Cell Biology Basics

Cell Membrane

• Thin layer of lipid and protein molecules that surrounds the cell
• Semi-permeable, allowing certain substances to pass through while keeping others out
• Composed of:
  • Phospholipid bilayer (hydrophobic tails and hydrophilic heads)
  • Proteins (integral and peripheral)
  • Cholesterol (helps maintain fluidity and stability)
• Functions:
  • Regulates what enters and leaves the cell
  • Maintains cell shape
  • Provides mechanical support

Cell Division

• Process by which a cell becomes two daughter cells
• Types:
  • Mitosis (somatic cells, results in two identical daughter cells)
  • Meiosis (gametes, results in four non-identical daughter cells with half the number of chromosomes)
• Stages of mitosis:
  1. Interphase (cell grows and prepares for division)
  2. Prophase (chromatin condenses, nuclear envelope breaks down)
  3. Metaphase (chromosomes line up at the center of the cell)
  4. Anaphase (sister chromatids separate)
  5. Telophase (nuclear envelope reforms, chromatin uncoils)
  6. Cytokinesis (cytoplasm divides, cell splits)

Mitochondria

• Organelles found in the cell's cytoplasm
• Often referred to as the "powerhouses" of the cell
• Functions:
  • Generate energy for the cell through cellular respiration
  • Regulate cell growth and division
  • Involved in apoptosis (programmed cell death)
• Structure:
  • Outer membrane
  • Inner membrane (folded into cristae, increasing surface area)
  • Mitochondrial matrix (contains enzymes and mitochondrial DNA)

Chromosomes

• Thread-like structures composed of DNA and proteins
• Found in the nucleus of eukaryotic cells
• Functions:
  • Carry genetic information
  • Play a crucial role in cell division
• Structure:
  • Centromere (region where sister chromatids attach)
  • Telomeres (regions at the ends of the chromosome)
  • Chromatin (coiled DNA and proteins)

Genes

• Basic units of heredity
• Segments of DNA that code for a specific protein or function
• Functions:
  • Provide instructions for protein synthesis
  • Regulate gene expression
• Structure:
  • Coding region (exons)
  • Non-coding region (introns)

DNA

• Deoxyribonucleic acid
• Molecule that contains the genetic instructions for an organism
• Functions:
  • Stores genetic information
  • Provides instructions for protein synthesis
• Structure:
  • Double helix model (two complementary strands twisted together)
  • Nucleotides (A, C, G, and T) linked by hydrogen bonds

DNA Structure

• Double helix model:
  • Sugar-phosphate backbone
  • Nitrogenous bases (A, C, G, and T)
  • Hydrogen bonds between complementary bases
• Base pairing rules:
  • A-T (two hydrogen bonds)
  • G-C (three hydrogen bonds)

DNA Replication

• Process by which DNA is duplicated
• Occurs before cell division
• Steps:
  1. Initiation (unwinding of DNA at the origin of replication)
  2. Unwinding (double helix is unwound, and an enzyme called helicase unwinds the double helix)
  3. Binding (an enzyme called primase adds short RNA primers to the template strands)
  4. Synthesis (DNA polymerase synthesizes new DNA strands by adding nucleotides to the primers)
  5. Elongation (DNA polymerase continues to add nucleotides to the growing DNA strands)
  6. Ligation (an enzyme called ligase seals the gaps between the nucleotides, forming a continuous strand)
  7. Termination (replication is complete, and the new DNA molecules are formed)

Cell Membrane

• Thin layer of lipid and protein molecules surrounding the cell, regulating what enters and leaves the cell
• Semi-permeable, allowing certain substances to pass through while keeping others out
• Composed of phospholipid bilayer, proteins, and cholesterol, maintaining cell shape and providing mechanical support

Cell Division

• Process by which a cell becomes two daughter cells, with two main types: mitosis and meiosis
• Mitosis: somatic cells, resulting in two identical daughter cells with the same number of chromosomes as the parent cell
• Meiosis: gametes, resulting in four non-identical daughter cells with half the number of chromosomes as the parent cell
• Stages of mitosis: interphase, prophase, metaphase, anaphase, telophase, and cytokinesis

Mitochondria

• Organelles found in the cell's cytoplasm, generating energy for the cell through cellular respiration
• Regulating cell growth and division, and involved in apoptosis
• Structure: outer membrane, inner membrane (folded into cristae), and mitochondrial matrix (containing enzymes and mitochondrial DNA)

Chromosomes

• Thread-like structures composed of DNA and proteins, carrying genetic information
• Found in the nucleus of eukaryotic cells, playing a crucial role in cell division
• Structure: centromere, telomeres, and chromatin (coiled DNA and proteins)

Genes

• Basic units of heredity, providing instructions for protein synthesis and regulating gene expression
• Segments of DNA that code for a specific protein or function
• Structure: coding region (exons) and non-coding region (introns)

DNA

• Deoxyribonucleic acid, storing genetic information and providing instructions for protein synthesis
• Double helix model, consisting of sugar-phosphate backbone, nitrogenous bases, and hydrogen bonds
• Nucleotides (A, C, G, and T) linked by hydrogen bonds, following base pairing rules

DNA Replication

• Process by which DNA is duplicated, occurring before cell division
• Steps: initiation, unwinding, binding, synthesis, elongation, ligation, and termination
• Resulting in two identical DNA molecules, each containing one old strand and one new strand