Lecture 2 A&P (membranes) Flashcards
What are integral plasma membrane proteins?
Span the plasma membrane at least part way. Can be transport proteins, enzymes or receptors
What are peripheral plasma membrane proteins?
Bind to some other protein or lipid on either the inside or outside of cell.
eg enzymes, cell to cell links, support, motor, some form of glycocalyx
Explain the process of signal transduction via integral membrane protein (general)?
Extracellular signaling molecule (ligand) binds the receptor (integral membrane protein) which have specificity for ligand. In turn, this elicits an intercellular response. The ligand causes a conformational change. It can enter the cell but doesn’t have to.
What are the three roles of membrane receptors?
1 - Contact signalling (sensing of nearby cells)
2 - Chemical signaling (receptor/ligand interaction)
3 - G protein-linked receptors (2nd messenger)
What could happen when contact signaling is lost between cells?
Tumor formation; cells grow when they’re not supposed to
perhaps caused in mutation in receptor.
How does a G-protein receptor work (4 steps)
1 - Agonist activates membrane bound receptor
2 - G protein is activated and produces effector
3 - Effector stimulates second messenger synthesis
4 - 2nd msgr activates intercellular process
What are two molecules that act as 2nd messengers?
cAMP
Calcium (in conjunction with calmodulin)
What is the first messenger in a 2nd messenger system?
The ligand that binds the protein receptor.
What is the role of a carbohydrate in a plasma membrane?
To form glycocalyx
Other glycoproteins are often responsible for recognition where the carb is the “bait”
What is glycocalyx
An extracellular glycoprotein that functions in protection of the cell
eg, slime on fish, bacterial biofilms
What are three kinds of lipids found in the plasma membrane and their relative percentages?
1 - phosopholipids (75%)
2 - Glycolipds (5%)
3 - Cholesterol (20%
What are lipid rafts? What are their four components and what is a raft’s function?
These are phospholipids, sphingolipids, and cholesterol that function as stable platforms for cell signaling molecules. Also incorporate transmembrane proteins. They are “fishing” for the correct thing for the transmembrane proteins. They make up 20% of the outer membrane surface.
What determines whether or not a substance can passively permeate a membrane
Concentration gradient
lipid solubility of the substance
channels of appropriate size and charge
carrier proteins
What is facilitated diffusion?
Lipophobic molecules use carrier proteins or integral channel proteins to cross the plasma membrane. These exhibit specificity, are saturable, and can be regulated in activity and quantity.
Passive transport
What are the six factors that affect net rate of diffusion?
1 - Distance 2 - molecule size 3- Temperature 4 concentration gradient 5 electrical potential 6 pressure differences
What is Carrier mediated facilitated diffusion
diffusion via a protein carrier specific for one chemical. binding a substrate causes shape change in transport protein
eg sugars and aa
Passive transport
What is channel mediated facilitated diffusion?
Can be leaky or gated
Mostly ions selected on basis of size and charge
Passive transport
What are 2 different kinds of channel mediated facilitated diffusion
ungated (leaky)
gated
What are 3 kinds of gated channel mediated facilitated diffusion
chemically
voltage
mechanically
Define osmolarity
The measure of total concentration of solute particles.
What is osmotic flow?
Movement of water driven by osmosis
What is osmotic pressure?
Indication of force of pure water moving into a solution with higher solute concentration.
What is hydrostatic pressure
Fluid force, can be estimate of osmotic pressure when applied to stop osmotic flow.
What is tonicity?
The ability of a solution to shrink or swell. (isotonic, hypertonic, hypotonic)
What are the three basic passive process across the plasma membrane?
1 - Simple diffusion
2 - facilitated diffusion
3 - Osmosis
Compare/contrast passive/active transport
Passive down concentration gradient
Active against conc grad
Passive can involve a channel or carrier
Active ALWAYS involves a carrier (pump)
Passive requires no additional energy
Active requires energy (ATP)
Define primary and secondary active transport
Primary
molecules are “pumped” against a conc gradient at the expense of energy (direct use of energy)
Secondary
transport is driven by the energy stored in the conc gradient of another molecule (indirect use of energy)
Which type of protein performs primary active transport?
Carrier proteins
What is the relationship between a NA/K pump and osmotic balance
NA/K pumps help regulate osmotic balance by maintaining NA/K balance therefore osmolarity on inside of the cell.
How much energy does our cell dedicate to Na/K pumps
1/3 to 2/3
Draw out the mechanism of Na/K pump (8 steps)
1 - 3 Na enter pump on inside of cell
2 - ATP - ADP cleaving a phosphate
3 - Phosphate attaches to ATPase (pump)
4 - Change on conformation (opens to outside while closing to inside)
5 - Na no longer fits (so dissociate to outside of cell)
6 - 2 K enter the pump on outside of cell
7 - Phosphate pops off ATPase
8- Back to original conformation where K can release to inside of cell (Na can bind again)
At rest, what are the relative concentrations given in terms of high and low of Na/K
High Na outside
High K inside
Maintained by ATPase
What is the resting mV of the inside of a cell?
