Chapter 12

 1928 – Griffith  Discovered bacteria transferred something between them that changed them into a new strain.  Called this “bacterial transformation”.

Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease- causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia Section 12-1

 1944 – Avery  Determined the transforming factor was DNA.  He destroyed different parts of the bacteria, and only when the DNA was destroyed did transformation not occur.

 1952 – Hershey and Chase  Using a blender and bacteriophage, determined that DNA, not protein, was the genetic material.

Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Section 12-1

Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Section 12-1

Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Section 12-1

 1952 – Rosalind Franklin  Used x-ray crystallography to show the structure of DNA was a helix.

 1953 – Watson and Crick  Determined the structure of DNA was a double helix, and proposed a model for DNA replication.

 DNA is a chain (polymer) of nucleotides.  A nucleotide consists of a sugar, phosphate and nitrogenous base.

PurinesPyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose Section 12-1

 DNA is a double helix (twisted ladder).  Two nucleotide polymers are held together by weak hydrogen bonds.  Nitrogen bases always pair up this way:  Adenine with thymine A-T  Cytosine with guanine C-G  The backbone of the ladder is alternating sugars and phosphates.  The steps of the ladder are the base pairs.

Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Section 12-1

12-2

 Prokaryotic cells (bacteria)  No nucleus  Single circular chromosome  Bacterial DNA is about 1.6mm long  Eukaryotic cells (all else)  1000X more DNA than bacteria  DNA in nucleus (protected)  Multiple chromosomes  Human DNA (combined) is over 1 meter long

Chromosome E. coli bacterium Bases on the chromosome

 Eukaryotic DNA is tightly packed and folded.  It is wound about proteins called histones.

Chromosome Structure of Eukaryotes Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2

 DNA Packing DNA Packing

 A cell copies its DNA before dividing.  The DNA uncoils.  Then it “unzips” – the two strands separate along the weak hydrogen bonds.  Complimentary nucleotides are added with the help of the enzyme DNA Polymerase.  The result: two identical molecules of DNA.

Section 12-2 Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

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12-3

 DNA makes RNA makes Proteins makes You.

 Single-stranded chain of nucleotides  No thymine - its replaced by uracil  Sugar is ribose, not deoxyribose

 Messenger RNA (mRNA)  Carries a copy of the genetic code (gene) for a protein into the cytoplasm.  Ribosomal RNA (rRNA)  A component of ribosomes where proteins are made.  Transfer RNA (tRNA)  Carries amino acids to the ribosome for assembly into proteins.

 The process of DNA making mRNA in the nucleus is called transcription.  A section of DNA (gene) unwinds and separates  Enzymes add complimentary RNA nucleotides to make mRNA.  mRNA leaves the nucleus and goes to a ribosome in the cytoplasm.  What is the complimentary nucleotide sequence for this DNA sequence?  DNA = A-T-T-C-G-C-G

RNA DNA RNA polymerase Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only)

 C:\Users\Carolyn\Videos\RealPlayer Downloads\Transcription.flv C:\Users\Carolyn\Videos\RealPlayer Downloads\Transcription.flv

 The process of mRNA being read on a ribosome to make a protein is called translation.  mRNA attaches to a ribosome.  tRNA carries amino acids to the ribosome.  The mRNA codon (3 nucleotide sequence) matches up with a complimentary tRNA anticodon (complimentary sequence).  The amino acid is dropped off and added the growing polypeptide chain.  What is the amino acid sequence for the following mRNA sequence? See the universal genetic code chart…  mRNA = AUAAGCGCU

 C:\Users\Carolyn\Videos\RealPlayer Downloads\Translation.flv C:\Users\Carolyn\Videos\RealPlayer Downloads\Translation.flv

 C:\Users\Carolyn\Videos\RealPlayer Downloads\From DNA to Protein.mp4 C:\Users\Carolyn\Videos\RealPlayer Downloads\From DNA to Protein.mp4

 C:\Users\Carolyn\Videos\RealPlayer Downloads\DNA Transcription and Protein Assembly.mp4 C:\Users\Carolyn\Videos\RealPlayer Downloads\DNA Transcription and Protein Assembly.mp4

 Proteins are made of several polypeptide chains folded together.  The shape is important to how the protein functions.  One gene codes for the production of one polypeptide.  Therefore, several genes are needed to make one protein.

12-4

 Mistakes made when DNA is copied are called mutations.  Two kinds: gene and chromosome mutations

 Gene mutations affect only one gene.  There is a change in the sequence of bases in DNA.  This causes the protein made by that gene to be incorrect. (sometimes)  Ex: lactose intolerance

 Changes in the number or structure of chromosomes are called chromosome mutations.  Ex: An extra chromosome causes Down Syndrome.

 Substances that can cause mutations are called mutagenic agents.  UV light, chemicals, radiation

Inherited only if the mutation occurs in a sex cell.  Harmful mutations – cause many genetic disorders.  Ex: cystic fibrosis  Neutral mutations – have no effect on gene expression or protein function (most).  Beneficial mutations – source of genetic variability.  Breeders artificially select for these traits