4 - The Molecular Basis of Inheritance

Question 1

who was friedrich miescher

Answer 1

the discoverer of nucleic acid

Question 2

Frederick Griffith (1928)

Answer 2

discovered transformation in bacteria

Question 3

Oswald Avery (1944)

Answer 3

identified the “transforming substance” of Griffith’s experiment — DNA

Question 4

Hershey-Chase Experiment

Answer 4

confirmed that DNA is the genetic material because only radiolabeled DNA could be found in bacteriophage-infected bacteria

Question 5

Chargaff’s Rule

Answer 5

A=T and C=G

Question 6

what are the 3 components of a nucleotide?

Answer 6

sugar, phosphate, nitrogenous base

Question 7

What is a purine base?

Answer 7

It has 2 rings- Adenine and Guanine

Question 8

what is a pyrimidine base?

Answer 8

It has 1 ring- Thymine and Cytosine

Question 9

which nitrogenous bases are found in DNA?

Answer 9

adenine, guanine, cytosine, thymine

Question 10

adenine, guanine, cytosine, thymine

Answer 10

• composed of polynucleotides
• Has a doubled helix that is formed by hydrogen bonds between polynucleotides
• Densely compacted into chromosomes to fit into nucleus

Question 11

Explain semi-conservative replication

Answer 11

One strand acts as a template

Each new DNA molecule contains one original strand and one new strand

Question 12

which enzymes are involved in DNA replication?

Answer 12

DNA helicase and DNA polymerase

Question 13

what is the role of DNA helicase in replication?

Answer 13

unwinds the DNA molecule for replication

Question 14

What is the leading strand?

Answer 14

The strand where replication moves towards the replication fork (follows helicase)

Question 15

Synthesis of leading strand

Answer 15

• Priming: primase
• Elongation: DNA polymerase
• Replacement of RNA primer by DNA: DNA polymerase

Question 16

What is the lagging strand?

Answer 16

The strand where DNA replication moves away from the replication fork

Question 17

synthesis of lagging strand

Answer 17

1. primer added
2. first fragment synthesized
3. second fragment synthesized
4. primer replaced
5. gap closed

Question 18

Mehelson Stahl Experiment

Answer 18

experimental proof for semi conservative replication

1. Bacteria cultured in medium with 15N (heavy isotope)
2. Bacteria transferred to medium with 14N (lighter isotope)
3. DNA sample centrifuged after 1st replication
4. All DNA of intermediate density = 1 light strand and 1 heavy strand

Question 19

what is the role of single-strand binding proteins

Answer 19

hold the helix open

Question 20

what is the role of primase?

Answer 20

synthesises the RNA primers needed for initiation of DNA synthesis

Question 21

what is the role of DNA polymerase III?

Answer 21

extends the DNA( or RNA) strand from the 3’ end, copying the template

Question 22

what is the role of DNA polymerase I?

Answer 22

removes the RNA primer and fills in gaps between Okazaki fragments

Question 23

removes the RNA primer and fills in gaps between Okazaki fragments

Answer 23

seals the gaps between Okazaki fragments

Question 24

DNA polymerase

Answer 24

• Requires:
– Single-stranded template DNA
– All four nucleoside triphosphates (dNTPs)
– Free 3’ hydroxyl (primer)
• Synthesises DNA in 5’ to 3’ direction
• Inserts complementary nucleotides
• Uses energy from breaking phosphate bonds
•“Proof-reading” ability – can remove incorrectly inserted nucleotides