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Cellular and Molecular Biology
Topic 4: Central dogma
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Nucleic acids
are
polymeric
macromolecules
forming the chemical basis for the
transmission
of
genetic trait
Two main classes of nucleic acids
deoxyribonucleic
acid (
DNA
)
ribonucleic
acid (
RNA
)
Nucleotide
Monomer made of
5-carbon sugar
,
nitrogenous base
, and phosphate group
Nucleoside
Sugar
+
Base
Nitrogenous bases
Adenine
(A)
Guanine
(G)
Thymine
(T)
Cytosine
(C)
Uracil
(U)
Purines
Adenine (A) and Guanine (G)
Pyrimidines
Thymine (T),
Cytosine
(C) and
Uracil
(U)
Base pairing in DNA
G
≡ C (3
H-bond
)
A =
T
(2
H-bond
)
Total concentration of purines equals the
concentration
of
pyrimidines
in DNA
bonds between
nucleotides
are the key to the specificity of all
nucleic acid-based
tests used in the molecular laboratory
GC rich region
Higher melting temperature
(Tm)
AT rich region
Lower
Tm
Nucleotide
Nucleoside with a
phosphate
group attached at carbon atom
5'
Polynucleotide
Two
nucleotides
covalently bonded with a
3'-5'
phosphodiester bond
General structure of DNA
Two
polynucleotide
strands coiled in a
double helix
Complementary
and
anti-parallel sugar-phosphate
backbones
Bases oriented towards central axis, forming
H-bonds
and
stacking interactions
Major DNA conformations
A-form
B-form
Z-form
Differences between DNA conformations
Helix sense,
base pairs
per turn, diameter of
helix
, distance between adjacent base pairs, rotation per base pair
Functions of DNA
Store
genetic
information
Direct
RNA
transcription
Contain instructions for
development
,
survival
, and reproduction
Denaturation
of DNA
Loss of the helical structure (
double
strand to
single
strand)
Methods to denature DNA
Thermal
denaturation
Alkaline
method
Other
denaturing
agents
Hypochromic
effect
Decreasing
ability to absorb
light
Hyperchromic effect
Increasing ability to
absorb light
Melting
temperature (Tm)
Temperature at which
half
of the
DNA
molecules are denatured
Renaturation of DNA (Annealing)
Rewinding of denatured
DNA
strands to form
double helix
Central Dogma of
Molecular
Biology
Genetic
information flows from DNA to RNA to
protein
Transcription
DNA template to
RNA
by
RNA Polymerase
Translation
RNA
to
protein
Naked DNA is roughly
2
nm in diameter, but the
length
of a stretched single molecule may be up to several dozens of centimetres
DNA compaction in prokaryotes and eukaryotes
Prokaryotes:
nucleoid-associated
proteins
Eukaryotes: DNA wrapped around
histone
proteins to form
nucleosomes
and chromatin
Kingdoms of Life
Monera
Protista
Fungi
Plantae
Animalia
Prokaryotes are classified into
Bacteria
and
Archaea
Differences between prokaryotic and eukaryotic cells
Presence of
membrane-bound
organelles,
nuclear
envelope, cytoskeleton, and complex internal structures in eukaryotes
Nuclei
Eukaryotic
nuclei are ~
10
μm in diameter and contain 46 chromosomes (2× 3.3G base pairs), consisting of ~2.2 m of DNA in total
If DNA is stored naked inside a
nucleus
or a cell, it would become
tangled
Prokaryotes
Nucleoid-associated
proteins resemble the functions of the
histone
proteins found in eukaryotes
Eukaryotes
Double helix DNAs are wrapped around spools of histone proteins to form
nucleosomes
, which package together to produce
chromatin
Kingdoms of Life
Monera
Bacteria
Archaebacteria
A classification for living organisms can be
5-Kingdom
or
6-Kingdom
Prokaryotic and eukaryotic cells have differences and exceptions
Eukaryotes include
animal
and
plant
cells
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