Chapter 16: The Molecular Basis of Inheritance

Question 1

List some properties of DNA structure

Answer 1

• double helix
• antiparallel strands
• nucleotide pairs (A,T/G,C)
• has a sugar phosphate backbone
• hydrogen bonding (non covalent) b/w paired bases (ATGC)

Question 2

Explain the steps of DNA replication.

Answer 2

1. The two strands of DNA pull apart
2. Replication forks form
3. Helicase separates the strands
4. DNA polymerase adds primers and forms a row of DNA attached to the original (for the leading strand)
5. RNA primase adds primers and DNA polymerase starts forming DNA; as the strand continues to open, new primers keep being added and more DNA is added
6. DNA polymerase replaces RNA with DNA
7. DNA ligase binds the gaps together

Question 3

DNA replication occurs in the ___ to ___ direction.

Answer 3

5’ to 3’

Question 4

DNA polymerase catalyzes the formation of ______________.

Answer 4

Phosphodiester bonds

Question 5

What is the function of phosphodiester bonds in DNA replication?

Answer 5

They cause the free floating nucleotides (ATGC) to attach to the newly synthesized primers

Question 6

What do single-strand binding proteins do?

Answer 6

Prevents the DNA strands from closing before DNA is replicated

Question 7

What is the function of topoisomerase?

Answer 7

Unravels the DNA, stops it from over coiling

Question 8

What are Okazaki fragments?

Answer 8

Short, newly synthesized DNA fragments that form along the lagging strand.

Question 9

Explain how DNA corrects any mistakes

Answer 9

If there is a minor error, it will backspace (remove the last couple free floating nucleotides) and redo it.

If there is a large error, it will do Nucleotide Excision Repair.
This is when:
- enzymes look for something unfamiliar in the DNA
- they cut it out
- DNA polymerase will make new DNA
- ligase comes along again and bonds everything

Question 10

What is the end problem of DNA replication?

Answer 10

• The lagging strand needs to be able to read the next few nucleotides in order to replicate more.
• It will stop replicating a few nucleotides short because it hasn’t read enough.
• As a result, the overall chromosomes will shorten (b/c chromosomes are made of DNA)

Question 11

How is the end problem of DNA replication solved?

Answer 11

By Telomerase

Question 12

What is a telomere?

Answer 12

• The 3’ end of the lagging strand

Question 13

What does telomerase do?

Answer 13

• Telomerase recognizes that the 3’ end of the lagging strand doesn’t have any replicated DNA across from it
• Telomerase lengthens the Telomere
• The lagging strand is then completed by adding RNA primers
• The 5’ end then extends out to meet the extra nucleotides being added
• Now the 3’ and 5’ end are equal in length

Question 14

What do telomeres and telomerase look like in cancer cells?

Answer 14

• longer telomeres
• greater expression of telomerase
• more activity of telomerase enzyme