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Chapter 16: The Molecular Basis of Inheritance
- You will understand that DNA is genetic material
- You will understand that many proteins work together in DNA replication and repair
- A chromosome is DNA packed together with proteins
Proof that nucleic acid is what codes phenotypes
-Hershey Chase experiment
-Concluded that the protein didn’t enter the cell
and that DNA is what produces phenotypes
Chargaff
-Found that Adinine
and Thymine
occurred in equal
amounts in Nucleic
Acid
-Ratios of C and G
also equaled
Structure of DNA
-Purines (Guanine, Adinine)
-Double Helix
-Pyrimidines (Tymine, Cytosine)
-Ribose
-Hydrogen Bonds
-Phosphate Group
-Nucleotide
-Chargaff’s Rule
Human Genome
-6 billion base pairs
-Genome will fill 1,200 AP bio books
-Replicated in just a few hours
-Errors occur in 1/10 billion base pairs
-Most of Replication is known about
prokaryotic cells – Eukaryotic is similar to
Prokaryotic
What is the driving force behind gene
expression? (Quote from Watson and Crick p. 311)
-Complimentary base pairs allow for an accurate replication
mechanism
-Basics of the DNA Replication
1. Double Helix
2. The two strands “unzip”
3. Free nucleotides bond to the parent DNA strands
Replication Stage 1: Initiation
-”Start” DNA sequence
-Creates replication bubble
-Uses a variety of enzymes
Topoisomerase – Relieves stress on rest of Helix
Helicase – Untwists the Helix and separates the DNA
Single-stranded binding proteins – Stabilize single
stranded DNA
Primase – adds RNA to the parent DNA and will act as a
primer for DNA to form (3’ to 5’)
DNA Polymerase
-Speeds up the reaction of a single
nucleoside with the new chain
-There are many types of polymerases
-Phosphate groups are highly reactive
-Add to the 3’ end of the new chain
Leading Strand Synthesis
-Continuous
-Adds in a 5’ to 3’ direction
-DNA Poly III is the enzyme that adds the nucleosides
Replication Fork: Solving the Anti-parallel
problem in a Bacterial Cell
Lagging Strand
-Has to add in a 5’ to 3’ direction
-Needs to use multiple RNA Primers (Use of primase)
-Telomeres are repeating DNA units at the
end of Chromosomes that help combat the
natural shortening of chromosomes due to
replication.
-DNA Poly III synthesizes nucleoside addition until reaches next Primer
-DNA Poly I then replaces the RNA primer with DNA
-DNA Ligase connects the Okazaki fragments
-Nucleas is an enzyme that cuts out
damaged or incorrect DNA pairings
DNA Packaging
DNA is packaged
in a Double Helix
Histones are proteins
that are made mostly
out of positively
charged amino acids
DNA wraps twice
around Histones
Supercoils of DNA
Histones are
linked together
by the Linker
DNA