The Molecular Basis of Inheritance

1
Chapter 16

• The Molecular Basis of Inheritance

2
Processes(5 3)

• Replication
• Transcription
• protein synthesis
• Translation

3
Quantity of DNA

• Bacteria (prok) 2 pages
• Yeast (euk) 1 book
• Human (euk) 900 books (1000 pages)

4
Is the genetic material DNA or protein?

• Chromosome contains
• 60 protein
• 40 DNA

5
Research

• Frederick Griffith (1928)
• evidence that bacteria transform
• molecule from dead cells transformed living cells

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Research, cont.

• Oswald Avery, Maclyn McCarty, Colin MacLeod
  (1944)
• transforming agent was DNA

7
Research, cont.

• Alfred Hershey Martha Chase (1952),
• viral DNA can program cells

8
Research, cont.

• Erwin Chargaff (1947)
• Chargaffs rules
• AT, CG
• true of every species studied

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Research conclusion

• By 1950s DNA was accepted as the genetic
  component
• 3-D structure of the DNA was unknown

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What is the 3-D structure of DNA?

• the covalent arrangement was established (A-T
  and C-G)
• the 3-D structure was unknown

11
Research, cont.

• Rosalind Franklin
• x-ray diffraction photo of DNA

12
Research, cont.

• James Watson Francis Crick
• (1960s),
• double helix
• model explained Chargaffs rules

13
ReplicationDNA DNA

• Semiconservative Method
• Prokaryotic replication
• Eukaryotic replication
• during S phase of Interphase

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Prokaryotic Replication

• circular dsDNA
• 1. Origin of replication
• (replication fork)
• 2. Bidirectional movement
• 3. Termination of replication and form 2
  circular dsDNA

15
Eukaryotic Replication 5 to 3

• Chemical direction 5 to 3
• examine the pentose
• pentose with 5 carbons (no. 1-5)

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Enzymes in Euk. Replication

• 1. helicases
• 2. single-strand binding proteins
• 3. DNA polymerases
• 4. DNA ligase

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1. Helicases

• unwind double helix

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2. Single-strand binding proteins

• stabilize the single strands

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3. DNA polymerases

• add new DNA nucleotides

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4. DNA ligase

• joins DNA ends

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Euk. Replication

• leading strand
• lagging strand

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leading strand

• synthesized continuously

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lagging strand

• synthesized discontinuously
• Okazaki fragments (1000-2000)

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Priming DNA Synthesis

• DNA cannot initiate replication
• primer is formed
• 10 nucleotide stretch of RNA
• primase
• enzyme that makes the primer

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Priming DNA Synthesis,cont.

• DNA polymerases
• adds DNA nucleotides to primer
• replaces RNA with DNA
• DNA ligase
• joins new Okazaki fragment to the chain

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Replication Results

• 5 A T 3
• G C
• 3 C G 5
• 5 A T 3 5 A T 3
• G C G C
• 3 C G 5 3 C G 5

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Chapter 15

• END