These are Lectures of Basic molecular pharmacology presented by Dr.Omer Yahia In coordination with faculty of pharmacy university of Khartoum, al-Neelen medical research center, GENOM Professional training center and National center of Research (Ministry of science and communication).
4. Eukaryotes: (meaning “true nucleus”)
are organisms with cells within
which the genetic material
(DNA)is located in the nucleus.
Nucleus: is a discrete structure
bounded by a nuclear envelope .
It is selectively permeable and
has pores about 20 to 80 nm in
diameter that allow certain
materials to move between the
nucleus and the cytoplasm
Chromatin is the stainable material
in a cell nucleus: DNA and
proteins.
Cell and Molecular Biology concepts and experiments 6 edition page 10
6. Histones and nonhistones are two major
types of proteins associated with DNA
in chromatin.
Histones: are small basic proteins with a net
positive charge that facilitates their
binding to the negatively charged DNA.
Five main types of histones are associated
with eukaryotic nuclear DNA: H1, H2A,
H2B, H3, and H4.
Nonhistones : Include proteins that play a
role in the processes of DNA replication,
DNA repair, transcription (including
gene regulation), and recombination.
o A number of anti-cancer drugs
(e.g., Zolinza) are currently being
tested that act by inhibiting HDAC
enzymes .
Cell and Molecular Biology concepts and experiments 6 edition page 520
7. Ploidy
• Ploidy : is the number of copies of
chromosomes.
• Diploidy: Presence of two copies of
genes per cell, one from each
parent.
• Haploidy: one copy of each gene
per cell rather than two as in most
eukaryotic cells
• Aneuploidy: A condition in which a
cell has an abnormal number of
chromosomes that is not a multiple
of the haploid number.
Diploid
MEIOSIS
Haploid
Aneuploidy (Photo) chromosome 21 trisomy in Down syndrome)
Cell and Molecular Biology concepts and experiments 6 edition page 596
9. Mitochondrion
• Mitochondrion is inherited
maternally.
• It has an Important role in
sequestering and releasing
Ca++.
• It is responsible for cellular
respiration and energy
production.
• It carries important biochemical
reactions (e.g. aerobic glycolysis)
• It mediates intrinsic apoptotic
path way
• (Picture)A premature-aging
phenotype caused by increased
mutations in mtDNA.
Mitochondrial DNA
T. Strachan, A. Read - Human Molecular Genetics 4ed(2011) page 258
10. Mitochonderial DNA vs. Nuclear DNA
T. Strachan, A. Read - Human Molecular Genetics 4ed(2011) page 260
12. …... •G1 Phase: cell growth and
progress for mitosis.
• S Phase: DNA replication and
chromosome duplication.
•G2 Phase: cell grows and
carries out normal
metabolism;
organelles duplicate.
M Phase: Mitosis.
Cell and Molecular Biology concepts and experiments 6 edition page 261
How cell cycle work
13. Stages of mitosis
• Interphase: Technically not part
of mitosis, but rather
encompasses stages G1, S, and
G2 of the cell cycle which prepare
the cell for mitosis.
• Prophase: Chromatin in nucleus
condense; nucleolus disappears.
Centrioles begin moving to
opposite ends of the cell and
fibers extend from the
centromeres.
• Metaphase: Spindle fibers align
the chromosomes along the
middle of the cell nucleus. This
line is referred to as the
‘metaphase plate.’
• Anaphase: The paired
chromosomes separate at the
kinetochores and move to
opposite sides of the cell. Motion
results from the physical
interaction of polar microtubules.
14. Stages of mitosis (cont.)
• Telophase: Chromatids arrive at
opposite poles of cell, and new
membranes form around the
daughter nuclei. The
chromosomes disperse.
• Cytokinesis: Results when a fiber
ring composed of a protein called
actin around the center of the
cell contracts, pinching the cell
into two daughter cells, each with
one nucleus.
15. Mitosis
• Mitosis is the process by which a cell duplicates the chromosomes in its cell
nucleus in order to generate two, identical, daughter nuclei.
