Chapter 3 Part 1: Cells-The Living Units Flashcards
Cell Theory
- the cell is the basic structural and functional unit of life
- organismal activity depends on individual and collective activity of cells
- cellular activity depends on the relative number of specific sub cellular structures
- continuity of life has a cellular basis. Cells can only arise from other cells
Plasma Membrane (general)
- selectively permeable barrier surrounding the cell
- plays a dynamic role in cellular activity
- provides biological markers for cell-cell recognition
Fluid Mosaic Model
Plasma membrane is a bilayer of lipids with imbedded, dispersed proteins
Membrane Lipids
- phospholipids have hydrophobic “tails” and hydrophilic “heads”
- hydrophobic tails make up the interior of the membrane
- glycolipids: are lipids with bound carbohydrate chains on the outer surface of the cell membrane
- cholesterol: helps stabilize the membrane fluidity
Integral Proteins
Firmly embedded in the cell membrane
Most protrude from both sides of the membrane as transmembrane proteins
Peripheral Proteins
More loosely attached at the surface
Glycoproteins
Have attached carbohydrate chains
Functions of Membrane Proteins
- Transport
- Enzyme Activity
- Receptors for signal transduction
- Intercellular joining
- Cell-cell recognition
- Attachment to the cytoskeleton and extracellular matrix
Glycocalyx
Carbohydrate area on the cell surface (glycolipids and glycoproteins)
Provides biological markers for cell recognition and instruction
Specialization of the Cell Membrane
Microvili and Membrane junctions
Microvili
Fingerlike projections on the cell membrane that increase Membrane surface area
Membrane Junctions
Tight Junctions
Anchoring Junctions
Gap Junctions
Tight Junctions
Impermeable (watertight) junction of interlocking Proteins encircling the cell
Anchoring Junctions
Anchors 2 cells together
-desmosomes: anchoring junctions that consist of an internal protein plaque and external linker proteins
Gap Junctions
Collection of hollow protein channels (connexons) that allow substances to pass between cells
Plasma Membrane Functions
Membrane Transport
Membrane Potential
Cell-environment Interactions
Membrane Transport: Passive Processes
no cellular energy required
Diffusion: the tendency for molecules or ions to disperse evenly
*concentration gradient: a difference in concentration of a substance between 2 areas (drives diffusion)
Passive Processes: simple diffusion
- Non-polar and lipid-soluble substances
- Diffuse directly through the lipid bilayer
Passive Processes: Facilitated Diffusion
- Small lipid insoluble solutes
- Diffuse through channel proteins
- Large polar molecules such as simple sugars combine with carrier proteins which move them across
Passive Processes: Osmosis
-osmosis: diffusion of water across a semipermeable membrane
(occurs when the concentration of water on opposite sides of a membrane)
Osmolarity: total concentration of solute particles in a solution
Osmotic Pressure
Pressure required to resist further water entry into a cell
- equal to hydrostatic pressure inside the cell
- in plant cells, creates internal pressure and stops net water movement
- animal cells tend to shrink or swell in response to osmotic imbalances
Tonicity
Measure of the ability of a solution to change cell shape or tone by promoting water flow
- hypertonic
- hypotonic
- isotonic
Hypertonic
- a solution with high concentration of solutes than inside the cell
- cell loses water and shrinks
Hypotonic
- a solution with lower concentration of solutes than inside the cell
- cell gains water and swells
Isotonic
-a solution with the same concentration of solutes than inside the cell
Passive Processes: Filtration
The passage of water and solute through a membrane by hydrostatic pressure
(ex: filtration if urine through the kidney tubes)
- pressure gradient pushes fluid from a higher pressure area to a lower pressure area
Active Processes
Use ATP to move solutes across a membrane
2 Major Mechanisms:
Active Transport
Vesicular Transport
Symport Systems
2 substances are moved across a membrane in the same direction
Antiport Systems
2 substances are moved across a membrane in opposite directions
Active Transport
Primary: direct result of hydrolysis of ATP causing conformational change in the Transport protein. (e.g. Na+-K+ pump)
Secondary: use of an exchange pump (e.g. Na+-K+ pump) indirectly to drive the Transport of other solutes
Vesicular Transport
Transport of large particles and macromolecules across plasma membrane in membrane vesicles.
Exocytosis
moves substances from the cell interior to the extracellular space
Endocytosis
enables large and macromolecules to enter cell
Phagocytosis
Pseudopodia engulf solids and bring them into cell’s interior
Pinocytosis
Cell drinking
Receptor-Mediated endocytosis
Uses receptors in pits all the major mechanisms for specific uptake of macromolecules
Membrane Potential
*Voltage across a membrane
*Resting Membrane Potential
-results mostly from Na+ and K+ concentration gradients across the membrane due to:
~differential permeability of the plasma membrane to Na+ and K+
~sodium potassium pump
Cell-Environment Interactions
Role of Cell Adhesion Molecules
Role of membrane receptors
Cell Adhesion Molecules
- Anchor cells to the extracellular matrix and each other
- assist in movement of cells last one another
- direct white blood cells to injured or infected areas
- respond to tension at the cell surface
Roles of Membrane Receptors (Proteins and Glycoproteins)
- contact signaling
- electrical signaling
- chemical signaling
- g protein-linked receptors and second messengers
Contact Signaling
Important in normal tissue development and immunity
Electrical Signaling
Voltage regulated “ion” gates in nervous and muscle tissue respond to voltage changes
Chemical Signaling
Signal chemicals it ligands (e.g. Neurotransmitters and hormones) bind to membrane receptors
G protein linked receptors
Binding of a ligand activated a g-protein, causing the release of a second messenger (e.g. Cyclic AMP)
