Cell Structure and Function: Study Notes for Biological Sciences

Cell Structure and Function

Introduction to Cells

The cell is the fundamental structural and functional unit of all living organisms. In humans, the body is composed of 50 to 60 trillion cells, each organized in diverse shapes and functions. Understanding cell structure and function is essential for studying tissues, organs, organ systems, and the human organism as a whole.

• Cell Theory: All living things are composed of cells, which are the basic units of life.

• Basic Activities of Cells: Cells perform essential activities such as metabolism, growth, response to stimuli, and reproduction.

• Three Major Parts of a Cell:

  1. Plasma Membrane: The outer boundary that regulates the movement of substances in and out of the cell.

  2. Nucleus: The control center containing genetic material (DNA).

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

Cell Compartments

• Cell:

  • Plasma Membrane: Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates. It is selectively permeable.

  • Nucleus: Contains nucleolus and chromosomes; responsible for genetic control.

  • Cytoplasm:

    • Cytosol: The fluid portion of the cytoplasm.

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

    • Inclusions: Non-living substances such as glycogen granules, lipid droplets, and pigments.

• Body Fluids:

  • Intracellular Fluid: Fluid within cells.

  • Extracellular Fluid: Fluid outside cells, including plasma and interstitial fluid.

Plasma Membrane Structure and Function

• Phospholipid Bilayer: Forms the basic structure of the membrane, providing fluidity and flexibility.

• Membrane Proteins:

  • Integral Proteins: Span the membrane and are involved in transport and signaling.

  • Peripheral Proteins: Attached to the membrane surface, involved in cell signaling and structural support.

  • Receptors: Bind to specific molecules and initiate cellular responses.

  • Enzymes: Catalyze chemical reactions at the membrane surface.

• Glycoproteins and Glycocalyx: Contribute to cell recognition and protection.

• Selective Permeability: Allows gases and nonpolar molecules to pass freely, while restricting others.

Cell Organelles

• Ribosomes: Sites of protein synthesis.

• Endomembrane System:

  • Rough and Smooth Endoplasmic Reticulum: Synthesis and transport of proteins and lipids.

  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

  • Vesicles: Transport materials within the cell.

  • Lysosomes: Contain digestive enzymes for breaking down waste.

• Mitochondria: Powerhouse of the cell, site of ATP production.

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

• Centrosome and Centrioles: Involved in cell division.

• Cytoskeleton:

  • Microtubules: Provide structural support and facilitate movement (e.g., cilia, flagella).

  • Intermediate Filaments: Provide mechanical strength (e.g., myosin, keratin, neurofilaments).

  • Microfilaments: Involved in cell movement and shape (e.g., actin, microvilli).

Cell Mechanisms

• Exocytosis and Endocytosis: Processes for moving materials out of and into the cell, respectively.

• Cell Cycle: The sequence of events in cell growth and division, including interphase, mitosis, and cytokinesis.

• Mitosis: Division of a cell's nucleus resulting in two identical daughter cells.

• Meiosis: Division process that reduces chromosome number by half, producing gametes.

• Specialized Cell Types: Cells with unique shapes and functions, such as nerve cells, muscle cells, and blood cells.

Summary Table: Major Cell Components and Functions

Component	Main Function
Plasma Membrane	Regulates entry/exit of substances; cell signaling
Nucleus	Genetic control; DNA storage and replication
Cytoplasm	Site of metabolic activities; contains organelles
Mitochondria	ATP production (energy)
Ribosomes	Protein synthesis
Endoplasmic Reticulum	Protein and lipid synthesis/transport
Golgi Apparatus	Protein modification and packaging
Lysosomes	Digestion of cellular waste
Cytoskeleton	Structural support; cell movement

Key Terms and Definitions

• Cell: The smallest unit of life, capable of independent existence.

• Organelle: Specialized subunit within a cell with a specific function.

• Phospholipid Bilayer: Double layer of phospholipids forming the plasma membrane.

• Selective Permeability: Property of membranes to allow certain substances to pass while restricting others.

• Exocytosis: Process by which cells expel materials using vesicles.

• Endocytosis: Process by which cells take in materials by engulfing them.

• Mitosis: Cell division resulting in two identical cells.

• Meiosis: Cell division producing gametes with half the chromosome number.

Example: Cell Cycle Phases

• Interphase: Cell grows and DNA replicates.

• Mitosis: Division of the nucleus (prophase, metaphase, anaphase, telophase).

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

Formulas and Equations

• Surface Area to Volume Ratio: Important for cell efficiency. $\text{Surface Area to Volume Ratio} = \frac{\text{Surface Area}}{\text{Volume}}$

• Osmosis (Water Movement): $\Delta \Psi = \Psi_s + \Psi_p$ Where $\Psi$ is water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Additional info: These notes are expanded from a syllabus/outline for a biological sciences course, not statistics. The content covers cell biology, not statistical methods.