Cell Structure and Function Quiz

Cell Structure and Function

• Definition: The cell is the fundamental structural unit of all living organisms. It comprises the cytoplasm and nucleus.

The Cell

• Cytoplasm: Composed of a matrix containing organic and inorganic chemicals; also includes organelles and cytoskeleton, inclusions.

• Organelles: These are metabolically active structures within the cytoplasm performing specific functions.

  • Membranous Organelles: examples include cell membrane, mitochondria, Golgi apparatus, endoplasmic reticulum (rough and smooth), lysosomes, secretory vesicles
  • Non-membranous Organelles: examples include ribosomes, microtubules, microfilaments, intermediate filaments, centrioles, cilia, flagellum

• Cytoskeleton: Fibrillar elements within the cytoplasm providing structural support and facilitating movement. -Includes microtubules, microfilaments, intermediate filaments

• Cytosol: The liquid portion of the cytoplasm, the fluid component.

• Inclusions: Non-living material within the cytoplasm (e.g., stored nutrients).

I- Cell Membrane

• Structure: A thin, double-layered structure (unit membrane), composed of lipids, proteins and carbohydrates.

  • Lipids: Primarily phospholipids and cholesterol, arranged in two layers (bilayer).
    • Hydrophilic heads face outward, hydrophobic tails inward.
  • Proteins: Integral and peripheral proteins embedded within or associated with the lipid bilayer.
    • Integral proteins: partially or completely span the lipid bilayer
    • Peripheral proteins: located on the inner side of the membrane.
  • Carbohydrates: Polysaccharides attached to proteins and lipids on the outer surface forming the glycocalyx.

• Functions:

  • Separates the cell from its environment.
  • Controls movement of substances in and out of the cell.
  • Utilizes mechanisms such as passive diffusion (ions, water), active transport, facilitated diffusion (glucose etc.)., selective transport (receptors).

II- Mitochondria

• Structure: Rod-shaped or spherical organelles with two membranes (inner and outer).
  • Inner membrane is folded into cristae, creating more surface area for chemical reactions.
  • The intermembrane space and matrix space are the spaces between the inner and outer membranes respectively, and filled with matrix containing DNA, RNA, ribosomes, and proteins.
• Functions: The powerhouse of the cell; site of oxidative phosphorylation, generating energy for cellular processes.
  -Contains enzymes for the Krebs cycle. -Regulates calcium levels.

III- Ribosomes

• Structure: Small particles composed of proteins and ribosomal RNA (rRNA), having a large and small subunit.
• Location: Found free in the cytoplasm or attached to the rough endoplasmic reticulum (RER).
• Function: Sites of protein synthesis

IV- Endoplasmic Reticulum (ER)

• Structure: System of interconnected tubes, vesicles, and flattened saccules (cisternae) surrounded by a limiting membrane.
  • Two types: rough and smooth.
• Rough ER (RER): Studded with ribosomes; involved in protein synthesis and transport.
• Smooth ER (SER): Lacks ribosomes; involved in synthesis of lipids, steroids, detoxification, glycogen metabolism and calcium regulation

V- Golgi Complex/Apparatus

• Structure: Stacks of flattened membranous sacs (cisternae).
  -Has a forming (cis) face and a maturing (trans) face.
• Function: Modifies, sorts, and packages proteins and lipids. It is involved in protein secretion. Processes and delivers various cellular constituents.

VI- Secretory Granules (Vesicles)

• Structure: Membranous sacs containing secretory products from the Golgi apparatus.
• Function: Store products for later release from the cell (exocytosis).

VII- Lysosomes

• Structure: Membranous sacs containing hydrolytic enzymes.
• Function: Digest cellular waste, worn-out organelles, or foreign materials
• Types: Primary lysosomes contain digestive enzymes within the vacuole. Secondary lysosomes result from the fusion of primary lysosomes with other vesicles.

Cell Membrane Processes

• Phagocytosis: Engulfing solid materials
• Pinocytosis: Engulfing liquid materials.
• Exocytosis: Releasing waste materials.