DNA and RNADNA and RNA

Chapter 12Chapter 12

What is genetic material What is genetic material made of?made of?

Is it protein, carbohydrates, Is it protein, carbohydrates, DNA….DNA…. 1928 – 1928 – Frederick GriffithFrederick Griffith determined that determined that

somethingsomething transformedtransformed harmless (rough) harmless (rough) strep bacteria into disease-causing strep bacteria into disease-causing (smooth) bacteria.(smooth) bacteria.

What transformed the What transformed the bacteria?bacteria?

1944 – 1944 – AveryAvery, MacLeod, and McCarty , MacLeod, and McCarty recreated Griffith’s experiment and recreated Griffith’s experiment and tested the transformed bacteria.tested the transformed bacteria.

Subjected to Subjected to enzymesenzymes that broke down that broke down proteins, lipids, and carbohydrates….the proteins, lipids, and carbohydrates….the bacteria still were transformed.bacteria still were transformed.

When When DNA-destroying enzymesDNA-destroying enzymes were were added, transformation failed to occur.added, transformation failed to occur.

DNADNA is found to be the is found to be the genetic materialgenetic material..

Avery, McLeod, and McCarty’s Avery, McLeod, and McCarty’s experimentexperiment

Confirmation by Hershey-Confirmation by Hershey-ChaseChase

1952 – Alfred 1952 – Alfred HersheyHershey and Martha and Martha ChaseChase use bacteriophages (viruses) use bacteriophages (viruses) to confirm DNA is the hereditary to confirm DNA is the hereditary material.material.

They labeled phages with They labeled phages with radioactive radioactive phosphorusphosphorus and and sulfursulfur. . (P is part of DNA)(P is part of DNA)

The phages infected bacteria, they The phages infected bacteria, they were dislodged using a blender and were dislodged using a blender and the material was analyzed…the material was analyzed…

Radioactive Radioactive phosphorusphosphorus was found was found inside the bacteriainside the bacteria..

Hershey-Chase ExperimentHershey-Chase Experiment

What is DNA made of?What is DNA made of?

Experiments determined that DNA Experiments determined that DNA is made of is made of nucleotidesnucleotides: a : a deoxyribosedeoxyribose (a sugar), a (a sugar), a phosphatephosphate group, and one of four nitrogenous group, and one of four nitrogenous basesbases::

Adenine (Purine)Adenine (Purine) Thymine (Pyrimidine)Thymine (Pyrimidine) Cytosine (Pyrimidine)Cytosine (Pyrimidine) Guanine (Purine)Guanine (Purine)

But what is the structure?But what is the structure?

Chargaff’s RulesChargaff’s Rules Edwin ChargaffEdwin Chargaff analyzed DNA in living analyzed DNA in living

things and found matching things and found matching pairspairs..

A and T, C and G, but what is A and T, C and G, but what is the structure?the structure?

1950’s – 1950’s – Rosalind Rosalind FranklinFranklin studied DNA studied DNA using X-ray using X-ray crystallographycrystallography..

Her Her photographs photographs suggested DNA suggested DNA was twisted was twisted into a into a helixhelix..

Watson and Crick’s DNA Watson and Crick’s DNA ModelModel

1953 – 1953 – James WatsonJames Watson and and Francis Francis CrickCrick were working on a model of were working on a model of DNA, but couldn’t make it work.DNA, but couldn’t make it work.

Using Rosalind Franklin’s X-ray of Using Rosalind Franklin’s X-ray of DNA (without her knowledge or DNA (without her knowledge or consent) they finally determined that consent) they finally determined that DNA was a DNA was a double helixdouble helix, with bases , with bases connecting in the middle, and a connecting in the middle, and a phosphorus backbone.phosphorus backbone.

They won the Nobel Prize. Rosalind They won the Nobel Prize. Rosalind Franklin died of cancer.Franklin died of cancer.

Watson and Crick’s ModelWatson and Crick’s Model

DNA – Deoxyribonucleic AcidDNA – Deoxyribonucleic Acid

Where is DNA found in Where is DNA found in Cells?Cells?

In In ProkaryotesProkaryotes (bacteria), DNA is (bacteria), DNA is found in a closed loop in the found in a closed loop in the cytoplasm. Stretched out it would cytoplasm. Stretched out it would be about 1.6 millimeters long!be about 1.6 millimeters long!

In In EukaryotesEukaryotes, DNA is found , DNA is found wrapped up tightly with chromatin wrapped up tightly with chromatin around proteins called around proteins called histoneshistones. . Then condensed even more to form Then condensed even more to form chromosomeschromosomes. Chromosomes are . Chromosomes are only formed during cell division. If only formed during cell division. If your DNA from one cell were your DNA from one cell were stretched out, it would be over 1 stretched out, it would be over 1 meter long!meter long!

SEM and KaryotypeSEM and Karyotype

DNA ReplicationDNA Replication

In the In the G PhaseG Phase of the cell cycle, DNA of the cell cycle, DNA is not tightly coiled to allow for genes is not tightly coiled to allow for genes to be easily accessed. to be easily accessed.

