Honors Biology Unit 3

Unit 3 Study Notes

Introduction to the Cell

  • Textbook Reference: Sections 4.1-4.4 (pp. 54-57)

Historical Context

  • Robert Hooke (1635-1703): Credited with naming "cells" after observing cork under a microscope.

Cell Theory

  • Definition: A fundamental concept that unifies biological sciences.

    • Components:

    • Cells are the fundamental units of life.

    • All organisms are composed of one or more cells.

    • All cells arise from pre-existing cells.

Cell Sizes

  • Sizes of various cells and structures:

    • Human height: 10 m

    • Length of 1 m: 1000 mm

    • 10 mm: (1 cm) Some nerve and muscle cells

    • Chicken egg: 100 mm

    • Frog egg: 1 mm

    • Paramecium: 100 μm, Human egg: 10 μm, Most plant and animal cells: 1 μm

    • Nucleus: 100 nm, Most bacteria: 10 nm

    • Mitochondrion: Smallest bacteria: 1 nm, Viruses: 0.1 nm

    • Ribosome: 10 nm, Proteins: 1 nm, Lipids: 0.1 nm, Small molecules: Atoms

Microscopy Techniques

Light (Optical) Microscope

  • Uses visible light to generate images.

    • Simple Microscope: Has more than one lens.

    • Compound Microscope: Allows greater magnification and clarity.

    • Types:

    • Monocular and Biocular microscopes

    • Fluorescence microscopes: Specialized for viewing fluorescent objects.

    • Dissecting and Inverted microscopes: For various specimen views.

Electron Microscope

  • Utilizes electron beams to produce high-resolution images.

    • Types:

    • Transmission Electron Microscope (TEM)

    • Scanning Electron Microscope (SEM)

    • Reflection Electron Microscope (REM)

    • Scanning Transmission Electron Microscope (STEM)

    • Atomic Force Microscopes (AFM)

Plasma Membrane

  • Structure: Phospholipid bilayer with embedded proteins and biomolecules.

  • Function: Provides a selectively permeable boundary for cells and organelles.

Surface Area to Volume Ratio

  • Definition: As cells grow larger, their volume increases at a higher rate than surface area, limiting size.

  • Importance:

    • Smaller cells maintain a higher surface area-to-volume ratio, enhancing efficiency in nutrient uptake and waste removal.

Cell Types

Prokaryotic Cells

  • Domains: Bacteria and Archaea

    • Single-celled organisms with free-floating DNA (circular chromosome).

Eukaryotic Cells

  • Domain: Eukarya (including fungi, animals, plants)

    • Single and multi-celled organisms with DNA housed in a nucleus (linear chromosomes).

    • Membrane-bound organelles facilitate complex metabolic processes.

Cell Compartmentalization

  • Enhances surface area and supports complex functions in eukaryotic cells.

Cell Structure and Functions

Major Organelles

  • Nucleus: Contains DNA, including nuclear envelope, chromatin, and the nucleolus.

  • Ribosomes: Sites of protein synthesis, found floating in the cytoplasm or attached to rough ER.

  • Endomembrane System: Includes several organelles that function in synthesizing and processing biomolecules.

    • Components:

    • Nucleus

    • Endoplasmic Reticulum (ER - Rough and Smooth)

    • Golgi apparatus

    • Lysosomes

    • Vesicles

    • Vacuoles

    • Cell membrane

  • Mitochondria and Chloroplasts: Energy-converting organelles.

Energy-Converting Organelles

Mitochondria

  • Involved in cellular respiration, converting food energy into a usable form (ATP).

Chloroplasts

  • Conduct photosynthesis in plants, converting sunlight into chemical energy.

Endosymbiotic Theory

  • Description: Ancestral eukaryotic cells engulfed prokaryotic cells that evolved into mitochondria and chloroplasts.

  • Evidence:

    • Mitochondria and chloroplasts have their own DNA (circular, like prokaryotes) and replicate independently from the host cell.

Cytoskeleton

  • Structure: Network of protein fibers (microtubules, microfilaments, intermediate filaments).

  • Functions:

    • Provides internal support.

    • Facilitates movement and transport within the cell.

    • Involved in cell division (e.g., centrioles).

Extracellular Matrix and Cell Junctions

  • Extracellular Matrix: Network of proteins (like collagen) that support tissue structure.

  • Types of Cell Junctions:

    • Tight junctions: Prevent passage between cells.

    • Anchoring junctions: Provide strength and support.

    • Gap junctions: Allow communication between cells.

Cell Wall (Plant Cells)

  • Rigid structure providing support, composed mainly of cellulose.

Overview of Eukaryotic Cell Structures and Functions

  • Genetic Control: Nucleus, Ribosomes

  • Manufacturing and Distribution: ER, Golgi Apparatus, Lysosomes

  • Energy Processing: Mitochondria, Chloroplasts

  • Structural Support: Cytoskeleton, Cell walls, and junctions.

Membrane Structure

  • Components of Plasma Membrane:

    • Primarily composed of phospholipids with hydrophilic heads and hydrophobic tails.

    • Membrane proteins serve various roles: enzymatic activity, cell recognition, and transport.

  • Fluid Mosaic Model: Describes the dynamic structure of the plasma membrane (movement of lipids and proteins).

Mechanisms of Cell Transport

Passive Transport

  • Does not require energy, substances move down the concentration gradient.

    • Types:

    • Simple diffusion: Small nonpolar molecules.

    • Facilitated diffusion: Hydrophilic molecules through specific channels.

    • Osmosis: Diffusion of water across a membrane.

Active Transport

  • Requires energy (ATP) to move substances against the concentration gradient.

    • Types:

    • Protein pumps: Move ions against their gradients (e.g., Ca²⁺ pump).

    • Endocytosis and Exocytosis: Bulk transport of materials into/out of the cell.

Energy and Chemical Reactions

Laws of Thermodynamics

  1. First Law: Energy cannot be created or destroyed but can change forms.

  2. Second Law: Entropy increases over time; energy conversions are inefficient.

Energy Transformations in Cells

  • Cellular Respiration: Converts chemical energy in food to ATP energy.

  • Photosynthesis: Converts solar energy to chemical energy in sugars.

Enzyme Function

  • Enzymes lower the activation energy of biochemical reactions, facilitating rapid reactions.

    • Catalysts: Substances that speed up reactions without being consumed.

  • Enzyme Activity Factors:

    • Temperature, pH, substrate concentration, enzyme concentration, and presence of inhibitors.

Types of Enzyme Inhibition

  1. Competitive inhibition: Inhibitor competes with substrate for the active site.

  2. Noncompetitive inhibition: Inhibitor binds elsewhere, altering the enzyme's shape.

Feedback Inhibition

  • The final product of a metabolic pathway inhibits the first enzyme, regulating the pathway and maintaining homeostasis.