DNA Structure

By the early 1900s it was known that the chromosomes carry the genetic (hereditary) information

Chromosomes consist of DNA (deoxyribonucleic acid)

I. Chemical Structure of DNANucleotide:1. Thousands of repeating units that make up the DNA (DNA is a polymer)

a phosphate group

a deoxyribose molecule (5-carbon sugar)

a nitrogenous baseadenine, thymine, guanine, cytosine

(There are four different types of nucleotides, depending on which of the four bases is present- A, T, C, or G)

II. The Watson-Crick Model of the Structure of DNADNA consists of two chains of nucleotides in a ladder-like structure which is twisted(Double Helix)

James Watson & Francis Crick:Used data of M.H.F. Wilkins and Rosalind Franklin, early 50sWilkins and Franklin studied the structure of DNA crystals using X-rays.The X pattern suggested the structure of DNA was a helix.Distance between the two backbones of DNA is constant along the length of the molecule

Used data of Erwin Chargaff, 1940s and early 50's

Chargaffs Rule: His data showed that in each species, the percent of A equals the percent of T, and the percent of G equals the percent of C.

Watson and Crick (1953)

Watson and Crick Model:The sides of the ladder are made up of alternating molecules of phosphate and deoxyriboseB. The bases make up the rungs of the ladder

C. The bases that make up the rungs of the ladder are attracted by a weak chemical bonds called hydrogen bonds

Base Pairing Rule

Adenine (A) pairs with Thymine (T)

Guanine (G) pairs with Cytosine(C)

Structure of DNA Animationshttp://207.207.4.198/pub/flash/24/menu.swfhttp://www.pbs.org/wgbh/nova/genome/dna.html#

Watson and Cricks Double Helix Model explained:

1. How replication of DNA during mitosis produces exact copies for the daughter cells

2. How DNA acts as a code, specifying how proteins are made by the cell

DNA Replication

The double-stranded DNA molecule separates or unzips along the weak hydrogen bonds between the base pairs

2. Free nucleotides that are present in the nucleus attach themselves by hydrogen bonds to the exposed bases(A-T, C-G)

3. Two identical strands form from each strand of DNA

DNA Replication Animationshttp://www.lewport.wnyric.org/JWANAMAKER/animations/DNA%20Replication%20-%20long%20.html

http://www.johnkyrk.com/DNAreplication.html

If the order of bases along one strand of DNA is AGGTTACTGCAC what is the order of bases on the complementary strand?

TCCAATGACGTG

How Does DNA Act As A Code?

The order of bases on the DNA strand instructs the ribosomes how to synthesize proteins

Gene: portion of DNA that codes for the production of a specific polypeptide

Polypeptide: building block of a protein

In terms of decreasing size:Nucleus Chromosome Gene DNA