Introduction to Cell Structure and Function

Introduction to Cell Structure and Function

• Cell: Basic structural and functional unit of living organisms.
• Cells: Make up living things and carry out activities that keep a living thing alive.
• Cell Theory: Collection of ideas and conclusions from scientists about cells and their operation.
  • All known living things are made up of one or more cells.
  • All living cells arise from pre-existing cells by division.
  • The cell is the basic unit of structure and function in all living organisms.
• Cell Theory Timeline:
  • 1665: Robert Hooke discovered cells.
  • 1674: Anton Van Leeuwenhoek observed living cells.
  • 1883: Robert Brown discovered the nucleus.

Unicellular and Multicellular Organisms

• Unicellular organism: An organism made up of only one cell (e.g., Euglena, Paramecium, Yeast).
• Multicellular organisms: An organism made up of more than one cell (e.g., Plants, Animals, Fungi).

Cell Size

• Cell size variation: Cells vary significantly in size.
• Microscopic cells: Most cells are microscopic (very small).
• Macroscopic cells: Some cells can be very large.
• Micrometer (µm): Unit used to measure cell size (1 µm = 1/1000 millimeter).
  • Smallest cell: Mycoplasma (0.1 µm).
  • Largest cell: Ostrich egg (18 cm).
• Human cell sizes:
  • Smallest: Sperm cell (5 µm).
  • Largest: Ovum cell (120 µm).
  • Longest: Nerve cell (1 m).

Cell Shape

• Cell shape variation: Cells vary in shape, depending mainly on their function.
• Fixed shape: Most cells have a fixed shape.
• Changing shape: Some cells (e.g., Euglena, Amoeba) can change their shape.
• Human RBCs: Circular, biconcave shape for easy passage through capillaries.
• Human WBCs: Change shape to engulf microorganisms that enter the body.
• Nerve cells: Branched to conduct impulses from one point to another.

Cell Structure

• Compound microscope: Used to study cell structure (magnification 2000X).
• Electron microscope: Used to see the detailed structure of cells (ultrastructure) (magnification 500000X).
• Ultrastructure: Detailed structure of a cell as seen under an electron microscope.

Animal Cell Structure

• Nucleus: Contains DNA, controls cellular activities
• Golgi body: Modifies, sorts, and packages synthesized materials
• Vesicle: Small sac containing cell components
• Plasma membrane: Boundary of the cell, controls what enters/leaves
• Mitochondria: Produces energy (ATP) for the cell
• Cytoskeleton: Provides structure and support to the cell
• Cytoplasm: Jelly-like material containing organelles
• Centrioles: Help in cell division
• Lysosome: Contains enzymes to break down waste materials
• Rough ER: Involved in protein synthesis
• Smooth ER: Involved in lipid synthesis
• Nucleolus: Creates ribosomes

Plant Cell Structure

• Vacuole: Storage area for water and other materials
• Cell wall: Rigid outer layer providing support
• Chloroplasts: Site of photosynthesis
• Other structures similar to animal cells: Nucleus, Golgi body, Mitochondria, Plasma membrane, ER, Lysosomes, Cytoplasm

Bacterial Cell Structure

• Capsule, Cell wall, Plasma membrane, Cytoplasm, Flagellum, Food granules , Plasmid (DNA), Ribosomes, Nucleoid, Pili

Parts of a Cell

• Plasma membrane Semi-permeable barrier, regulates substances
• Nucleus: Contains DNA, controls cell function
• Cytoplasm: Contains organelles and cytosol
  • Cell Organelles:
    • Endoplasmic reticulum (rough and smooth)
      • Rough ER: Protein synthesis
      • Smooth ER: Lipid synthesis
    • Golgi body: Modifies and packages proteins
    • Lysosomes: Break down cellular wastes
    • Vacuoles: Store substances, maintain pressure
    • Mitochondria: Generates energy (ATP)
    • Centrosome: Involved in cell division
    • Cytoskeleton: Provides structure and support

Plasma Membrane

• Structure: Extremely delicate, thin, elastic, living; semi-permeable membrane; made of two layers lipid molecules; protein molecules are floating
• Thickness: Ranges from 75-110 Å
• Observation: Can be observed only under an electron microscope.
• Functions: Maintains shape and size; protects internal contents; regulates entry/exit of substances; maintains homeostasis.

