U4L1 - Dna Replication and Repair

Question 1

What is DNA?

Answer 1

DNA is a double helix polymer.
The 2 helices are antiparallel —> run in opposite directions.

Question 2

What is DNA made of?

Answer 2

It is made up of nucleotide monomers.

Question 3

What are nucleotides made of?

Answer 3

• deoxyribose (sugar)
• a phosphate group
• nitrogenous bases (A, T, C, and G)

Question 4

What are purines?

Answer 4

A and G are purines (have 2 rings)

Question 5

What are pyrimidines?

Answer 5

T and C are pyrimidines (have 1 ring)

Question 6

Why does A always binds to T and G always binds to C (Chargaff’s Rule)?

Answer 6

• diameter of DNA constant at 2 nm
• BUT If the two purines bonded together, the DNA molecule would be wider (than 2nm) at some points
• if the two pyrimidines bonded together, the molecule would be less than 2 nm in some places.

Question 7

Explain the antiparallel structure of DNA

Answer 7

Anti-parallel direction is consistent with the 3.4nm of each turn of the helix and the 0.34 nm distance between each base pair

Question 8

What do hydrogen bonds do?

Answer 8

Hydrogen bond (holds nucleotide bases together). This is a weaker bond (easier to break)

Question 9

What do Phosphodiester bonds do?

Answer 9

Phosphodiester bond (holds sugar-phosphate backbone together). This is a strong bond (difficult to break)

Question 10

Who were important scientists that helped uncover DNA structure?

Answer 10

Griffith, Hershey/Chase, Franklin, Wilkins, Chargaff, Daly and most importantly, Rosalind Franklin.

Question 11

What are the steps to DNA rep?

Answer 11

1) Replication begins at an origin of replication, causing replication bubbles to open.
2) DNA Helicase unwinds the double helix.
3) Single stranded binding proteins (SSBPs) keeps the helices apart.
4) DNA Topoisomerase relieves tensional forces.

Question 12

Leading strand - What way are the Nucleotides added?

Answer 12

Leading strand is created from 5’ –> 3’

Question 13

Explain the process of DNA rep for the leading strand

Answer 13

1) RNA Primase adds a primer to the beginning of the strand.
2) DNA Polymerase III then adds nucleotides continuously.

Question 14

Lagging strand - What way are the Nucleotides added?

Answer 14

DNA is synthesized in the 3’ to 5’ direction.

Question 15

Explain the process of DNA rep for the lagging strand

Answer 15

1) RNA Primase adds RNA primers. Nucleotides are added in short Okazaki Fragments by DNA Polymerase III
2) DNA Polymerase I replaces the RNA primers with DNA
3) DNA Ligase “glues” the Okazaki fragments together. (Phosphodiester bonds)
4) 4. Replication in the lagging strand is non-continuous.

Question 16

Explain DNA Repair

Answer 16

DNA polymerase II is a prokaryotic enzyme that repairs damage only –> If there are mistakes, these enzymes can act as an exonuclease, meaning that they can cut out and replace the mistake.

Question 17

What are Telomeres?

Answer 17

Telomeres are repeating sequences of DNA at the ends of chromosomes. Without telomeres, chromosomes would shorten every time a cell divides, and DNA would be lost.