Unit 3: Genetics
Animations
Study Guide
Chapter 16
The Molecular Basis of Inheritance
Review
The physical structure of nucleic acids such as RNA or
was
discovered
by Watson and Crick from photos of
crystallography made by Rosalind
Franklin.
DNA is a double
, with the sugar-phosphate backbones on the
outside,
and pairs of
bases on the inside.
Weak
bonds form between the complementary base
pairs:
(A) always pairs with
(T), and
(C) always pairs with
(G).
The base-pairing rules are used for DNA
: each strand acts as a
for building a
strand.
The replication occurs in three phases:
,
, and
.
Initiation
begins at
of replication, where the two strands are unwound by
. The enzyme
adds a sequence of RNA
nucleotides at the
replication
.
Elongation
is the addition of more
to the primer by DNA
III.
Termination
occurs when
replaces the primer with DNA nucleotides, and DNA
joins together the fragments to complete the new strand.
Summary: DNA replication
Base-pairing is about 99.999% accurate, an error occurs about 1 in
base pairs. DNA
can "proofread" during polymerization and replace most incorrect
nucleotides.
Uncorrected DNA can be repaired by nucleotide
repair.
The overall error rate is about 1 in 10
nucleotides, or 99.99999999%
accurate.
Eukaryotic DNA is packaged with
proteins
to form
, which condense into visible chromosomes during mitosis.
The ends of linear eukaryotic chromosomes get
with each
round
of replication.
Each chromosome terminates in a
, that
postpones
the erosion of genes near the
ends.
Eukaryotic
cells contain the enzyme
to
lengthen
telomeres in gametes.
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