1

DNA and RNAReplication, Transcription,

and Translation

2

Genetic Controversy

Two schools of thoughta. Some said protein was materialb. Some said DNA was material

How was the controversy settled? - The scientific experiments of Griffith, Avery, Hershey and Chase

3

Griffith and Transformation

- 1928 - England - Trying to develop a vaccine against pneumonia causing bacteria - Two strains - S(smooth) and R(rough)

4

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 pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

5

RESULTS

- Showed that heat killed S strain

and live R strain would kill mice - Something was “transforming” the R strain to an S strain - Called it transformation - What was the material?

6

Oswald Avery - 1944 - Wanted to identify Griffith’s transforming material

- Used two enzymesa. protein killingb. DNA killing

- Showed that no transforming took

place when DNA “killed”

7

D. Hershey and Chase - 1952

- Working with a bacteriophage

- Virus that infects bacteria

- Made of only two thingsa. protein coatb. DNA (genetic) core

8

9

Bacteriophage with phosphorus-32 in DNA

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

Phage infectsbacterium

No radioactivity inside bacterium

Radioactivity inside bacterium

Hershey and Chase

10

Recap:Was DNA or protein

injected?

- DNA has phosphorus - Protein has sulfur - Used radioactive phosphorus 32P and radioactive sulfur 35S

- Let virus infect bacteria - New viruses full of 32P

DNA was being injected!

11

12

The Components and Structure of DNA

1. Called deoxyribonucleic acid

2. Long and thread-like (twisted)

3. Many subunits linked together

4. Subunits called nucleotides

5. 1000’s in a chain-like structure

13

The structure of a nucleotide

1. Phosphate group - same in all

2. Five carbon sugara. deoxyribose sugar

3. Nitrogenous base - 4

different ones that name the nucleotide

14

Nitrogenous Bases

1. Are different in each nucleotide

2. Names of the four basesa. adenine (A)b. guanine (G)c. thymine (T)d. cytosine (C)

Two classes of bases

A. purines1) large

double ring

2) A & G

B. pyrimidines1) small

single ring

2) T & C

15

Purine and Pyrimidine Structure

16

H. Chargaff - 1949

- Studying the amounts of bases in DNA of living things

- His results showed that:a. A always = Tb. C always = G

- Called Chargaff’s rule

- Also called the base pair rule

17

The molecule is completed…

- Franklin and her X-ray

diffraction picture showed

a helix - Watson and Crick addsthat it is a double helix

with bases in the middle - Called it a “spiral

staircase”

- Strands are complements of each other

- Think of a step laddera. “sides” are alternating

sugar and phosphate

groups

b. “rungs” are base pairs

1) A = T2) C = G

18

Nucleotide

Sugar-phosphate backbone

Hydrogen bonds

Adenine

Thymine

Cytosine

Guanine

19

Chromosomes and DNA Replication

A. DNA Can Make Copies of Itself 1. Process called replication 2. Done during S phase 3. Needed for new cells 4. DNA unwound using helicases 5. Hydrogen bonds broken between bases 6. DNA polymerase puts new nucleotides in place (A to T and C with G) 7. New copy just like original

20

From Genes To ProteinsFrom Genes To Proteins

DNADNADouble-Double-strandedstranded

DeoxyriboseDeoxyriboseThymineThymine

RNARNASingle-Single-strandedstranded

RiboseRiboseUracilUracil

21

RNA RNA (ribonucleic acid)(ribonucleic acid)

3 forms of RNA3 forms of RNA mRNA (messenger)mRNA (messenger) tRNA (transfer)tRNA (transfer) rRNA (ribosomal)rRNA (ribosomal)

RNA is used to take the information in DNA RNA is used to take the information in DNA and make proteins (and make proteins (gene expressiongene expression))

2 stages of gene expression2 stages of gene expression TranscriptionTranscription TranslationTranslation

22

During gene expression, During gene expression, the info in DNA is first the info in DNA is first transcribedtranscribed as mRNA and as mRNA and then then translatedtranslated via tRNA via tRNA and used to build a and used to build a protein.protein.

The Big Idea…

23

1. 1. TranscriptionTranscription: :

making mRNAmaking mRNAfrom DNA to from DNA to carry carry information information

to the to the ribosomes.ribosomes.

From Genes To Proteins…

24

- ALL organisms - ALL organisms have a genetic have a genetic code made of code made of three nucleotide three nucleotide sequences called sequences called codons. codons.

- Codons - Codons correspond to correspond to particular AA particular AA and stop and stop signals. signals.

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

The Genetic Code

26

QuickTime™ and a decompressor

are needed to see this picture.

The Genetic Code

From Genes To Proteins…

2. 2. TranslationTranslation: : Using tRNA to build Using tRNA to build proteins from the proteins from the information in information in mRNA.mRNA.

- Each tRNA - Each tRNA molecule carries an molecule carries an amino acid to the amino acid to the ribosomes, by ribosomes, by matching its matching its anticodon to a anticodon to a specific codon from specific codon from the mRNAthe mRNA

http://www.youtube.com/watch?http://www.youtube.com/watch?v=NJxobgkPEAov=NJxobgkPEAo

28

GENETIC MUTATIONSGENETIC MUTATIONS

MutationsMutations (gene or chromosomal) (gene or chromosomal)

Changes in DNAChanges in DNA Effect depends on where Effect depends on where mutation occurs (body or sex mutation occurs (body or sex cell) & what type of mutationcell) & what type of mutation

Can be helpful, harmful, or Can be helpful, harmful, or neutralneutral

29

Different Types of Gene Different Types of Gene MutationsMutations

SubstitutionsSubstitutions = UGU to UGC = UGU to UGC Effect depends on translationEffect depends on translation

InsertionsInsertions = nucleotides added = nucleotides added

DeletionsDeletions = nucleotides deleted = nucleotides deleted

Transposons=Transposons= DNA segments move DNA segments move spontaneously from one location to spontaneously from one location to another in the same DNA moleculeanother in the same DNA molecule

30

Ex. Ex.

THE CAT ATE THE RATTHE CAT ATE THE RAT

(meaningful)(meaningful)

Deletion of C =Deletion of C =

THE ATA TET HER ATTHE ATA TET HER AT

(meaningless)(meaningless)

31

Types of Chromosomal Types of Chromosomal MutationsMutations

Deletions (whole or part deleted)Deletions (whole or part deleted)

Duplications (extra copies of parts)Duplications (extra copies of parts)

Inversions (reverses parts of Inversions (reverses parts of chromosomes)chromosomes)

Translocations (parts break off and Translocations (parts break off and relocate)relocate)

32

Causes of Mutations?Causes of Mutations?

SpontaneousSpontaneous

Mutagens (come from Mutagens (come from environment)environment) UV lightUV light ChemicalsChemicals Carcinogens (cancer causing)Carcinogens (cancer causing)