In the In the S phaseS phase, DNA is , DNA is replicatedreplicated to to prepare for cell division. prepare for cell division.

An exact copy of all of the An exact copy of all of the chromosomes must be made, chromosomes must be made, without mistakes.without mistakes.

The enzyme The enzyme helicasehelicase unwinds the unwinds the helix, and helix, and DNA polymeraseDNA polymerase attaches attaches complementary base pairs and complementary base pairs and proofreads the new strands.proofreads the new strands.

DNA ReplicationDNA Replication

Protein SynthesisProtein Synthesis

The way you look (The way you look (phenotypephenotype) is an ) is an expression of your genes (expression of your genes (genotypegenotype).).

GenesGenes code for your cells to make code for your cells to make specific proteins. specific proteins. ProteinsProteins make up make up your hair, muscle, skin, enzymes, etc.your hair, muscle, skin, enzymes, etc.

When a specific protein is needed, a When a specific protein is needed, a chemical signal is sent to your DNA to chemical signal is sent to your DNA to begin the process of making that begin the process of making that protein.protein.

Two steps: Two steps: TranscriptionTranscription and and TranslationTranslation

TranscriptionTranscription

TranscriptionTranscription – from the words – from the words “across” and “write”, making a “across” and “write”, making a copy of the gene needed from the copy of the gene needed from the DNA template.DNA template.

The The promoterpromoter is a site on the DNA is a site on the DNA that tells the RNA polymerase that tells the RNA polymerase where to begin copying the gene.where to begin copying the gene.

Messenger RNAMessenger RNA (mRNA, (mRNA, ribonucleic acid) is created.ribonucleic acid) is created.

mRNA is complimentary, with mRNA is complimentary, with thyminethymine being replaced by being replaced by uraciluracil. .

TranscriptionTranscription

After transcription, the After transcription, the RNA is edited. RNA is edited. IntronsIntrons are pieces are pieces that are cut out, and that are cut out, and ExonsExons are pieces that are pieces that are kept.are kept.

Introns can allow for Introns can allow for genetic variability.genetic variability.

ProkaryotesProkaryotes have very have very few introns.few introns.

TranslationTranslation

After the mRNA is edited, it exits the After the mRNA is edited, it exits the nucleus through the nuclear pores.nucleus through the nuclear pores.

TranslationTranslation is the process by which is the process by which the mRNA is “translated” into a protein.the mRNA is “translated” into a protein.

Translation occurs in the cytoplasm on Translation occurs in the cytoplasm on the the ribosomesribosomes. (Ribosomes also have . (Ribosomes also have ribosomal RNA)ribosomal RNA)

mRNA is made up of mRNA is made up of codonscodons, three , three base-pair sections. Examples: AUG, base-pair sections. Examples: AUG, GCC.GCC.

TranslationTranslation

At the ribosome, codons are paired At the ribosome, codons are paired with with anticodonsanticodons..

Anticodons are complimentary bases Anticodons are complimentary bases which are part of which are part of transfer RNAtransfer RNA (tRNA).(tRNA).

Transfer RNA have Transfer RNA have amino acidsamino acids attached to them. Amino acids are attached to them. Amino acids are the building blocks of protein.the building blocks of protein.

At the At the ribosomeribosome, the amino acids are , the amino acids are placed in order based on the mRNA placed in order based on the mRNA code. As the protein chain grows, it code. As the protein chain grows, it is released.is released.

TranslationTranslation

The Genetic CodeThe Genetic Code

Mistakes in the Genetic Mistakes in the Genetic CodeCode

MutationsMutations – changes in the – changes in the genetic material due to mistakes in genetic material due to mistakes in copying, carcinogens, etc. copying, carcinogens, etc.

Gene mutationsGene mutations – changes in a – changes in a single genesingle gene

PointPoint mutations are changes in one mutations are changes in one or a few nucleotides. Examples: or a few nucleotides. Examples: Substitutions, insertions, deletionsSubstitutions, insertions, deletions

FrameshiftFrameshift mutations are insertions mutations are insertions or deletions that can affect the or deletions that can affect the entire message. The entire protein entire message. The entire protein can be ruined.can be ruined.

MutationsMutations

Chromosome mutationsChromosome mutations

When chromosomes When chromosomes are damaged, and are damaged, and large chunks are large chunks are altered, major altered, major problems can occur.problems can occur.

Fragile XFragile X is an is an example of a gene example of a gene mutation which mutation which causes a chromosome causes a chromosome end to break off.end to break off.

Gene RegulationGene Regulation

Genes are not always “on” and Genes are not always “on” and making proteins. They are making proteins. They are regulated.regulated.

An An operonoperon is a group of genes that is a group of genes that regulate the protein production.regulate the protein production.

Example: The lac operon is turned Example: The lac operon is turned off by repressors and turned on by off by repressors and turned on by the presence of lactose. Therefore, the presence of lactose. Therefore, lactaselactase is produced when is produced when lactoselactose needs to be broken down.needs to be broken down.