nucleic acids

Question 1

What is the function of DNA?

Answer 1

Stores genetic information

Question 2

What is the function of RNA?

Answer 2

Transfers genetic information from DNA to ribosomes

Question 3

What are the differences between DNA and RNA

Answer 3

DNA nucleotides》
- pentose sugar deoxyribose
- thymine base
RNA nucleotides》
- pentose sugar ribose
- uracil base

Question 4

Draw a DNA & RNA nucleotide

Answer 4

phosphate group
base

DNA 》 Deoxyribose
RNA 》 Ribose

Question 5

What bonds are formed by condensation polymerisation of DNA / RNA nucleotides

Answer 5

phosphodiester bonds

Question 6

Which bases are complimentary?

Answer 6

DNA 》 A-T C-G
RNA 》 A-U C-G

Question 7

Give the full name of each base

Answer 7

A - Adenine
T - Thymine
U - Uracil
C - Cytosine
G - Guanine

Question 8

How is the structure of DNA related to its functions?

Answer 8

Weak hydrogen bonds between bases 》 can be unzipped for replication

Double helix with sugar phosphate backbone 》 protects bases and hydrogen bonds

Long molecule 》 store lots of genetic information

Coiled double helix 》 compact

Question 9

What is semi-conservative replication and who proved it?

Answer 9

• Each of the two new DNA molecules are composed of one ‘new’ and one ‘old’ strand
• Proved by Meselsohn and Stahl

Question 10

Name two other types of replication?

Answer 10

Conservative

Dispersive

Question 11

Process of DNA replication [9]

Answer 11

• DNA helicase breaks hydrogen bonds between bases
• unwinding the double helix
• making two strands which act as templates
• free floating DNA nucleotides attracted to exposed bases via specific complimentary base pairing
• hydrogen bonds form
• DNA polymerase joins adjacent nucleotides on a new strand by condensation
• forming phosphodiester bonds
• replication is semi-conservative
• ensures genetic continuity between generations of cells

Question 12

What type of strands does DNA have?

Answer 12

antiparallel strands

Question 13

What is DNA polymerase? [3]

Answer 13

• an enzyme
• can only bind to and add nucleotides to the 3’ end of the developind strand
• works in a 5’ to 3’ direction

Question 14

Evidence for semi-conservative replication [9]

Answer 14

• Bacteria grown in nutrient solution containing heavy nitrogen (N15) for several generations
• Nitrogen incorporated into bacterial DNA bases
• Bacteria then transferred to a nutrient solution containing light nitrogen (N14)
• allowed to grow and divide twice
• DNA from different samples extracted
• spun in a centrifuge
  sample 1 = 2 heavy strands
  sample 2 = 1 original heavy + 1 new light strands
  sample 3 = 50% of molecules contain 1 heavy + 1 light
  50% of molecules contain both light