DNA

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Discovery Discovery of DNAof DNA• Many People

contributed to the discovery of DNA.

• Function: Carried genetic material

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Frederick GriffithFrederick Griffith Transformation

• In a series of experiments with Diplococcus pneumonia (bacterium responsible for pneumonia), witnessed a miraculous transformation.

•These experiments are recognized as the first in a series that lead to the conclusion that DNA is the carrier of genetic information, the genetic material.

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1928

Avery• Repeated Griffith’s experiment• Looking for “what” is being

transferred.• Used enzymes to break up

carbohydrates, lipids and proteins-transformation still took place

• Used enzymes to break up DNA-transformation did not happen

• Conclusions: genes are composed of DNA

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1944

Hershey and Chase• Studying virus• Wanted to know if proteins or DNA carried

genetic information.• Used radioisotopes as markers on the viruses

protein coat.• Allowed virus to infect the bacteria, and then

tested the bacteria for the markers.• Almost all of the bacteria has the marker.• Conclusion: The genetic material is DNA not The genetic material is DNA not

protein.protein.

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1952

Hershey- Chase experiment

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Rosalind Franklin•Used x-ray

diffraction to see that the DNA is twisted like a spiral staircase

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1952

Erwin Chargaff• Discovered that the

amt. of adenine = amt. Thymine & the amt. of cytosine = amt. of cytosine.

• True in all organisms tested.

• At this point, he still didn’t know why.

• This is called Chargaff’s Rule.

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1952

Watson and Crick

“Put it all together”

Developed the structure of DNA that we know today. 99

1953

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Shape of Shape of DNADNA1.1.Double HelixDouble Helix..

-Twisted ladder or -Twisted ladder or spiral staircasespiral staircase

2.2.Two strandedTwo stranded

3.3.Held together by Held together by hydrogen bondshydrogen bonds

4.4.Made of four Made of four NucleotidesNucleotides

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Remember:

• DNA is a nucleic acid.

• Nucleic acids are made of nucleotides.

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Structure of Structure of DNADNA

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Nucleotides• DNA is a long chain

of Nucleotides• There are four

nucleotide that make up DNA

• Each nucleotide has three parts: a sugar molecule, a phosphate group, and a nitrogenous base.

• The sugar is Deoxyribose

• There are four bases

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4 Bases

• Adenine• Guanine• Cytosine• Thymine

• Purines• Pyrimidines

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Sides of Sides of the the “Ladder” “Ladder” are made are made up of up of sugar sugar and and phosphatphosphate.e.

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AdenineAdenine always pairs with always pairs with ThymineThymine

CytosineCytosine always pairs with always pairs with GuanineGuanine

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Would Thymine be able to pair up with Guanine?NO!!

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DNA DNA ReplicationReplication

• Before mitosis, the DNA must be replicated exactly.

• Each strand can be used to make the other strand.

• Many enzymes are involved.

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Chromosome Structure

• DNA is packed very tightly in the nucleus.

• Human nucleus has 1 meter of DNA!• Smallest human chromosome has 30

million base pairs.• A chromosome has DNA and protein-

chromatin.• Tiny sections of DNA are called genes

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Steps:• The two

parent strands are unwound with the help of DNA helicases.

Replication Bubble

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2. DNA polymerase attached new nucleotides to the part strands

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• As the DNA strands unwind and separate, new complementary strands are produced by the hydrogen bonding of free DNA nucleotides with those on each parent strand.

• As the new nucleotides line up opposite each parent strand by hydrogen bonding, enzymes called DNA polymerases join the nucleotides .

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DNA replication website

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How a protein How a protein is madeis made

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DNA codes for all of DNA codes for all of the cell proteins.the cell proteins.

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• DNA is located in the Nucleus• Proteins are made on the ribosomes.• DNA makes a copy (send a message) called “mRNA”

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Two Steps of Protein Synthesis1. Transcription 2. Translation

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Transcription• During transcription a copy of the DNA

is made…the copy is called messenger RNA or mRNA. The mRNA takes the code to the ribosome.

