Molecular base of
Inheritance DNA
Premedical - biology
Proof that DNA is carrier of
genetic information - 1928
• Griffith‘s experiment - Bacterial transformation
• Recombination of bacterial genetic material by
transmission of naked DNA into recipient cells
• Avery, McLeod, McCarthy (1944) – the same effect
with isolated DNA
Streptococcus pneumonie – S strain and R strain
1953 - James D. Watson a Francis Crick
used x-ray diffraction data collected by Rosalind Franklin
• proposed the double helix as the threedimensional
structure of DNA
• the main role is the long-term storage of information
• ability to manage its own replication
• DNA manage the development of biochemical, anatomical
and physiological and behavioral traits of all known living
organism
Monomers - nucleotides: organic molecule called a
nitrogenous base, a pentose (five-carbon sugar) and
phosphate group
Two families of nitrogenous bases: pyrimidines, purines
Pyrimidine has a six-membered ring of cabron and nitrogen;
Cytosine (C), Thymin (T) and Uracil (U)
Purins the six-membered ring fused to a five-membered ring
Adenin (A), Guanin (G)
Bases - Adenine, guanine and cytosine are found in both
types of nucleic acid. Thymine is found only in DNA and
uracil only in RNA.
Sugars - Ribose in nucleotides of RNA
Deoxyribose in DNA
Nucleoside - nitrogenous base joined to sugar
Nucleotides are bonded by covalent bonds called
phosphodiester linkages between phosphate of one
and the sugar of the next.
Two polynucleotides spiral around imaginary axis to form
double helix
Two polynucleotides are held
by hydrogen bonds between
the paired bases and
by van der Waals attractions
between the stacked bases.
DNA molecules - thousands or millions of base pairs
Adenine always pairs with thymine,
Guanine always pairs with cytosine.
Two strands of double helix
are complementary and
are antiparallel.
In preparation for cell division,
each strand serves
as a template to order nucleotides
into a new complementary strand
= Semiconservative replication
Cell cycle
Replication
Origins of replication
•
circular bacterial chromosome has a single origin
•
Replication starts in many places (Eukaryotes)
simultaneously and asynchronnous
•
DNA replication proceeds in both direction
•
At each end of replication bubble is replication fork
•
DNA polymerase – addition of nucleotides only to the
free 3‘ end, new strand can elongate only in one direction
(5´→ 3´) + and correction of mistakes
A new strand in direction 5´→ 3´ leading strand
The other strand – lagging s. is synthetized
discontinuously - Series of segments = Okazaki fragments
enzyme DNA Ligase joins them
Primase RNA primers
Helicase
Correction of mistakes
• One /10 000bp in replication
• DNA polymerase
• special enzymes
• continuous monitoring and repair
• nucleotid excision repair
Human chromosomes:
22 pairs of autosomes
1 pair of gonosomes (heterochromosomes)
• Karyotype: men 46, XY, women 46, XX
Euchromatin
• despiralized in interphase
• spiralized in mitosis
• contains structural genes
Heterochromatin
– repetitive sequences
Constitutive – centromers of all
chromosomes
Facultative - structurally
euchromatin, but behaves as
heterochromatin
= one of
two X chromosomes in
women = genetically inactive
=
X chromatin (sex
chromatin= Barr body)
Ultrastructure of chromosomes
• DNA
• Histones – basic proteins
H1,H2A, H2B,H3,H4
• Non-histone proteins
The whole length DNA cca 2 m
human genome contains cca 30 000
structural genes
Organization of chromatin in interphase
Nucleosome:
DNA double helix + histone core
• Histone core = octameres of two copies of H2A,
H2B, H3, H4
• DNA double helix is winded around the core
• spacer segment DNA between two nucleosomes is
free or associated with H1 histone (appearance of
beads on a string)
Condensation of chromatin into chromosomes
• String of nucleosomes is coiled into
solenoid (6 nucleosomes in each
turn)
• Solenoid is packed into loops attached
to the nonhistone protein scaffold
(Laemli loops)
• nonhistone protein scaffold with loops
is coiled into spiral structure of
chromatides
Karyotype of woman 46,XX – G banding
Karyotype of man - 46,XY – G bands
Chromosome / in metaphase
metacentric
submetacentric
p
telomere
centromere
q
acrocentric
satellite
sat. stalk (NOR)
chromatids
p = short arm
q = long arm
NOR = nucleolus organizer region (rRNA genes)
Telomeres
• multiple repetitions of one short nucleotide
sequence TTAGGG [human]
• telomeric DNA protects genes from being eroded,
protects from fusions
• telomerase special enzyme
• reduction of number of telomeres after each
replication
• abnormal activity of telomerase in tumor cells
Nucleotides
• are structural units of RNA and DNA
• serve as sources of chemical energy: ATP, GTP
• participate in cellular signaling: cAMP, cGMP
• are incorporated into important cofactors of
enzymatic reactions: CoA, FAD, FMN, and NADP
ATP powers cellular work
• multifunctional nucleotide used in cells as a coenzyme
• "MOLECULAR UNIT OF CURRENCY" of intracellular
energy transfer
• produced by photophosphorylation and cellular
respiration
• used in many cellular processes, including biosynthetic
reactions, motility, and cell division.
ATP - closely related to one type of nucleotide found in
nucleic acid [base adenine bonded to ribose]
• in RNA one phosphate group is attached to the ribose
• chain of three
phosphate groups
attached to ribose
Hydrolysis - inorganic phosphate leaves ATP
became adenosine diphosphate - ADP
The reaction is exergonic
High-energy phosphate bonds
Cyclic adenosine monophosphate (cAMP)
is a second messenger important in many biological
processes. cAMP is derived from adenosine triphosphate
(ATP) and used for intracellular signal transduction in
many different organisms.
Guanosine-5'-triphosphate (GTP)
• a substrate for the synthesis of RNA during transcription
and a source of energy for protein synthesis
• a source of energy or an activator of substrates in
metabolic reactions
Cyclic guanosine monophosphate - cGMP
• is derived from guanosine triphosphate (GTP)
• a second messenger much like cyclic AMP
• activating intracellular protein kinases
Nicotinamide adenine dinucleotide,
abbreviated NAD+
• is a coenzyme found in all living cells
• NAD+ is involved in redox reactions, carrying electrons
from one reaction to another.
cofactor is a non-protein
chemical compound that is
bound to a protein and is
required for the protein's
biological activity
Nicotinamide adenine dinucleotide
phosphate (NADP+)
• is used in anabolic reactions
• NADPH is the reduced form of NADP+
NADP+ differs from NAD+ by the
presence of an additional
phosphate group on the 2' position
of the ribose ring in NADP+
Flavin adenine dinucleotide - FAD
• is a redox cofactor involved in several important reactions
in metabolism
• FAD can exist in two different redox states.
• The molecule consists of
a riboflavin moiety (vitamin B2)
bound to the phosphate group of
an ADP molecule.
Flavin mononucleotide (FMN)
• is a biomolecule produced from riboflavin (vitamin B2)
• acts as prosthetic group of various oxidoreductases
including NADH dehydrogenase.
tightly-bound cofactors termed
prosthetic groups
Coenzyme A (CoA, CoASH, or HSCoA)
• is a coenzyme, notable for its role in the synthesis and
oxidation of fatty acids
• the oxidation of pyruvate in the citric acid cycle
Alternate DNA structures
DNA exists in many possible conformations that include
A-DNA, B-DNA, and Z-DNA forms.
only B-DNA and Z-DNA have been directly observed in
functional organisms.
From left to right, the structures of A, B and Z DNA
Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson,
Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings
Publishing Company, 1996 –2010.