• It is followed immediately by cytokinesis, which divides the nuclei, cytoplasm,
organelles and cell membrane into two daughter cells containing roughly equal
shares of these cellular components.
• Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle.
• Mitosis is a normal cellular process necessary to sustain life, but its deregulation in
one form or another is found in all cancer cells.
• Mitosis can often become abnormal by the change in, or absence of, the normal
cell cycle checkpoints.
17. Cell cycle checkpoints
• Cell cycle checkpoints are points in the cell cycle which act to ensure correct
transmission of genetic information during cell division. These checkpoints
look for abnormalities within the cycle, specifically chromosomal aberrancy.
• Checkpoints take place towards the end of each phase of mitosis and must be
passed before the cell can get clearance to enter into the next stage of mitosis.
• If errors are found during checkpoints, the cell acts quickly to correct them,
arresting cell growth and not proceeding with mitosis until the error has been
fixed.
• If these errors cannot be fixed, the cell normally undergoes apoptosis, or
programmed cell death.
19. Factors regulate cell cycle
• Cyclin - dependent kinases (CDK): enzymes that control progression of
cells through cell cycle.
• Cyclins : are proteins required to activate cyclin dependent kinases to
form an active cyclin-CDK complex (e.g. MPF )
• APC/SCF: complexes: they are two classes of multi subunits complexes
that function as ubiquitin ligasis . These complexes recognizes the
protein to be degraded and linked it to the polyubiquitin chain , that
ensure their destruction by Proteosome
Cyclins:(named because their concentration increases and decreases in a regular pattern through the cell cycle)
24. What is Cancer?
• Cancer is the deregulation of normal cellular processes. Cells that have
been transformed tend to proliferate in an uncontrolled and deregulated
way and, in some cases, to metastasize (spread).
• Cancer is not one disease, but a group of more than 100 different and
distinctive diseases.
• Cancer can involve any tissue of the body and take on many different
forms in each area.
25. Continue…..
• Cancer cells become deregulated in many different ways.
• One way: Mutations in one or more mitotic checkpoints allow the cell to
move from one phase of mitosis to another unchecked.
• Another way: Mutations in cellular machinery itself so that mitotic errors
are not properly detected/repaired, and the cell is allowed to move
through mitosis unchecked.
26. Continue…..
• The cell is allowed to move through the cell cycle and grow unchecked,
and more mutations are accumulated over time that extend past the cell
cycle to the cellular machinery itself.
• These mutations, in combination with the genetic mutations accrued
through abnormal mitotic progression, eventually cause the cell to be
completely deregulated in its growth and proliferation.
• It becomes unstoppable and even immortal.
28. Molecular Pharmacology
• Check points defects as
anticancer target:
1. Spindle defects: (by using anti-
microtubule drugs)
2. growth conditions: (by using
anti proliferative factors e.g.
DNA damage, ionizing
radiation and UV)
3. Replication faults: (by using
anti-metabolites) .
4. Chromosome catenation: (by
using topoisomerase
inhibitors )
29. Antimitotic Agents
• Antimitotic agents: Anti-tumor
agents that inhibit the function of
microtubules through the binding of
their subunits or through direct
cessation of their growth.
• What are microtubules (MTs)?
Protein polymers formed by a-Tubulin
and B-tubulin heterodimers that play
an important role in critical cell
functions such as movement,
phagocytosis and axonal
transport. They also play a key role in
the formation of the mitotic spindle
apparatus and cytokinesis at the end
of mitosis.
• In normal cells, microtubules are
formed when a cell starts dividing
during mitosis. Once the cell
stops dividing, microtubules are
broken down or destroyed.
• The crucial involvement of MTs in
mitosis makes them a prime
target for anti-cancer agents.
36. • Prevent the growth of cancer cells by affecting
microtubules.
• Overall, they encourage microtubule formation, then
they stop the microtubules from being broken down
so that the cells become so clogged with
microtubules that they cannot continue to grow and
divide. This results in the cell’s arrest in mitosis.
• Eventually, cell DEATH by apoptosis.
