Nucleic Acids and DNA Replication

Question 1

What are nucleotides?

Answer 1

The monomers that make up polynucleotides (DNA & RNA).

Question 2

What is DNA made up of?

Answer 2

• Deoxyribose (Pentose sugar).
• Phosphate.
• Nitrogen containing base (Adenine, thymine, cytosine, guanine).

Question 3

What is RNA made up of?

Answer 3

• Ribose (pentose sugar).
• Phosphate.
• Nitrogen containing base (Adenine, guanine, cytosine and uracil).

Question 4

What does DNA stand for?

Answer 4

Deoxyribonucleic acid.

Question 5

What does RNA stand for?

Answer 5

Ribonucleic acid.

Question 6

What features does DNA have?

Answer 6

• Double stranded (double helix).
• Long polymer/polynucleotide.
• Carries the genetic information which codes for proteins.

Question 7

What features does RNA have?

Answer 7

• Single stranded.
• Short polynucleotides.
• Transfer genetic code from DNA (nucleus) to ribosomes in the cytoplasm.
• Ribosome formed from RNA and proteins.

Question 8

What type of bond forms between nucleotides?

Answer 8

Phosphodiester bonds.

Question 9

What does adenine pair with?

Answer 9

Thymine (DNA) or Uracil (RNA).

Question 10

What does guanine pair with?

Answer 10

Cytosine.

Question 11

what is the structure of polynucleotides?

Answer 11

• Sugar-phosphate backbone.

- Hydrogen bonds between antiparallel strands.

Question 12

What method if widely accepted as the method for DNA replication?

Answer 12

Semi-conservative DNA replication.

Question 13

What are the stages of semi-conservative DNA replication?

Answer 13

1) DNA helices unwinds DNA by breaking the H-bonds.
2) Both strands act as templates.
3) Free DNA nucleotides attach by complementary base pairing.
4) DNA polymerase joins nucleotides, forming phosphodiester bonds.
5) H-bonds reform.

Question 14

Why is DNA replication referred to as semi-conservative?

Answer 14

The new DNA contains one new strand and one original strand.

Question 15

How did Meselson and Stakl prove DNA replication is semi-conservative?

Answer 15

• Population cultured in a growth medium containing heavy nitrogen (15N) only (when centrifuged only one heavy band is observed).
• Cells transferred to a medium with only light nitrogen (14N).
• After one replication the DNA band was intermediate (twice the thickness).
• After two replications in light nitrogen, intermediate and light bands were observed.
• Proving DNA replication is semi-conservative.

Question 16

What is the DNA antisense strand?

Answer 16

Template strand that acts as the template for mRNA. its complementary to genes on the sense strand.

Question 17

What is the DNA sense strand?

Answer 17

Contains the genes and does not act as the template for mRNA.

Question 18

What process forms mRNA from pre-mRNA?

Answer 18

Splicing.

Question 19

What is pre-mRNA strand?

Answer 19

The same as DNA sense strand except U replaces T.

Question 20

Why did many scientists doubt that DNA carried the genetic code?

Answer 20

Its relative simplicity.

Question 21

Which scientists discovered the structure of DNA and suggested that its replication was semi-conservative?

Answer 21

Watson and Crick.

Question 22

What does semi-conservative replication ensure?

Answer 22

Genetic continuity between generations of cells.