lecture 1 cell cycle new

Molecular Pharmacology course lecture No.1

Cell CycleDr.Omer Yahia ElhusseinB.sc. Pharmacy.M.sc. Molecular Medicine.

Where do we find DNA?

Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

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

What do you now about epigenetic ?

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

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

What do you know a bout mitochonderia?

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

Mitochonderial DNA vs. Nuclear DNA

T. Strachan, A. Read - Human Molecular Genetics 4ed(2011) page 260

When do cell divide?

…... •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 261How cell cycle work

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.

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.

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.

Cell Cycle regulation

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.

Cell cycle check points

• Cell cycle shows 3 major check points :

a) G1 / S check point : (restriction point) Is environment favorable ?

B) G2 / M check point: Is all DNA replicated ? Is environment favorable ?

C) Metaphase to Anaphase transition : Are all chromosomes attached to

spindle ?

Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin

Cummings.

Cell cycle control

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)

Check Point Regulation

At the G1toS checkpoint, two different G1 cyclin Cdk complexes form, resulting in activation of the kinases.The kinases catalyze a series of Phosphorylationsof cell cycle Control proteins, affecting the functions of those proteins and leading, therefore, to transition into the S phase.

PRB: Retino Plastoma Protein. It is a tumor suppressor protein associated with a familial (inherited) eye’s cancer .Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin

Cummings.

How do check points prevent cancer ?

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.

Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

P53 is a tumor suppressor protein; have a molecular importance in many cancers

To BE CONTINUED…….15 MIN. BREAK

Cell Cycle and cancer

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.

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.

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.

Molecular Pharmacology

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 )

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.

Spindle defects

sciencedirect.com

Spindle defects

• 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

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 .

Spindle defects

Vinca alkaloids and its role in cancer treatment

Catharanthus roseus is known as the common or Madagascar periwinkle

Originally native to island of Madagascar.

Spindle defects

Vincristine and Vinblastine Inhibit mitosis in metaphase by binding tubulin

Spindle defects

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.

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.

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

discussion

Thank you

Three apples;Adam’s,Newton’s, And Steve Jobs