Chapter 12 DNA

Section 12.1 Identifying the Subsrance of Gene

Summarize the process of bacterial transformation.

Describe the role of bacterio-phages in identifying genetic material.

Identify the role of DNA in heredity.

Biological characteristics are inherited through genes that are passed from parents to offspring.

the molecule make genes

Griffith’s Experiments Streptococcus pneumoniae

S Strain (smooth) deadly R Strain (rough) hramless

Griffith’s Experiments

Ran for tests on mice:

1)S-type injected into mice -Mice die

2)R-type injected into mice -Mice live3)Heat-killed S-type injected into mice -Mice live4)Heat-killed S-type and R-type injected into mice -Mice die

Transformation

•Conclusion Some material from dead S-type changed R-type into S-type •Transformation -one type of bacteria had been changed permanently into another -the transforming factor had to be a gene

The Molecular Cause of Transformation

•Which molecule was most important for transformation in the heat-killed bacteria?

•Avery

•Used enzymes to destroy either the proteins, DNA, or RNA of the cells and then tried to transform the bacteria.

R-type + S-type with

destroyed proteins transformation

R-type + S-type with

destroyed RNA transformation

R-type + S-type with

destroyed DNA no transformation

Conclusion:

DNA must be needed to transform bacteria cells, so it must be the key to heredity

Bacterial Viruses

•viruses—tiny particles that can infect living cells

•The kind of virus that infects bacteria is known as a bacteriophage.

The Hershey-Chase Experiment

bacteriophage made of just DNA and a protein coat

Labeled DNA and protein coat of virus with radioactive P and S isotopes

The Hershey-Chase Experiment

The Hershey-Chase Experiment

•E.coli+Virus with labeled protein no radioactivity in offspring

•E.coli + Virus with labeled DNA radioactivity in offspring

•Conclusion: DNA, not proteins, are passed on to offspring

The Role of DNA

What is the role of DNA in heredity?

The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell.

•Storing InformationGenes must contain the instructions that cause a single cell to develop into a mature individual.

•Copying InformationBefore a cell divides, it must make a complete copy of every one of its genes.

•Transmitting InformationWhen a cell divides, each daughter cell must receive a complete copy of the genetic information.

Section 12.2 the Structure of DNA

Identify the chemical components of DNA

Discuss the experiments leading to the identification of DNA as the molecule that carries the genetic code

Describe the steps leading to the development fo the double-helix model of DNA

The Components of DNA

•What are the chemical components of DNA? -Deoxynucleic Acid / polymer

-deoxynucleotide / monomer

-covalent bonds form between sugar and phosphate groups.

Nitrogenous Bases and Covalent Bonds

•four kinds of nitrogenous bases: adenine (A) guanine (G) purines cytosine (C) thymine (T) pyrimidines•Chargaff’s Rules [A] = [T] and [G] = [C]

Franklin’s X-Rays

• There are two strands in the structure.•The strands in DNA are twisted around each other like a helix.•The nitrogenous bases are near the center of the DNA molecule.

The Work of Watson and Crick

•They built three-dimensional models of the molecule.•the double helix model

The Double-Helix Model

•Antiparallel Strands

-The two strands of DNA run in opposite directions.

-The nitrogenous bases on both strands meet at the center of the molecule

Hydrogen Bond and Base Pairing

-between certain nitrogenous bases -Base Pairing •Adenine with Thymine•Guanine with Cytosine

-weak chemical bond

-allow two strands to separate easily

Section 12.3 DNA Replication

Summarize the events of DNA replication

Compare DNA replication in prokaryotes with that of eukaryotes

Replication of DNA ( 复制 )

•The DNA in the chromosomes is copied in a process called DNA replication.

Replication of DNA ( 复制 )

•separation of strands replication forks•base pairing A-T; C-G template •bonding of bases

Replication of DNA ( 复制 )

The Role of Enzymes

•break the hydrogen bonds•unwind the two strands

DNA polymerase

•principle enzyme •join individual nucleotides•check new DNA strand

Telomeres

•the tips of chromosomes

Telomerase•add short, repeated DNA sequences to telomeres

Replication in Living Cells•Prokaryotic cells single circular DNA

• Plasmids additional DNA rings based between different bacteria; help protect against their environment

•Eukaryotic cells long DNA in the nucleus bigger chromosomes

Prokaryotic DNA Replication

•Single starting point, ori•Two directions; one large replication bubble•DNA attaches to the cell membrane to steady itself

Eukaryotic DNA Replication•Dozens or hundreds starting points; many replication bubbles•Chromatin condenses

That’s All

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