Biology Cell Structure and Function Quiz

Cell Biology Course Outline

• This course covers cell biology (cytology)
• Topics include: Cell Structure, Cell Signaling, Cell Cycle, Cellular Communication/Tissue Organization & Advanced Topics in Cell Biology
• The academic year is 2024-2025 and the course is for 2nd year medicine students.
• The course is illustrated by Dr. Ghenwa NASR.

1. The Cell

• The cell is the basic structural and functional unit of living organisms.
• Cells are the 'building blocks' of all living organisms.
• The term 'cell' comes from the Latin word 'cellula', meaning 'small room'.
• Cells are small membrane-enclosed units filled with a concentrated aqueous solution of chemicals, the cytoplasm.
• Many cells contain organelles with specific functions.
• Cells are complex and their individual components have various functions in an organism.
• Cells are responsible for the continuity of life through their growth and division.

1.2. The Cell: A Historical Overview

• Pre-17th Century: The concept of the cell wasn't understood.
• 1590s: Hans and Zacharias Janssen created the first compound microscope, enabling observation of small structures.
• 1665: Robert Hooke used a microscope to examine cork, coining the term 'cell' to describe the box-like structures observed.
• 1830: The development of the cell theory.

1.3. The Cell Theory

• Until microscopes became powerful enough to view individual cells, the composition of living organisms was unknown.
• Robert Hooke is considered the first person to view cells, and coined the term.
• Matthias Schleiden and Theodor Schwann proposed the cell theory in 1837.
• The cell theory states that:
  • All living organisms are composed of one or more cells.
  • Cells are the basic functional units in living organisms.
  • New cells are produced from pre-existing cells.
• The modern cell theory elaborates on the original theory by adding:
  • Cells contain hereditary information (DNA).
  • Cells share a fundamental chemical composition.
  • Energy flow occurs within cells.
  • Cell activity depends on the activities of sub-cellular structures (organelles).

2. The Diversity of Cells

• Cells vary greatly in shape and function.

• Unicellular organisms differ from multicellular organisms.

• Even cells within the same multicellular organism can vary widely in appearance and activity.

  • Despite these differences, all cells share a fundamental chemistry and other common features.

• Cells vary enormously in appearance and function due to: size, shape, chemical requirements, function, and internal organization.

• Size: Cells vary in size, most being microscopic but some macroscopic, such as ostrich eggs.

• Shape: Shapes vary depending on the cell type and function. Example: human RBCs are biconcave to fit through capillaries while nerve cells have branching shapes to transmit impulses across the body.

• Chemical Requirements: Some cells require oxygen while others may find it deadly. Some require CO2, sunlight or water for basic function, others require complex mixtures of molecules produced by other cells.

• Function: Cells function varies depending on the type or organism

• Internal Organization: The internal organization of cells determines whether they are prokaryotic or eukaryotic cells.

3. Prokaryotic and Eukaryotic Cells

• Based on complexity, cells are categorized into prokaryotic and eukaryotic.

3.1. Prokaryotic Cells

• Prokaryotes are single-celled organisms without a nucleus or other membrane-bound organelles.
• They are derived from the Greek words "pro" (before) and "karyon" (kernel).
• Prokaryotes include two domains: Bacteria and Archaea
• Prokaryotes are typically spherical, rod-shaped, or spiral-shaped.
• Prokaryotic cells range in size from 0.1 to 5.0 µm in diameter.
• The cell's hereditary material (DNA) is often found in a region called the nucleoid.

3.2. Eukaryotic Cells

• Eukaryotes are advanced organisms with a well-defined nucleus and membrane-bound organelles.
• They are thought to have originated from the prokaryotes about 2.7 billion years ago.
• Eukaryotes can be unicellular or multicellular.
• Eukaryotes reproduce both asexually (mitosis) and sexually (meiosis and gamete fusion)
• Eukaryotic cells are categorized into four groups or domains: protozoa (or protists), fungi, plants, and animals.

4. Techniques in Cell Biology

• Microscopy: Light and electron microscopy are used to visualize and study cells.
• Cell Fractionation and Imaging: separating cell components to determine functions of organelles.

5. Cellular Organelles and Their Function

• Cells are composed of various organelles
• Nucleus: The largest organelle, containing genetic material (DNA) and controlling cell activities.
• Endoplasmic Reticulum (ER): A network of interconnected tubules and vesicles involved in protein and lipid synthesis, folding, and transport.
  • Rough ER (RER): has ribosomes and synthesizes proteins.
  • Smooth ER (SER): lacks ribosomes and synthesizes lipids.
• Golgi Apparatus: Modifies, sorts, and packages materials for transport within or outside the cell.
• Mitochondria: The powerhouse of the cell; responsible for cellular respiration.
• Lysosomes: Degradative organelles containing enzymes to digest organic materials.
• Peroxisomes: Oxidative organelles involved in breaking down fatty acids and other substances.
• Cytoskeleton: A network of protein filaments providing structural support, facilitating movement and cell shape.
  • Microtubules: tube-like structures, aiding in transportation and cell division.
• Ribosomes: Involved in protein synthesis.

6. The Plasma Membrane

• Structure and Composition: The plasma membrane is a phospholipid bilayer with proteins and carbohydrates embedded in it, acting as a selective barrier to regulate what enters and leaves the cell.

• Membrane Lipids:

  • Phospholipids: form the basic structure of the membrane (bilayer), with hydrophobic tails facing inwards and hydrophilic heads toward the exterior/interior.
  • Cholesterol: maintains membrane fluidity (rigidity) in animals.
  • Glycolipids: carbohydrate chains attached to lipids, important in cell communication.

• Membrane Proteins:

  • Integral Proteins: permanently embedded within the membrane (transmembrane).
  • Peripheral Proteins: temporarily associated with the membrane.

• Membrane Carbohydrates:

  • Glycoproteins: linked to proteins, crucial in cell signaling and communication.
  • Glycolipids: linked to lipids, maintain membrane stability and facilitate communication.

• Properties: the membrane has asymmetry; the lipid bilayer has fluidity, influenced by temperature; and it's selectively permeable, allowing certain substances to pass.

• Functions:

  • Maintaining cell shape; protecting and defending the cell (barrier); and maintaining homeostasis and concentration gradient.
  • Signal transduction: Receiving and processing extracellular signals.
  • Catalysis of chemical reactions: Using enzymes.
  • Cell communication: Allows exchange (receiving and sending) of messages between adjacent cells.

• Transport Mechanisms:

• Passive Transport: (no energy required)

  • Simple Diffusion: movement of substances from high to low concentration (across the membrane).

• Facilitated Diffusion: Diffusion with the help of transport proteins (channel or carrier proteins specific to certain molecules).

• Active Transport: (requires energy - ATP)

  • Primary Active Transport: directly uses ATP to move substances against their concentration gradients (such as sodium-potassium pump).
  • Secondary Active Transport: couples the movement of one substance down its gradient to the movement of another against its gradient (against the electrochemical gradient).

• Vesicular Transport: (Large materials - requires energy)

  • Exocytosis: Moves materials from inside the cell to outside; fuses with cell membrane to release contents.
  • Endocytosis: Brings materials from outside the cell into a vesicle by engulfing it..
    • phagocytosis (large particles in vesicles),
    • pinocytosis (fluid in vesicles)
    • receptor-mediated endocytosis (specific molecules and their receptors).