Cell Structure and Function Quiz

Cell Structure and Function

• All living things are made of one or more cells, which are the smallest units of living things.
• Cells in the body vary in function, shape, and size.
• Examples include nerve cells and kidney cells.
• Cells can be rounded, oval, flat, cubical, columnar, spindle, or fusiform.
• Cell sizes vary, with lymphocytes being among the smallest (6µm) and fat cells/ova being among the largest (160µm).

Cell Types

• Cells are categorized into prokaryotic and eukaryotic cells.
• Prokaryotic cells lack a nuclear membrane and membrane-bound organelles in their cytoplasm. They are surrounded by a cell wall. Examples include bacteria and blue-green algae.
• Eukaryotic cells possess a nuclear membrane and membrane-bound organelles in their cytoplasm. They're enveloped by a plasma membrane. Examples include plant and animal cells.

Eukaryotic Cell Components

• Eukaryotic cells contain:
  • Cell (plasma) membrane: A thin membrane, only 7.5-10 nanometers thick, that separates the intracellular and extracellular environments. It's composed of a phospholipid bilayer, proteins, cholesterol, and short-chain sugars. The membrane is flexible due to proteins and phospholipids moving laterally.
  • Protoplasm: The fluid-like material inside the cell, encompassing the cytoplasm (surrounding the nucleus) and nucleoplasm (inside the nucleus). It includes organelles, inclusions, and other substances like water, proteins, carbohydrates, lipids, nucleic acids, and minerals.
  • Nucleus: Contains the nucleoplasm and nucleolus where genetic material (DNA) is stored.

Cell Membrane Structure

• The cell membrane is a lipid bilayer with hydrophilic heads facing outwards and hydrophobic tails facing inwards.
• Proteins are embedded in the membrane, some spanning the entire membrane (transmembrane) and others partially embedded (monotopic). Peripheral proteins are loosely attached to the membrane surface.

Cell Membrane Lipids

• The phospholipids have a polar head composed of phosphate groups (soluble in water) and non-polar tails composed of fatty acids (soluble in lipids).
• Cholesterol molecules are also dissolved in the middle of the phospholipid bilayer, contributing to membrane fluidity.

Cell Membrane Proteins

• Integral proteins: Transmembrane proteins span the entire membrane (e.g., ion channels). Monotopic proteins are embedded only in one side of the membrane. They can act as enzymes.
• Peripheral proteins: Do not penetrate the cell membrane; they are loosely attached to the membrane surface.

Cell Membrane Functions

• Proteins in the cell membrane perform various functions, including structural support, transporting molecules (through channels or carriers), cell-cell recognition, hormone and antigen reception, and enzymatic control of chemical reactions.
  • Carbohydrates on the cell surface attach to proteins (glycoproteins) and lipids (glycolipids) forming a glycocalyx, that helps in cell adhesion and recognition.

Transport Across Cell Membranes

• Passive transport: Movement of materials across the membrane without energy input. It follows the concentration gradient (high concentration to low concentration). Types include simple diffusion, osmosis, and facilitated diffusion.
• Bulk transport/Active transport: Utilizes energy. Endocytosis is the process of transporting substances into the cell (e.g., phagocytosis, pinocytosis, receptor-mediated endocytosis). Exocytosis is the process of transporting substances out of the cell.

Solutions and Osmosis

• Solutions are classified as isotonic (same concentration as body fluids), hypertonic (higher concentration than body fluids), or hypotonic (lower concentration than body fluids) based on their concentration.
• The different concentrations of a solution affect osmosis (water movement) and cell behavior, leading to cell swelling, shrinking or no change.

Cell Membrane Transport Mechanisms

• Simple diffusion: Small molecules (e.g., O2, CO2) diffuse through the lipid bilayer to areas of lower concentration.
• Osmosis: Water moves across a selectively permeable membrane to an area of higher solute concentration.
• Facilitated diffusion: Large molecules (e.g., glucose, amino acids) move through membrane proteins to areas of lower concentration.
• Active transport: Moves substances against the concentration gradient using protein carriers and energy (ATP).

Bulk Transport

• Endocytosis: Engulfing large substances into the cell. Types include phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis.
• Exocytosis: Releasing substances from the cell by fusing vesicles with the cell membrane.