Cell Membrane and Transport Quiz

Cell Membrane and Vesicular Transport

• Cell membranes have diverse functions, relating to molecular structure of membrane lipids and integral/peripheral molecules.
• The fluid mosaic model describes membrane structure.
• Endocytosis and exocytosis are vital processes for transport across the cell membrane.
• Different types of endocytosis exist under normal and pathological conditions.

Cell Components

• Cells are composed of cytoplasm and nucleus.
• Cytoplasmic components are typically not easily distinguished in standard staining.
• The nucleus stains dark blue/black.
• Plasma membrane (plasmalemma) separates cytoplasm from external environment.
• Cytoplasm contains cytosol, organelles, cytoskeleton, and deposits of carbohydrates, lipids, and pigments.
• Cells organize into tissues, organs, and systems.

Plasma Membrane Structure

• Composed of phospholipids, cholesterol, proteins, and oligosaccharides.
• Functions as a selective barrier.
• Membranes are thin (7.5-10nm) and only visible under electron microscopes.

Membrane Phospholipids

• Two nonpolar hydrocarbon tails linked to a hydrophilic head group.
• Tails are hydrophobic; heads are hydrophilic.
• Cholesterol is also a constituent.

Membrane Proteins

• Integral proteins are embedded within the lipid bilayer.
• Peripheral proteins are loosely associated with membrane surfaces.
• Organelle-specific proteins confer unique functions to organelles.

Carbohydrates (Glycocalyx)

• Carbohydrate-rich layer lining the cell exterior (glycocalyx).
• Linked to membrane proteins and lipids, and cell-secreted components.
• Involved in cell recognition and attachments.

Membrane Transport

• Passive transport (simple and facilitated diffusion).
• Active transport (pump and cotransport carrier).
• Bulk transport (endocytosis and exocytosis).

Endocytosis

• Nonselective processes: phagocytosis (cell eating) and pinocytosis (cell drinking).
• Receptor-mediated endocytosis is a selectively endocytotic process.
• Involves receptors binding with cargo molecules.
• Cargo receptors are transmembrane proteins and molecules such as LDLs or protein hormones bind to these receptors.

Endosome Fate

• Early endosomes may recycle receptors to the cell surface or transfer them to late endosomes for degradation.
• Late endosomes fuse with lysosomes.
• Contents of endosomes are broken down; this includes cargo molecules, receptors, and sometimes the whole vesicle.
• Receptor-ligand complexes are also returned to cell membrane for reuse.

Lipid Structure & Functions in Bio-Membranes

• Membranes are "fluid mosaic model", meaning they are flexible to allow cell motion of components.

Phospholipids

• Ionic compounds with hydrophilic heads and hydrophobic tails.
• Two main classes: glycerophospholipids (phosphoglycerides) and sphingophospholipids.
• Glycerophospholipids have a glycerol backbone attached to two fatty acids and a phosphate group.

Cholesterol

• A steroid with four interconnected rings.
• Amphipathic.
• Controls membrane fluidity; increases fluidity at low temperatures and decreases fluidity at high temperatures.
• Helps secure proteins.

Lipid Rafts

• Specialized microdomains in the plasma membrane enriched in cholesterol and sphingolipids.
• Involved in signal transduction and other cellular processes.
• Example of microdomains include caveolae

Test your knowledge on cell membranes and vesicular transport with this quiz. Explore the complex structures and functions of cell membranes, the fluid mosaic model, and the processes of endocytosis and exocytosis. Understand how cells organize into larger systems.