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Chapter 12
DNA: The Carrier of Genetic Information
29
Biology
Undergraduate 1
03/05/2010

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Term
Evidence for DNA
Definition
Transformation experiments:
-DNA of one strain of bacteria can transfer genetic characteristics to related bacteria

Bacteriophage Experiments:
-Virus infects bacterium, only DNA from virus enters cell
-Virus reproduces and forms new viral particles from DNA alone
Term
Many early geneticists thought genes were...
Definition
-Proteins
-Proteins are complex and variable
-Nucleic acids are simple molecules
Term
Griffith's Transformation Experiment
Definition
Q: Can a genetic trait be transmitted from one bacterial strain to another?
A: Yes.
-They experimented on mice by injecting R(mouse lived) and S(mouse dies) cells when R and heat-killed S cells injected the mouse still died because the harmful S transmitted its trait to the un-harmful.
Term
Avery's Experiments
Definition
Q: What molecule is responsible for bacterial transformation?

A: DNA
Term
Hershey-Chase Experiments
Definition
Q: Is DNA or protein the genetic material in bacterial viruses(phages)?
A: DNA.
-Bacterial viruses were grown in 35S to label protein, and 32P to label DNA
-Virus infect bacteria, agitate cells in blender, and separate by centrifugation
-35S protein is supernatant, bacteria in pellet contains 32P DNA
-Viral reproduction inside bacterial cells from pellet
-Cell lysis
Term
Watson and Crick
Definition
-DNA model

Demonstrated:
-How info is stored in molecules structure
-How DNA molecules are templates for their own replication
Term
Nucleotides
Definition
-DNA is a polymer of nucleotides

Each nucleotide subunit contains:
-Nitrogenous base
Purines(A/G)
Pyrimidines(T/C)
-Pentose sugar(Deoxyribose)
-Phosphate group
Term
Forming DNA Chains
Definition
Backbone:
-Alternating sugar and phosphate groups joined by covalent phosphodiester linkages
Phosphate group attatches to:
-5' C of one deoxyribose
-3' C of the next dexoyribose
Term
The DNA building blocks consist of
Definition
-4 nucleotide subunits:
T
C
A
G
Term
DNA Molecule
Definition
-2 polynucleotide chains associated as double helix
-Discovered by Rosalind through X-ray diffraction image of DNA
-Watson and Crick used her image as a way of discovering the double helix structure
Term
Double Helix
Definition
Antiparallel:
-chains run in opposite directions
5' End:
-phosphate attached to 5' deoxyribose C
3' End:
-hydroxyl attached to 3' deoxyribose C
Term
What is the active part of DNA
Definition
-Phosphate group
Term
Base Pairs
Definition
H Bonding:
-between specific base pairs
-Binds 2 chains of helix
A with T:
-forms 2 H bonds
G with C:
-forms 3 H bonds
Term
Chargaff's Rules
Definition
Complementary base pairing
-between A-T & C-G
-Therefore A=T, C=G

If base sequence of 1 strand is known, base sequence of other strand can be predicted
Term
What are the 3 models of DNA replication?
Definition
Conservative:
-Copies entire strand of DNA

Semiconservative:
-Separates sides
-makes copies based on sides

Dispersive:
-Parts of original separate and fill in the gaps, cut up and rearrange
Term
Meselson-Stahl Experiment
Definition
-Confirmed semiconservative
-Grew bacteria in 15N medium,transferred some to 14N medium
-Add CsCl DNA molecules move to positions where their density equals that of the CsCl solution
-15N on bottom, hybrid 14-15N in midle, 14N at top
Term
Semiconservative Replication
Definition
Each daughter double helix consists of:
-1 original strand from parent molecule
-1 complimentary strand
Term
DNA Replication
Definition
-2 strands of double helix unwind, each is template for complementary strand

-Replication is initiated
DNA primase synthesizes RNA primer

-DNA strand grows
DNA polymerase adds nucleotide subunits
Term
What enzymes are involved in DNA replication?
Definition
DNA helicase:
-open/split the double helix
Topoisomerases:
-prevent tangling and knoting
Term
Bidirectional Replication
Definition
-Starting at origin of replication, and proceeding in both directions

Eukaryotic chromosome:
-May have multiple origins of replication, may replicate at many points at same time
Term
DNA Synthesis
Definition
-Always proceeds in 5'->3'

-Leading Strand (5'):
synthesized continuously

-Lagging Strand(3'):
synthesized discontinuously
forms short okazaki fragments
DNA primase synthesizes RNA primers
DNA ligase links okazake fragments
Term
Replication in Bacteria and Eukaryotes
Definition
-Eukaryotic chromosome DNA contains multiple origins of replication
-DNA synthesis proceeds in both directions from each origin until adjacent replication bubbles eventually met.
Term
DNA Polymerases
Definition
-Proofread each new nucleotide against template nucleotide

Find errors in base pairing:
-remove incorrect nucleotide
-insert correct one
Term
How do enzymes proofread and repair errors in DNA
Definition
DNA polymerases
Term
Mismatch Repair
Definition
-Enzymes recognize incorrectly paired nucleotides and remove them
-DNA polymerases fill in missing nucleotides
Term
What are the steps to nucleotide excision repair?
Definition
1. Repairs DNA lesions caused by sun or harmful chemicals

2. 3 enzymes
-Nuclease cuts out damaged DNA
-DNA polymerase adds correct nucleotides
-DNA ligase closes breaks in sugar-phosphate backbone
Term
Telomere
Definition
Eukaryotic chromosome ends:
-noncoding, repetitive DNA sequences

Shorten slightly with each cell cycle

Can be extended by telomerase
Term
What causes cell aging?
Definition
-May be caused by absence of telomerase activity
-Cells lose ability to divide after a limited number of cell divisions
Term
How do cancer cells use telomerase?
Definition
-Cancer cells have telomerase to maintain telomere length and possibly resists apoptosis

-Cancers such as:
breast, lung, colon, prostrate, pancreas
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