Nucleotides
I. nucleotides: sub units „³ DNA A. Phosphate group B. 5-carbon
sugar
molecule (deoxyribose) C. nitrogen base 1. Adenine 2. Guanine 3.
Thymine 4.
Cytosine Chargaff „³ base pairing rule: 1 = 3 and 2 = 4 II.
Maurice Wilkins
and Rosalind Frankilin „³ 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. „³ 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 „³ twisting
prevented D. Replication fork : where double
helix separates 1. DNA
polymerases: enzymes that move along each strand „³
adding nucleotides to the
exposed bases. 2. Proofreading „³ 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.