Biology: The Cell Basics

Study Notes

Cells serve as the fundamental structural and functional units of multicellular organisms.
Essential for maintaining homeostasis.
Composed of two primary components: all organisms consist of cells, and cells arise only from pre-existing cells.

Prokaryotic Cells:
- No nucleus.
- Cell walls primarily made of peptidoglycan.
- Lack membrane-bound organelles.
- Examples: Have pili, fimbriae for adhesion, and flagella for movement.
- Size: Ranges from 0.5 to 100 µm.
Eukaryotic Cells:
- Contain a nucleus.
- Cell walls (if present) are made of cellulose or chitin (in fungi).
- Possess membrane-bound organelles allowing compartmentalization.
- Examples: Have cilia or flagella for movement.
- Size: Ranges from 10 to 150 µm.

Animal Cells:
- Generally smaller, lack cell walls.
- Do not possess plastids.
- Many small vacuoles, single prominent Golgi complex, possess centrosome and centrioles.
Plant Cells:
- Larger, have a rigid cell wall made of cellulose.
- Contain plastids.
- Typically have a larger central sap vacuole.
- Have simpler units and a prominent Golgi complex (dictyosomes).
- Lack centrosome and centrioles.

Cell Membrane:
- Acts as a barrier between internal and external environments.
- Provides shape, size, and selective permeability.
- Facilitates cellular communication.
Cytoplasm:
- Contains organelles and cytosol, the fluid part mostly composed of water.
Organelles:
- Subcellular structures with specific functions.

Layers:
- Mucopolysaccharide/carbohydrate layer.
- Outer protein with antigen and receptor sites.
- Lipid bilayer characterized by a fluid mosaic model, comprising phospholipids, cholesterol, and glycolipids.
- Inner protein layer with channels/pores and transporters.

Cilia: Short projections that move fluids across the cell surface.
Flagella: Longer projections that facilitate whole-cell movement, notable in sperm cells.

Typically contains one nucleus per cell, except for red blood cells and platelets.
Muscle cells can be multinucleated.
Functions include regulating metabolic activities and housing genetic material (DNA).

Nucleolus:
- Small, RNA-rich body responsible for ribosome synthesis and cell division regulation.
Nuclear Envelope:
- Double membrane separating the nucleus from the cytoplasm, with outer and inner membranes.
Nuclear Pore:
- Protein-embedded openings that regulate material exchange between the nucleus and cytoplasm.

Network of protein filaments for structural support.
Types of Filaments:
- Microfilaments: Flexible chains of actin molecules.
- Intermediate filaments: Ropelike fibers formed from various proteins.
- Microtubules: Structures that can elongate and shorten to aid in cell function.