Cell Structure and Function Quiz

Cell Structure and Function

• Cells are the fundamental units of the human body, varying in shape, size, and arrangement, but sharing similar components with specific functions.
• The human body develops from a single cell, the zygote (fertilized egg), which undergoes repeated divisions to form the estimated 75 trillion cells in an adult.

Learning Objectives

• Understand cell structure and function
• Grasp cell division processes
• Delve into membrane transport mechanisms (passive and active transport, bulk transport)

Cell Structure

• A cell comprises a plasma membrane enclosing a cytoplasm filled with organelles and a watery fluid called cytosol.
• Organelles are specialized structures with unique, specific functions.
  • Examples include: nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, centrosomes, cytoskeleton (microfilaments, microtubules), cilia, flagella, microvilli.

Plasma Membrane

• Selectively permeable, allowing some substances to pass while preventing others.
• Composed of a phospholipid bilayer with proteins and sugar molecules embedded.
• The phospholipid molecules have a hydrophilic head and a hydrophobic tail, arranging in a double layer with heads facing the interior and exterior of the cell, and tails sandwiched between.

Plasma Membrane Proteins

• Perform various functions:
  • act as markers for cell identification
  • serve as receptors for hormones
  • act as enzymes, catalyzing biochemical reactions
  • act as carrier molecules for transport across the membrane.

Cytoplasm/Cytosol

• The gel-like substance inside the cell, containing organelles and various substances including electrolytes, metabolic waste products, nutrients (sugars, amino acids), and dissolved organic molecules.

Nucleus

• The control center of the cell, containing the genetic material (DNA) organized into 46 chromosomes.
• Found in all cells except mature red blood cells (which lack nucleuses).

Mitochondria

• Sausage-shaped, known as the "powerhouse" of the cell.
• Releases energy in the form of ATP to the cell via process of cellular respiration.
• Uses oxygen and glucose in a chemical reaction to produce energy.

Ribosomes

• Tiny granules found throughout the cytoplasm, often attached to the endoplasmic reticulum.
• Comprised of ribosomal RNA and proteins.
• Involved in protein synthesis.
  • Some ribosomes function within the cytoplasm to produce proteins that are used within the cell.
  • Other ribosomes are attached to the endoplasmic reticulum (RER) to synthesize proteins for export from the cell.

Endoplasmic Reticulum (ER)

• Network of membranes within the cytoplasm:
  • Rough ER: Studded with ribosomes and involved in protein synthesis (primarily of proteins meant for secretion or insertion into the cell membrane)
  • Smooth ER: Synthesis of lipids and steroid hormones, detoxification of certain drugs and poisons.

Golgi Apparatus

• Series of flattened membranous sacs within the cytoplasm.
• Packages proteins and lipids from the endoplasmic reticulum (RER and SER) into vesicles for transport and secretion.

Lysosomes

• Vesicles containing digestive enzymes.
• Break down cellular waste products (organelles, cellular debris, foreign matter).

Cytoskeleton

• Provides structural support and shape to the cell, forming the "bones" and "muscles" within.
• Composed of three protein fibers:
  • Centrosome: Organises microtubules. Within the centrosome are two centrioles that organise the microtubules.
  • Microtubules: Support the cell and involved in cell division.
  • Microfilaments: Support cell shape and movement, e.g., muscle contraction.
  • Cilia: Hair-like structures used for movement.
  • Flagella: Whip-like structures used for movement.
  • Microvilli: Small projections to increase surface area (e.g., in the digestive tract for nutrient absorption).

Cell Division (Mitosis)

• Process of cell duplication to create two genetically identical daughter cells.
• Occurs in four phases: Prophase, Metaphase, Anaphase, and Telophase.

Interphase

• The period before cell division.
• Cells grow in size and replicate their DNA.
• Preparation for normal cell division and chromosome duplication.

Active, Passive, and Bulk Transport

• Methods of movement of particles through the cell membrane.

Passive Transport

• Movement down the concentration gradient, requiring no energy

  • Diffusion: Movement of particles (molecules, ions) from high concentration areas to areas of low concentration. (e.g.Oxygen,Carbon Dioxide)
  • Facilitated diffusion: Movement of particles, aided by carrier proteins, that can't directly pass through the membrane.
  • Osmosis: Movement of water across a semipermeable membrane from a region of low solute concentration to a region of higher solute concentration.

• Isotonic: The concentration of solutes outside the cell is the same as inside the cell.

• Hypotonic: The concentration of solutes outside the cell is lower than inside the cell, causing water to move into the cell. (Cells swell or even burst)

• Hypertonic: The concentration of solutes outside the cell is higher than inside the cell, causing water to move out of the cell. (Cells shrink)

Active Transport

• Movement against the concentration gradient, requiring energy (ATP).
  • Transports certain substances like ions.

Bulk Transport

• Movement of large molecules through vesicle formation, either into or out of the cell.
  • Endocytosis: Movement of materials into the cell
    • Phagocytosis: "Cell eating," engulfing solids.
    • Pinocytosis: "Cell drinking," engulfing liquids.
  • Exocytosis: Movement of materials out of the cell.