Dna And Rna

Question 1

What caused many scientists to doubt that DNA carried the genetic code?

Answer 1

DNA has a relatively simple chemical composition.

Question 2

Describe how DNA double helix is formed from two polynucleotide stands.

Answer 2

Two DNA polynucleotide strands join together by hydrogen bonding between complementary base pairs — A with T and G with C. Two hydrogen bonds form between A and
T, and three hydrogen bonds form between C and G.

The antiparallel strands then twist round each other to form the DNA double helix.

Question 3

What is the nucleotide base called?

Answer 3

Nitrogen containing organic base

Question 4

Scientists analysed a section of stranded DNA.
There were 68 bases in total (34 base pairs) and 22 bases of adenine.

How many of the bases were

A) thymine
B) cytosine
C) guanine

Answer 4

A) thymine - 22

B) cytosine - 12

C) guanine- 12

Question 5

Compare and contrast the DNA in eukaryotic with DNA in prokaryotic cells

5 marks

Answer 5

Comparisons
1. Nucleotide structure is identical;

2. Nucleotides joined by phosphodiester bond;
   OR
   Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;

Contrasts
4. Eukaryotic DNA is longer;

5. Eukaryotic DNA contain introns, prokaryotic
   DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular,
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;