Franklin’s photo below proved model on left to be correct for DNA

WatsonCrick

Franklin

Wilkins

Pauling

Most important scientific paper in

Biology in last 100 years

First time DNA double helix seen in print

By Watson and Crick,

1953

2 April 1953MOLECULAR STRUCTURE OF NUCLEIC ACIDS

A Structure for Deoxyribose Nucleic Acid 

“We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of

considerable biological interest.”

From the original Watson and Crick article – first published “double helix” diagram

Proof of double helix

Summary of a few people involved with DNA:

Pauling and Corey – “telephone pole” model for DNA

Franklin – x-ray photos proved Pauling wrong

Wilkins – gave x-rays to Watson and Crick

Watson, Crick, Wilkins – Nobel Prizes for DNA structure

Watson & Crick Pauling and Corey

Rosalind Franklin Lise Meitner

First to discover structure of DNA

First to describe the physics to split the atom

Nobel Prize

Otto Hahn

Nobel Prizes

06

Basic Terms:DNA Nucleotide (monomer)

Subcomponents of nucleotide

sugar = deoxyribose

phosphate

bases – 4 of them

adenine (A) guanine (G)cytosine (C)thymine (T)

Nucleic Acid (polymer) – chain of nucleotides

Double helix – two chains of nucleic acids

PPPPP S S S S S

B B B B B

Nucleic acid (polymer) = chain of nucleotides (monomers)

Base = A, G, C, Tphosphate

sugar

Nucleotide (DNA or RNA)

B

SP

Nucleotide

Sugar phosphate base Nucleic acid

Double helix of nucleic acid

Base Pairing in DNA double helix

G-C

A-T

C-G

T-A

Only one base pairing is possible

(a)

Nucleosome = protein

+ DNA

DNA

Nucleosome

Protein

Nucleosomes

Fig. 13.11

Heterochromatin = inactive DNA = condensed

Euchromatin = active DNA = decondensed

Nucleosome

DNA

DNA Replication

DNA replication:

One double helix forms two identical double helices

Double Helix separates

New strands forms by base pairing

T A C A T G

A

T

G T

A C

Double helix separates

New nucleotides are added to the “old” or original DNA

nucleotides by base pairing with the

help of enzymes (not shown here)

Base pairing

Fig. 11.08

Mutant normal

Protein Synthesis

Protein gives life structure

Protein gives life function

Amino acid sequence gives protein its structure and function

Question: How is amino acid sequence determined?

Review

Gene = section of DNA that codes for amino acid sequence in a protein

Yeast Fruit Fly Worm Green Plant

6034 genes 13,061 genes 19,099 genes 25,000 genes

DNA

(m)RNA (copy)

Protein

Transcription

Translation

Overview

Retire already!!!

Base pairing is the genetic code

G-C

C-G

A-T

T-A

Sugar–phosphate backbone

DNA double helix separates

RNA nucleotides attach to DNA

Base pairing makes RNA copy of DNA

T replaced by U

Transcription = (m)RNA copy of one side of DNA

Transcription of mRNA

mRNA transcript

DNA

DNA

Codon = three RNA nucleotides = code for particular amino acid

Translation – conversion of mRNA nucleotide sequence (codons) into amino acid sequence of protein

Codon – group of three mRNA nucleotides

Each amino acid has at least one specific codon.

Alanine (Ala) has the codon GCU.

Glycine has the codon GGU

Tyrosine has the codon UAU

Codon = three RNA nucleotides = code for particular amino acid

review

Codon 1 Codon 2 Codon 3 Codon 4 Codon 5 Codon 6

Transcribed strand

Nontranscribed strand

3’

5’

TranscriptionDNA

Polypeptide

Translation

Translation = mRNA codons place amino acids in proper order

review

Human skin

UV-AUV-B

Sun screen

products

A C G T T C C A

T G C A A G G T

A C G T T C C A

T G C A A G G T

Thymine Dimer mutation DNA from U.V. light

UV light

Thymine dimer

Thymine dimer removed DNA repair enzymes

New DNA replaces hole

left by damaged DNA

Every cell in the body has the same DNA, but each specific type of cell makes proteins unique to those cells?

In other words every cell in your body has the exact same book of blueprints but only certain pages are read in certain cells.

http://www.dynamist.com/aaa/blastocyst.gif

Human embryos are totipotent = can become any cell in the human body

Why?

because it has DNA to make every cell in the body.

6 day old embryo is totipotent –

produce all cells

4 week old embryo is

pluripotent – produce most

cells

Salamander – many tissues can be regenerated if damaged.

http://www.luc.edu/depts/biology/dev/regen.gif

Salamander can re-grow new limbs because adult stem cells behave like embryonic cells.

Heterochromatin - inactive

Euchromatin - active

Nucleosome

DNA

Transcription of DNA to make new leg

Salamander leg cells damaged

Polymerase Chain Reaction

Polymerase Chain Reaction (PCR)

DNA replication

After 20 replications (a few hours) – over 1,000,000 helices formed

Small amount of DNA left at crime scene

Restriction enzyme (Eco R1) cuts DNA into fragments

DNA

DNA

Fragments (-) migrate through gel because of electric current

DNA fragments loaded into wells in gel (like Jell-O)

DNA fragments have (-) charge

(+) (-)

DNA fingerprinting – compares fragments of DNA

formed by restriction enzymes

Like a barcode

Father #1Baby’s DNA Father #2