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DNA vs. RNA

• Double Stranded

• AGTC

• Deoxyribose

• NEVER!

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• Single Stranded

• AGUC

• Ribose

• YES!

• During transcription the DNA unzipped and RNA nucleotide are paired up with the DNA bases.

• Website

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•Once the mRNA copy is made, it can go to the ribosome to be translated.

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• Remember….Proteins are made out of amino acids.

• There are 20 different amino acids.

• 3 bases code for each amino acid.

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• Once the mRNA get to the ribosome, the protein can be assembled.

• Transfer RNA brings the amino acids to the ribosome.

• Website 4422

• The three letter code on the mRNA is called a codon.

• The three letter code on the tRNA that is matched up with the mRNA is called an anticodon.

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Mutations•A sudden change in the genetic

code is called a mutation.•Most mutations have little or no

effect on the organism.•Mutations can be spontaneous or

may be caused by environmental factors called mutagens.

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Mutations in DNA usually occur through one of two

processes:1- DNA damage from

environmental agents such as ultraviolet light (sunshine), nuclear radiation or certain chemicals.

2- Errors that occur when a cell replicates its DNA in preparation for cell division.

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A substitution mutation is a

simple change in a single base of

the gene sequence. 4848

Frame-shift MutationsFrame-shift Mutations In a frame-shift

mutation, one or more bases are deleted or

inserted, the equivalent of adding or removing letters in a sentence.

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In an________ mutation, and entire section of DNA

is ____________.

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Review of DNA MutationsHarmful, Helpful, Neutral

• SubstitutionsSubstitutions• FrameshiftFrameshift

– DeletionsDeletions– InsertionsInsertions

• Causes:Causes:– MutagensMutagens

•UV lightUV light•RadiationRadiation•Free radicalsFree radicals•Chemicals Chemicals (ex: substances in tobacco products)(ex: substances in tobacco products)

– Replication errorsReplication errors

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Which of the Which of the following is the following is the

correct base-pairing correct base-pairing rule for DNA?rule for DNA?

A A-U; C-GB A-G; T-CC A-T; G-CD A-C; T-G

DNA TECHNOLOGY

forensicsforensics

agricultu

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agricultu

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DNA fingerprinting

DNA fingerprinting

medicine medicine

industryindustry

genetic recombinationgenetic recombination..

There are many uses for DNA technology. Police labs use DNA technology to identify people through a process known as DNA fingerprinting.

Today, researchers use recombinant DNA technology to analyze genetic changes. They cut, splice together, and insert the modified DNA molecules from different species into bacteria or another type of cell that rapidly replicates and divides. The cells copy the foreign DNA right along with their own DNA. An example of this is the gene for human insulin. When the gene is transferred into a bacterium, the bacterium will use the “recombined” genetic code to produce human insulin. This is how human insulin is mass produced.

Not only does genetic engineering have applications in medicine and the environment, it also has uses in industry and agriculture. Sheep are used in the production of alpha-1 antitrypsin, which is used in the treatment of emphysema. Goats are also producing the CFTR protein used in the treatment of cystic fibrosis.

In the plant world, the buds of cotton plants are vulnerable to worm attacks. The buds of a modified cotton plant resist these worms, resulting in increased cotton production.These gene insertions are ecologically safer than pesticides. They affect only the targeted pest.

Plant biologists have used DNA technology to produce plants with many desirable traits. These include increased disease resistance, herbicide resistance, and increased nutritional content.

Scientists today have developed Scientists today have developed genetically altered bacteria. genetically altered bacteria. Among them are strains of bacteria Among them are strains of bacteria that that

eat up oil spillseat up oil spillsmanufacture alcohol and other manufacture alcohol and other chemicalschemicalsprocess minerals. process minerals.

There is concern about possible risks There is concern about possible risks to the environment and the general to the environment and the general population as genetically engineered population as genetically engineered bacteria are introduced.bacteria are introduced.

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