Chapter 3 Pt.1: Cellular Level of Organization

Overview

This chapter introduces the fundamental components and processes of the animal cell, focusing on cell structure, organelles, membrane transport, and the cell cycle. Understanding these concepts is essential for studying human anatomy and physiology at the cellular level.

Components of a Typical Animal Cell

• Plasma Membrane: The outer boundary of the cell, regulating entry and exit of substances.

• Cytoplasm: The region between the plasma membrane and nucleus, containing organelles and cytosol.

• Nucleus: The control center housing genetic material (DNA).

• Organelles: Specialized structures performing distinct cellular functions (e.g., mitochondria, ribosomes).

• Inclusions: Non-living substances within the cytoplasm (e.g., glycogen, lipid droplets).

Plasma Membrane: Structure and Function

• Phospholipid Bilayer: Composed of hydrophilic heads and hydrophobic tails, forming a semi-permeable barrier.

• Proteins: Embedded within or attached to the membrane, facilitating transport and communication.

• Cholesterol: Stabilizes membrane fluidity.

• Carbohydrates: Attached to proteins/lipids, forming the glycocalyx for cell recognition.

Integral vs. Peripheral Proteins

• Integral Proteins: Span the membrane; function as channels, carriers, or receptors.

• Peripheral Proteins: Attached to membrane surface; involved in signaling and structural support.

Cytoskeleton and Glycocalyx

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) providing structural support, shape, and movement.

• Glycocalyx: Carbohydrate-rich area on cell surface, important for cell recognition and protection.

Cell Surface Specializations: Microvilli, Cilia, and Flagella

• Microvilli: Finger-like projections increasing surface area for absorption (e.g., intestinal cells).

• Cilia: Hair-like structures moving substances across cell surfaces (e.g., respiratory tract).

• Flagella: Long, whip-like structures enabling cell movement (e.g., sperm cells).

Membranous vs. Non-Membranous Organelles

• Membranous Organelles: Surrounded by membranes (e.g., nucleus, mitochondria, ER, Golgi complex, lysosomes, peroxisomes).

• Non-Membranous Organelles: Not surrounded by membranes (e.g., ribosomes, centrioles, cytoskeleton).

Structure and Functions of Major Organelles

• Nucleus: Contains DNA; controls cellular activities.

• Smooth Endoplasmic Reticulum (Smooth ER): Synthesizes lipids and detoxifies chemicals.

• Rough Endoplasmic Reticulum (Rough ER): Studded with ribosomes; synthesizes proteins for export.

• Ribosomes: Sites of protein synthesis; found free in cytosol or attached to rough ER.

• Golgi Complex: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Mitochondria: Powerhouse of the cell; produces ATP via cellular respiration.

• Centrioles: Organize microtubules during cell division.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.

Organelles vs. Inclusions

• Organelles: Functional structures within cells (e.g., mitochondria, ER).

• Inclusions: Non-functional, stored substances (e.g., glycogen, lipid droplets, pigments).

Definitions: Cytoplasm, Cytosol/Intracellular Fluid (ICF), and Extracellular Fluid (ECF)

• Cytoplasm: All cellular contents between the plasma membrane and nucleus.

• Cytosol/ICF: Fluid portion of cytoplasm containing dissolved substances.

• ECF: Fluid outside the cell, including interstitial fluid and plasma.

Cell Cycle: G1, S, and G2 Phases

• G1 Phase: Cell grows and carries out normal functions.

• S Phase: DNA replication occurs.

• G2 Phase: Cell prepares for division; organelles replicate.

Stages of Mitosis and Cytokinesis

• Prophase: Chromatin condenses; spindle fibers form.

• Metaphase: Chromosomes align at the cell's equator.

• Anaphase: Sister chromatids separate and move to opposite poles.

• Telophase: Nuclear envelopes reform; chromosomes decondense.

• Cytokinesis: Division of cytoplasm, resulting in two daughter cells.

Diffusion and Osmosis

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Osmosis as Diffusion: Osmosis is a specific type of diffusion involving water molecules.

Equation for Diffusion Rate:

Where J is flux, D is the diffusion coefficient, and is the concentration gradient.

Solution Tonicity: Isotonic, Hypertonic, Hypotonic

• Isotonic: Solute concentration equal inside and outside the cell; no net water movement.

• Hypertonic: Higher solute concentration outside the cell; water moves out, cell shrinks.

• Hypotonic: Lower solute concentration outside the cell; water moves in, cell swells.

Membrane Transport Mechanisms

• Filtration: Movement of substances across a membrane due to pressure.

• Facilitated Diffusion: Passive transport using carrier proteins.

• Passive Transport: Movement without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement against concentration gradient using energy (ATP).

Membrane Carrier Types

• Uniport: Transports one type of molecule in one direction.

• Symport: Transports two molecules in the same direction.

• Antiport: Transports two molecules in opposite directions.

Bulk Transport: Endocytosis and Exocytosis

• Bulk Transport: Movement of large particles or fluids via vesicles.

• Endocytosis: Uptake of substances into the cell by vesicle formation.

• Exocytosis: Release of substances from the cell via vesicle fusion with the membrane.

Types of Endocytosis: Phagocytosis and Pinocytosis

• Phagocytosis: "Cell eating"; cell engulfs large particles or microorganisms.

• Pinocytosis: "Cell drinking"; cell engulfs extracellular fluid and dissolved solutes.

• Steps in Phagocytosis:

  1. Recognition and attachment

  2. Engulfment

  3. Formation of phagosome

  4. Fusion with lysosome

  5. Digestion and release of residues

• Steps in Pinocytosis:

  1. Invagination of plasma membrane

  2. Formation of vesicle containing fluid

  3. Vesicle internalization

Summary Table: Membranous vs. Non-Membranous Organelles

Summary Table: Types of Membrane Transport

Additional info: Academic context and examples have been added to expand upon the brief points in the original notes, ensuring completeness and clarity for exam preparation.