BIOL 101

GENERAL BIOLOGY I

LAB #3

Isolation of DNA from

Wheat Germ

WHAT IS DNA?

WHERE IS IT LOCATED IN A CELL?

Instructions providing all of the information necessary for

a living organism to grow and live reside in the nucleus of

every cell

These instructions tell the cell what role it will play in

your body

Found in the nucleus of eukaryotic cells and in the nucleoid region of prokaryotic

cells

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DNA is the hereditary material in humans

and almost all other organisms

DNA is like a large

recipe book that

determines all of the

characteristics that

are specific to

individual organisms

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DNA Is Found in all Living Organisms

The germ is the

embryo or sprouting

section of the seed.

DNA = GENETIC INFORMATION

Chromosomes = condensed (coiled) threadlike structures

of DNA and associated proteins

Chromatin = DNA & associated proteins in a

dispersed, rather than condensed state

DNA is composed of 4 nucleotides

Each nucleotide consists of…

Nitrogenous

Base

Phosphate

group

Sugar

HOW CAN A MOLECULE HOLD INFORMATION?

DNA HAS 4 NITROGENOUS BASES

Adenine

Cytosine

Thymine

Guanine

RUNGS OF LADDER CONSIST OF PAIRED NITROGENOUS BASES

Complementary base pairing rules:

Adenine (A) pairs only with thymine (T)

Cytosine (C) pairs only with guanine (G)

Each pair of bases

held together by

hydrogen bonds

HOW CAN ONLY 4 LETTERS TELL THE CELL

WHAT TO DO?

The DNA strand is made of letters

The letters make words

The words make sentences

These “sentences” are called genes.

Genes tell the cell to make other molecules called

proteins and proteins enable a cell to perform special

functions.

WHY ISOLATE DNA?

Genetic Testing

Body Identification

Analysis of forensic evidence

INTRODUCE AND PERFORM DNA

EXTRACTION PROTOCOL

ISOLATION OF PLANT DNA:

USING WHEAT GERM

Wheat germ is the DNA source in this protocol.

Comes from wheat seeds.

The "germ" is the embryo, which is the part of the seed that can

grow into a new wheat plant.

EXTRACTING THE DNA:

WHY USE HOT WATER?

Heat softens the cellulose in the cell wall that

surrounds the plant cell.

The cell wall is the first barrier that keeps us from

getting to the DNA.

The grinding of the wheat germ in the mortar, with the

pestle, also helps to physically break down the cell wall

so that we can more easily get to the DNA inside the

nucleus.

EXTRACTING THE DNA:

WHY USE DETERGENT? Detergent contains sodium laurel sulfate, which cleans dishes by

removing fats and proteins.

It acts the same way in the DNA extraction protocol, pulling

apart the fats (lipids) and proteins that make up the membranes

surrounding the cell and nucleus.

The plasma membrane as well as the nuclear membrane are the

remaining barriers that keep us from getting to the DNA inside

the nucleus.

Both soap and grease molecules organize themselves in bubbles

(spheres) with the more polar heads outside to face the water and

hydrophobic tails inside to hide from the water

WHY USE DETERGENT?

When detergent comes close to the cell, it captures the

lipids and proteins and releases the DNA.

EXTRACTING THE DNA:

WHY USE MEAT TENDERIZER?

Cells contain enzymes called DNA-ase and endonuclease in their

cytoplasm.

These are proteins which cut apart DNA into such small fragments that

the fragments would not be visible.

Meat tenderizer contains proteases such as papain and substilisin. A

protease is an enzyme that breaks apart the peptide bonds between amino

acids in proteins and denatures them.

Denatured enzymes lose their 3-D shape, and thus become inactive.

Enzymes also denature at 60° Celsius, and DNA denatures at 80° Celsius.

This is why we use hot water in this extraction protocol, but not boiling

water.

The DNA released from the cell nucleus is dissolved

in the water/detergent/wheat germ solution and

cannot be seen because this solution is polar.

DNA precipitates out of solution in alcohol, a more

nonpolar solvent.

Besides allowing us to see the DNA, the alcohol

separates the DNA from the other cell components,

which are left behind in the water solution.

EXTRACTING THE DNA:

WHY USE ALCOHOL?

DISCUSS GENETIC

MODIFICATION OF DNA

GENETIC INFORMATION ENCODED IN EXACT

SEQUENCE OF BASES

Genome - an organism’s complete set of DNA

Gene – segment of DNA with instructions for producing a particular

protein (polypeptide) Human genome consists

of 20,000–25,000 genes

Humans are identical in

99.9% of the sequences of

their genes

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Small Sections of DNA are Called

Genes

Genes are like the

ingredients that are needed

to make up each individual

recipe

HOW DOES DNA DIRECT CELLULAR ACTIVITIES?

DNA codes for mRNA, which codes for proteins

Proteins play structural or functional roles in cells

In next week’s lab we will study the processes of transcription and translation!!

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Biotechnology: organisms, cells, and their

molecules are modified to achieve practical

benefits

Genetic Engineering: Adding, deleting, or transplanting genes from one organism to another, to alter the organisms in useful ways

Agriculture Human Health

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Because the genetic code is universal, genes

of one organism can be expressed in

another organism

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Insect Resistance

ALMOST EVERYONE IN THE UNITED STATES

CONSUMES GENETICALLY MODIFIED FOODS

REGULARLY WITHOUT KNOWING IT.

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Genetically modified crops in the U.S. are insect and herbicide resistant!

FEARS AND RISKS: ARE GENETICALLY MODIFIED FOODS

SAFE?

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This new breed had

the desired trait but

also exhibited

undesirable traits.