Essential Questions • How do genes work? • What are they made of and how do they determine the characteristics of organisms? • Are genes single molecules or are they longer structures made up of many molecules?
12-1 DNA Griffith and Transformation • 1928, Frederick Griffith, investigated pneumonia • Two different pneumonia bacteria • Colonies with rough edges- harmless • Colonies with smooth edges- pneumonia
Transformation- when a bacteria picks up foreign DNA. This changes the bacteria. • Griffith’s hypothesis- • 1) some factor was transmitted from the heat-killed cells to the harmless living cells. • 2) This factor must contain information that would change the harmless cells into disease-causing cells. • 3) This factor could be passed onto offspring
Oswald Avery, 1944 Smooth Destroy: Proteins Lipids Carbohydrates RNA Rough
Oswald Avery, 1944 Smooth Destroy: DNA Rough
Avery’s conclusion • DNA must store and transmit genetic information from one generation to the next
Hershey-Chase Experiment • Alfred Hershey and Martha Chase, 1952 • What transmits hereditary information: DNA or proteins? • Bacteriophage- a virus that infects bacteria • Composed of DNA or RNA core • Protein coat
A bacteriophage will inject virus DNA or RNA into a bacteria. The viral genes will use the cell to make more viruses and also destroy the cell.
Components Structure of DNA • 5-carbon sugars • Deoxyribose • Phosphates • Nitrogenous bases
Components Structure of DNA Nucleotide: • 5-carbon sugar (deoxyribose) • Phosphate • Nitrogenous base
Nitrogenous bases Purines (2 rings): • Adenine • Guanine Pyrimidines (1 ring): • Cytosine • Thymine
Chargaff’s Rule • Erwin Chargaff % of Guanine = % of Cytosine % of Adenine = % of Thymine
Rosalind Franklin • Early 1950s • Used x-ray diffraction to Study the structure of DNA
James Watson and Francis Crick 1953 created a model to explain the structure of DNA They used Franklin’s photographs
Double Helix • 2 strands wrapped around each other
Nucleotides are linked together • G bind to C • T binds to A • Bases are connected to opposite bases by hydrogen bonds • G to C by three bonds • T to A by two bonds
12-2 Chromosomes and DNA Replication DNA Prokaryotes- one single chromosome, DNA is circular Eukaryotes- multiple chromosomes, DNA is linear
DNA Length E. Coli 4,600,000 base pairs 4,000 genes 1.6mm long Human DNA 3,000,000,000 base pairs 35,000 genes 2 meters long
Histones- protein that DNA is coiled around • Nucleosome-histone with DNA wrapped around it
What do histones and nucleosomes do? • Histones: • DNA held tightly= turned off • DNA held loosely= turned on Nucleosomes: aid in folding and packing of DNA
DNA Replication • Prokaryotes- one site to begin replication
DNA Replication • Prokaryotes- two complete complementary DNA strands created.
DNA Replication • Eukaryotes- multiple sites along the linear DNA strand begin replication
DNA Replication • Complementary bases are added to the template strand. CATGTGATCATAGATA- template strand
DNA Replication • Complementary bases are added to the template strand. CATGTGATCATAGATA- template strand GTACACTAGTATCTAT- copied strand
DNA Replication • DNA is unwound by an enzyme- Helicase • Helicase breaks the hydrogen bonds between bases • Replication bubble- Where the helicase unwinds the DNA to begin copying
Replication fork- The end of the bubble where DNA is being unwound.
DNA Replication • DNA polymerase- an enzyme that adds new nucleotides on the complementary strand • DNA polymerase- proof reads the new strand to make sure no mistakes are made. It ensures that the right base is added on the complementary strand. CATGTGATCATAGATA- template strand GTACACT - copied strand G A G G A T C C T G T C G A C A T T T A C G C G G
12-3 RNA and Protein Synthesis • Genes- coded DNA instructions that control the production of proteins within the cell
The Structure of RNA • Similarities between RNA and DNA • Both are composed of nucleotides (5-carbon sugar, phosphate, nitrogenous base)
Differences between RNA and DNA • 1. 5-carbon sugar is ribose (not deoxyribose)
Differences between RNA and DNA • 2. Usually single stranded (not double stranded)
Differences between RNA and DNA • 3. Contains uracil instead of thymine
Types of RNA • Messenger RNA (mRNA) • Contains instructions for assembling amino acids into proteins • Long single strand of RNA
Types of RNA • Ribosomal RNA (rRNA) • Proteins and rRNA make up ribosomes • Amino acids are linked together to make proteins at the ribosome.
Types of RNA • Transfer RNA (tRNA) • A molecule that carries an amino acid to a ribosome in order to make a protein
Transcription Transcription- Transcribing a DNA sequence into an RNA sequence • RNA polymerase- separates DNA strands and copies one strand of the DNA. It creates a complementary strand of RNA.
How does RNA polymerase know where to copy? • RNA polymerase starts copy by binding to promoter- a specific sequence of DNA • RNA polymerase stops copying when it reaches a terminator- a specific sequence of DNA
Transcription • RNA polymerase creates a mRNA (messenger RNA). • The mRNA strand is complementary for the DNA sequence from which it was copied. It has “U” instead of “T”. RNA- GUACCAUGAUCAUG DNA- CATGGTACTAGTAC
mRNA editing The mRNA is edited: 5’ Cap- A cap is added to the front. It includes a Guanine and three phosphates. Poly A Tail- A tail is added to the end. It is a long string of “A” nucleotides. 5’ G-P-P-P- CAGUAGAUCAUGA-AAAAAAAA
mRNA editing The mRNA is edited: Introns- parts of the mRNA that are cut out Exon- parts of the mRNA that are left in 5’ G-P-P-P- CAGUCGUACUAUGACACUAGAUCAUGA-AAAAAAAA 5’ G-P-P-P- CAGUCUGACAC AUGA-AAAAAAAA 5’ G-P-P-P- CAGUCUGACACAUGA-AAAAAAAA