Chapter 4 – Genes & DNAChapter 4 – Genes & DNA

Section 1 – What Does Section 1 – What Does DNA Look LikeDNA Look Like

GenesGenes Gives instructions for building and Gives instructions for building and

maintaining cellsmaintaining cells Able to be copied so cell can divideAble to be copied so cell can divide

NucleotidesNucleotides DNA made of subunits called nucleotidesDNA made of subunits called nucleotides Each nucleotide has:Each nucleotide has:

SugarSugar PhosphatePhosphate BaseBase

4 Nucleotides due to 4 different bases4 Nucleotides due to 4 different bases Adenine (A)Adenine (A) Thymine (T)Thymine (T) Guanine (G)Guanine (G) Cytosine (C)Cytosine (C)

Key PlayersKey Players

Erwin ChargaffErwin Chargaff 1950s biochemist1950s biochemist Chargaff’s RulesChargaff’s Rules

Amount of adenine = amount of thymineAmount of adenine = amount of thymine Amount of guanine = amount of cytosineAmount of guanine = amount of cytosine

Rosalind FranklinRosalind Franklin X-ray diffraction to see DNA moleculesX-ray diffraction to see DNA molecules DNA has a spiral shapeDNA has a spiral shape

Key Players Cont’dKey Players Cont’d James Watson & Francis CrickJames Watson & Francis Crick

Used Franklin’s imagesUsed Franklin’s images DNA is a long, twisted ladderDNA is a long, twisted ladder Made the double helix modelMade the double helix model

James Watson

Francis Crick

DNA StructureDNA Structure

Double helix - twisted ladder modelDouble helix - twisted ladder model Sides of ladderSides of ladder

Alternating sugar and phosphate partsAlternating sugar and phosphate parts

Rungs of ladderRungs of ladder Pairs of basesPairs of bases A + T OR C + GA + T OR C + G

Copying DNACopying DNA

Replication – making copies of DNAReplication – making copies of DNA Base pairs are complementaryBase pairs are complementary

Each base only pairs with its corresponding Each base only pairs with its corresponding basebase

AT or CGAT or CG

For example:For example: ATGCA only pairs with TACGTATGCA only pairs with TACGT

ReplicationReplication DNA molecule is DNA molecule is

“unzipped” down the “unzipped” down the middlemiddle Ladder rungs are cut in halfLadder rungs are cut in half

Complementary Complementary nucleotides are added to nucleotides are added to the 2 strandsthe 2 strands

1/2 of DNA molecule is 1/2 of DNA molecule is “old” DNA and 1/2 is “old” DNA and 1/2 is “new” DNA“new” DNA

Proteins in the cell control Proteins in the cell control the replication processthe replication process

Section 2 – How DNA Section 2 – How DNA WorksWorks

Every cell in your body has about 2 Every cell in your body has about 2 meters or 6 feet of DNA!meters or 6 feet of DNA!

Packaging DNAPackaging DNA Wound around proteins – histonesWound around proteins – histones Coiled into strandsCoiled into strands Bundled into chromosomesBundled into chromosomes

Gene – a string of nucleotidesGene – a string of nucleotides

Genes & ProteinsGenes & Proteins

DNA read in 1 direction from one end to otherDNA read in 1 direction from one end to other Amino acidsAmino acids

Groups of 3 bases give code to form amino acidGroups of 3 bases give code to form amino acid For example – CCA is code for amino acid prolineFor example – CCA is code for amino acid proline 20 different amino acids20 different amino acids Human body can only produce 10Human body can only produce 10 Other 10 come from our food – Other 10 come from our food – Essential amino Essential amino

acidsacids Proteins – long strings of amino acids linked Proteins – long strings of amino acids linked

togethertogether

Proteins & TraitsProteins & Traits

Proteins have several functionsProteins have several functions Chemical triggersChemical triggers Messengers for processes in a cellMessengers for processes in a cell

