1. The Molecular Basis of Inheritance
Chapter 16
The Molecular Basis of Inheritance

2. Searching for Genetic Material, I
Mendel: modes of heredity in pea plants
Morgan: genes located on chromosomes
Griffith: bacterial work
Transformation: change genotype/phenotype by assimilating external substance
Avery: transformation agent was DNA

3. Note: several animals were harmed in the making of this experiment
Note: several animals were harmed in the making of this experiment. A moment of silence please (bioethics).

4. Searching for Genetic Material, II
Hershey and Chase
bacteriophages (phages)
DNA, not protein, is the hereditary material
Expt: sulfur(S) is in protein, phosphorus (P) is in DNA; only P was found in host cell
Animation: Phage T2 Reproductive Cycle

6. Animation: DNA Double Helix
DNA Structure
Chargaff
N base ratios
A=T & C=G
Watson & Crick (Wilkins, Franklin)
Double Helix
Nucleotides:
nitrogenous base (ATCG)
sugar (deoxyribose)
phosphate group
Animation: DNA Double Helix

7. Animation: DNA and RNA Structure
DNA Bonding
Purines: ‘A’ & ‘G’
Pyrimidines: ‘C’ & ‘T’
‘A’ H bonds (2) with ‘T’
‘C’ H bonds (3) with ‘G’
Animation: DNA and RNA Structure

8. Animation: DNA Replication Overview
Watson & Crick
strands are complementary; nucleotides line up on template according to base pair rules (Watson), Antiparralel (crick)
Meselson & Stahl
replication is semiconservative;
Expt: varying densities of radioactive nitrogen
New strands were half “heavy”, half “light”
Animation: DNA Replication Overview

10. DNA Replication: a closer look
Origin of replication (“bubbles”): beginning
Replication fork: ‘Y’-shaped region where new DNA strands elongate
Helicase: catalyzes untwisting DNA at replication fork
DNA polymerase: catalyzes elongation of new DNA
Animation: Origins of Replication

11. DNA Replication, II Antiparallel :
sugar/phosphate backbone runs in opp. directions
One runs 5’ to 3’, other runs 3’ to 5’
DNA polymerase only adds nucleotides at 3’ end
DNA builds in 5’ to 3’ direction only

12. DNA Replication, III Leading strand:
synthesis toward replication fork (5’ to 3’ direction from 3’ to 5’ template)
Lagging strand:
synthesis away from replication fork (Okazaki fragments); joined by DNA ligase (5’ to 3’ direction in pieces)
Initiation:
Primer (short RNA sequence w/primase enzyme)
begins the replication process

13. DNA Repair Mismatch repair: DNA polymerase Excision repair:
Nuclease
Telomere ends:
telomerase
age

15. Enzymes and Proteins Review
DNA Polymerase: elongate DNA, replace RNA primers, fix mistakes
DNA Ligase: Joins Okazaki fragments together.
Primase: Joins RNA nucleotides to make a primer.
Helicases: Untwist double helix and separate the old strands.
Single-strand Binding Proteins: hold separated strands apart.
Nuclease: cuts out damaged DNA in an excision repair
Telomerase: Catalyzes the lengthening of telomeres

16. Sugar-phosphate backbone
Fig. 16-UN2 G C A T T A
Nitrogenous bases G C
Sugar-phosphate backbone C G A T C G
Hydrogen bond T A

17. You should now be able to:
Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl
Describe the structure of DNA
Describe the process of DNA replication; include the following terms: antiparallel structure, DNA polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase, topoisomerase, single-strand binding proteins
Describe the function of telomeres
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings