Unit 5_Cell Structure and Function Comprehensive Study Notes

Foundations of Cell Structure and Function

  • Two Basic Types of Cells:

    • Prokaryotic cells: This category consists ONLY of Bacteria.

    • Eukaryotic cells: This category includes all other living things, specifically Animals, Plants, Fungi, and Protists.

  • Universal Characteristics (Shared by ALL Cell Types):

    • Every cell, regardless of type, possesses four common characteristics:

      • Cell (Plasma) membrane.

      • Cytoplasm.

      • DNA: Functions to store genetic information.

      • Ribosomes.

  • Size Comparison:

    • Prokaryotic cells are significantly smaller than eukaryotic cells.

Common Organelles in All Cells (Prokaryotic and Eukaryotic)

  • Organelle Definition:

    • Defined as ‘tiny organs’ or specific cell parts that perform distinct functions for the cell.

  • Cell Membrane:

    • Properties: A semi-permeable membrane that surrounds the cytoplasm of all cells.

    • Function: It maintains homeostasis by controlling the movement of substances in and out of the cell.

  • Cytoplasm:

    • Composition: A jelly-like mixture consisting mostly of water.

    • Function: It surrounds all organelles within the cell and serves to suspend (hold) all other organelles in place inside the cell.

  • Ribosomes:

    • Nickname: Protein Factories.

    • Function: They form our DNA (per transcript).

    • Location: Found freely within the cytoplasm and also attached to the rough endoplasmic reticulum (ER).

  • Genetic Material (DNA):

    • Present in both eukaryotic and prokaryotic cells.

    • Prokaryotic DNA:

      • Structure: Circular.

      • Quantity: Only 1 chromosome.

    • Eukaryotic DNA:

      • Structure: Typically linear.

      • Quantity: Ranges from 1 to multiple chromosomes.

      • Physical State: Exists in the form of chromatin until the cell undergoes meiosis or mitosis.

Specialized Organelles and Movement Structures

  • Mitochondria:

    • Occurrence: Found only in eukaryotic cells.

    • Nickname: The ‘Powerhouse’ of the cell.

    • Function: Produces cellular energy in the form of ATP (Adenosine Triphosphate).

    • Biological Process: It is the site of cellular respiration.

  • Flagella and Cilia:

    • Occurrence: Found in both eukaryotic and prokaryotic cells.

    • Primary Function: Both are utilized for movement.

    • Cilia: Characterized by wavelike movement. An example in eukaryotic animal cells includes lung cells.

    • Flagella: Characterized by propulsion or swimming. An example in eukaryotic animal cells is sperm cells; they are also found in prokaryotic bacteria.

  • Endoplasmic Reticulum (ER):

    • General Function: Acts as lipid and protein factories.

    • Smooth ER: Responsible for lipid production.

    • Rough ER: Responsible for protein production; it is ‘rough’ because it contains ribosomes.

  • Nucleus:

    • Nickname: Control center of the cell.

    • Function: Protects genetic material. Genetic material is usually in the form of chromatin but organizes into chromosomes during mitosis and meiosis.

    • Nucleolus: The specific site where ribosomes are created.

  • Golgi Apparatus:

    • Nickname: The ‘Post Office’.

    • Function: Processes, sorts, and packages proteins and lipids.

    • Transport: Transports materials via vesicles.

    • Vesicle Types:

      • Lysosomes: Used for digesting materials.

      • Peroxisomes: Used to break down toxic substances.

      • Includes several other specialized types.

Organelles Specific to Certain Eukaryotic Cells

  • Cell Wall (Plant Cells):

    • Function: Provides structural support to the cells.

    • Location: Situated outside the cell membrane.

    • Physical Effect: Partially responsible for the ‘crunch’ associated with crisp vegetables and plants.

  • Chloroplast (Plant Cells):

    • Function: The organelle where photosynthesis occurs.

    • Pigmentation: Green pigmentation, which is responsible for plant coloring.

  • Vacuole:

    • Occurrence: Found in both plant and animal cells.

    • Function: Acts as a storage area for water or nutrients.

    • Central Vacuole (Plants):

      • Provides turgor pressure.

      • Stores water.

      • When full, it is partially responsible for the ‘crunch’ of fresh lettuce and other vegetables.

Comparing Prokaryotic vs. Eukaryotic Cell Structure

  • Prokaryotic Cells (PRO-NO):

    • Includes Bacteria ONLY.

    • No nucleus (no nuclei or nuclear membrane).

    • No membrane-bound (M.B.) organelles.

    • Unicellular ONLY (made of one cell).

    • Size: Much smaller than eukaryotic cells.

    • Complexity: Simple, can divide much faster.

    • DNA: Circular DNA located in the cytoplasm.

  • Eukaryotic Cells (Eu-DO):

    • Includes Plant, Animal, Protists, and Fungi cells.

    • Have a nucleus that contains linear DNA.

    • Have many membrane-bound organelles.

    • Complexity: Can be unicellular or multicellular.

    • Size: Much larger.

    • Complexity: Much more complex, take longer to divide.

Evolutionary Theories of Cell Development

  • Endosymbiosis Theory:

    • Core Concept: Complex cells (Eukaryotes) evolved from simple prokaryotic cells.

    • Mechanism: Mitochondria and chloroplasts were originally free-living prokaryotes that were engulfed by a larger ‘host cell,’ leading to a mutually beneficial relationship.

    • Supporting Evidence:

      • Mitochondria and chloroplasts possess their own unique genetic material.

      • Mitochondria and chloroplasts replicate via binary fission, which is the same process used by prokaryotic cells.

      • Each contains their own ribosomes.

  • Autogenous Theory:

    • Core Concept: Organelles evolved internally within cells from the folding and internalization of the cell membrane.

    • Supporting Evidence:

      • The structure of the nuclear envelope, ER, and Golgi can be explained by the folding of the cell membrane.

      • The structure and composition of these specific organelles are similar to that of the cell membrane.

Questions & Discussion

  • Check for Understanding 1: Prokaryotes:

    • Question: Circle/highlight all that apply to Prokaryotes.

    • Options: Have a nucleus / Do Not Have a Nucleus; Have M.B. Organelles / Do NOT have M.B. Organelles; Smaller in size / Larger in Size; Bacteria ONLY / Plants, Animals, Fungus & Protist; More Complex / Less Complex.

  • Check for Understanding 2: Image Justification:

    • Question: Is this a picture of a prokaryote or eukaryote? Justify your answer.

  • Check for Understanding 3: Evolutionary Timeline:

    • Question: So, which came first: prokaryotes or eukaryotes? Explain what happened in your own words.

  • Check for Understanding 4: Theory Sorting:

    • Instruction: Sort the following statements/organelles into the correct category (Endosymbiotic Theory vs. Autogenous Theory):

      • a. Formation of Chloroplasts in eukaryotic cells.

      • b. Formation of Mitochondria.

      • c. Formation of Endoplasmic Reticulum.

      • d. Formation of Golgi complex.

      • e. Creation of plant and animal cells.

      • f. Creation of host eukaryotic cell.

      • g. Components of membrane are same as organelles.

      • h. Organelles contain own DNA.

      • i. Host cell engulfs free-living prokaryotes.