Chapter 7 Flashcards
(53 cards)
Plasma membrane
- the boundary that separates the living cell from its nonliving surroundings
- exhibits selective permeability allowing some substances to cross more easily than others
?-extracellular matrix is nonliving
-size, charge, shape, what’s on the surface of a cell can determine what can get in
Cellular membranes are a…
- bilayer
- fluid mosaics (mixture) of lipids, proteins, and carbohydrates
Phospholipids structure
the most abundant lipid in the plasma membrane
- are amphipathic molecules
- arranged according to the fluid mosaic model
Amphipathic
contains both hydrophobic and hydrophilic regions
Fluid Mosaic Model
a membrane is a fluid (flexible/moveable) structure with a “mosaic” of various proteins embedded in it
-dynamic
Phospholipids in the plasma membrane
- can readily move within the bilayer
- with the proteins drifting within the bilayer
- can move laterally really fast (x10^7per sec/ spontaneously)
- can flip-flop very slowly (once per month)/ not spontaneous
Membrane fluidity
influenced by specialized motor proteins, temperature, and lipid composition
Flippases
- enzyme that catalyze the phospholipid flip-flop from one side to another
- help accelerate to move phospholipids quicker
The type of hydrocarbon tails in phospholipids affects …
the fluidity of the plasma membrane
Saturated fatty acids
- are less fluid than unsaturated fatty acids
- are more tightly packed
Unsaturated fatty acids
are more fluid
steroid (cholesterol)
has different effects on membrane fluidity at different temperatures
?what affects the fluidity
- type of fatty acids
- type of steroid
- specialized proteins
- temperature
Warm temperatures (37C)
cholesterol restrains (“holds on” because of hydrophobicity) the movement of phospholipids and reduces fluidity
Cool temperatures
- cholesterol maintains fluidity by preventing packing
- molecular motion slows down, doesn’t let the phospholipids compress
Membrane is a collage of …
different proteins embedded in the fluid matrix of the lipid bilayer that help to determine the membrane’s specific functions
i.e. collagen proteins help hold cells together
The cellular membrane is composed of two pieces/layers
1) inner layer (cytoplasmic side)
2) outer layer (extracellular side)
AKA. leaflets
Integral Proteins
- embedded within
- penetrate the hydrophobic core of the lipid bilayer
- often transmembrane proteins that completely span the membrane
Peripheral Proteins
- appendages loosely bound to the surface of the membrane
- are loosely attached to surface of the cell
- can come-and-go
- doesn’t go all the way through the membrane
- may embed in one of the leaflets
6 major functions of membrane proteins
1) Transport
2) Enzymatic Activity
3) Signal Transduction
4) Cell-Cell Recognition
5) Intracellular Joining
6) Attachment to the cytoskeleton and extracellular matrix (ECM)
Transport
a protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute
- can change shape or use ATP
- to get into the cell
Enzymatic activity
a protein in the membrane may be an enzyme with its active site exposed to substances in the adjacent solution
- can carry out sequential steps of metabolic pathway
- can control what they do
i. e. proteins in mitochondria will affect different
- can localize proteins
- improves efficiency
Signal Transduction
a membrane protein may bind an external messenger (signal) that causes a message to be sent inside of the cell
- function as a receptor
- lock and key
- i.e. endorphine and pain response
Cell-Cell Recognition
some glycoproteins serve as identification tags that are specifically recognized by other cells, facilitating cell-cell recognition
- cell circular and move around the body
- or adjacent cells in tissues
- use proteins to associate with other proteins to determine if adjacent cells are a part of that organism
- “handshake”
i. e. foreign vs. immune cell