DNA

Question 1

Can you name the structure of a Nucleotide?

Answer 1

Yes

Question 2

Is DNA positively or negatively charged?

Answer 2

Negatively, due to oxygens on phosphate group.

Question 3

Explain the structure of DNA.

Answer 3

• Twisted ladder structure
• Rails: pentose sugar
• Rungs: nitrogen-containing bases

Question 4

What kind of bonds join bases to hold two strands of DNA together? What bases are paired in specific combinations?

Answer 4

Hydrogen Bonds
A-T
C-G

Question 5

What is meant by an anit-parallel arrangement?

Answer 5

The strands run in opposite directions, parallel to one another. It runs 3’-5’ and 5’-3’ linkage.

Question 6

What are the 4 steps to DNA Replication?

Answer 6

1. Unwind
2. Priming
3. Synthesis
4. Ligate

Question 7

What happens in the 1st step of DNA replication?

Answer 7

Unwind:
- Helicase enzyme (unzipping enzyme) breaks through the hydrogen bonds that holds the DNA bases together, separating the two strands of DNA.
- Then the SSBP proteins stabilize the unwound DNA preventing them from coming back together.

Question 8

What happens in the 2nd step of DNA replication?

Answer 8

Priming:
- Priming enzyme (initializer enzyme) synthesizes a short section of RNA. Makes it so DNA polymerase can figure out where to go.
- The primer is made of RNA (RNA primer)

Question 9

What happens in the 3rd step of DNA replication?

Answer 9

Synthesis:
- Polymerase enzyme (builder enzyme) replaces DNA molecules to build new strands of DNA.
- Pol 3 adds nucleotides to the 3’ end and Pol1 replaces RNA.

Question 10

What happens in the 4th step of DNA replication?

Answer 10

Ligate:
- Ligate enzyme (gluer enzyme) seals the gap in the backbone with covalent bonds.

Question 11

What are the 2 key aspects of DNA polymerases?

Answer 11

• Polymerases can’t add nucleotides without a primer
• Polymerase can’t add nucleotides to the 5’ end.

Question 12

What’s the difference between the Leading & Lagging strands?

Answer 12

• The leading strand is replicated continuously.
• The lagging strand is added in fragments.

Question 13

What are Okazaki fragments?

Answer 13

Short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication.

Question 14

What does it mean to say that the process of DNA replication is “semi-conservative”?

Answer 14

The new DNA always contains one strand of the original DNA and one strand of new DNA.

Question 15

Explain why the telomeres get shorter every time a chromosome is copied.

Answer 15

DNA replication always leaves some portion of 5’ end unmatched. A little DNA is lost after each replication.