DNA –The Language Of Life

Chapter 11

11.1 What is the chemical in genes?

Computer keyboard analogy. 100+ keys ; it’s all about the order.

Students in the classroom.Same partsSame chemicals.It’s the combination =the many different characteristics.

Chemicals form DNA.

DNA is the chemical of genes

What does DNA do in cell cycle- DNA replicates

DNA divides in mitosis/meiosis.

So every cell has a genetic blueprint (instructions).

How we know DNA is the genetic material:

Griffith’s Experiments- Identified a Transforming Factor.2 Strains of pneumonia bacteria.

Smooth strain- capsule.–Causes pneumonia in mice.

Rough strain - no capsule.–Does not cause pneumonia.

Heat killed smooth strain.Does not cause pneumonia.

Combined heat-killed smooth strain and rough strain bacteria.

Caused disease in mice .

Griffith’s Experiment

                                                                                                                                                                           

Figure 11-1 Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."

What happened?

The Rough strain was transformed to become smooth.

All descendents of the transformed bacteria were smooth &caused disease.

Griffith called the substance “transforming factor”.

Further Experiments-

identify the transforming factor

Chromosomes are made up of proteins and DNA.

Is the factor DNA or Protein?

Most scientists then-thought the hereditary material was protein not DNA.

Avery’s ExperimentAvery used different enzymes.

Protein destroying enzymes were used on Griffith’s heat treated and live rough mixture.

Result- bacteria were transformed.

Protein was not transforming factor.

DNA destroying enzymes were used.Result- bacteria were not transformed.

So….

DNA was the transforming factor.

Hershey and Chase- Bacteriophage Experiment

Hershey & Chase’s Bacteriophage Experiment - DNA is the genetic material

Viruses are not cells.DNA wrapped in a protein coat.Only reproduce in a living cell.Viral genetic material directs host cell to make more virus.

Bacteriophage -viruses that attack bacteria..

outer coat of proteininner core of DNA.

Radioactive sulfur labels protein coat.

Radioactive phosphorous labels DNA.

When phage protein coats are labeled, radioactivity was outside of the cell.

When phage DNA is labeled

radioactivity is inside the cell.

Conclusion : phage DNA enters bacterial cell , NOT protein.

So- DNA is the genetic material !

11.2 Structure of DNA

pp 229-231

Nucleic Acids-

Function - store and transfer genetic information. Genes are made of DNA.

Nucleic Acids- made up of many units of nucleotides(monomers)

Nucleotides are the building blocks.

DNA- Deoxyribonucleic Acid4 different nucleotides.

A=adenine

G=guanine

C=cytosine

T=thymine

NUCLEOTIDE STRUCTURE

3 PARTS OF A NUCLEOTIDE:

1. Deoxyribose - 5 Carbon sugar2. Phosphate Group- Phosphorous

atom with 4 atoms of oxygen3. Nitrogen base.

Single ring-pyrimidineDouble rings-purines

The 4 nucleotides of DNA:

The nitrogenous base is the difference.

Pyrimidines- single-ring structures.

Thymine- T.

Cytosine- C.

Purines- double-ring structures.

Adenine- A.

Guanine- G.

The letters T,C,A,G are used to represent the bases and also the nucleotides that contain them.

Sugar-phosphate DNA backboneDouble helix (ladder )model

Outside of the ladderRepeating pattern

Sugar of one nucleotide is connected to the phosphate group of the next.

Attached nitrogen bases are on the inside (rungs)of the double helix model.

Nucleotide chains can vary in length.

Nucleotides can combine in many different sequences represented by the letter symbols.

CTAGCCTTGAC

Nitrogenous Base Pairing:A=T ( by 2 hydrogen bonds)

G=C (by 3 hydrogen bonds)

Called Complimentary Base Pairing.

Base-pairing rule- each base must pair up with its complementary base.

Double Helix Structure1950s- Franklin- X-ray crystallography.

Showed basic shape to be a helix

1953- Watson and Crick modelUsed Franklin’s photosTwisting shape-double helix ; 2 nucleotides twist around each other.Sugar-phosphate backbone on outsideNitrogenous bases on the inside joined by hydrogen bonds.

11.3 DNA Replication-the process of copying a DNA molecule.

Template mechanism1.The 2 strands of the double helix

separate.DNA helicase (enzyme) “unzips” the DNA, breaking the hydrogen bonds between the base pairs.Each strand is template for a new, complementary strand to form.Base-pairing rules are followed.

A-TG-C

DNA Replication Continued2. DNA polymerase (enzyme)

“glues” the bonds between the nucleotides of the new DNA strand.

“proof-reads” new DNA.

DNA replication begins at specific sites called points of origin.

Replication (copying) proceeds in an outward directions from the points of origin resulting in replicating bubbles.

The parent DNA strands open up as new daughter strands grow.

Result of DNA replication:

Result- 2 double stranded DNA molecules;

one old & one complementary new strand.

DNA replication occurs before a cell divides.

In what stage of the cell cycle?