Biology: DNA and Cell Structure

DNA Structure and Function

• DNA is a double-helix structure
• The backbone is made of alternating sugar (deoxyribose) and phosphate molecules
• Nitrogenous bases pair as follows: adenine (A) with thymine (T), and cytosine (C) with guanine (G)
• DNA strands are antiparallel (one runs 5' to 3', the other 3' to 5')
• Hydrogen bonds hold complementary bases together
• Nucleotide: Basic unit of DNA
• Base Pairing: A-T and C-G
• Antiparallel: Opposite directions of DNA strands
• Hydrogen Bond: Weak bond between bases

Cell Structure and Organelles

• Prokaryotic cells lack a nucleus and membrane-bound organelles
• Eukaryotic cells are compartmentalized, with organelles like the nucleus, mitochondria, and Golgi apparatus
• Key organelle functions:
  • Ribosomes: Protein synthesis
  • Golgi Apparatus: Modifies and packages proteins
  • Lysosomes: Digests macromolecules and debris
  • Mitochondria: ATP production via cellular respiration
• Prokaryote/Eukaryote: Types of cells
• Organelle: Specialized cell structure
• Cytoplasm: Jelly-like fluid where reactions occur

Membrane Structure and Transport

• The fluid mosaic model: phospholipid bilayer with embedded proteins
• Transport methods:
  • Passive Transport: Diffusion, osmosis, facilitated (no energy required).
  • Active Transport: Requires energy (e.g., protein pumps).
  • Endocytosis/Exocytosis: Materials move into/out of cells via vesicles.
• Hydrophilic substances attract water; hydrophobic substances repel water
• Phospholipid: Molecule forming the bilayer
• Osmosis: Movement of water from high to low water potential.
• Protein Pump: Active transport protein
• Hypotonic/Hypertonic: Water movement into or out of cells

Stem Cells and Cell Differentiation

• Stem cells can divide and differentiate into specialized cells
• Types of stem cells:
  • Totipotent: Can form all cell types (including placental/embryo)
  • Pluripotent: Can form most cell types (except placental/embryo)
  • Multipotent: Can form a limited range of cells (e.g., blood cells)
• Stem cells are key in growth, repair, and medical therapies
• Specialization: Development into specific cell types
• Differentiation: Process by which cells become specialized
• Therapeutic Cloning: Producing stem cells for treatment

Enzymes and Proteins

• Proteins are made of amino acids linked by peptide bonds
• Protein denaturation occurs due to temperature, pH, or mechanical stress
• Enzymes speed up chemical reactions and lower activation energy
• Peptide bonds form during condensation reactions
• Peptide Bond: Link between amino acids
• Denaturation: Loss of protein structure/function
• Active Site: Region of an enzyme that binds substrates

Water and its Properties

• Water is a polar molecule, forming hydrogen bonds
• Properties of water: cohesion, adhesion, and high heat capacity
• High latent heat of vaporization, Universal solvent, Density anomaly (ice is less dense than liquid water), Transparency, High surface tension, Capillary action
• Hydrophilic substances dissolve in water, hydrophobic substances do not
• Cohesion: Water molecules sticking together
• Adhesion: Water sticking to other substances
• Polar: Uneven charge distribution in a molecule

Experimental Techniques and Skills

• Centrifugation separates substances based on density
• Hypotonic solutions cause cells to swell; hypertonic solutions cause them to shrink
• Use diagrams to label prokaryotic cells, plasma membranes, and organelles
• Data interpretation and evaluation are crucial for experimental analysis
• Centrifugation: Separation technique
• Hypotonic: Lower solute concentration outside the cell
• Hypertonic: Higher solute concentration outside the cell

Secretory Cell and Organelle Functions

• Structure and function of organelles involved in protein synthesis and secretion:
  • Ribosomes: Synthesis of polypeptide chains
  • Rough Endoplasmic Reticulum: Modifies and folds polypeptides
  • Golgi Apparatus: Processes and packages proteins into vesicles for secretion
  • Vesicles: Transports proteins within and out of the cell
• Transport mechanisms: Exocytosis (active transport mechanism for releasing proteins)
• Advantages of cell compartmentalization:
  • Efficient separation of incompatible reactions
  • Increases efficiency by localizing enzymes and substrates

Types of Stem Cells

• Definitions and differences between:
  • Totipotent Stem Cells: Can differentiate into all cell types, including placental cells
  • Pluripotent Stem Cells: Can differentiate into most cell types (e.g., embryonic stem cells)
  • Multipotent Stem Cells: Can differentiate into a limited range of cell types (e.g., blood cells)
• Real-world applications of stem cells in medicine (e.g., regenerative therapies)

Osmosis and Water Potential

• Why water moves from high to low water potential (osmosis principles)
• Effects of osmosis on plant and animal cells:
  • Plant Cells in Hypotonic Solutions: Become turgid (cell wall prevents bursting)
  • Animal Cells in Hypotonic Solutions: Burst (no cell wall)
  • Plant and Animal Cells in Hypertonic Solutions: Shrink (plasmolysis in plants, crenation in animals)

Fluid Mosaic Model

• Components of the plasma membrane:
  • Phospholipid bilayer: Hydrophilic heads and hydrophobic tails
  • Proteins: Integral (e.g., pumps, channels) and peripheral proteins
  • Cholesterol: Stabilizes membrane fluidity
  • Carbohydrates: Attached to proteins or lipids (glycoproteins, glycolipids) for cell recognition

Protein Structure and Denaturation

• Amino acid structure: Unique R group (side chain) determines chemical properties
• Amino and carboxyl groups
• Central alpha carbon atom
• Formation of peptide bonds through condensation reactions
• Causes of protein denaturation: High temperature, extreme pH, or mechanical stress
• Effects of denaturation: Loss of tertiary/quaternary structure and function

Data Interpretation and Experimental Design

• Key functions of life (e.g., metabolism, excretion) as demonstrated by experimental data
• Analysis of diagrams or graphs related to:
  • Osmosis experiments with animal/plant cells
  • Enzyme activity under varying conditions (e.g., temperature or pH)