Nucleotides Essay, Research Paper

I. nucleotides: sub units ?? DNA

A. Phosphate group

B. 5-carbon sugar molecule (deoxyribose)

C. nitrogen base

1. Adenine

2. Guanine

3. Thymine

4. Cytosine

Chargaff ?? base pairing rule: 1 = 3 and 2 = 4

II. Maurice Wilkins and Rosalind Frankilin ?? X-ray diffraction photos of DNA molecule

- DNA molecules: tightly coiled helix and composed of two or three chains of nucleotides

III. Chargaff builds a model of the double helix: ??a spiral staircase?? of 2 strands of nucleotides twisting around a central axis.

A. alternating sugar and phosphate units

B. purine and pyrimidines paired up

- A can only form hydrogen bonds with T

- C can only for ?? ?? with G.

?? 2 strands that are complementary to each other

IV. Copying of DNA:

A. Replication: process of synthesizing a new strand of DNA.

B. Helices: open up the double helix by breaking the hydrogen bonds that link the complementary bases.

C. Two strands separated: additional enzymes and proteins attach to the individual strands and hold them apart ?? twisting prevented

D. Replication fork : where double helix separates

1. DNA polymerases: enzymes that move along each strand ?? adding nucleotides to the exposed bases.

2. Proofreading

?? one old and one new DNA strand

8.3 The Structure of a Gene

- genes hold info specifying how to build particular proteins

- affects the phenotype of an individual because of the activity of the protein that it specifies

- DNA encoded info that specifies particular proteins; each gene is made of a specific sequence of nucleotides

I. Genes in Eukaryotes

A. interruped by necleotides that have no coding info.

1. Introns:: noncoding sequences/ intervening

- must be removed

2. Exons :nucleotide segments that code for amino acids

-stitched together once all introns are removed

II. Multigene families: clusters of almost identical sequences; cells exist in multiple copies

A. Some are ??silent?? genes: don??t make protein

B. Some are only active during embryonic or fetal development

C. Some encode the two chains of