Cell Division: Mitosis and Meiosis

Mitosis

• Mitosis is a process where a cell divides to produce two identical daughter cells.
• It only occurs in somatic (body) cells, and takes up about 10% of the cell cycle.
• The other 90% is interphase, which is the preparation phase for mitosis, where the chromosome is in the form of chromatin.
• Interphase consists of Gap 0, Gap 1, S phase, and Gap 2.

Mitosis Phases

• Prophase: Chromatin condenses, nucleus disintegrates and spindle fibers form.
• Prometaphase: Nuclear envelope dissolves, centrosomes move to opposite poles, and spindle fibers finish forming.
• Metaphase: Microtubules attach to chromosomes in the middle of the cell.
• Anaphase: Mitotic spindle fibers separate sister chromatids and move them to opposite poles.
• Telophase: The now daughter chromosomes decondense.
• Cytokinesis: The cell divides into two daughter cells.

Meiosis

• Meiosis is a process that undergoes PMAT and cytokinesis twice to produce sex cells (gametes).
• The number of chromosomes decreases to half during meiosis.
• Meiosis 1 is a reduction division, reducing the number of chromosomes.
• Meiosis 2 is an equational division, restorering the chromosome number during fertilization.

Significance of Mitosis and Meiosis

•  Mitosis maintains genetic material (genome).
•  Mitosis ensures proper cell function and maintains the same number of chromosomes by duplicating and dividing chromosomes.
•  Meiosis reduces chromosome number by half producing gametes for sexual reproduction.
•  Meiosis also introduces genetic variation through crossing over.

Significance of Meiosis

•  Reduction of genetic material and sexual reproduction.
•  Genetic diversity.
•  Survival.

Biological Significance of Crossing Over

•  Crossing over is an exchange of genetic material/segments which helps to increase genetic diversity and enhances genetic variation.

Cancer

•  Cancer is an error in cell checkpoints that stops apoptosis which causes abnormal growth.
•  Neoplasm forms when defective cells grow into tumors.
•  Early detection is the most effective way to treat cancer.

Nondisjunction Disorders

• Polyploidy: Abnormal number of sets of chromosomes.
• Aneuploidy: Abnormal number of chromosomes.
  • Down syndrome: An example of an aneuploidy disorder where there is an extra chromosome 21 (Trisomy 21).

Other Genetic Disorders

• Patau Syndrome (Trisomy 13): Characterized by cleft lip, cleft palate, cerebral defects, and holoprosencephaly.
• Edward Syndrome (Trisomy 18): Characterized by heart complications.
• Turner Syndrome (Monosomy X): A chromosomal disorder affecting females, causing characteristic features, short stature, broad shoulders, and developmental delays.
• Warkany Syndrome (Chromosome 8): Characterized by stiff joints, congenital abnormalities, and delayed development.

Stem Cells

• Undifferentiated cells that can become specialized cells.
• Stem cell technology is used in replacing old and damaged cells.
• Stem cells derive from embryonic stem cells or adult stem cells.

Genetic Engineering

•  Genetic engineering is a process to directly modify the DNA of an organism to produce new traits.
• All genetically engineered organisms are GMOs, but not all GMOs are genetically engineered.

Cellular Transport

• Diffusion: Movement of molecules from a higher concentration to a lower concentration until equilibrium is reached.
• Osmosis: Movement of water across a semi-permeable membrane from a lower solute concentration to a higher solute concentration.

Passive Transport

• Simple Diffusion: Movement of small, nonpolar molecules across a membrane without the aid of transport proteins.
• Facilitated Diffusion: Movement of molecules across a membrane with the help of transport proteins.

Active Transport

• Active Transport: Movement of molecules against their concentration gradient, requiring energy.
• Sodium-Potassium Pump: An example of an active transport mechanism that moves sodium ions out of a cell and potassium ions into a cell.

Bulk Transport

• Vesicles: Small sacs that transport materials within and between cells.
• Exocytosis: Vesicles fusing with the plasma membrane to release their contents outside the cell.
• Endocytosis: The process of taking substances into the cells by enveloping them in a vesicle.
  • Phagocytosis: Cell eating, engulfing particles (bacteria).
  • Pinocytosis: Cell drinking, engulfing fluids.
  • Receptor-mediated Endocytosis: Specialized endocytosis usingreceptor proteins to capture specific molecules.

Factors Affecting Cell Transport

• Concentration Gradient: Difference in concentration between two areas.
• Size of molecules: Smaller molecules diffuse faster than larger ones.
• Membrane permeability: How easily substances can pass through a membrane.