-70mV
Name 2 other clinically relevant active transporters (Atlases) not Na/K
Ca2+ ATPase in SR
H+ pump with is H+ATPase
Name two different categories of secondary active transport.
1 - Uniport
2 - Cotransport
What are two subcategories of cotransport?
1 - Symport (Secondary active transport)
2 - Antiport (Secondary active transport)
What is vesicular transport for and name three types
For transport of large particles, macromolecules and fluids across plasma membrane (Active transport)
1 - Endocytosis
2 - Exocytosis
3 - Transcytosis
What are three types of endocytosis?
1 - Pinocytosis
2 - Phagocytosis
3 - Receptor mediated endocytosis
Explain pinocytosis
Cell drinking
Formation of endosomes with ECF
No receptor proteins involved
Brings fluid and small molecules into cell
Explain phagocytosis
Cell eating (large molecules) Form pseudopodia to make phagosome Phagosome is the vesicle created by membrane invagination Produces phagosomes Can merge with lysosomes no receptors involved Only performed by phagocytes and macrophages Results in exocytosis of waste material
Explain receptor mediated endocytosis
Brings specific molecules into cell using receptor molecules on membrane surface
- ligand binds receptor
plasma membrane folds around receptors forming pocket that pinches off
endosome is coated with clatherine
receptors are in on inside of endosome
vesicle fuses with lysosomes
ligands are freed from receptors and enter cytosol
lysosome detaches from vesicle
vesicle fuses with plasma membrane again
What are the four steps of exocytosis
1 - membrane bound vesicle migrates to plasma membrane
2 - there, V-SNARES (vesicle) bind with T-SNARES (plasma membrane)
3 - vesicle and plasma membrane fuse and a pore opens up
4- vesicle contents are released to the cell exterior
T snares stay in plasma membrane
V snares dissociate in cytosol
Why are ion channels important?
Action potential in nerves, opening voltage gated channels for muscle contraction.
Name 4 types of specialized intercellular contacts
1 - tight junctions
2 - adhesion belt
3 - Gap junctions
4 - desmosomes
Explain tight junctions
points of attachment between cells so tight they prevent water and solutes from passing between cells. They are formed by interlocking junctional proteins. Found in GI tract.
What is an adhesion belt?
Continuous belt that locks together terminal webs of neighboring cells. Help form larger structures of cells. They are attached to the cytoskeleton. they prevent distortion, and leakage.
What are gap junctions?
Formed by interlocking transmembrane proteins called connexons, which form narrow channels that let small molecules pass for communication between cells.
These are good for coordination activities between cells like mucociliary escalator.
What are desmosomes?
The strongest specialized intercellular junction.
interlock cytoskeletons of adjacent cells via CAMS or they can connect cells to basement membrane when bonded by hyaluronan.
Hemidesmosome is the attachment of a cell to a basement membrane.
What is a hemidesmosome
Hemidesmosome is the attachment of a cell to a basement membrane.
What are the roles of cellular adhesion molecules?
Anchor cells to extracellular matrix or to each other Assist in movement CAMS of blood cells attract WBC Can stimulate synthesis or degradation Transmit intracellular signals.
What are the 4 purposes of a plasma membrane?
1 - Separation from outside/inside
2 - regulation (respond to external signals)
3 - communication (inter/intra cellular)
4 - Structural
Which molecules can diffuse across the lipid bilayer
lipids
lipid soluble molecules
soluble gases
Which molecules diffuse through membrane channel proteins?
Water
small water soluble molecules
ions
Which molecules can not diffuse and need a carrier mechanism
Large molecules
Which 3 biomolecules make up the plasma membrane
lipids
carbohydrates
proteins
What are the 6 functional classes of membrane proteins
1 - anchoring 2 - recognition 3 - enzymes 4 - receptor proteins 5 - carrier proteins 6 - channels
What are anchoring proteins
attach plasma membrane to other structures and stabilize its position. Inside the cell membrane proteins are bound to the cytoskeleton
What are recognition proteins
Detected by cells of the immune system
In what two forms are enzymes found as membrane proteins
integral/peripheral
ATPase is integral
How do receptor proteins function in a plasma membrane
bind to specific ligands
ligand can either be brought into the cell or not
What do carrier proteins do
bind solutes and transport them across the plasma membrane
What are channels?
integral proteins containing a central pore that forms a passageway completely through the plasma membrane; can be selective by size or charge
In the plasma membrane, what does cholesterol do?
Provides fluidity.
