DNA is the genetic code, Instructions for heredity, Components of genes, Director of protein synthesis A type of nucleic acid A type of organic compound A polymer {a compound made of repeating

subunits}

Discovery of the DNA double helixDNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.(1952)

C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)

•DNA had specific pairing between the DNA had specific pairing between the nitrogen bases:nitrogen bases:

ADENINEADENINE – – THYMINETHYMINE

CYTOSINECYTOSINE - - GUANINEGUANINE

•DNA was made of DNA was made of 22 long stands of long stands of nucleotides arranged in a specific way nucleotides arranged in a specific way called the called the “Complementary Rule”“Complementary Rule”

DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.

A molecule of DNA is made up of millions of tiny subunits called Nucleotides.

Each nucleotide consists of:1. Phosphate group2. Pentose sugar3. Nitrogenous base

Phosphate

PentoseSugar

NitrogenousBase

The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.

There are four types of nitrogenous bases.

A

Adenine

T

Thymine

G

Guanine

C

Cytosine

Pyrimidines are single ring bases.

Purines are double ring bases.

11

C

C

C

C

N

N

OO

N

C

C

C

C

N

N

N

N

N

C

Each base will only bond with one other specific base.

Adenine (A)Thymine (T)

Cytosine (C)Guanine (G)

Form a base pair.

Form a base pair.

A=T – double hydrogen bond

G C – triple hydrogen bond

Nucleotide (3 chemical groups) Sugar – deoxyribose

contains 5 Carbon atoms

Phosphate group A base (A, T, G, C)

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

Major Features of DNA Double Helix:  1.    Two polynucleotide chains coil together to

form right-handed helix.  2.    The two chains are anti-parallel; both run from

5’ to 3’ but their orientations are opposite. 3.    The nitrogen bases of opposite chains pair to

one another and form H bonds: G – C and A – T  

4. The base pairs stack on each other and located on the inside of the helix.

5. Each complete turn of DNA is 3.4nm long and contains 10 bases. 6. Each turn along the molecule contains one major

grove and one minor grove. 

AdenineAdenine must pair with ThymineThymine

GuanineGuanine must pair with CytosineCytosine

Their amounts in a given DNA molecule will be about the sameabout the same.

G CT A

CG

H-bonds

T A

Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

G

G

A

T

T

A

A

C

T

G

C

A

T

C

To crack the genetic code found in DNA we need to look at the sequence of bases.

The bases are arranged in triplets called codons.

A G G - C T C - A A G - T C C - T A GT C C - G A G - T T C - A G G - A T C

A gene is a section of DNA that codes for a protein.

Each unique gene has a unique sequence of bases.

This unique sequence of bases will code for the production of a unique protein.

It is these proteins and combination of proteins that give us a unique phenotype.

DNA must be copied

The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:

A-T, G-C

•Each strand of the original DNA serves as a template for the new strand

Semiconservative Model:

1. Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

Parental DNA

DNA Template

New DNA

DNA has a lagging strand 3’-5’ and a leading strand 5’-3’

The 5’ end matches with a 3’ end in a double helix

DNA replication occurs every 20 minutes in E. coli (widely used to reproduce DNA)

Copying DNA molecule Each DNA strand

(double helix) unzips itself

Happens before cell division (mitosis and meiosis)

Done in PCR (polymerase chain reaction) to make a lot of the same DNA (mass replication) for analysis through fingerprinting.

Protein

DNA

Gene

Trait

DNA from a single human DNA from a single human cell extends in a single cell extends in a single thread for almost 2 meters thread for almost 2 meters long!!!long!!!

It contains information It contains information equal to some 600,000 equal to some 600,000 printed pages of 500 words printed pages of 500 words each!!! each!!! (a library of about 1,000 books)(a library of about 1,000 books)

The average human has 75 trillion cells.

The average human has enough DNA to go from the earth to the sun more than 400 times.

DNA has a diameter of only 0.000000002 m.

30

The earth is 150 billion mor 93 million miles from the sun.

Electrophoresis separates DNA and Proteins using electricity through a porous material.

Movement of the DNA and Protein is a function of size.

•DNA speed is based on size.

•Smaller is Faster and Bigger is slower.

It’s like McDonalds on a busy weekend.

AutoradiographyRadioisotopes

Intercalating Dyes Ethidum Bromide