DNADNA

Ch 8Ch 8

Standard 4Standard 4

History of DNAHistory of DNA

1.1. Hershey & ChaseHershey & Chase proved DNA is the proved DNA is the

genetic material found in cellsgenetic material found in cells

Erwin ChargaffErwin ChargaffDNA compositionDNA composition

all 4 bases not in equal quantity bases present in characteristic ratio

A = T ~ 40% G = C ~ 60%

varies from species to species

Rosalind FranklinRosalind Franklin took x-ray photos of took x-ray photos of DNA that showed itDNA that showed it’’s 3-D structures 3-D structure

Watson & CrickWatson & Crick

made the first 3-D model of DNA in 1953 made the first 3-D model of DNA in 1953

Won the Nobel Prize in 1962Won the Nobel Prize in 1962

Why is DNA important?Why is DNA important?

It stores genetic information in cells It stores genetic information in cells & this information is used to make & this information is used to make

proteinsproteins

DNA StructureDNA Structure

DNA is a double helix (twisted ladder)DNA is a double helix (twisted ladder)

DNA is DNA is made of made of

nucleotidesnucleotides

3 nucleotide parts

1. Deoxyribose sugar

2. Phosphate

3. Nitrogen base

- adenine (A)

- thymine (T)

- guanine (G)

- cytosine (C)

Base Pair Rules:Base Pair Rules:

- Adenine binds only with Adenine binds only with Thymine (AThymine (AT)T)

- Cytosine binds only with Cytosine binds only with Guanine (CGuanine (CG)G)

----Straight letters together----Straight letters together

Curvy letters together-------Curvy letters together-------

• Deoxyribose SugarsDeoxyribose Sugars & phosphatesphosphates make up the sides of the ladder

• Phosphodiester bondsPhosphodiester bonds hold the sugars to the phosphates

• Nitrogen basesNitrogen bases are held together by hydrogen bondshydrogen bonds

A T = 22 hydrogen bonds

G C = 33 hydrogen bonds

• The Base pairsBase pairs make up the steps (rungs) of the DNA Ladder

Base Pair ShapeBase Pair ShapePurinePurine

Double ring basesDouble ring bases

(Adenine or Guanine)(Adenine or Guanine)

PyrimadinePyrimadine

Single ring basesSingle ring bases

(Thymine or Cytosine)(Thymine or Cytosine)

Difference in their shapes causes the DNA to twist

Each Base Pair is made of one Purine and one Pyrimadine

Hydrogen BondsHydrogen Bonds

H

H

H H

O

O

H

C

C

C C

N

N

C

ThymineH

N

H

H

N

C C

C

C

N

N H

N

C

Adenine

H

O

N

H C

C C

N

N

C

Cytosine

H

H

H

N

C C

C

C

N

N H

N

C

Guanine

NH

O

H

Adenine

GuanineCytosine

Thymine

PracticePracticeIf one side of DNA has this base If one side of DNA has this base

sequence, what does the other side sequence, what does the other side have?have?

A T G G A C T A CA T G G A C T A C

T A C C T G A T GT A C C T G A T G

DNA ReplicationDNA Replication

How Does DNA Replicate How Does DNA Replicate

Process discovered by Process discovered by Meselson & StahlMeselson & StahlSemi-conservative replicationSemi-conservative replication

Half old strand, Half new strandHalf old strand, Half new strand

Anti-parallelAnti-parallel New strands are made in opposite directionsNew strands are made in opposite directions

When does DNA replicate?When does DNA replicate? During the cell cycle before mitosis & meiosisDuring the cell cycle before mitosis & meiosis

Why does DNA replicate?Why does DNA replicate?

So new So new cells cells

will have will have their their

own copy own copy of DNAof DNA

Six Steps of DNA ReplicationSix Steps of DNA Replication1)1) DNA is unzipped by the DNA is unzipped by the HelicaseHelicase enzyme enzyme

(breaks hydrogen bond)(breaks hydrogen bond)

2)2) DNA polymeraseDNA polymerase enzyme binds DNA enzyme binds DNA begins attaching complimentary nucleotidesbegins attaching complimentary nucleotides

3)3) Same thing happens on the other side, but in Same thing happens on the other side, but in opposite directionopposite direction

4) 4) Bonds ReformBonds ReformHelicase reforms Hydrogen bonds Helicase reforms Hydrogen bonds

(between bases)(between bases)Ligase reforms Phosphodiester Ligase reforms Phosphodiester

bonds bonds (sugar & phosphate)(sugar & phosphate)5) 5) DNA polymeraseDNA polymerase ““proofreadsproofreads””

checking each strand for errors. checking each strand for errors. 6) DNA rewinds itself into 6) DNA rewinds itself into two two

identical double helix strandsidentical double helix strandsLetLet’’s watchs watch

http://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Lecture.html

Once more time….. Once more time…..

