Cytology 3

Plasma Membrane

The cell membrane that acts as a barrier, protects the cell, controls interactions between cells, and selectively transports molecules.

Membrane Organelles

Internal compartments of eukaryotic cells, such as the nucleus and cytoplasmic organelles, that are defined by membranes and maintain differences between their contents and the cytosol.

Fluid-Mosaic Model

A model of membrane structure that proposes a bilayer of phospholipids with embedded protein molecules, forming a mosaic pattern.

Glycolipids

Lipids with a carbohydrate chain attached, found in the outer monolayer of the plasma membrane, involved in cell-cell adhesion and regulating material exchange.

Lipids

The fundamental building blocks of cell membranes, including phospholipids, sphingolipids, glycolipids, and cholesterol.

Phospholipids

Amphipathic molecules with hydrophobic fatty acid tails and hydrophilic phosphate-containing head groups, forming the basic structure of biological membranes.

Cholesterol

A lipid that inserts into the lipid bilayer, making the membrane more impermeable to most biological molecules.

Integral Membrane Proteins

Proteins embedded directly within the lipid bilayer of the membrane.

Peripheral Membrane Proteins

Proteins associated with the membrane indirectly, generally through interactions with integral membrane proteins.

Transmembrane Proteins

Integral membrane proteins that span the lipid bilayer, with portions exposed on both sides of the membrane.

Channel and Pumps

Membrane proteins that allow the passage of small ions, molecules, and water across the plasma membrane, providing active and passive transport.

Receptors and Linker Proteins

Membrane proteins that allow recognition and binding of ligands, as well as anchoring the cytoskeleton to the extracellular matrix.

Enzymes

Membrane proteins involved in specific biochemical reactions, such as ATP synthesis and digestion.

Structural Proteins

Membrane proteins that form junctions with neighboring cells and provide building material for the membrane.

Cell Wall

A rigid extracellular matrix that surrounds plant cells, providing support, protection, and transport channels.

Primary Cell Wall

The initial thin and extensible wall of plant cells, formed during cell division.

Secondary Cell Wall

A rigid wall produced by depositing new layers inside the primary wall, providing additional strength and support.

Peptidoglycan

A chemical found in bacterial cell walls, made of polypeptides bonded to modified sugars.

Gram Stain

A widely used method of identifying bacteria based on the staining of their cell walls.

Gram Positive Bacteria

Bacteria that retain the violet color after the decolorization step in the gram stain method, indicating a thick cell wall.

Gram Negative Bacteria

Bacteria that lose the violet color after the decolorization step in the gram stain method, indicating a thin cell wall.

Peptidoglycan

A dense layer of polysaccharides and peptides that forms the main component of the cell wall in gram positive bacteria.

Teichoic Acids

Polymers of glycerol or ribitol joined by phosphate groups, found in the cell wall of gram positive bacteria.

Cell-Cell Interactions

Direct interactions between cells that are critical for the development and function of multicellular organisms.

Cell Adhesion Molecules (CAMs)

Transmembrane proteins that mediate selective adhesion between cells of specific types.

Selectins

A group of CAMs involved in transient adhesion between cells, particularly in the immune system and inflammation.

Integrins

A group of CAMs involved in stable adhesion between cells and the extracellular matrix.

Immunoglobulin (Ig) Superfamily

A group of CAMs, including intercellular adhesion molecules (ICAMs) and nerve cell adhesion molecules (N-CAMs), involved in cell-cell adhesion.

Cadherins

CAMs that mediate stable adhesion between cells, particularly in epithelial cell sheets.

Tight Junctions

Cell-cell junctions that seal cells together in an epithelium, preventing the leakage of molecules between cells.

Gap Junctions

Cell-cell junctions that allow the passage of small molecules and electrical signals between cells.

Plasmodesmata

Cell-cell junctions in plant cells that directly connect the cytoplasms of adjacent cells.

Anchoring Junctions

Cell-cell and cell-matrix junctions that mechanically attach cells and their cytoskeletons to their neighbors or the extracellular matrix.

Zonula Occludens

Another term for tight junctions, which seal cells together in an epithelium.

Claudins

Transmembrane adhesion proteins that are essential for tight junction formation and function.

Gap Junction Channels

Channels formed by connexins that allow the passage of small molecules and ions between coupled cells.

Desmosomes

Button-like points of intercellular contact that rivet cells together and anchor intermediate filaments.

Integrins

Transmembrane adhesion proteins that bind cells to components of the extracellular matrix and form cell-matrix junctions.

Hemidesmosomes

Half-desmosomes that connect the basal surface of an epithelial cell to the underlying basal lamina.

Basal lamina

The extracellular matrix that separates the epithelial cells from the underlying connective tissue.

Integrins

Cell surface proteins that mediate the adhesion between the extracellular domains and the laminin protein in the basal lamina.

Laminin

A protein found in the basal lamina that binds to the extracellular domains of integrins.

Plectin

An anchor protein that binds to the intracellular domain of integrins and connects them to keratin intermediate filaments.

Keratin intermediate filaments

Structural proteins that provide mechanical support to epithelial cells.

Desmosomes

Cell junctions that connect adjacent epithelial cells and distribute tensile or shearing forces.

Desmosomal plaques

Protein structures within desmosomes where keratin filaments make lateral attachments.