Semester Exam: membrane functions/structures Flashcards
plasma membrane
lipid and protein bilayer, changing fluid mosaic
seperates intrecellular and extracellular fluid
membrane lipids
phospholipids
glycolipids
cholesterol
phospholipids
Phosphate heads: polar and hydrophilic
Fatty acid tails: nonpolar and hydrophobic
glycolipids
Lipids with polar sugar groups on outer membrane surface
cholesterol
Increases membrane stability and fluidity
integral proteins
inserted in membrane, function transporting proteins, enzymes, or receptors
peripheral proteins
loosely attached to integral proteins
Include filaments on intracellular surface and glycoproteins on extracellular surface
peripheral proteins function
enzymes, motor proteins, support
functions of membrane proteins
Transport
Receptors for signal transduction
Attachment to cytoskeleton and extracellular matrix
membrane junctions three types
tight
desmosome
gap
tight junctions
Impermeable junctions Prevent fluids and most molecules from moving between cells
desmosomes
rivets that anchor cells together
gap junctions
Transmembrane proteins form pores that allow small molecules to pass from cell to cell, communicating junctions
passive transport
No cellular energy (ATP) required
Substance moves down its concentration gradient
active transport
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
Channels of appropriate size
Carrier proteins
passive transport types
Simple diffusion
Carrier-mediated facilitated diffusion
Channel-mediated facilitated diffusion
Osmosis
Simple Diffusion
Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through the phospholipid bilayer
Facilitated Diffusion
Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins
both channel proteins and carrier proteins
Exhibit specificity (selectivity) Are saturable; rate is determined by number of carriers or channels
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
Aqueous channels formed by transmembrane proteins selectively transport
ions or water
Facilitated Diffusion Using Channel Proteins 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
osmolarity
`The measure of total concentration of solute particles
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
Hypertonic
A solution having greater solute concentration than that of the cytosol
Hypotonic
A solution having lesser solute concentration than that of the cytosol
cells in isotonic solution
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as inside
cells; water moves in and out).
cells in hypertonic solution
Cells lose water by osmosis and shrink in a hypertonic solution (outside contains a higher concentration of solutes than are present inside the cells)
cells in hypotonic solution
Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (outside contains a lower concentration of solutes than are present in cells).
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
vesicular transport
Transport of large particles, macromolecules, and fluids across plasma membranes
Requires ATP
Exocytosis
out of cell
endocytosis
into cell
transcytosis
transport into,across, and then out of cell
Phagocytosis
pseudopods engulf solids and bring them into cell’s interior
food, macrophages, white blood cell
pinocytosis
bringing extracellular fluid and solutes into interior of the cell
Nutrient absorption in the small intestine