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Biology DNA
1.1 The Structure of DNA
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Paula Koch
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RNA
Ribonucleic acid
Nucleic acids
DNA
RNA
DNA
Deoxyribonucleic acid
Nucleotide
A
sugar
,
phosphate
, and
nitrogen
base joined together
DNA
Double stranded
Bases
:
A
,
T
,
C
,
G
Coiled around
histones
to form
chromosomes
Uncoiled
DNA is called
chromatin
RNA
Single
stranded
Bases:
A
,
U
,
C
,
G
Base Pairing Rule
A always pairs with
T
(complementary base pairs)
C always pairs with
G
(complementary base pairs)
In RNA, A pairs with
U
(complementary base pairs)
Human chromosomes
46
chromosomes arranged in
23
pairs
Homologous
pairs:
1
maternal and
1
paternal chromosome with the same genes in the same locus
Each gene has
2
alleles,
one
from each parent
DNA replication
is the process of copying DNA to make
2 identical
copies before
cell division
Chromosome
Coiled
DNA
, made up of
2 chromatids
joined at the
centromere
DNA Replication
1. Step 1:
Helicase
separates the
double strand
of
DNA
into
2 strands
2. Step 2:
Free nucleotides
join with the
template strands
to their
complementary bases
3. Step 3:
DNA Polymerase
joins the
sugar-phosphate molecules
to the new
nucleotides
together to form the
backbone
DNA replication in eukaryotic cells
Occurs in the
nucleus
DNA replication is
'semi-conservative'
as each new copy contains
one old
/
template DNA strand
and
one new strand
DNA replication
in
prokaryotic cells
Occurs in the
cytoplasm
DNA runs
antiparallel
, with one strand running
5'
to
3'
and the other
3'
to
5'
DNA polymerase adds nucleotides in a
5'
to
3'
direction, leading to a
leading
and
lagging
strand during DNA replication
