Chapter 10 DNA structure and Replication

Question 1

Describe the structure of a strand of DNA; include the location of the deoxyribose, phosphate group, and nitrogenous base

Answer 1

DNA is a double helix – like a twisted ladder

• Deoxyribose + phosphate makes up the “backbones”
• Nitrogenous bases make up the rungs of the ladder

Question 2

Explain how DNA is packaged in a cell’s nucleus; include the following terms in your explanation - histone, nucleosome, chromatin, chromosome

Answer 2

-Strands of DNA are wrapped around proteins called histones
DNA + Histone =Nucleosome

-Nucleosomes are linked together like beads on a necklace
○Called chromatin

-Chromatin is condensed (wrapped around itself) forming chromosomes

Question 3

If given a sequence of DNA, be able to write out the complementary sequence

ATAATTCGTTGGAC

Answer 3

T=A
G=C

TATTAAGCAACCTG

Question 4

Enzymes involved in the steps of DNA replication

Answer 4

• Helicase - unwinds DNA helix & separates strands
• Primase - adds a primer (i.e. short sequence of RNA)
• DNA polymerase - adds DNA nucleotides
• Exonuclease - removes the RNA primer
• Ligase - fills in gaps (due to removing primer) with DNA nucleotides

Question 5

Explain the steps of DNA replication

Answer 5

1. Helicase unwinds helix and separates strands
2. Primase adds RNA primers
3. DNA polymerase adds DNA nucleotides to 3’ end of primers
4. The “leading strand” is built continuously
5. The “lagging strand” is built in segments called “Okazaki fragments”
6. Exonuclease removes the RNA primers
7. Polymerase fills in the primer “gaps” with DNA nucleotides
8. Ligase connects the DNA nucleotides that filled in the primer gaps to the rest of the strand