DNA DNA. DNA is often called the blueprint of life. DeoxyriboNucleic Acid DNA contains the instructions for making proteins within the cell.

The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix. Two strands twisted together.

One Strand of DNA phosphate The backbone of the molecule is alternating phosphate and deoxyribose parts. bases. The teeth are nitrogenous bases. phosphate deoxyribose bases

One deoxyribose together with its phosphate and base make a nucleotide. CC C O Phosphate O C C O -P O O O Nitrogenous base Deoxyribose

Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases.

Complementary base pairs Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

DNA codes for proteins The sequence of nucleotides in DNA codes for proteins.

Have your DNA and eat it too! 1. Assemble one side of your DNA molecule. 2. Match the chemical base pairs. 3. Complete your DNA molecule. 4. Twist your model. 5. Label your model Sequence : T A C G T A T G A A A C

DNA in Your Cells During most of a cell’s life, the cell’s DNA is a form called chromatin Chromatin is loose uncoiled strands of DNA

Before the cell divides; the DNA will wrap itself around proteins to form a chromosome Our genes are on our chromosomes

A chromosome contains two identical parts called chromatids The point at which the two chromatids attach to each other is called the centromere 2 chromatids = chromosome

Homologous Chromosomes Two similar chromosomes They are the same size, shape, length, and code for the same traits You get one from your mother and one from your father

Body cells are called somatic cells  Some examples of somatic cells are muscle cells and skin cells  In a somatic cell, you have 46 chromosomes; you have 23 pairs of homologous chromosomes Sex chromosomes determine your sex  XX – Female  XY – Male Types of chromosomes

DNA Replication DNA has to be copied before a cell divides This happens during the S or synthesis phase of interphase in the cell cycle Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase

Replication is Semi-conservative The double stranded DNA is unzipped (breaking the weak hydrogen bonds) to form two single strands, each having the information needed to make a copy of the original.

DNA Extraction Lab

DNA by the numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only m. The earth is 150 billion m or 93 million miles from the sun.

Two Kinds of Bases in DNA Pyrimidines are single ring bases. Pyrimidines are single ring bases. Purines are double ring bases. Purines are double ring bases. C C C C N N O N C C C C N N N N N C

Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms. Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms. Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine, And adenine always pairs up with thymine. (Adenine and thymine are shown here.) C C C C N N N N N C C C C C N N O O C

Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

sister chromatid DNA in Your Cells