Pathology - Cell Structure Flashcards
What are the main components that make up the Plasma Membrane?
The Plasma Membrane or Lipid Bilayer is made up of phospholipids, cholesterol, proteins and lipid rafts.
What are the functions of the Plasma Membrane?
It acts as a selective barrier, and is the structural base for enzymes and receptors.
What are lipid rafts composed of?
Sphingomyelin and cholesterol.
Which lipid types are found primarily on the outer surface of the plasma membrane?
Phosphatidylcholine and Sphingomyelin; and Glycolipids.
Which lipid types are found primarily on the inner surface of the plasma membrane?
Phosphatidylethanolamine and Phosphatidylserine.
What two lipid types can be found on both the inner and outer surfaces of the plasma membrane.
Phosphatidylinositol and Cholesterol.
What is the significance of Phosphatidylserine, especially in terms of phagocytosis?
Phosphatidylserine carries a negative charge and is involved in electrostatic protein interactions.
When it flips to the outer membrane, it sends an “Eat Me” signal to phagocytes. It also signals to Platelets for blood clotting.
What is the importance of Glycolipids and Sphingomyelin in the Plasma Membrane?
They are important in Cell-to-Cell interactions and in Cell-to-Matrix interactions.
What are the functions of Proteins and Glycoproteins in the Plasma Membrane?
- Ion and Metabolite transport
- Fluid phase and receptor-mediated uptake of macromolecules
- Cell-ligand, Cell-matrix and Cell-Cell interactions
Describe Passive Transport.
Molecules move down a concentration or electrical gradient
Ex. Water moves freely across the cell membrane down an osmotic gradient.
Describe Active Transport.
Molecules move against a gradient, by utilizing energy of ATP.
Ex. Na-K-ATPase pump transports K+ intracellularly and Na+ extracellularly against the concentration gradients.
What type of molecules can move by Passive Diffusion?
- Small, non-polar molecules (O2, CO2)
- Hydrophobic molecules (estradiol, Vitamin D)
- Polar molecules
How can larger molecules make it through the Plasma Membrane?
- Channels: Create hydrophillic pores and permit rapid movement of solutes.
- Carriers: bind a specific solute, undergo conformational changes to transport the solute across the membrane. Movement of solutes is much slower.
- Endocytosis: by Potocytosis or Pinocytosis
What is Potocytosis and what is Pinocytosis?
Potocytosis, or “cellular sipping” is caveolae-mediated endocytosis. Involved in signaling or cell adhesion via internalization of receptors and integrins. Resulting in non-coated vesicles.
Pinocytosis, or “cellular drinking” is receptor-mediated endocytosis. Membrane pinches off to form a clathrin-coated vesicle. Contents of vesicle is recycled via exocytosis or fuses with a lysosome after shedding clathrin.
The Cytoskeleton gives cells the ability to….
- Adopt a certain shape
- Maintain polarity
- Organize the relationship of intracellular organelles
- Mobilize
Define cell polarity.
It refers to the spatial differences in shape, structure and function of cells.
What are the three major structures that make up the cytoskeleton?
- Actin microfilaments
- Intermediate filaments
- Microtubules
Describe the structure and function of Actin microfilaments.
They are the thinnest filaments and are made of globulin protein (G-protein) subunits.
In muscle cells they interact with myosin in the contraction process, and in non-muscle cells they control cell shape and movement (motility).
Describe the structure and function of Intermediate filaments.
They are a large family and individual types are tissue specific (Cytokeratin, Vimentin, Desmin).
There are many functions: strength, shape, signal transduction, adhesion, motility, etc.
Describe the structure and function of Microtubules.
They are the thickest filaments. They are hollow tubes, that are constantly elongating or shrinking, with defined polar ends.
They function as connecting cables for molecular motor proteins (Kinesins move antegrade - to +, and Dyneins move retrograde + to -) and they can adapt to form motile cilia or flagella.
Match the junctions with their types. Tight junction, Desmosome, Gap Junction: Anchoring junction, Occluding junction, Communicating junction.
Tight junction = Occluding junction
Desmosome = Anchoring junction
Gap junction = Communicating junction
Junctions are utilized for communication between cells and they enable surface receptors to recognize ligands on other cells.
What are the functions of Tight (occluding) Junctions?
- Create a continuous barrier between cells that does not allow paracellular ion movement.
- Allow the segregation of apical and basolateral domains to cells to maintain cell polarity.
- Dissociate and reform as needed (in epithelial proliferation and in inflammatory cell migration)
What are the functions of Desmosome (anchoring junctions)?
They mechanically attach cells and their intracellular cytoskeletons to other cells or to the extracellular matrix, which allows:
- Extracellular forces to dissipate over multiple cells.
- Influences in cells shape and motility
- Intracellular signals to be generated in response to stress.
What are the functions of Gap (communicating) Junctions?
- Mediate the passage of chemical or electrical signals from one cell to another.
- Contain pores that allow for the passage of small molecules.
- Are Critical in communication! Ex. In Cardiac myocytes, cell-to-cell calcium fluxes coordinate waves of myocardial contraction.
