MCAT Bio Notes

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  • MCAT bio notes

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Cell Theory

  • All living organisms are composed of cells.

  • Cells contain DNA.

  • Cells are the basic unit of life.

  • Cells arise from previous cells.

Types of Cells

  • Eukaryotic Cells: Contain a true nucleus.

  • Prokaryotic Cells: Do not contain a nucleus.

Cell Membrane Information

  • Each cell has a cell membrane enclosing a semifluid cytosol where organelles are suspended.

  • The membrane consists of a phospholipid bilayer.

    • Surface: Hydrophilic and interacts with the aqueous environment.

    • Inside: Hydrophobic.

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Cytosol Functions

  • Allows diffusion of molecules throughout the cell.

Eukaryotic Reproduction

  • Eukaryotic cells reproduce exclusively through mitosis.

The Nucleus

  • Surrounded by a nuclear membrane that creates a separate environment from the cytoplasm.

  • Has nuclear pores allowing selective two-way exchange.

  • Nuclear membrane envelope allows for transcription.

    • Contains DNA and histones.

    • DNA is wound into chromosomes.

  • The nucleolus synthesizes RNA.

Mitochondria

  • Contains outer and inner membranes.

  • The outer membrane separates the inner environment from the cytosol.

  • The inner membrane has cristae that increase surface area and contain enzymes needed for cellular respiration.

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Mitochondria Continued

  • Mitochondria contain their own DNA and replicate independently via binary fission.

  • They control apoptosis through enzymes.

    • Apoptosis: Programmed cell death.

Lysosomes

  • Contain hydrolytic enzymes to break down various substrates.

  • Can produce enzymes that lead to autolysis (programmed cell death from lysosomes).

Endoplasmic Reticulum (ER)

  • Divided into:

    • Rough ER: Has ribosomes for protein translation.

    • Smooth ER: No ribosomes; used for lipid synthesis and detoxification.

Golgi Apparatus

  • Composed of stacked membrane-bound sacs.

  • Transports materials from the ER to Golgi via vesicles.

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Golgi Apparatus Continued

  • Golgi modifies materials (may add carbohydrates, phosphates, sulfates).

  • Sends products to specific cellular locations via vesicles or exocytosis.

  • Not all cells have the same distribution of organelles.

    • Example: Sperm cells have a high concentration of mitochondria for energy.

    • Secretion cells have a higher concentration of rough ER and Golgi apparatus.

  • Peroxisomes: Contain hydrogen peroxide; primary function is to break down very long-chain fatty acids via β-oxidation.

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Cytoskeleton

  • Provides structure and maintains cell shape; acts as a conduit for material transport.

  • Composed of three components:

    • Microfilaments: Solid rods of actin; resistant to compression; involved in muscle contraction and cytokinesis.

    • Microtubules: Hollow polymers of tubulin; provide pathways for kinesin and dynein; form cilia and flagella.

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Microtubules Continued

  • Cilia and flagella are motile structures composed of microtubules.

    • Cilia: Line respiratory tract to move mucus.

    • Flagella: Propel cells (e.g., sperm cells).

  • Centrioles found in centrosome organize microtubules during mitosis.

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Intermediate Filaments (IF)

  • Diverse group of filamentous proteins (e.g., keratin, desmin).

  • Provide mechanical support, maintain cell shape, and anchor organelles.

  • Function is tissue-specific, critical for cell adhesion and integrity of the cytoskeleton.

Tissue Formation

  • Epithelial Tissue: Covers body and lines cavities; protects against pathogens.

    • Types of Tissue: Epithelial, Connective, Muscle, Nervous.

    • Polarized: One side faces lumen, the other interfaces with blood vessels.

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Classification of Epithelial Tissues

  • Simple Epithelia: One layer of cells.

  • Stratified Epithelia: Multiple layers.

  • Pseudostratified Epithelia: Appears to have multiple layers due to different heights of cells.

  • Types: Cuboidal (cube-shaped), Columnar (tall & thin), Squamous (flat, scale-like).

Connective Tissue

  • Supports body and provides framework for epithelial cells.

  • Contributes to stroma, the support structure.

  • Produces and secretes collagen and elastin for extracellular matrix.

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Key Functions of Cellular Structures

  • Centriole: Synthesizes DNA, produces ATP, breaks down materials.

  • Epithelial: Transports materials to Golgi.

  • Connective: Keratin and desmin involved in structure.

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Prokaryotic Cell Classification and Structure

  • Prokaryotes are simple organisms (all bacteria).

  • Do not contain membrane-bound organelles.

  • DNA: Single circular molecule in nucleoid region.

  • Two Domains: Archaea and Bacteria, with different characteristics.

Facts about Archaea

  • Use alternative energy sources; may be photosynthetic or chemosynthetic.

  • Resistant to many antibiotics, divide by binary fission or budding.

Facts about Bacteria

  • Major roles include producing Vitamin K and being symbiotic or pathogenic.

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Classification of Bacteria by Shape

  • Cocci: Spherical (e.g., Streptococcus).

  • Bacilli: Rod-shaped (e.g., E. coli).

  • Spirilli: Spiral-shaped (e.g., Treponema pallidum).

Oxygen Requirements of Bacteria

  • Obligate Aerobes: Require oxygen for metabolism.

  • Obligate Anaerobes: Cannot live in oxygenated environments.

  • Facultative Anaerobes: Can switch between aerobic and anaerobic metabolism.

  • Aerotolerant Anaerobes: Cannot use oxygen but can survive in its presence.