Finger Print of LifeFinger Print of Life

What does DNA look like?

macroscopic view: nanoscopic view:

DNA is an organism’s “blueprint”

Tells your cells what proteins they need to make Proteins determine what physical traits and characteristics

you (and all organisms) have

General Function of DNA

There are three parts to every nucleotide:

There are four nitrogenous bases: Adenine, Thymine, Cytosine, Guanine

Nucleotides

a phosphate group a 5-carbon sugar“deoxyribose”

1 of 4 nitrogenous(nitrogen-containing)

bases

DNA (DeoxyriboNucleic Acid) is a double helix

Backbone is made of sugar-phosphate

Base pairs bind the backbone together

Adenine always pairs with Thymine

Guanine binds with Cytosine

Published in 1871 First to isolate and identify DNA and suggested its role in

heredity.

Friedrich Miescher

Published in 1950 Found that the amount of adenine was the same as

thymine and the amount of cytosine was the same as guanine in any DNA sample

Erwin Chargaff

Worked together ~1950 Studied DNA using x-ray diffraction techniques

Both worked together (on and off again) at King’s College in London

Maurice Wilkins & Rosalind Franklin

Published in 1953 Determined the structure of DNA (a double helix) and

published a one-page article in Nature in April 1953

James Watson & Francis Crick

The Double Helix Watson & Crick explained

that hydrogen bonds hold the nitrogen bases together: A always pairs with T C always pairs with G

Hydrogen bonds provide just enough force to hold the strands together, yet can be easily broken if needed.

Before a cell divides, it must make a copy of its genetic

material. DNA is copied in a process called

DNA Replication “Each strand has all the information needed to reconstruct

the other half by the process of base-pairing!”-Watson & Crick

How does DNA make copies?

1. DNA helicase (an enzyme) “unzips” the

base pairs, unwinding the DNA double helix

2. Free DNA nucleotides find their complementary bases along the new strands

3. DNA polymerase (an enzyme) helps assemble the sugar-phosphate backbone to complete the new DNA strands

DNA Replication

The result is two DNA molecules identical to each other

and to the original molecule Each DNA molecule has one original strand and one new

strand; we call this the semi-conservative replication process.

DNA Replication

Watch the following video clip to see an animation of how

DNA replication works!

http://www.youtube.com/watch?v=2iVltkYy0jg&safe=active

DNA Replication

Base pairs A-T – double hydrogen

bond G -C – triple hydrogen

bond

Nucleotide (3 chemical groups) Sugar – deoxyribose

contains 5 Carbon atoms

Phosphate group A base (A, T, G, C)

How Does DNA Copy Itself?How Does DNA Copy Itself?

History of Replication

Watson & Crick – realized that complementary base pairing provided a way for DNA to copy itself - base pairing could allow a new strand to be built on an old strand - 3 possible models of DNA replication

3 Models of Replication

3 Models of Replication:

Semi-conservative Replication Each strand in a DNA molecule is used as a template to build a new strand using complementary base pairing Results in new molecule with one original DNA strand and one new strand

3 Models of Replication:

Conservative Replication

Leaves the original DNA intact and produces another molecule of DNA identical to the first

3 Models of Replication:Dispersive Replication

Creates two molecules that are a mix of new and old DNA interspersed along each strand of the molecule

The Question is Answered

1957 Matthew Meselson & Franklin Stahl -conducted an experiment proving replication is semiconservative - each DNA molecule has one new strand and one old strand

DNA Replication: Process

Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles

DNA Replication: Process

Multiple replication bubbles are opened simultaneously allows the molecule to be replicated quickly

DNA Replication: Process

The nitrogen bases on the original DNA strands are exposed in the replication bubbles. They serve as a template to build new DNA strands

DNA Replication

The ends of the replication bubbles known as the

replication fork is where replication begins

DNA Replication – DNA Polymerase

The enzyme DNA polymerase brings new nucleotides to the replication fork - it pairs them according to base

pairing rules A pairs with T C pairs with G

DNA Replication – Leading Strand

The process of replication proceeds from 5’ to 3’ leading strand- replication is continuous – it is built toward the

replication fork

DNA Replication – Lagging Strand

lagging strand- replication occurs in short segments - called Okazaki fragments - the new DNA strand grows away from the replication fork

DNA Replication- The Big Picture

Each Bubble has 2 Forks – each fork has a leading and lagging strand

DNA Replication

The process continues until 2 complete copies of the DNA are produced

Each copy of the DNA contains one strand of

DNA from the original DNA molecule and one new strand that was produced by replication

Known as semi-conservative replication

DNA Replication

DNA Replication-

Vocabulary

replication DNA helicase replication bubble replication fork DNA polymerase leading strand lagging strand Okazaki Fragment semi-conservative replication

DNA replication

Multiple Replication Forks During Multiple Replication Forks During EukaryoticEukaryotic DNA Synthesis DNA Synthesis

MUTATIONSMUTATIONS Changes in DNA that affect genetic

information

Gene MutationsGene Mutations Point Mutations – changes in one

or a few nucleotides– Substitution

THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT

– Insertion THE FAT CAT ATE THE RAT THE FAT CAT XLW ATE THE

RAT– Deletion

THE FAT CAT ATE THE RAT THE FAT ATE THE RAT

Chromosome MutationsChromosome MutationsChanges in number and structure of

entire chromosomes Original Chromosome ABC * DEFDeletion AC * DEFDuplication ABBC * DEFTransposition ACB * DEFInversion AED * CBFTranslocation ABC * JKL

GHI * DEF

Significance of MutationsSignificance of Mutations• Most are neutral

• Eye color• Birth marks

• Some are harmful• Cystic Fibrosis• Down Syndrome

• Some are beneficial• Sickle Cell Anemia to Malaria• Immunity to HIV

What Causes Mutations?What Causes Mutations? There are two ways in which DNA can

become mutated:– Mutations can be inherited.

Parent to child– Mutations can be acquired.

Environmental damageMistakes when DNA is copied