Taxol
37. Complicating Factors
• B-tubulin mutations which inhibit the binding of taxanes to
the correct place on the microtubules; this renders the drug
ineffective.
• In addition, some resistant cells also display increased aurora
kinase, an enzyme that promotes completion of mitosis .
41. Vinca Alkaloids
• The Vincas work through their ability to bind to the
B- tubulin subunit of microtubules, blocking their
ability to polymerize with the a- tubulin subunit to
form complete microtubules.
• This causes the cell cycle to arrest in metaphase
because, in absence of an intact mitotic spindle,
duplicated chromosomes cannot align along the
division plate.
• The ultimate fate of such cells is to undergo
apoptosis.
42. Complicating Factors
• Resistance to the Vinca alkaloids comes in the form of cross-
resistance due to the structural similarity of the compounds
(multidrug resistance)
• Because of the heavy concentration of microtubules in the brain
and the drug’s disruption of this, patients treated with Vinca
alkaloids can experience severe neurotoxicity.
43. Another examples :
• Colchicine :Colchicine is an alkaloid derived from the autumn crocus
(Colchicum autumnale). It inhibits mitosis by inhibiting microtubule
polymerization. While colchicine is not used to treat cancer in humans, it is
commonly used to treat acute attacks of gout . It poison (PMN; Polymorph
nuclear Leukocytes ) that mediate joint inflammation .
• Podophyllotoxin: Podophyllotoxin and Podophyllin, derived from the may
apple plant, are used to treat viral skin infections.
• Griseofulvin: derived from a Penicillium mold, is an antifungal drug.
Spindle defects
Mitochondria (singular: mitochondrion) are large organelles surrounded by a double membrane-the inner membrane is highly convoluted. Mitochondria play a crucial role in processing energy for the cell. They also contain DNA that encodes some of the proteins that function in the mitochondrion and some components of
the Mitochondrial protein synthesis machinery.
Chloroplasts—large, triplemembraned, chlorophyll-containing organelles involved in photosynthesis Chloroplasts also contain DNA that encodes some of the proteins that function in the chloroplast and some components of the chloroplast protein synthesis machinery.
For example, messenger RNAs, which are translated in the cytoplasm to produce polypeptides, are synthesized in the nucleus and pass through the pores to reach the cytoplasm. In the opposite direction, enzymes for DNA replication, DNA repair, and transcription, and the proteins that associate with DNA to form the chromosomes are made in the cytoplasm and enter the nucleus via the pores.
Checkpoints at different points in the cell cycle are control points at which the cell cycle is arrested if there is damage to the genome or cell cycle machinery. This allows the damage to be repaired or, if it is not, the cell is destroyed. These processes are necessary to prevent the possibility of damaged cells dividing in an unprogrammed way, that is, from becoming cancerous.
The G1/S checkpoint. This checkpoint is especially important, because a cell that passes the G1lS boundary is committed to mitosis. The checkpoint is controlled by Cdk2/cyclin E. Entry into S phase is blocked when there is unrepaired DNA damage. Irreparable damage leads to apoptosis. Within S phase there are additional checkpoints at which DNA damage prevents new origins of replication from becoming active.
The G2/M checkpoint. Cells are blocked from entering mitosis unless DNA replication and the repair of any damage are complete. Entry into mitosis depends on the activation of Cdk1 / cyclin B by the phosphatase Cdc25C. Incomplete DNA replication or unrepaired damage generates a signal that activates inhibitors of Cdc25C, thus preventing Cdk1 from becoming active.
The spindle (or mitotic) checkpoint: Separation of chromatids at anaphase of mitosis is triggered by the anaphase-promoting complex (APC) or cyclosome. This multi protein ubiquitin ligase degrades cyclins A and B, and (indirectly) the cohesin glue that holds sister chromatids together. Kinetochores that are not attached to spindle microtubules secrete a signal that inhibits the APC. If this Signaling is defective, chromatids can start to separate before all of them have been correctly attached to spindle fibers, and there is then no way of ensuring that exactly one chromatid of each chromosome goes into each daughter cell.