Bio EC Exam 2

Cell Division and Cancer

Uncontrolled Cell Division Leads to Cancer

• Cancer is primarily caused by the uncontrolled division of cells, leading to tumor formation. The growth can be benign (non-cancerous) or malignant (cancerous) depending on the behavior of the cells.

Characteristics of Cancer Cells:

• High Proliferation Rate: Cancer cells divide rapidly, producing large clusters known as tumors.

• Altered Plasma Membranes: The structure of the plasma membranes in cancerous cells differs from normal cells, affecting their signal transduction and adhesion capabilities.

• Lack of Contact Inhibition: Unlike normal cells, cancer cells do not stop dividing when they come into contact with adjacent cells, allowing them to invade surrounding tissues.

Cell Cycle Phases

Overview of the Cell Cycle:

• The cell cycle is a series of stages that cells go through to grow and divide. The sequence involves several phases:

  • Interphase: the cell prepares for division.

  • Prophase: chromatin condenses into chromosomes.

  • Prometaphase: nuclear envelope breaks down; spindle fibers attach to chromosomes.

  • Metaphase: chromosomes align at the cell's equatorial plane.

  • Anaphase: sister chromatids are pulled apart to opposite ends of the cell.

  • Telophase: chromosomes de-condense, and the nuclear envelope re-forms.

S Phase:

• This phase specifically initiates DNA replication, ensuring that each new cell will receive an identical set of genetic instructions.

Genetics and Phenotype Ratios

Mendelian Genetics:

• The principles of inheritance can be exemplified through Mendelian genetics, particularly the dihybrid cross:

  • 9:3:3:1 Phenotypic Ratio: This ratio represents the expected outcome when studying two traits simultaneously (using the example of yellow and green peas).

• Codominance: In ABO blood typing, an individual with both A and B alleles expresses both phenotypes simultaneously, a clear example of codominance.

• Allele Examples:

  • R is dominant for round peas.

  • r is recessive for wrinkled peas.

Photosynthesis Context

Carbon Fixation in C3 Plants:

• The primary product of carbon fixation in C3 plants is 3-phosphoglycerate (3-PGA), which is crucial for the Calvin cycle.

• The Calvin cycle requires both ATP and NADPH, produced during the light-dependent reactions of photosynthesis.

Photorespiration:

• This process is more likely to occur in warm weather due to the closure of stomata, which prevents the entry of CO2 into leaves, thus reducing photosynthetic efficiency.

Genetic Variations and Chromosome Behavior

Mitosis vs. Meiosis:

• Mitosis: Produces two genetically identical daughter cells, facilitating growth and tissue repair.

• Meiosis: Produces four haploid cells from diploid cells through two rounds of division (Meiosis I and II), essential for sexual reproduction.

• Recombination: A genetic variation mechanism that occurs during Prophase I of meiosis, involving the exchange of genetic material between non-sister chromatids.

Cell Cycle Regulatory Mechanisms

Maturation Promoting Factor (MPF):

• Addition of MPF to cells during the G2 phase catalyzes the initiation of mitosis, signaling the cell that it is ready to divide.

Cellular Checkpoints:

• Regulatory Checkpoint During Mitosis: Monitors for chromosomal abnormalities and DNA damage, ensuring that only healthy cells proceed with division.

• G2 Checkpoint: Specifically checks if the cell is adequately prepared for the processes of mitosis, preventing errors in cell division.

Cystic Fibrosis Example

Autosomal Recessive Disorder:

• Cystic Fibrosis is caused by mutations in the CFTR gene and is inherited in an autosomal recessive manner. This condition typically leads to the production of thick mucus that can cause severe respiratory and digestive issues.

• Genetic Counseling: Genetic counselors provide guidance for parents regarding the risks of passing cystic fibrosis to their children. For example, if one parent is a carrier (Aa) and the other is not (AA), there is a 50% chance that their offspring will be carriers.

Electron Transport in Photosynthesis

Non-Cyclic Electron Pathway Order:

• The order of events in the non-cyclic electron transport chain during photosynthesis is as follows:

  • Water is split at Photosystem II, releasing oxygen.

  • Electrons travel through the Electron Transport Chain.

  • Electrons reach Photosystem I and are re-energized.

  • Finally, the electrons combine with NADP+ to form NADPH.

Development and Inheritance

Embryonic Development:

• Embryonic development begins from a single fertilized zygote, which undergoes a series of mitotic divisions, organizing into multiple cell layers and specialized cell types.

• Cell Count After Divisions: After four rounds of mitotic divisions, the resulting number of cells is 16, highlighting the exponential growth that occurs during early development.

Apoptosis

Programmed Cell Death:

• Apoptosis is a crucial cellular process for removing damaged or potentially harmful cells. It prevents damage from cells with irreparable DNA damage, maintaining the overall health of the organism.