DNA

Question 1

Explain the experiment by Avery and co-workers that indicated DNA contains the genetic material of life.

Answer 1

Tested to see which component in cell (RNA, protein, DNA, lipid, carbohydrate) were responsible for changes (non to virulent).

Question 2

What was the previous discovery in 1929 about Rough > Smooth form Pneumococci that Avery used in his experiment design? Who performed this?

Answer 2

Griffith found that nonvirulent cells became virulent even though it was mixed with heat-killed virulent cells. => changes cell charact.

Question 3

Explain the experiment by Hershey and Chase that indicated DNA contains the genetic material of life.

Answer 3

They tested if DNA or protein in T2 phage is passed into the bact. by radioactively labelling it. Found radioactive DNA remained in cell while protein was not. => DNA associated w/ molecule of life

Question 4

Draw basic structure of deoxynucleotide. Note position of 3’ and 5’

Answer 4

5’(PO4)\ /O\ /[Base]
……………._/
………….3’OH

Question 5

What is the difference between a nucleotide and a nucleoside?

Answer 5

…side: base + sugar

…tide: base + sugar + PO4

Question 6

What is the Central Dogma of Molecular Biology?

Answer 6

Converting DNA -> RNA -> protein

Replication, transcription, translation

Question 7

What is the semiconservative model of DNA replication?

Answer 7

Means old strand acts as a template to create new strands. And daughter strands are identical to parent strand

Question 8

What experiment was performed by Meselson and Stahl to demonstrate DNA
replication is semiconservative?

Answer 8

Meselon-Stahl exp: Bact. cultured in 15N (heavy) medium, then bact. transfered into 14N (light) to allow replicaion 3x. Density in each stage was monitiored.

Question 9

Given that DNA replication is semiconservative, where does the information
about the nucleotide sequence come from when a new strand of DNA is being
made?

Answer 9

Single strand of parent/old DNA act as a template

Question 10

State three requirements of DNA Polymerase for DNA synthesis to occur

Answer 10

Single strand DNA template; deoxynucleotide triphosphate; primer

Question 11

What is a phosphodiester bond?

Answer 11

bond that links 5’ of a nucleotide w/ the 3’ of another

Question 12

At a DNA replication fork are Okazaki fragments found in the leading strand or
in the lagging strand?

Answer 12

Lagging strand

Question 13

List (6) enzymes required for DNA replication and explain the function of each.

Answer 13

1. Helicase: Unzip double-stranded DNA into single
2. Polymerase a/ primase: RNA primer synthesis
3. Polymerase d (delta): lagging strand synthesis
4. Polymerase E (epsilon): leading strand synthesis
5. DNA poymerase I: replace primer w/ DNA
6. DNA ligase: links 5’ to 3’ to complete strand

Question 14

Briefly explain why telomerase activity is required in some eukaryotic cells.

Answer 14

During embryonic development. (uses its RNA as template to fill gap @ telomere (end of cell)

Question 15

Are histone proteins found in prokaryotic or eukaryotic cells?

Answer 15

Eukaryotic cells

Question 16

Which direction is DNA synthesised?

Answer 16

Nucleotides added in a 5’ to 3’ direction. (Bc need free -OH group)

Question 17

Hayflick limit

Answer 17

Finite replicative capacity in normal cells (telomere shortens every replication)

Question 18

Ori/ RO site

Answer 18

replication origin

Question 19

What does the string and beads model indicate?

Answer 19

Beads: 8 histones
String: DNA

Question 20

Describe the structure of dsDNA helix

Answer 20

• 2 antiparallel polynucleotide chains wound clockwise
• helix is uneven: major & minor grooves
• 2 Hbond in A+T; 3 Hbond in C+G
• 1 turn of helix contains 10 bases

Question 21

Briefly describe steps of DNA replication

Answer 21

1. Replication bubble forms @ origin of replication
2. Replication fork forms
3. Strand separate by helicase & ss binding proteins
4. RNA primers made by DNA pol. a OR primase (prok.)
5. strand elongation by DNA pol. d & e OR III (prok.)
6. RNA primers removed (DNA primase I)
7. breaks in strand sealed by DNA ligase

Question 22

What are telomeres & function?

Answer 22

repeated base sequences

> protect genes @ end of chromosome

Question 23

Why does telomere shorten after each replication?

Answer 23

bc located @ primer end of the strand is removed but can’t be replaced by DNA pol. I bc no primer