DNA Discovery - PowerPoint Presentation

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DNASlide2

Discovery

Griffith

First major experiment that led to DNA in 1928

Studied 2 strains of

Streptococcus

pneumoniae

Sugar coated strain (S) caused pneumonia

Non sugar coated strain (R) does not cause pneumoniaSlide3
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DNA Discovery cont

Avery -- 1944

Identified the particular macromolecule

Isolated DNA, Lipids and Protein from both R and S strains

Found the DNA release changed the R strain to deadly

Hershey and Chase

Supplied further evidence by using a

bacteriophage

(virus that attacks bacteria)

Need use of host to reproduceSlide5

DNA discovery cont

Hershey and Chase cont.

Used radioactive labeling to determine

Used sulfur and phosphorus to label

Proteins have sulfur, DNA has phosphorus

Further testing showed phosphorus labeled DNA inside bacteriaSlide6

People Involved

Chargaff

Discovered that the amounts of G and C were almost equal and the amounts of A and T were almost equal

Determined bonding order A-T G-CSlide7

Watson and Crick and the Discovery of DNA

The Start

Wilkins

Researcher at King’s College in London

Working with X-ray Diffraction

Technique that involved aiming x-rays at DNA

Rosalind Franklin

Joined the staff at King’s College in 1951

Took famous Photo 51Slide8

DNA structure cont

Photo 51 indicated that DNA is a double helix

Watson and Crick used this

i

mage to determine spacing of

b

ases.Slide9

DNA Structure Cont

Important features

1) two outside strands consist of alternating deoxyribose and phosphate

2) cytosine and

gaunine

pair with 3 hydrogen bonds

3) adenine and thymine pair with 2 hydrogen bondsSlide10

DNA StructureSlide11

DNA cont

Made of nucleotides

Sugar (deoxyribose)

Phosphate group

Nitrogen Base

Adenine (purine)

Guanine (purine)

Cytosine (pyrimidine)

Thyomine (pyrimidine)Slide12

Chromosome Structure

Length of a human chromosome is 51 million to 245 million base pairs.

If a DNA strand of 145 million base pairs was stretched out it would measure 5 cm

Average cell size: 10-100 um. (.001 to .01 cm)

How does it fit?Slide13

Chromosome cont

DNA is tightly coils around histones

Phosphates negative charged attracted to histones positive charge

Creates Nucleosomes

Nucleosomes group together

into chromatin fibers

Chromatin fibers super coil

to make chromosome.Slide14

Replication

Semi conservative replication

DNA

seperates

Both strands serve as templates

Unwinding process:

DNA

Helicase

– responsible for unwinding DNA (unzips)

RNA

primase

adds RNA primer

Base pairing

DNA polymerase

Adds appropriate nucleotides

Always added to the 3’ endSlide15

DNA ReplicationSlide16

DNA replication cont

2 strands being replicated at once

Leading Strand

Elongated and copied as DNA is unwound

Built continuously 3’ – 5’

Lagging Strand

Elongates away from the replication fork

Built discontinuously in small fragments called Okazaki fragments

Reconnected by DNA

Ligase

Each fragment is about 100-200 nucleotides longSlide17

More replication

DNA is replicated continuously, but often in many places at once.

When DNA polymerase comes to an RNA primer, it removes the primer and fills in the place with DNA.

After primer is removed, DNA

ligase

re-joins the segmentsSlide18

Eukaryotes V Prokaryotes

Eukaryotes (complex organisms) separates and replicates in multiple sections simultaneously

DNA is organized into genes.

Genes are segments of DNA that code for protein or RNA molecules.

A single molecule of DNA has thousands of genes.

Genes determine development and functionSlide19

Eukaryotic Cells

DNA is organized into genes.

Genes are segments of DNA that code for protein or RNA molecules.

A single molecule of DNA has thousands of genes.

Genes determine development and function.Slide20

BACTERIA

Prokaryotes (bacteria) DNA is found in a circular form called a plasmid

DNA is still replicated in both directions, but only at one point

Bacteria DNA is circular and attached to the inner membrane.

Go through binary fission.

Asexual reproduction that produces identical offspring.

First, DNA is copied

Second, the cell divides

Adds a new cell membrane, then pinches off.Slide21

RNA

RNA – Similar molecule and structure to DNA

Can go out of the cell

Use

Uracil

instead of Thymine

Types of RNA

mRNA – Messenger RNA

Used to take the genetic information from the DNA to the Ribosome

rRNA

– Ribosomal RNA

RNA that makes up the ribosomeSlide22

PreRNA

tRNA

– Transfer RNA

Use to gather amino acids and bring them to the ribosome for protein synthesis

Transcription

Synthesis of mRNA from DNA

DNA code is transferred into mRNA (T changed to U)

mRNA moves freely to the cytoplasmSlide23
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Intron

: Non-coding piece of mRNA

Exon

: Coding piece of mRNA

Introns

are cut out by restriction enzymes to form the final coding section of a geneSlide25
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Post RNA

Introns are removed and RNA must be prepared for leaving the nucleus

5’ cap added to protect RNA

Poly A tail added to protect

Also determines life of RNASlide27

Translation

DNA/mRNA is split into many sets of 3 nucleotides called

codons

Example DNA: ATCGGTAGCTTACGTGAG

ATC GGT AGC TTA CGT GAG

Example mRNA: UAGCCAUCGAAUGCACUC

UAG CCA UCG AAU GCA CUCSlide28

The mRNA is taken into a ribosome in the cytoplasm for protein synthesis

The Ribosome reads the

codons

(5’ to 3’) and call for the correct

tRNA

.

tRNA

consist of anti-

codons

(3 letter segments of RNA)

EXAMPLE: If the

codon

is AUG then the anti

codon

would be UACSlide29

Attached to the various

tRNAs

are amino acids

The amino acids are joined

by the ribosome

A large string of Amino

acids is a proteinSlide30

As the mRNA passes through the ribosome, the first complimentary

tRNA

strand moves into the P site of the ribosome

The second

tRNA

will follow shortly into the A site of the ribosome

The ribosome then joins the amino acids in P and A together

The

tRNA

in the P site moves out and the A moves into the P

The cycle continues! Slide31
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