DNAStructure and

ReplicationPart 1 - DNA

DNA• Deoxyribonucleic Acid• DNA contains all the instructions for all the

traits of a living organism.• What is a trait?

Images: MSOffice Powerpoint

• DNA is found in the nucleus of a cell.• DNA makes up the chromosomes.• Humans have 23 pairs of chromosomes in the

nucleus of each cell.

DNA

http://www.yorku.ca/kdenning/images/1-3-4-6-0-0-0-0-0-0-0.jpg

This is a picture of the chromosomes found in every human cell. Notice how there are 23 matching pairs. The last two determine the gender. XY means this is a boy.

• A gene is a small segment of DNA.• Genes have the instructions for all the traits in

an organism.• Genes “code” for such traits as eye color, hair

type, skin color, height, and even diseases.

Genes

Don’t forget! Those are all

traits!

Images: MSOffice Powerpoint

Let’s label!

http://publications.nigms.nih.gov/thenewgenetics/images/ch1_dnagenes.jpg

Discovery of DNA• Several scientists are given credit with the

discovery of DNA.• James Watson and Francis Crick discovered

DNA in 1952.• Rosalind Franklin also helped discover DNA.

http://virtuallaboratory.colorado.edu/Biofundamentals/labs/WhatisScience/graphics/franklin.jpg

DNAStructure and

ReplicationPart 2- Structure

Structure of DNA• DNA resembles a “twisted ladder”• DNA is made up of many nucleotides.• One nucleotide has 3 parts:– 1. Phosphate– 2. Sugar (Deoxyribose)– 3. Base• There are four types of bases:– Adenine (A)– Thymine (T)– Guanine (G)– Cytosine (C)

• The Phosphates (P) and Sugars (D) make up the sides of the DNA “ladder”.

• The bases (A, T, C, G) make up the rungs (steps) of the ladder.

Structure of DNA

http://www.biologycorner.com/resources/DNA-colored.gif

Nucleotides• Nucleotides will only join in very specific ways.• This is similar to a jigsaw puzzle. Only certain

pieces fit together.• Adenine (A) only bonds with Thymine (T)• Cytosine (C) only bonds with Guanine (G)

Image courtesy of Jennifer Richardson

• When DNA is untwisted, it looks much like a ladder.

• Notice how the sides of the ladder are alternating sugar and phosphate molecules.

• The rungs (steps) are the nitrogen bases.

• Also notice how G always pairs with C.

• And A always pairs with T

http://www.woisd.net/moodle/file.php/6/assets/images/ks4/dna.gif

Making more DNA• During mitosis and meiosis (cell

division) DNA gets copied before a cell divides.

• Notice in the picture that the left side of the DNA molecule is identical to the right side.

• A always joins with T• C always joins with G(like puzzle pieces)

http://scn1ddna.tripod.com/sitebuildercontent/sitebuilderpictures/trans98.jpg

DNAStructure and

ReplicationPart 3- Replication

Replication• DNA replication is a process that copies the

DNA in the nucleus of a cell before it divides.• This is so each new cell will have a complete

set of DNA.• Replication happens during mitosis and

meiosis.• Replication makes sure that every new cell will

have instructions for how to work.

The steps of DNA Replication

http://scn1ddna.tripod.com/sitebuildercontent/sitebuilderpictures/replication-simple.gif

1. DNA molecule “unzips” by breaking the bonds that hold the bases (A,T,C,G) together.

2. New bases (shown in blue below) are added to each strand of the DNA.

3. Notice that the two new strands are identical to each other.

http://www.woisd.net/moodle/file.php/6/assets/images/ks4/dnacopy.gif

You practice!• Which bases would match the following DNA

strand during DNA Replication?

G C A T A T G G T C A__ __ __ __ __ __ __ __ __ __ __

Hint:

The Answer!• Which bases would match the following DNA

strand during DNA Replication?

G C A T A T G G T C AC G T A T A C C A G T

Hint: