Study Notes on Cells first half Organelles

Functional Unit of the Body

  • Basic Unit of Life

    • The cell is identified as the basic structural and functional unit of the body.

    • Cells with similar structure and function unite to form tissues.

  • Variety of Cell Types

    • Cells exhibit diverse shapes and sizes.

    • Different cell types perform unique functions throughout the body.

Types of Cells

  • Prokaryotic Cells

    • Characteristics:

    • Lack a nucleus.

    • Examples:

    • Not human body cells, often found as pathogens causing diseases.

    • Beneficial prokaryotic cells known as normal flora assist in digestion (e.g., located in the gut and on the skin).

    • Note: Prokaryotic cells are not the primary focus; further details are covered in dedicated courses.

  • Eukaryotic Cells

    • Characteristics:

    • Contain a nucleus and membrane-bound organelles.

    • House DNA within the nucleus.

    • Importance of Nucleus:

    • Acts as the control center containing genetic information necessary for cellular functions.

    • Components of Nucleus:

    • Nuclear Envelope: Regulates movement in and out of the nucleus.

    • Nucleolus: Center portion involved in ribosome production.

    • Chromatin: Genetic material present outside the nucleolus.

Plasma Membrane

  • Structure:

    • Unlike a solid wall, it is dynamic and flexible, surrounding all cells.

    • Contains specialized pumps and gates that regulate nutrient and waste movement.

  • Functions:

    • Separates extracellular fluid (outside) from cytoplasm (inside).

    • Maintains a large surface area facilitating enzyme activity,

    • Enables regulatory movement of substances in and out of the cell.

Cytoplasm and Extracellular Fluid

  • Cytoplasm:

    • Also called cytosol, it is the fluid within the cell that suspends organelles.

  • Extracellular Fluid:

    • Total fluid outside the cell, which may contain interstitial fluid (fluid between cells in tissues).

Cytoskeleton

  • Function:

    • A network of protein fibers providing structure and shape to the cell, analogous to a skeleton in humans.

    • Dynamic nature allows rapid assembly and disassembly to facilitate movement of cell components.

  • Components of Cytoskeleton:

    • Microtubules:

    • Structure: Hollow cylinders made of tubulin subunits.

    • Functions: Involved in chromosome movement during cell division; form cilia and flagella; maintain cell structure.

    • Cilia and Flagella:

    • Flagella: Long whip-like structures enabling propulsion through fluids.

    • Cilia: Shorter structures found in large numbers, necessary for moving debris and mucus, particularly in the respiratory tract.

    • Microfilaments:

    • Structure: Smaller, flexible solid fibers made of actin.

    • Functions: Assist in cell division and muscle contraction (actin and myosin interaction).

Chromosomes and Genetic Material

  • Chromosomes:

    • Packaged form of DNA made up of nucleotides (A, T, G, C).

    • Gene: A section of DNA that encodes for a specific protein.

    • Information Flow:

  • mRNA (Messenger RNA): Transcription of DNA information carried to ribosomes for protein synthesis.

    • Different types of RNA present but focus on mRNA is crucial.

Ribosomes

  • Function:

    • Sites of protein synthesis, acting as manufacturing plants within the cell.

    • Utilizes information from mRNA, processed in codons (groups of three nucleotides), to assemble amino acids into polypeptides.

  • Types of Ribosomes:

    • Free ribosomes (in cytoplasm) and rough endoplasmic reticulum (attached ribosomes).

Endoplasmic Reticulum (ER)

  • Rough ER (RER):

    • Ribosome-covered ER involved in protein synthesis and modification.

  • Smooth ER:

    • Lacks ribosomes and is primarily involved in lipid synthesis (especially in liver cells).

Golgi Apparatus

  • Structure:

    • Composed of flattened sacs with separate compartments for processing.

  • Function:

    • Acts as the cell's UPS center for receiving, packaging, and transporting proteins.

    • Creates vesicles for intracellular and extracellular protein movement and secretion.

Lysosomes

  • Structure:

    • Small sacs of digestive enzymes, functioning as the recycling center of the cell.

  • Function:

    • Breaks down large biomolecules into smaller components for reuse within the cell or for excretion.

    • Can fuse with vesicles to destroy pathogens (important for immune response).

  • Pathology Example:

    • Tay-Sachs Disease: Genetic disorder due to absence of a digestive enzyme in lysosomes, leading to lipid accumulation in the brain, resulting in fatal outcomes.

Proteasomes

  • Structure:

    • Non-membrane bound organelles focused specifically on protein recycling.

  • Function:

    • Chops up damaged or misfolded proteins, supporting cellular maintenance and apoptosis (programmed cell death).

  • Quiz Yourself: Pause to review your knowledge of cell function and organization, focusing on key concepts from this module.