AP Biology

D.N.A Once the bell rings, please take out

your pencil and prepare to finish the Unit 4 Genetics Test

You will have 20 minutes

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ANNOUNCEMENTS AP BIOLOGY MIDTERM IS ON FRIDAY

JANUARY 28th at 8 am

AP Biology 2006-2007

DNAThe Genetic Material

UNIT 8: MOLECULAR BIOLOGY

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Genes are on chromosomes Morgan’s conclusions

genes are on chromosomes but is it the protein or the

DNA of the chromosomes that are the genes? initially proteins were thought

to be genetic material… Why?

1908 | 1933

What’s so impressiveabout proteins?!

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The “Transforming Principle” 1928

Frederick Griffith Streptococcus pneumonia bacteria

was working to find cure for pneumonia

harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice

a substance passed from dead bacteria to live bacteria to change their phenotype “Transforming Principle”

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The “Transforming Principle”

Transformation = change in phenotypesomething in heat-killed bacteria could still transmit disease-causing properties

live pathogenicstrain of bacteria

live non-pathogenicstrain of bacteria

mice die mice live

heat-killed pathogenic bacteria

mix heat-killed pathogenic & non-pathogenicbacteria

mice live mice die

A. B. C. D.

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DNA is the “Transforming Principle” Avery, McCarty & MacLeod

purified both DNA & proteins separately from Streptococcus pneumonia bacteria which will transform non-pathogenic bacteria?

injected protein into bacteria no effect

injected DNA into bacteria transformed harmless bacteria into

virulent bacteria

1944

What’s theconclusion?

mice die

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1952 – Alfred Hershey & Martha Chase

Is it protein or DNA that is the genetic material?

Used bacteriophages (viruses that infect bacteria) to show that since DNA enters the bacterial cells, but protein doesn’t, DNA must be the genetic material

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Chargaff DNA composition: “Chargaff’s rules”

varies from species to species all 4 bases not in equal quantity

humans:

A = 30.9%

T = 29.4%

G = 19.9%

C = 19.8%

1947

That’s interesting!What do you notice?

RulesA = TC = G

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Early 1950s – Maurice Wilkins & Rosalind Franklin

Rosalind Franklin took X-ray crystallography diffraction photograph of DNA

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1953 – James Watson & Francis Crick

Constructed model of DNA as a double helix

Purine + pyrimidine for consistent width C-G 3 hydrogen

bonds A-T 2 hydrogen

bonds

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Late 1950s – Matthew Meselson & Franklin Stahl

Semi-conservative replication of DNA

Each new molecule of DNA (after DNA replication) contains 1 old and 1 new strand

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But how is DNA copied? Replication of DNA

base pairing suggests that it will allow each side to serve as a template for a new strand

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” — Watson & Crick

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proteinRNA

The “Central Dogma”

DNAtranscription translation

replication

Flow of genetic information in a cell

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The Structure of DNA

Double helix Each nucleotide is

made up of: Deoxyribose (sugar) A phosphate group A nitrogenous base

Adenine, guanine, cytosine, thymine

A, G = purines 2 carbon rings

C, T = pyrimidines 1 carbon ring

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The Structure of DNA

Base-Pairing Rules:

(Chargaff’s Rules) Guanine pairs with cytosine Thymine pairs with adenine

DNA strands are antiparallel They run in opposite

directions 5’ and 3’ ends

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DNA Replication

Big Picture: A new and identical

molecule of DNA is made, using the old one as a template

Occurs in the nucleus

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DNA Replication

DNA replication begins at the origin of replication, a special sequence of DNA

2 strands are separated by the enzyme, helicase, forming a replication bubble

Replication fork is formed at each end of the replication bubble

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DNA Replication

At replication fork, nucleotides “line up” with their complementary mates, according to the base-pairing rules

DNA polymerase III attaches the nucleotides to the exposed bases of the DNA strand

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DNA Replication: A Summary

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Leading Strand

DNA replication is different on the 2 strands

Along one template strand, the leading strand, DNA polymerase III just follows the replication fork (replicates continuously in one strand)

Polymerase III only synthesizes DNA from 5’ to 3’

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Lagging Strand

On the other strand of DNA, the lagging strand – DNA polymerase must work in the opposite direction of the replication fork

Short segments of DNA– Okazaki fragments – are made

Okazaki fragments are joined by DNA ligase

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DNA Proofreading DNA polymerase I proofreads each

nucleotide as it is added to the DNA strand

If there’s a mistake… it backs up removes the wrong nucleotide adds the right nucleotide

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Enzymes & Their Job in Replication

Helicases- unwind the DNA strand Single strand binding protein- holds the single

strands apart for replication. RNA – initiates DNA replication DNA Polymerase III- adds complementary bases to

3’ end of primer or new DNA strand. DNA Polymerase I- removes RNA primer & inserts

DNA nucleotides. (also proofreads) DNA Ligase- “sews” Okasaki fragments of lagging

strand together with covalent bonds.