactivity will halve.

Question 7

The scientist let the Ecoli bacteria divide for a second generation in the phosphorus-31 nutrient broth. Suggest what results the scientist would see when the level of radioactivity is measured for the DNA from this new sample.

Answer 7

The level of radioactivity would be half of sample 2 or a quarter of sample 1

Question 8

Answer 8

• The diagram in fifure 2 shows that each strand of DNA runs in the opp diection to eachother
• The strands are antiparallel. Fugure 2 also shows that the 3’ end of each DNA is different from the 5’ end.
• The AS of an enzyme liek DNA polymerase us a specific shape
• Therefore, DNA polymerase can only bind to one of these ends- teh complementary end
• And since teh strands run in oppn d, this means the DNA polymerase myst also move in teh opp d