Protein SynthesisProtein Synthesis

DNADNA RNA RNA Proteins Proteins

DNADNA

1.sugar=deoxyribose1.sugar=deoxyribose

2.bases = A, C, G, T2.bases = A, C, G, T

3.double strand3.double strand

4.stays in nucleus4.stays in nucleus

RNARNA

1.sugar = ribose1.sugar = ribose

2.Bases=A, C, G,U2.Bases=A, C, G,U

3.single strand3.single strand

4.leaves nucleus4.leaves nucleus

3 Types of RNA3 Types of RNA1.1. mRNAmRNA made from DNA in nucleusmade from DNA in nucleus

““messengermessenger””

2.2. tRNAtRNA brings amino acids to the brings amino acids to the ribosomes; found in cytoplasmribosomes; found in cytoplasm

““transfertransfer””

3. 3. rRNArRNA part of the ribosome; part of the ribosome; this is where proteins are madethis is where proteins are made

““ribosomalribosomal””

DNA vs. RNADNA vs. RNA

TRANSCRIPTION TRANSCRIPTION How RNA is made from DNAHow RNA is made from DNA

Transcription StepsTranscription Steps1.1. DNA is unzipped by HelicaseDNA is unzipped by Helicase

all genes start with the code all genes start with the code ““TACTAC””

2.2. RNA polymerase adds RNA RNA polymerase adds RNA nucleotides to the DNA strand nucleotides to the DNA strand

3.3. mRNA is complete when it reaches a mRNA is complete when it reaches a stop code on DNAstop code on DNA

4.4. mRNA then leaves nucleus & carries mRNA then leaves nucleus & carries code into the cytoplasmcode into the cytoplasm

DNA never leaves the nucleusDNA never leaves the nucleus

DonDon’’t Confuse t Confuse Replication with Transcription!Replication with Transcription!

DNA ReplicationDNA Replication

A – TA – T

C – GC – G

G – CG – C

T - AT - A

TranscriptionTranscription

A – UA – U

C – GC – G

G – CG – C

T - AT - A

Transcribe this……Transcribe this……

| | | | | | | | | | I

TranslationTranslation Decoding the MessageDecoding the Message

StepsSteps1.1. mRNA leave nucleus and enters ribosome mRNA leave nucleus and enters ribosome

2.2. mRNA codons read & tRNA brings matching mRNA codons read & tRNA brings matching amino acid to the ribosome amino acid to the ribosome

3.3. Amino acids are strung together like beads on Amino acids are strung together like beads on a necklacea necklace

4.4. Amino Acids are held together by peptide Amino Acids are held together by peptide bondsbonds

5.5. 1000 or more Amino Acids = protein1000 or more Amino Acids = protein

Use the Use the ““Genetic CodeGenetic Code””

Convert mRNA 3 letter Convert mRNA 3 letter

groupings called groupings called codonscodons

Example:Example:

AUG= Methylamine (Start)AUG= Methylamine (Start) The The mRNAmRNA Code tells us Code tells us

what what amino acidamino acid each each codon codes for.codon codes for.

WHEN WE DECODE DNAWHEN WE DECODE DNA

Transcribe and Translate this Transcribe and Translate this DNA StrandDNA Strand

without looking at your noteswithout looking at your notes

TACAGTACCATAATCTACAGTACCATAATC

NOW, Label the DNA, mRNA, tRNA, rRNA

Which part is transcription

Which is translation ?

DNADNA TACAGTACCATAATCTACAGTACCATAATCmRNAmRNA AUGUCAUGGUAUUAGAUGUCAUGGUAUUAG tRNAtRNA UACAGUACCAUAAUCUACAGUACCAUAAUCrRNArRNA MET-SER-TRP-TYR-STOPMET-SER-TRP-TYR-STOP

DNA RNA Protein

A, T, C, G A, U, C, G Amino Acids

Transcription Translation

Double Strand Single Strand Codons & Anti-codons

In The Nucleus In Cytoplasm

Is it all DNA?Is it all DNA? Entire chromosome is made of DNAEntire chromosome is made of DNA

Humans~ 3 billion base pairsHumans~ 3 billion base pairs Only part of the DNA codes for GenesOnly part of the DNA codes for Genes

GeneGene: The DNA that codes for a Protein. There are different parts of the chromosomeThere are different parts of the chromosome Exons and IntronsExons and Introns

Introns are cut out before translationIntrons are cut out before translationExons are left, and get Exons are left, and get TranslatedTranslated to make to make

ProteinsProteins

GENETIC VARIATIONGENETIC VARIATION

There are some variations in genes ~every 1350th bp (average) Known as polymorphisms “different

forms” Different forms of genes are called

alleles Effects

How well the protein works. EX: Melanin How the protein interacts with another

protein or substrate. EX: Enzymes

Proteins do the work of the cellProteins do the work of the cellProteins are chains of amino Proteins are chains of amino

acids. acids. The amino acids are coded The amino acids are coded

by the bases that make up by the bases that make up that genethat gene

Each gene codes for a Each gene codes for a different protein.different protein.

Gene ExpressionGene ExpressionAll cells within an organism have the All cells within an organism have the

same DNA and genes.same DNA and genes.What makes cells different from each What makes cells different from each

other is that different genes are turned other is that different genes are turned on and turned off in different cells.on and turned off in different cells. Ex: Pigment in eyes or skinEx: Pigment in eyes or skinEx: Keratin in nails or hairEx: Keratin in nails or hair

How can organisms be different How can organisms be different from each other if their DNA is from each other if their DNA is made of the same nucleotides?made of the same nucleotides?

•Two individuals DNA are different because of the Two individuals DNA are different because of the order of nitrogen basesorder of nitrogen bases

•The more closely related two organisms are, the The more closely related two organisms are, the more alike the order of nucleotides in their DNA will more alike the order of nucleotides in their DNA will be.be.