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Chapter 3: Cells

Cell Structure and Hierarchy

• Organelle:

  • A membrane-bound structure within a cell with a specific function.

  • Example: Chloroplast.

• Cell:

  • The fundamental unit of life.

  • Multicellular organisms consist of many cells; unicellular organisms consist of one cell.

  • Example: Leaf cell.

• Tissue:

  • A collection of specialized cells that function in a coordinated manner. (Multicellular only)

  • Example: Epidermis of leaf.

• Molecule:

  • A group of joined atoms.

  • Example: DNA.

• Atom:

  • The smallest chemical unit of a pure substance (element).

  • Example: Carbon atom.

• Organism:

  • A single living individual.

  • Example: One acacia tree.

• Population:

  • A group of the same species living in the same place and time.

  • Example: Multiple acacia trees.

• Organ:

  • A structure consisting of tissues organized to interact and carry out specific functions. (Multicellular only)

  • Example: Leaf.

• Organ System:

  • Organs connected either physically or chemically functioning together. (Multicellular only)

  • Example: Aboveground part of a plant.

• Community:

  • All populations that occupy the same region.

  • Example: All populations in a savanna.

• Ecosystem:

  • The living and nonliving components of an area.

  • Example: The savanna.

• Biosphere:

  • The global ecosystem; parts of the planet and atmosphere where life is possible.

Section 3.1 - Fundamental Unit of Life

• Cell Theory:

  • All living organisms are made up of cells.

  • All cells come from pre-existing cells.

  • All known life forms are composed of cells.

  • Cells are the smallest unit considered to possess "life".

Size of Biological Components

• Biological components vary greatly in size, with cells typically around 1-100 μm.

• Smallest to largest common components include:

  • Atoms and molecules

  • Proteins

  • Viruses

  • Most bacteria and archaea

  • Most plant and animal cells

  • Frog eggs

  • Ants

Why Cells Are Small

• Everything is composed of very small cells regardless of the organism's total size.

• Physical Limitations:

  • Three-dimensional objects have constraints that maintain cells at a small size.

Surface Area to Volume Ratio

• Cell volume and surface area limit cell size:

  1. Chemical reactions are proportional to reaction volume – Larger volume allows for more chemical reactions.

  2. Cells must effectively transport materials across the membrane to maintain homeostasis and function properly.

Cell Size Dynamics

• As cell size increases, volume increases faster than surface area, creating a limiting factor:

  • Surface Area increases at a squared function

  • Volume increases at a cubed function.

• Large cells struggle to maintain efficient transport of resources and may accumulate toxic waste.

• Ideal cell size range is 1-100 μm in diameter.

Microscopy and Visualization

• Most cells are microscopic and can be visualized using different types of microscopes:

  • Light microscope: Can magnify 50 million X and reveal detailed textures.

  • Electron microscope: Can magnify 1600 X, allowing visualization of internal structures.

Learning Outcomes for Section 3.1

• Describe the three principles of cell theory.

• Arrange chemical and biological examples by size.

• Explain why surface area to volume ratio limits cell size.

• Compare and contrast different types of microscopes used to image biological samples.

Section 3.2 - Cell Types in the Domains

• Common Features of All Cells:

  • DNA organized in chromosomes.

    • Prokaryotes: one circular chromosome.

    • Eukaryotes: multiple, linear chromosomes.

  • Cytosol: Jelly-like fluid containing organelles except the nucleus.

  • Cell membrane: Lipid-rich bilayer that encloses the cell.

Differences Between Eukaryotic and Prokaryotic Cells

• Prokaryotic:

  • Nucleus: Absent

  • Membrane-bound Organelles: Absent

  • Size: 1-10 μm

• Eukaryotic:

  • Nucleus: Present

  • Membrane-bound Organelles: Present

  • Size: Generally larger, 10-100 μm

Eukaryotic Cell Functions and Organelles

• Nucleus: Houses DNA and is where gene expression begins (transcription).

• Ribosomes: Protein synthesis, can be free or bound.

• Endoplasmic Reticulum (ER): Rough (with ribosomes) and smooth ER functions.

• Golgi Apparatus: Modifies proteins and sends them to their destinations.

• Lysosomes: Break down waste and recycling of cellular components.

• Chloroplasts and Mitochondria: Energy production and photosynthesis structures.

Learning Outcomes for Section 3.2

• List components found in all cells.

• Differentiate cell types and domains.

• Compare and contrast prokaryotes and eukaryotes.

• Compare and contrast animal and plant cells.

Section 3.3 - Cell Membranes

• Cell (Plasma) Membrane: Phospholipid bilayer protecting the cell with hydrophilic heads and hydrophobic tails.

• Fluid Mosaic Model: Describes the dynamic nature of the membrane, incorporating proteins, cholesterol, and glycocalyx.

Selective Permeability

• The membrane restricts movement of polar and charged molecules.

• Only small non-polar molecules (O2, CO2) can freely cross the membrane; others need protein carriers.

Membrane Proteins and Their Roles

• Integral Proteins: Embedded in the hydrophobic layer, involved in transport and communication.

• Peripheral Proteins: Assist in structure and signaling without crossing the membrane.

Learning Outcomes for Section 3.3

• Describe the function of a cell membrane.

• Explain the semi-permeable nature of the plasma membrane.

• Describe membrane structure and the roles of its components.

Section 3.4 - Eukaryotic Endomembrane System

• Nuclear Function: Protects DNA and is center for gene expression.

• Transcription/Translation: DNA is transcribed into mRNA, which is then translated into proteins at ribosomes.

• Endomembrane System: Includes ER, Golgi, vesicles for synthesizing, modifying, and transporting cellular products.

Organelles and Their Functions

• Rough ER: Protein synthesis and folding; has ribosomes attached.

• Smooth ER: Lipid synthesis and detoxification.

• Golgi Apparatus: Modifies and packages proteins for delivery.

• Lysosomes: Breakdown of waste material, containing acidic enzymes.

• Mitochondria: Energy production through ATP synthesis, originating from endosymbiosis.

Learning Outcomes for Section 3.4

• Compare and contrast organelles.

• Describe each organelle's function and the consequences of malfunctions.

Section 3.5 - Cytoskeleton

• Cytoskeleton: Acts as cell’s internal scaffolding, providing shape and movement.

• Composed of protein filaments that can dynamically change according to the cell's needs.

Functions of the Cytoskeleton

• Provides structure and support.

• Facilitates movement at cellular and tissue levels.

• Organizes cell components and aids in division.

Learning Outcomes for Section 3.5

• Compare and contrast cytoskeleton components.

• Discuss functions and locations of the cytoskeleton.

Section 3.6 - Cell Junctions

• Plant Cell Walls: Connected through plasmodesmata, allowing communication and substance transfer between cells.

• Animal Cell Junctions: Types include:

  • Tight Junctions: Prevent movement between cells, maintaining tissue directionality.

  • Anchoring Junctions: Provide strong connections to withstand mechanical stress.

  • Gap Junctions: Protein channels allowing communication and coordination.

Learning Outcomes for Section 3.6

• Illustrate communication methods between plant cells.

• Diagram animal cell connection components.

Summary and Review

• Review Chapter 3 summary in the textbook and learning outcomes for thorough understanding.