Chapter 9

DNA: The Genetic Material

Identifying The Genetic Material• What is your genetic information made of? Proteins or DNA• Griffith’s work• Discovery of “Transformation” or a change in the genes by

taking in foreign information• Avery’s work• Demonstrated that DNA contains the genetic information

• Hershey and Chase’s work• Used bacteria to prove DNA is where the genetic information is,

not proteins.

The structure of DNA• Watson and Crick receive credit for creating the first DNA model• Double helix: two strands twisted around each other, like a winding

stair case.• Each strand is linked nucleotides which is made up of 3 parts.• Phosphate group, five carbon sugar, and a nitrogen base

• Five carbon sugar is called deoxyribose (hence DNA= deoxyribonucleic acid)• Nitrogen bases:• Purines: 2 ringed molecules; Adenine and Guanine• Pyrimidines: single ringed molecules; thymine and cytosine

Chargaff’s observations:

• The amount of adenine always equals the amount of Thymine• The amount of guanine always equals the amount of CytosineWilkins and Franklin• Used X-ray diffraction to study the structure of DNA• Successfully imaged a DNAWatson and Crick (again)• Used all of the above in development of their model• Determined base-pairing rules:• Purine always matches to a pyrimidine• Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds• Cytosine (C) pairs with Guanine (G) via 3 hydrogen bonds

• Termed complementary base pairs

So therefore, complimentary base pair rules:

A-T-T-G-C-A-G-T-T-C-

DNA Replication: the process of making a “new” strand of DNA (occurs during the S phase)Steps:1.DNA unwinds (DNA helicases are the enzymes

responsible for this), other enzymes hold them apart, at replication forks.

2.DNA polymerases attach at replication forks adding new nitrogen bases to the exposed base

3.Upon completion, DNA polymerase detaches, two new strands are present, each being part new and part of the old strand.

Genes to Protein (this is found in chapter 10)• RNA (ribonucleic Acid) single strand, made from the genetic information found

on DNA• NO THYMINE, instead thymine is replaced with Uracil (which is a pyrimidine)• Two main stages in creating proteins, transcription and translation.

Transcription: info is transferred from DNA to an RNA.Steps:1. RNA polymerase binds to a specific spot on the DNA (the “start” spot)2. Unwinds a specific area of DNA3. RNA polymerase adds and links complimentary RNA nucleotides as it “reads”

the DNA4. Continues until it reaches the “stop” spot5. New strand that is created is modified and becomes mRNA (“messenger” RNA)

The Genetic Code (the three letter words)• Codons: are three letter words, sequences, that “code” for information on the

RNA• All are listed below, and no you don’t have to memorize it. I will give to you.

BUT you should be able to read it.

Translation: the synthesis of the proteins.

Steps:1.mRNA leaves nucleus and travels (in the cytoplasm) to a Ribosome2.There it joins the ribosome, and it starts to read the mRNA3.In the ribosome, reading begins with “start codon” at the P site4.Transfers to the A site and continues5.tRNA (or transfer RNA) has anti codons (or opposite of the codon

found on the mRNA) which as a specific amino acid attached to it.6.The amino acids are joined together, forming the protein.