Chapter 9-The Genetic Material 1928-Griffith preparation of a vaccine. Let’s look at Figure 2-page 191 Vaccine-A substance that is prepared from killed or weakened disease-causing agents, including certain bacteria. Virulent-Able to cause disease Transformation-Change in genotype caused when cells take up foreign genetic material.

Avery’s experiments-What changes the genotype when cells take up material? DNA is responsible for transformation Hershey and Chase- Performed an experiment that settled the controversy of whether proteins or DNA contained the genetic information. See handout for explanation.

Section 2-The structure of DNA Enzymes (as you know) are biological catalysts. They make biological reactions occur faster. DNA replication-The process of making a copy of DNA. Step 1-The double helix unwinds, using DNA helicases. These break the hydrogen bonds. Where the double helix separate is called the replication forks. Step 2-DNA polymerases move along each of the DNA strands. These add nucleotides to the exposed bases.

Step 3-The DNA replication process continues until all of the DNA has been copied and the polymerases are signaled to be detached. Checking for errors-DNA polymerases can backtrack and correct errors. Let’s watch YouTube video.

A winding staircase From the YouTube video we found out how DNA replicates. Now for some more. By the 1950’s scientist knew that genes were made of DNA. Watson and Crick modeled the DNA. They discovered it was a double helix. Double helix-Two strands twisted around each other, like a winding staircase. Nucleotides-The subunits that make up the DNA. Made up of a phosphate group, sugar, and nitrogen containing base.

NOTE DNA IS HELD TOGETHER BY H BONDS!!

Purines and Pyrimidines Four different nitrogen bases Adenine Guanine Cytosine Thymine Purines-Are made of two rings of carbon and nitrogen, adenine or guanine are purines Pyrimidines-Are made of a single carbon ring, thymine and cytosine are pyrimidines.

ADENINE-THYMINE- GUANINE- CYTOSINE-

Discovering the DNA’s structure Chargaff’s observations-Adenine=Thymine and Cytosine=Guanine Wilkins and Franklin’s photographs-Developed X-ray diffraction. Thus showing the coiled helix.

Watson and Crick Constructed the 3 dimensional structure of DNA. Understand most of what we know is because of scientists before Watson and Crick.

Pairing between bases A purine is ALWAYS paired with a pyrimidine. Base-pairing rules-The structure and size of the nitrogen bases allows for only these two paired combinations. Adenine forms two H bonds with Thymine. Cytosine forms three H bonds with guanine. The strictness of base-pairing results in two strands that contain complementary base pairs. Let’s go over an example.

Section 3- The Replication of DNA Watson and Crick proposed that one DNA strand serves as a template, or pattern, on which the other strand is built.