Unit 4 - Ch 12 - DNA Structure / Replication

Question 1

The nucleotide monomers that make up DNA:

Answer 1

1. Deoxyribose Sugar - 5 C sugar
2. Phosphate Group - acidic
3. Nitrogenous Base - 1 of 4 bases (variable)

DNA is a polymer of nucleotides

Question 2

What are the nitrogenous bases that form DNA?

Answer 2

Purines - double ring structure
                i. Guanine (G)
                ii. Adenine (A)
Pyrimidines - single ring structure
                i. Thymine (T)
                ii. Cytosine (C)

Question 3

Antiparallel Sugar

Answer 3

The two strands making up the backbone run in opposite directions of each other, thus they are antiparallel.

Question 4

Complementary Nitrogen Base Pairing

Answer 4

Purine pairs to pyrimidine

1. Adenine to Thymine - via 2 H-bonds
2. Cytosine to Guanine - via 3 H-bonds

Question 5

Double Helix

Answer 5

Two intertwined helices form DNA

• sides are phosphates and sugars (backbone)
• rungs are base pairs

“twisted ladder” analogy

Question 6

Location of DNA

Answer 6

Nucleus
Mitochondria
Chloroplasts

Question 7

Size of DNA in humans

Answer 7

5 cm in each human chromosome on average

= 2m total per cell

Question 8

Role of Histone Proteins

Answer 8

Histones coil and compact the DNA to form nucleosomes

Question 9

Central Dogma

Answer 9

“flow of information” in cells

DNA Replicates&raquo_space; Transcription forms mRNA»Translation forms protein

Question 10

Major steps of DNA replication

Answer 10

1. DNA unzips
   - breaks H-bonds between base pairs via DNA helicase
   - topoisomerase breaks the backbone to relieve strain
2. Nucleotides pair & release pyrophosphate
   - occurs via complimentary pairing via DNA polymerase
3. Proofreading - occasional mistakes occur (wrong base) - fixed via proofreading
   - proofreading mistakes are mutations

Question 11

Semiconservative replication

Answer 11

The unzipped DNA strands become parent strands, templates for two new daughter strands.

Question 12

Bidirectional Replication

Answer 12

DNA polymerase only adds bases to the free 3’ end

1. Leading Strand - synthesized continuously in one piece
2. Lagging Strand - synthesized in pieces
   Okazaki fragments - joined together into a continuous strand

Question 13

Purpose of DNA replication

Answer 13

To produce sister chromatids (exact copies)

occurs in the S portion of interphase for mitosis and meiosis