DNA

Question 1

Stabilizing Forces of DNA, and Structure

Answer 1

• Comp bases are H bonded
  
  • AT have 2 H binds
  • GC have 3 H bonds
• Hydrophilic phosphate backbone
• Hydrophobic bases stacked inside helix
• Strands are coiled around a common axis of symmetry
• DS DNA has major and monor grooves

Question 2

What causes denaturation

Answer 2

• DNA seperates when H bonds are disrupted
  
  • Alteration of pH
  • Increased heat
  • DNA replication
• Complementary DNA strands can reanneal (hybridize)
• Tm is temp at which 1/2 DNA is denatured
• GC has a higher Tm than AT

Question 3

Organization of DNA

Answer 3

46 choromosomes

DNA associated with histones forming Nucleosomes

Nucleosomes further arranged into increasingly comlex structures and eventually chromosomes

Question 4

Gen steps in DNA synthesis

Answer 4

• ID origins of replication
• Unwinding (denaturation) of ds DNA to provide ss DNA template
• Formation of replication fork and synthesis of RNA primer
• Initiation of DNA synthesis, elongation, and ligation of newly synthesized DNA segments
• Reconstitution of chromatin structure

Question 5

Where does DNA rep occur

Direction

Requires…

Answer 5

• Occurs at replication fork and is bidirectional
• Rep fork has leading and lagging (Okazaki) strands
• Semiconservative
• Proceeds 5 to 3
• Requires RNA primer
• High processivity
• Base selected based on H bonding and geometry
• High fidelity (low error rate)

Question 6

DnaA

Answer 6

Replication initiation factor

Promotes denaturation of DNA at origin of replication

Question 7

DNA Helicase

Answer 7

Binds ssDNA near the replication fork and uses ATP to unzip DNA

Question 8

SS DNA binding protein

Answer 8

Keeps DNA ss

Question 9

Topoisomerase

Answer 9

Cuts one or both strands of DNA to change DNA topology and relieve coiling

Question 10

Primase

Answer 10

Synthesizes RNA primers to prime DNA sysnthesis

Question 11

DNA polymerases

Answer 11

Replicate DNA

Question 12

Ligase

Answer 12

Links DNA by catalyzing phosphodiester bonds

Occurs during DNA rep by joining Okazaki fragments

DNA repair

Question 13

DNA Poly III

Answer 13

Adds correct nucleotide thru formation of phosphodiester bond

Exonuclease activity hydrolyzes phoshodiester bond

5–>3 activity, base removal from 5 terminus, removes RNA primer

3–>5 exonuclease activity mediates proofreading, Base removal from 3 terminus, removes misincorporated bases