Biology 1 Chapter 7 (Lecture) Flashcards
Plasma Membrane
- 8nm thick, 8000 plasma membranes to equal thickness of a page
- Controls traffic into and out of cell it surrounds
- Selective permeability allows some substances to cross it more easily than others.
Cellular membranes are
Fluid mosaics of lipids and proteins. The staple ingredients of membranes are lipids and proteins; carbohydrates are also important.
Most abundant lipid
Phospholipid which has a hydrophobic tail and a hydrophilic head.
Amphipate Molecule
One that has both nydrophilic region and hydrophobic region
Fluid Mosaic Model
The membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a double layer of phospholipids.
By 1915, knew membranes were
Lipids and proteins
By 1925, knew membranes were
phospholipid bilayer with proteins
Where were proteins?
- Sandwich with proteins being “bread” and phospholipids being “meat”– NOT TRUE
- *1972- fluid mosaic model- membrane proteins are dispersed individually inserted into phospholipid bilayer with hydrophilic regions protruding,
Membranes are NOT…
Static sheets of molecules locked rigidly in place.
Membranes are held together by
Hydrophobic interactions which are weaker than covalent bonds.
Most lipids and some proteins can shift about
laterally and also flip flop
Membrane remains fluid as the temperature
goes down until phospholipids settle into closely packed arrangement and membrane solidifies.
Cholesterol
Wedged between phospholipid molecules in plasma membranes of animal cells
- Higher temperature makes membrane less fluid by restraining phospholipid movement
- Hinder close packing of phospholipids
- Lowers temperature required for membranes to solidify
- Cholesterol is “Temperature buffer” for the membrane
Membranes must be
Fluid to work properly; usually as fluid as salad oil
Phospholipids form the main fabric of membrane but the
proteins determines most of the membrane’s function.
2 Major populations of Membranes
- Integral proteins- penetrate hydrophobic core of lipid bilayer; can be transmembrane proteins e.g. span the membrane
- Peripheral proteins- not embedded in lipid bilayer at all; appendages loosely bound to surface of membranes.
Some Functions of Membrane Proteins
- Transport
- Enzymatic activity
- Signal transduction
- Cell to cell recognition- glycoproteins serve as id tags
- Intercellular joining
- Attachment to cytoskeleton and extracellular matric (helps maintain cell shape)
Membranes have distinct
inside and outside faces.
Non Polar Molecules
(Hydrocarbons, CO2, O2) are hydrophobic and can dissolve in lipid bilayer of membrane and cross it easily w/o aid of membrane proteins.
Hydrophobic core impedes
The direct passage of ions and polar molecules through the membrane.
Glucose and other sugars, and water
Are polar, thus DO NOT cross rapidly
Cell membranes are permeable to
Specific ions and a variety of polar molecules by avoiding contact with lipid bilayer by passing through the transport proteins that span the membrane.
2 Types of Transport Proteins
- Channels
- Carriers
Channels
Function by working as a tunnel through the membrane
Aquaporins
Channel proteins that allow the entry of 3 billion water molecules/sec through its channel
Carrier Proteins
Transport proteins that hold onto their passengers and change shape in a way that shuttles them across the membrane.
A Transport Protein
Is specific for the substance it translocates allowing only a certain substance to cross the membrane.
Selective Permeability of a membrane depends on:
- The barrier of the lipid bilayer
- Specific transport proteins built into the membrane
Passive Transport
Is diffusion of a substance across a membrane with NO ENERGY INVESTMENT.
Diffusion
A result of thermal motion; the movement of molecules of any substance so that they spread out evenly into the available space; spontaneous process; no input of energy.
Any substance will diffuse…
Down its concentration gradient.
Osmosis
The diffusion of water across a selectively permeable membrane
Tonicity
The ability of a solution to cause a cell to gain or lose water.
Isotonic
When the concentration is the same inside as outside the cell; no “net” movement of water across a plasma membrane. (CELL STAYS THE SAME)
Hypertonic
There are more solutes in the environment than in the cell. The cell will lose water to its environment, shrivel and probably die if an animal cell. In plant cells, plasma membrane pulls away from wall (plasmolysis) can lead to plant death. (CELL SHRIVELS)
Hypotonic
Water will enter cell faster than it leaves, and the cell will swell and lyse like an overfilled water balloon if it is an animal cell. Plant cells become turgid (very firm). (CELL SWELLS)
Animal Cells
Happiest in ISOTONIC
Plant Cells
Happiest in Hypotonic
Facilitated Diffusion
Passive diffusion with the help of transport proteins that span the membrane.
- Channel
- Carrier
Active Transport
The movement of a solute across a membrane against its gradient REQUIRING WORK. All transport proteins involved in active transport are carrier proteins.
Sodium-Potassium Pump
Exchanges sodium for potassium across the plasma membrane in animals cells. Pumps 3 Na+ for every 2 K+ it pumps into the cell. Net transfer of 1+ charge to extracellular fluid.
Electrogenic Pump
A transfer protein that generates voltage across a membrane.
Membrane Potential
The voltage across a membrane; acts like a battery; inside of cell is NEGATIVE compared to the outside.
The 2 forces that drive diffusion of ions across a membrane
- Chemical force (Ions)
- Electrical Force: The effect of the membrane potential on the ion’s movement
Electrochemical Gradient
The combo of forces acting on an ion.
Electrogenic Pump:
- Sodium potassium pump in animals
- Proton pump in plants, fungi and bacteria-actively transports H+ out of cell
Contransport
The coupling of the “downhill” diffusion of one substance to the “uphill” transport of anothe against its own concentration gradient.
Exocytosis
The cellular ecretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
Endocytosis
The cell takes in biological molecules and particulate matter by forming new vesicles from the plasma membrane.
3 Types of Endocytosis
- Phagocytosis
- Pinocytosis
- Receptor Mediated Endocytosis
Phagocytosis
“Cellular Eating”
Pinocytosis
“Cellular Drinking”
Receptor Mediated Endocytosis
LDL acts as ligands for cholesterol
