DNA

Ms. Garcia

LN #21

California Content Standards

Genetics5a. Students know the general structures and functions of DNA, RNA, and protein.5b. Students know how to apply base-pairing rules to explain precise copying of DNA during semiconservative replication and transcription of information from DNA into mRNA.

Chromosomes & DNA………..• Chromosomes are made of DNA and

protein.– deoxyribonucleic acid (DNA)

• The total DNA in our 46 chromosomes would stretch for 3 meters.

• The reason all this DNA fits in our cells is because of the way DNA is coiled in our chromosomes.

• Our chromosomes contain 20,000 to100,000 genes, this makes up 10% of our DNA.– 90% of our DNA does not code for traits.

Double Helix

• DNA’s shape was first described in 1953 by Watson and Crick.– Rosalind Franklin was the

first to take an X-ray photograph of DNA.

• Watson and Crick described DNA as a double helix.

Double Helix

What is a Nucleotide?

• DNA is made of nucleotides.

• Nucleotides are repeating subunits that make up DNA.

• Nucleotides contain 3 parts.1. phosphate group2. sugar (deoxyribose)3. nitrogen base

1

2

3

Base Pairing Rules

• DNA contains 4 types of nitrogen bases.

• The nitrogen bases are categorized in 2 groups.– Purines

• Adenine (A)

• Guanine (G)

– Pyrimidines• Thymine (T)

• Cytosine (C)

• A always bonds with T • G always bonds with C

PyrimidinesPurines

Too big

Too small

Just right

Genetic Code

• Deoxyribose and the phosphate group make up the backbone of the DNA strands.

• The nitrogen bases form a code that contains the instructions for making proteins.

• Our bodies read DNA’s code to express our traits.

• DNA is located in the nucleus of cells.

DNA Replication

• Every cell in our body, with the exception of red blood cells, contain DNA.

• DNA replication ensures that every cell will have the correct amount of DNA after meiosis and mitosis have been completed.

• DNA replication takes place during interphase.

Summary

• What are chromosomes made of?

• What is a nucleotide?

• What are the three parts of a nucleotide?

• What is the general structure of DNA?

• What are the base pairing rules of DNA?

• Why is DNA replication important?

• Do Pre Reading 11.1 on page 287.