DNA AND REPLICATION
Test: Friday Nov. 19Covers Viruses and DNA/Replication
DNA- Deoxyribonucleic Acid
• DNA codes for genes which carry your genetic information.
History of DNA•1953
• Watson and Crick proposed the double helix, or spiral staircase, structure of the DNA molecule
• They were awarded the Nobel prize for this discovery
DNA Discovery• The Hershey-Chase Experiment
• Bacteriophages: a virus that attacks bacterial cells. They inject genetic material and take over the cell
• Radioactive markers: tag and stick to certain parts of the bacteriophage
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Hershey-Chase Experiment-pg290
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Hershey-Chase Experiment-pg290
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Hershey-Chase Experiment-pg290
Structure of DNA
Chargaff’s Rules
*base pairing rule of A+T & C + G
Source of DNA A T G C
Streptococcus 29.8% 31.6% 20.5% 18.0%
Yeast 31.3% 32.9% 18.7% 17.1%
Herring 27.8% 27.5% 22.2% 22.6%
Human 30.9% 29.4% 19.9% 19.8%
X-Ray Evidence of DNA• Rosalind Franklin• Suggested a twisted double helix
DNA Structure• DNA structure is made up of nucleotides
• Each nucleotide is made up of three parts:• Sugar (deoxyribose)• Phosphate• Nitrogenous Base
• (Adenine, Thymine, Guanine, Cytosine)
Hydrogen bonds (connect bases)
Nucleotide(3 parts)
Sugar/phosphateBackbone (sides)
Key
Adenine Thymine Cytosine Guanine
Structure of DNA
Deoxyribose sugar is attached to all bases
Base-Pair Rule• In a DNA molecule bases pair up in predictable ways• Adenine always pairs with Thymine• Guanine always pairs with Cytosine
• A = T• G = C
Base Pair Rule
One side: A T A T C A T G C G G G
Other side:
How the Code WorksThe combination of A,T,G,C determines what traits you might have, for ex.
C A T C A T = purple hair
T A C T A C = yellow hair
Think of the bases of DNA like letters.
Letters form words....
Words form sentences.... *endless combinations
All the activities of the cell are controlled by DNA.DNA is located in the nucleus of the cell.
A Chromosomeis tightly coiled DNA.
When a chromosome is unraveled, it reveals DNA’s double helix shape.
Just before cell division DNA coils to form chromosomes.
DNA Replication• When a cell divides each cell needs its own DNA
• DNA must replicate and produce two identical strands of DNA in order for this to happen
Process of DNA Replication1. An enzyme “unzips”
the existing DNA strand
2. Free floating nucleotides attach themselves to each side
3. TWO new strands of DNA are formed for each new cell
T A
C
T
G C
G
A
G
C
T A
GC
T
A
G
C
G
A
T
A
C
TT
C
G
A
G
T
C
A
G
A
T
C
G
C
A
G
T
C
This “double helix structure” makes it possible for DNA to make an exact copy
of itself.
GA T
A
C
T
C
G
Free-floating nucleotides
attach themselves
to each side.
DNA “unzips itself.”A T
G C
C G
T A
C G
A T
G C
T A
C G
This is known asreplicatio
n.
1
2
DNAPolymerase
DNA Replication Video
http://www.youtube.com/watch?v=hfZ8o9D1tus
DNA Fingerprinting• The only difference between your DNA and the DNA of the person sitting next to you is the order of the DNA base pairs
• Every person has a different sequence• DNA fingerprinting is a way to identify and distinguish among individual human beings
Who did it???
Who did it???
Comparing DNA Fingerprints
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