The cell can be divided into two: the plasma membrane and the cytoplasm.
Plasma Membrane (Cell Membrane)
Separates the cell contents, or cytoplasm, from the extracellular fluid.
Structure
The cell membrane is composed of a lipid bilayer and transmembrane proteins:
- Lipids:
- Phospholipids: Forms the lipid bilayer with a hydrophilic head and hydrophobic tail.
- Cholesterol
- Glycolipids
- Protein:
- Integral membrane proteins
- Peripheral membrane proteins
- Glycoproteins
Functions:
- Selectively permeable barrier; nutrients in, wastes out.
- Communication.
- Intercellular connections.
- Physical barrier.
- Singer and Nicholson’s model of cell membrane.
Cytoplasm
Is a general term for the material located between the plasma membrane and the membrane surrounding the nucleus. Its consistency varies from that of thin maple syrup to almost-set gelatin. Cytoplasm contains many more proteins than does extracellular fluid.
Cytoplasm can be subdivided into two: cytosol & organelles.
- Cytosol: The fluid part of the cytoplasm, also called intracellular fluid. It may contain various types of insoluble materials.
- Organelles (little organs): Intracellular structures with specific functions.
Organelles are further classified into membranous and non-membranous organelles.
- Membranous organelles: Which are isolated from the cytosol by phospholipid membranes, just as the plasma membrane isolates the cytosol from the extracellular fluid.
- Peroxisomes
- Lysosomes
- Golgi apparatus
- Nucleus
- Endoplasmic reticulum
- Mitochondria
- Non-membranous organelles: Are not completely enclosed by membranes, and in many, all of their parts are in direct contact with the cytosol.
- Cytoskeleton
- Microvilli
- Centrioles
- Cilia
- Ribosomes
STRUCTURE: A nucleoplasm (fluid in the nucleus) containing enzymes, proteins, DNA, and nucleotides; surrounded
by a double membrane, the nuclear envelope.
FUNCTION: Control metabolism; store and process genetic information; control protein synthesis.
STRUCTURE: Network of membranous sheets and channels extending throughout the cytoplasm.
FUNCTION: Synthesize secretory products; store and transport substances inside the cell.
- Smooth ER, which has no attached ribosomes, synthesizes lipids and carbohydrates.
- Rough ER, which has ribosomes bound to the membranes, modifies and packages newly synthesized proteins.
Smooth ER
Rough ER
Golgi Apparatus
STRUCTURE: Stacks of flattened membranes (cisternae) containing chambers.
FUNCTION: Modify and package proteins.
Mitochondrion
STRUCTURE: Double membrane, with inner membrane folds enclosing important metabolic enzymes.
FUNCTION: Produce 95% of the cell’s ATP.
STRUCTURE: RNA and proteins; fixed ribosomes bound to rough ER, free ribosomes scattered in cytoplasm.
FUNCTION: Synthesize proteins.
STRUCTURE: Vesicles containing digestive enzymes.
FUNCTION: Break down large organic compounds, damaged organelles, and pathogens (disease-causing agents).
STRUCTURE: Vesicles (membranous sacs) containing degradative enzymes.
FUNCTION: Break down fatty acids and organic compounds; neutralize toxic compounds generated in the process.
STRUCTURE: Membranous extensions containing microfilaments.
FUNCTION: Increase surface area to help absorption of extracellular materials.
STRUCTURE: Proteins organized in microfilaments (fine filaments) or microtubules (slender tubes); organizing center that contains a pair of centrioles.
FUNCTION: Strengthen and support cell; move cellular structures and materials.
