Chapter 3 cells Flashcards
cell theory
The cell is the smallest structural and functional living unit
all cells come from existing cells
Organismal functions depend on individual and collective cell functions
Biochemical activities of cells are dictated by their specific subcellular structures
Continuity of life has a cellular basis
membrane lipids
75% phospholipids (lipid bilayer)
5% glycolipids
20% cholesterol
glycolipids
for cell recognition
Lipids with polar sugar groups on outer membrane surface
cholesterol
Increases membrane stability and fluidity
Integral proteins
Firmly inserted into the membrane (most are transmembrane) Functions: Transport proteins (channels and carriers), enzymes, or receptors
tight junctions
Prevent fluids and most molecules from moving between cells
Impermeable junctions prevent molecules
from passing through the intercellular space.
Examples: kidneys, , bile duct
Desmosomes
Rivets” or “spot-welds” that anchor cells together
structure support, keep cell from pulling apart
gap junctions
Transmembrane proteins form pores that allow small molecules to pass from cell to cell
Communicating junctions allow ions and small mole-cules to pass
For electrical synapses (not in skeletal muscle)
For movement of ions
Passive processes
No cellular energy (ATP) required
Substance moves down its concentration gradient
diffusion, facilitated diffusion, osmosis
active processes
Energy (ATP) required
Occurs only in living cell membranes
What determines whether or not a substance can passively permeate a membrane
Lipid solubility of substance
( easier to remember: If water soluble or polar, simple diffusion won’t work)
Channels of appropriate size
Carrier proteins
facilitated diffusion
Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins, both of which: Exhibit specificity (selectivity) Are saturable; rate is determined by number of carriers or channels Can be regulated in terms of activity and quantity
Facilitated Diffusion Using Carrier Proteins
Transmembrane integral proteins transport specific polar molecules (e.g., sugars and amino acids)
Binding of substrate causes shape change in carrier
Facilitated Diffusion Using Channel Proteins
Aqueous channels formed by transmembrane proteins selectively transport ions or water
Two types:
Leakage channels
Always open
Gated channels
Controlled by chemical or electrical signals
osmosis
Movement of solvent (water) across a selectively permeable membrane
Water diffuses through plasma membranes:
Through the lipid bilayer
Through water channels called aquaporins (AQPs)
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions. Fluid volume remains the same in both compartments
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
tonicity
The ability of a solution to cause a cell to shrink or swell
isotonic
A solution with the same solute concentration as that of the cytosol
remains same
hypertonic
A solution having greater solute concentration than that of the cell, cell loses water and shrinks
hypotonic
A solution having lesser solute concentration than that of the cell, cell swells and can lysis
Two types of active processes
Active transport
Vesicular transport
Both use ATP to move solutes across a living plasma membrane
Active Transport
Requires carrier proteins (solute pumps)
Moves solutes against a concentration gradient
Primary Active Transport
Energy from hydrolysis of ATP causes shape change in transport protein so that bound solutes (ions) are “pumped” across the membrane
na k pump
Secondary Active Transport
Depends on an ion gradient created by primary active transport
Energy stored in ionic gradients is used indirectly to drive transport of other solutes
Cotransport
Cotransport—always transports more than one substance at a time
Symport system
Two substances transported in same direction
Antiport system
Two substances transported in opposite directions
