NUCLEIC ACIDSChapter 12 DNA and RNA

Where did we find Genes and who discovered them? In 1928 Frederick Griffith tried to figure out how

bacteria made people sick. What caused pneumonia? His experiments lead to the discovery of genes.

Frederick Griffith

Two different strains (types) of same bacteria, one strain caused pneumonia Strain S – smooth colonies (cause disease) Strain R – rough colonies (harmless)

Griffith injected mice with disease-causing bacteria (Smooth strain), the mice developed pneumonia and died

He injected mice with harmless bacteria (Rough Strain), the mice stayed healthy.

Griffith took a culture of the Smooth strain, heated the cells to kill them, and then injected the heat-killed bacteria into mice.

Mice survived.

He mixed the heat-killed, S-strain bacteria with live, harmless bacteria R strain and injected it into laboratory mice

Injected mice developed pneumonia, and died.

The heat-killed cells of the S strain (disease-causing) transferred its information into the live cells of the R strain (harmless) making it change from harmless to disease causing.

This is known as Transformation.

Transformation

Process where one strain of bacteria is changed by a gene from another strain of bacteria.

Avery

1944 Oswald Avery took Griffith’s work farther. Extracted a mixture of various molecules from the

heat-killed bacteria Added enzymes one at a time that broke down

proteins, lipids, carbohydrates, and RNA Transformation still occurred.

Avery’s team repeated the experiment using enzymes that would break down DNA

Transformation did not occur

DNA is the transforming factor.

Hershey and Chase

Experiment with bacteriophages Confirmed Avery’s results .

Bacteriophages

Virus that infects bacteria Attaches to the surface of the bacterial cell Injects its genetic information so new bacteriophages are produced.

Hershey-Chase Experiment

What part of the virus - the protein coat or the DNA core - entered the bacterial cell?

Hershey-Chase Experiment

Grew viruses in cultures containing radioactive isotopes of phosphorus-32 (P-32) sulfur-35 (S-35)

Proteins contain almost no phosphorus and DNA contains no sulfur.

If they found S-35 in the bacteria then the virus’s protein coat had been injected into the bacteria

If they found P-32 then the DNA core had been injected

They mixed the marked viruses with bacterial cells.

In the bacteria they found phosphorus P-32 , the marker found in DNA

DNA was the genetic material not the protein coat.

DNA

DNA is capable of storing, copying, and transmitting genetic information in a cell.

DNADNA is a long molecule made up of nucleotides. Nucleotide:

5 carbon sugar (Deoxyribose) Nitrogen base Phosphate group

DNADNA is made up of 4 kinds of nitrogen bases……

Kinds of Nitrogen Bases

Adenine and Guanine: Purines Purine bases have 2 ring structures

Cystosine and Thymine: Pyrimidines Pyrimidine bases only have 1 ring structures

Components and Structure of Components and Structure of DNA

The backbone of a DNA DNA chain is made up of the sugar and phosphate groups of each nucleotide.

Sugar and Phosphate Back Bone

Watson and Crick

Watson and Crick developed the DNA double helix model. Looks like a spiral staircase.

They discovered hydrogen bonds hold DNA together.

Confirmed base pairing.

Chromosomes and DNA

Where do we find DNA? Eukaryotes – DNA is inside the nucleus.

In the nucleus are chromosomes which store the DNA. Prokaryotes – DNA is in cytoplasm

Chromosomes Structure

Each chromosome has DNA and proteins in it. Chromatin: DNA coiled or wrapped around a histone

(protein). Many histones packed together are called a nucleosome.

Basically a chromosome is made up of DNA wrapped around proteins, coiled together to form nucleosomes that coil up into supercoils called a CHROMOSOME.

The structure of a Chromosome

DNA Double Helix

Histones

Nucleosomes

Supercoils

Chromosome