Lecture 2 The Structure of DNA

Question 1

Define nucleoside

Answer 1

This refers to a base attatched to a 2’ deoxyribose sugar group

Question 2

Define nucleotide

Answer 2

This is a base attatched to a 2’deoxyribose sugar and a phosphate group.

Question 3

What is the directionality of DNA

Answer 3

5’ to 3’

Question 4

What is the 5’ end

Answer 4

the phosphate terminus

Question 5

What is the 3’ end

Answer 5

an OH hydroxyl end.St

Question 6

What are three imporant of the DNA double helix

Answer 6

• Strands run antiparallel
• DNA has different forms, A,B and Z
• has a major groove and a minor groove

Question 7

State the names of the purine bases

Answer 7

Adenine and Guanine

Question 8

State the names of the pyrimidine bases

Answer 8

Cytosine and Thymine

Question 9

How many aromatic rings in purine bases

Answer 9

2

Question 10

How many aromatic rings in pyrimidine bases

Answer 10

1

Question 11

Which is the most common form of DNA found in the cell

Answer 11

B DNA

Question 12

State the names of the different forms of DNA found in the cells

Answer 12

B DNA
A DNA

Z DNA

Question 13

Describe the structure of B DNA

Answer 13

• Right handed helix
• major groove is wide and deep
• minor groove is narrow and shallow
• most common form of DNA found in the cell

Question 14

Describe the structure of A DNA

Answer 14

• Right handed helix
• major groove is narrow and deep
• Minor groove is wide and shallow
• rare form of DNA only forms in dehydrating conditons

Question 15

Describe the structure of Z DNA

Answer 15

• Left handed helix
• has a flat major groove
• has a narrow deep minor groove
• distorted helix structures with the most number of bases per turn of the helix.
• biologically active but its function is not yet known.

Question 16

What is the name of the bond between the nitrogenous base (A,G,T,C) and the 2’deoxyribose sugar

Answer 16

Beta-N-glycosidic bond

Question 17

Describe the structure of a nucleotide base

Answer 17

• base (a,g,c,t)
• 2’deoxyribose sugar
• phosphate group.

Question 18

Why is the pentose sugar of the nucleotide described as 2’

Answer 18

because in deoxyribose, an oxygen is missing at the 2’ position in the carbon ring.

Question 19

what is the OH terminus

Answer 19

The 3’ end

Question 20

What is the P terminus

Answer 20

The 5’ end

Question 21

In which direction does DNA run

Answer 21

5’ to 3’

Question 22

State the names of the 4 nucleotide bases

Answer 22

2’deoxyadenosine 5’ triphosphate dATP
2’deoxyguanine 5’triphosphate dGTP
2’deoxythymine 5’ triphosphate dTTP
2’deoxycytidine 5’ triphosphate dCTP

Question 23

What is meant by the GC content

Answer 23

the amount of cytosine and guanine base pairs

Question 24

What is the GC content of human DNA

Answer 24

40.3 percent

Question 25

What is the GC content in plasmodium falciparum

Answer 25

DNA content of 19 percent

Question 26

What is the GC content in streptomyces griseous

Answer 26

72.4 percent

Question 27

What is meant by complimentary base pairing and why is it important

Answer 27

• A always pairs with T
• C always pairs with G
• complementary base pairing is important as it allows DNA molecules to replicate. If the two polynucleotides in a DNA molecule are separated, then two perfect copies of the parent double helix can be made because the sequences of the pre-existing strands dictate the sequences of new comlementary strands.