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:
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