Proteins help determine traitsProteins help determine traits Genes are the codes for making proteinsGenes are the codes for making proteins

RNA & Making ProteinsRNA & Making Proteins RNA – RNA – Ribonucleic acidRibonucleic acid

Molecule that helps make proteinsMolecule that helps make proteins Messenger RNA – mRNAMessenger RNA – mRNA

Copy of a Copy of a piecepiece of DNA of DNA Moves from nucleus into cytoplasmMoves from nucleus into cytoplasm Goes into ribosome 3 bases at a timeGoes into ribosome 3 bases at a time

Transfer RNA – tRNATransfer RNA – tRNA translates RNA message into proteintranslates RNA message into protein Specific tRNA molecules have certain amino acids attachedSpecific tRNA molecules have certain amino acids attached tRNA matches up with complementary bases on mRNAtRNA matches up with complementary bases on mRNA Amino acids released by tRNAAmino acids released by tRNA Amino acids link up to produce a proteinAmino acids link up to produce a protein

tRNA

mRNA

amino acid

protein

DNA strand copied in nucleus

MutationsMutations Mutation – change in the Mutation – change in the

nucleotide-base sequence in nucleotide-base sequence in the gene or DNA moleculethe gene or DNA molecule

•3 kinds of mutations3 kinds of mutations

• Substitution – wrong base usedSubstitution – wrong base used

• Insertion – extra base added Insertion – extra base added inin

• Deletion – base left outDeletion – base left out

Do Mutations Matter?Do Mutations Matter?

Mutation – change in a gene or DNAMutation – change in a gene or DNA 3 possible outcomes3 possible outcomes

Improved traitImproved trait No changeNo change Harmful traitHarmful trait

Most errors are fixed by proteinsMost errors are fixed by proteins Some become part of genetic codeSome become part of genetic code Mutation in sex cells are passed on to Mutation in sex cells are passed on to

offspringoffspring

How do Mutations How do Mutations HappenHappen

Regularly due to random errors during Regularly due to random errors during replicationreplication

Mutagens – physical or chemical agents that Mutagens – physical or chemical agents that cause mutationscause mutations High energy radiation – x-ray, UV ray, cosmic rayHigh energy radiation – x-ray, UV ray, cosmic ray AsbestosAsbestos Cigarette smokeCigarette smoke

Harmful mutations – sickle cell disease, Harmful mutations – sickle cell disease, cancerscancers

Genetic EngineeringGenetic Engineering

Manipulating individual genes in organismsManipulating individual genes in organisms Create new productsCreate new products

Bacteria engineered to produce drugsBacteria engineered to produce drugs Plants or animals bred for superior qualitiesPlants or animals bred for superior qualities

Gene therapyGene therapy Replace defective genes with healthy genesReplace defective genes with healthy genes

Are there possible dangers?Are there possible dangers?

Genetic IdentificationGenetic Identification

DNA Fingerprinting – identify unique DNA Fingerprinting – identify unique pattern in each person’s DNApattern in each person’s DNA

Crime scenesCrime scenes Family relationshipsFamily relationships Trace hereditary diseaseTrace hereditary disease

CloningCloning Clone is an exact copy of another organisms DNAClone is an exact copy of another organisms DNA Identical twins are genetic clonesIdentical twins are genetic clones 3 types of cloning3 types of cloning

Somatic cell nuclear transfer – put DNA from one cell Somatic cell nuclear transfer – put DNA from one cell into another cell to create an exact copy of the original into another cell to create an exact copy of the original organismorganism

DNA cloning – put a piece of DNA into another DNA cloning – put a piece of DNA into another organism. Fluorescent DNA from jellyfish into bacteria organism. Fluorescent DNA from jellyfish into bacteria to make the bacteria glowto make the bacteria glow

Therapeutic cloning – produce human embryos for Therapeutic cloning – produce human embryos for medical research using stem cellsmedical research using stem cells

Scientific and ethical issues surrounding cloningScientific and ethical issues surrounding cloning