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