bio-membrane transport Flashcards
“fluid mosaic” model
Lumpy, constantly changing / shifting mosaic of “tiles” (proteins)
Functions of the plasma membranes
Isolates cells contents from environment
Regulates exchange of essential substances
Communicate with other cells
Creates attachments within and between other cells
Regulates biochemical reactions
Structure of cell membranes
Phospholipid bilayer with proteins scattered throughout
Describe phospholipid bilayer
2 rows of phospholipids, hydrophilic heads facing outwards on both sides, hydrophobic tails facing inwards in between
What drives the phospholipids to form a bilayer
The exterior and interior of the membrane face watery environments (extracellular fluid, cytosol), hydrophilic heads must face outwards in both sides with tails between
Purpose of cholesterol in membranes on animal cells
Keeps it flexible
What holds the phospholipids together
Weak interactions between phospholipids NOT BONDED TOGETHER
What happens if the fatty acid tails of the phospholipids are unsaturated? Saturated?
If it’s unsaturated there are kinks in their tails, if Saturated they are more straight
What makes the membrane fluid?
Individual phospholipids aren’t bound together,
Unsaturated fatty acids make membrane more fluid than if they were saturated
Where are proteins found in the membrane
Embedded within phospholipid bilayer (either floating or anchored in)
Glycoproteins
Proteins with attached carbohydrates
Categories of membrane proteins
Receptor proteins Recognition proteins Enzymatic proteins Attachment proteins Transport proteins
Receptor proteins
Trigger cellular responses upon binding specific molecules (look at pics in ppt)
Recognition proteins
Serve as identification tags on the surface of the cell
Enzymes
Promote chemical reactions that either make or break up biomolecules
Attachment proteins
Anchor the cell membrane to the inner cytoskeleton, to proteins outside the cell, and to other cells
Transport proteins
Regulate import/export of hydrophilic molecules
Types of transport proteins
Channel and carrier proteins
Homeostasis
Maintain a stable internal state
Biggest contributor in maintaining homeostasis in a cell
Cell membrane
What does it mean to reach equilibrium
All molecules are equally spread out
Opposite of equilibrium
Gradient
Fluid
A substance that can move or change shape in response to external forces
Solute
A substance that can be dissolved (dispersed as ions or molecules)in a solvent
Solution
A mixture in which one substance is dissolved evenly in another
Solvent
Fluid capable of dissolving a solute
Concentration
How much solute in a given amount of solvent
Gradient
A physical difference in temperature, pressure, charge, or concentration in 2 adjacent regions
Why do molecules move from one place to another
In response to a concentration gradient
Concentration gradient
A difference between concentrations in a space
Diffusion
When molecules spread from an area of high concentration to an area of low concentration until equilibrium is reached
The greater the concentration gradient…
…the faster the rate of diffusion
Diffusion cannot…
…move molecules rapidly over long distances
Supersaturated solution
Dissolves as much as it can, excess comes out
Ex: coffee with too much sugar, sugar settles at bottom
2 types of transport across plasma membrane
Passive transport
Active transport
Passive transport :
Which direction do molecules move (in terms of concentration gradient)?
Is energy is expended?
Molecules move down concentration gradient
**membrane proteins and phospholipids may limit what can cross, but not direction of movement
No energy expended
Active transport :
Which direction do molecules move (in terms of concentration gradient)?
Is energy is expended?
Molecules move against concentration gradient
Energy is expended
Selectively permeable
Membranes that allows some things through but not all, like the cell membrane
Types of passive transport
Simple diffusion
Facilitated diffusion
Osmosis
Simple diffusion
Lipid soluble molecules and very small molecules directly diffuse across the phospholipid bilayer
Facilitated diffusion
Water soluble molecules diffuse across the bilayer with the aid of channel and carrier (carrier changes shape) transport proteins (look at pics in ppt)
Osmosis
Diffusion of water
Types of solutions
Isotonic
Hypotonic
Hypertonic
What makes water less pure
More dissolved substances because -> Less free water molecules
Isotonic solutions
No net flow of water (equal amount flowing in and out)
When both sides of the membrane have an equal amount of water and dissolved substances
Hypertonic solution
Low water concentration/high dissolved particle concentration
More Water moves TOWARDS hypertonic solution (than the amount that’s going opposite direction)
Hypotonic solution
Higher concentration of water/lower concentration of dissolved particles
More Water moves AWAY from hypotonic solution (than going in opposite direction)
Red blood cell in isotonic solution
Equal water going in and out of cell
Red blood cell in hypertonic solution (ex: ocean water)
Red flood cell will shrivel up
net water movement is out of cell
Red blood cell in hypotonic solution
Cell will fill up and eventually burst
Net water movement is into the cell
Explain the contractile vacuole in freshwater Protists
Cytosol in protist is hypertonic to freshwater so water flows into protist, but contractile vacuole is pumped with salt, and becomes hypertonic to the cytosol, so water flows into the contractile vacuole where it is contracted out
Freshwater–> cytosol–> vacuole–> out to freshwater
Types of energy-requiring transport
Active transport
Endocytosis
Exocytosis
Why is active transport necessary
To stockpile things – must move against concentration gradient
Active transport
Uses Membrane proteins called pumps that have a molecule binding site and an ATP binding site
Molecule and ATP bind–> energy from ATP changes shape of transport protein –> molecule is moved across membrane (against concentration gradient)–> protein closes / goes back to original shape and used ATP is released as ADP and P
Purpose of endocytosis
To import large molecules or substances
Types of endocytosis
Pinocytosis
Receptor-mediated endocytosis
Phagocytosis
Pinocytosis (“cell drinking”)
A dimple forms in plasma membrane –> it deepens and fills with extracellular fluid–> membrane closes off the dimple, forming a vesicles filled with extracellular fluid
Receptor-mediated endocytosis
Only moves specific molecules into the cell
Receptor proteins for specific particles on coated pit sites–> receptors bind the particles and membrane dimples inward–> coated pit región encloses the receptors forming a “coated vesicle” that is released into cytosol
Phagocytosis (“cell eating”)
Moves large particles or even whole organisms into cell
Cell membrane extends pseudopods toward the particle–> ends of pseudopods fuse together, encircling the particle, and forming a vesicles called a “food vacuole”
Exocytosis
Vesicle fuses with the cell membrane and dumps its contents out
Problem with large cells
The organelles get further away from plasma membrane
There isn’t enough surface are of cell membrane to satisfy the needs of the large cell
Types of specialized junctions
Desmosomes
Tight junctions
Gap junctions/plasmodesmata
Desmosomes
Has protein strands that Attach cells together
Found where cells need to adhere tightly together under stresses of movement (ex: skin)
Tight junctions
Formed by strands of proteins
Make cell leakproof
Found where tubes and sacs must hold contents without leaking (ex: urinary bladder)
Gap junctions
Allow for communication
cell-to-cell channels allowing for passage of hormones, nutrients, and ions
Only in animals
Plasmodesmata
Allows for communication
Cytoplasmic connections with same function as gap junctions
Only in plants
How are plasma membranes adapted for caribous (who live in cold temperatures)?
Cell membranes near their hooves are made of more phospholipids with unsaturated fatty acid tails because unsaturated fats can stay liquid at cold temperatures, allowing the membrane to stay fluid
What does the plasma membrane have to do with snake and spider venoms?
The venoms have an enzyme that breaks down phospholipids, so the venoms attack cell membranes and destroy them, causing the cells and tissue to die