Nucleus

• Structure: Dense spherical body located near the cell center
• Size: Diameter varies from 10-25 μm
• Presence: Present in all cells except red blood and sieve tube cells. Well-developed in plant and animal cells; undeveloped in bacteria and blue-green algae.
• Nucleolus: Creates ribosomes
• Nucleoplasm: Colourless dense sap present inside nucleus
• Chromatin: Network of chromatin fibers
• Chromosomes: DNA strands that condense during cell division

Nucleus (Continued)

• Function: Controls all cell activities (metabolism, protein synthesis, growth, cell division), stores hereditary information in genes.

Cytoplasm

• Structure: Jelly-like material (80% water) between plasma membrane and nucleus; contains cytosol, various particles (proteins, carbohydrates, nucleic acids, lipids, inorganic ions); organelles with distinct structure and function.
• Observation: Some organelles are visible only under electron microscope; granular and dense in animal cells, thin in plant cells.

Endoplasmic Reticulum (ER)

• Structure: Network of tubular and vesicular structures, with connections to nuclear and cell membranes; smooth ER and rough ER
• Rough ER: Possesses ribosomes, involved in protein synthesis.
• Smooth ER: Lacks ribosomes, involved in lipid synthesis, detoxification, and calcium storage.
• Functions: Maintain cell shape and provide support to cytoplasm, protein and membrane protein synthesization, SER detoxification of drugs and poisons, Calcium storage in muscle cells.

Golgi Body

• Structure: Flattened sacs (cisternae), with cis and trans faces; interconnected with endoplasmic reticulum and plasma membrane
• Function: Modifies, sorts, packs materials (synthesized in the cell) ; Delivers materials within and outside cell , Produces vacuoles and secretory vesicles; forms plasma membrane and lysosomes.

Lysosomes

• Structure: Small, spherical membrane sacs; contain hydrolytic enzymes
• Function: Digest large molecules, protect from foreign invaders (bacteria, viruses), degrade worn-out organelles in dead cells (perform autolysis).

Vacuoles

• Structure: Membrane-bound sacs, temporary and small in animal cells, larger and more numerous in plant cells; may be contractile or non-contractile
• Function: Store substances (including waste products), maintain osmotic pressure of the cell, store food particles in amoeba cells, provide rigidity to plant cells.

Mitochondria

• Structure: Small, rod-shaped organelles with two membranes (inner and outer), inner membrane folded into cristae; inner cavity filled with matrix
• Function: Synthesize energy-rich compound ATP, ATP provides energy for vital activities of living cells.

Mitochondrial Disease

• Description: Failure of mitochondria, parts of the cell involved with producing energy. Affects various systems (brain, heart, liver, skeletal muscles, kidney, endocrine, and respiratory). Inherited or a result of a buildup from mutations in DNA.
• Effects: Damage to cells. Can cause problems with growth, muscle movement, swallowing, processing of nutrients and other systems.

Centrosome

• Description: Membrane-bound organelle present near the nucleus; consists of two centrioles (hollow structures made of microtubules).
• Function: Form spindle fibers for chromosome movement during cell division; help in formation of cilia and flagella.

Cytoskeleton

• Description: Network of protein filaments (microtubules and microfilaments; microtubules made of tubulin, and microfilaments made of actin).
• Function: Determine cell shape, give structural strength, and contribute to cell movements.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Nucleus is not developed, single chromosome; lack membrane-bound organelles; size range is 0.5-5 μm (examples:bacteria).
• Eukaryotic Cells: Nucleus is well-developed, multiple chromosomes ; membrane-bound organelles present; size range is 5-100 μm (examples: animals, plants, fungi).

Animal Cell vs. Plant Cell

• Animal Cell (differences from plant cell): Generally smaller, no cell wall, no plastids, vacuoles are smaller and fewer, centrioles are present.
• Plant Cell (differences from animal cell): Generally larger, has a cell wall, has plastids, vacuoles are larger and more, centrioles are absent.

Explore the fundamental concepts of cell structure and function, including the cell theory and the differences between unicellular and multicellular organisms. This quiz covers key historical discoveries and the significance of cells in living organisms. Test your knowledge of essential cell biology principles!