Lab 5 - DNA Extraction From Cells Lab

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After completing this activity, students will be able to:

• Observe the physical properties of DNA• Prepare a filtered extract of strawberry and

chicken liver DNA.• Demonstrate that DNA is a three dimensional

structure, and that it can be extracted from nearly any cell.

• Recognize DNA as the source of variation and the common link between all living things

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• DNA stands for deoxyribonucleic acid

• The shape of a DNA molecule is a double helix.

• The scientists James Watson and Francis Crick are credited with determining the structure in 1953.

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Parts of a DNA molecule

• Sugar and phosphate – these make up the backbone of the molecule—

the sides of the “ladder”• Nitrogenous bases (A, C, G, or T)

– these are the “steps” of the “ladder”– The order (aka sequence) of nitrogenous bases

determines each of your genes

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The Shape of DNA: double helix

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Deoxyribose – Sides of ladder

Nitrogenous bases- Rungs of ladder

DNA Double HelixAdenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

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A always goes with T

C always goes with G

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CHROMOSOME

Human Karyotype - Diploid

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One set of chromosomes from your mother’s egg, one set from your father’s sperm

Each organism has a different assemblage of DNA sequences – this variation is responsible for the differences between all organisms

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DNA is in the nucleus of (almost) all the cells in your body

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Red blood cells lack a nucleus, thus lack DNA

Based on this figure, is there more DNA in strawberries or liver?

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Why should I care about DNA?

• Every living thing has DNA• The same four bases (in different

combinations) make up all living things• DNA can help us investigate our ancestors,

and understand how we may be genetically predisposed in the future

• Our unique DNA makes us who we are, like a recipe for making an organism what it is.

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Lab Today• DNA molecules are long, slender molecules that carry the

heritable information of organisms on to future generations. • Because of its microscopic size, it is impossible to see a DNA

molecule with the naked eye. It would take about 300,000 DNA molecules side by side to make a bundle as thick as a human hair.

• When subjected to certain conditions, it is possible to collect “large” amounts of DNA to make it visible.

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Why do we purify DNA?• The purification of chromosomal

DNA is frequently the first step in molecular-cloning experiments.

• DNA is insoluble in alcohol and so it precipitates out of solution. This helps remove small molecules, such as salts, sugars, and amino acids, from nucleic acid precipitations because they remain in the solution.

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• Most animals are diploid (two copies of the genome), but some plants can have more than two copies

• Strawberry plants are octoploid, that is, each cell contains 8 sets of chromosomes.

• The liver of animals may become polyploid

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