1.3 - Review of DNA and RNA

Question 1

What is the composition of a nucleotide?

Answer 1

1. Nitrogenous base
2. A sugar
3. One or more phosphates

Question 2

What is a nitrogenous base composed of and what is the bond?

Answer 2

• Purine or pyrimidine ring
• Base is linked to the 1’ carbon on a pentose sugar by a glycosidic bond from the N1 of the pyrimidines or the N9 of the purines

Question 3

What is the sugar of DNA?

Answer 3

• Has a 2’-deoxyribose

Question 4

What is the sugar of RNA and why is it different to that of DNA?

Answer 4

• Has ribose
• Difference is that RNA has hydroxyl group on 2’ carbon of the pentose

Question 5

What is a nucleotide?

Answer 5

• A nucleoside linked to a phosphate of a 5’ carbon

Question 6

What is a polynucleotide?

Answer 6

• Compound composed of several nucleotides

Question 7

What are the 4 nitrogenous bases of nucleic acids?

Answer 7

In DNA and RNA:
1. Adenine
2. Guanine

In DNA only:
3. Cytosine
4. Thymine

In RNA only:
5. Uracil

Question 8

What direction is nucleic acids written in?

Answer 8

5’ to 3’

Question 9

What is the structure of DNA?

Answer 9

• Forms a double helix consisting of two polynucleotide chains that are antiparallel

Question 10

How does DNA maintain a constant width?

Answer 10

• The double helix maintains a constant width because purines always face pyrimidines in the complementary A-T and G-C base pairs.

Question 11

What is the minor groove?

Answer 11

• Twisting of double strands around each other form a minor groove of 1.2nm (12 A)

Question 12

What is the major groove?

Answer 12

• 22A or 2.2 nm

Question 13

How much is one helical turn?

Answer 13

• 34A in length (3.4 nm) and is approx. 10.5 base pairs

Question 14

What is the double helix composed of?

Answer 14

• Sugar phosphate backbone (negative charge) and hydrogen bonds holding strand together

Question 15

What is the difference between B-DAN, A-DNA and Z-DNA?

Answer 15

1. B-DNA is right-handed and turns clockwise
2. A-DNA is the same as B-DNA but just shorter and thicker
3. Z-DNA is longer and more narrow than B-DNA and is left-handed

Question 16

How does supercoiling affect the structure of DNA?

Answer 16

• only occurs in closed DNA (circular or linear) w/ no free ends
• there is +/- supercoiling (strands turn in same/different directions)

Question 17

What can closed DNA be characterized by?

Answer 17

Linking molecule (L) - the number of times one strand crosses over the other in space

Question 20

What are the two components of the linking molecule?

Question 21

What was the experiment for DNA replication?

Question 22

What were the results of the experiment?