The _______ ___________ is a boundary between what's inside and outside of the cell.
plasma membrane
until about 1970 the ____________ model was widely accepted. It had a layer of ______________ in the middle between two layers of ___________.
sandwich, phospholipids, proteins
Today we use the ________ __________ model which has ________ embedded into the phospholipid bilayer
fluid mosaic, proteins
What does semi-permeable mean?
Passage from one side of the membrane to the other is restricted due to multiple factors.
What is the most common molecule in the membrane according to the fluid mosaic model?
Phospholipids
Why do phospholipids form a bilayer?
Because they orientate their hydrophobic tails together and shield them from surrounding water with their hydrophilic heads.
Phospholipids are __________ molecules, containing hydrophobic and hydrophilic regions
amphipathic
What are the hydrophobic and hydrophilic regions of phospholipids made of?
Fatty acid tails and phosphate group heads
If you transposed part of a dog cell's membrane into a cat cell's membrane would they stay separate or would they mix? Why?
They would mix because the molecules of the membrane will move around
A membrane rich in unsaturated fatty acids will be more
(fluid/viscous) than
those rich in saturated fatty acids. Why is this?
Fluid
The bends in unsaturated fatty acids prevent close packing of the membrane
How does cholesterol affect the membrane?
At warm temperatures, it restrains movement of phospholipids and at
cool temperatures, it
maintains fluidity
__________ proteins are bound to the surface of the membrane
Peripheral
____________ proteins penetrate the hydrophobic core, and are embedded in the membrane
Integral
What are transmembrane proteins and are they integral or peripheral, why?
Integral, despite not reaching both sides of the bilayer they still penetrate the hydrophobic core of the membrane.
What does the hydrophobic regions of an integral protein consist of?
One or more stretches of nonpolar amino acids, often coiled into alpha helices
In the membrane, proteins have six major functions. What are they?
Transport
Enzymatic activity
Signal
transduction
Cell-cell recognition
Intercellular
joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
Which protein function does HIV take advantage of in order to enter the cell?
...
Extracellular surface molecules, often containing carbohydrates, do what?
Allow Cell-Cell Recognition when they bind to each other.
Membrane carbohydrates may be covalently bonded to ______ or more commonly to __________. The resulting molecules are called...?
lipids, proteins
glycolipids, glycoproteins
The Carbohydrates of plasma membranes vary among species, individuals, and cell types in an individual, true or false?
True
Does the plasma membrane have sidedness?
Yes
(nonpolar/polar) molecules can dissolve in lipid bilayer and pass through membrane rapidly.
nonpolar
___________ proteins allow hydrophilic substances to pass across membrane
Transport
_________ proteins have hydrophilic tunnel that certain molecules or ions can use as a tunnel
channel
Which channel protein is used to specifically transport water?
aquaporins
______ proteins bind molecules and change shape to shuttle them across membrane
carrier
A transport protein is specific for the substance it moves, true or false?
True
_________ is the tendency for molecules to spread out evenly into available space
Diffusion
In diffusion each molecule moves randomly, true or false?
True, however diffusion of a population
of molecules may be directional
Explain dynamic equilibrium.
When the total movement of molecules both directions across the membrane is net 0.
Substances diffuse (up/down) their concentration gradient
down
Diffusion of a substance across a biological membrane is ________ transport
passive
________ is the diffusion of water across a selectively
permeable membrane
Osmosis
Water diffuses across a membrane from the region of _____ solute concentration to the region of _____solute concentration
lower, higher
When does water stop diffusing across a membrane?
When the solute concentration is equal on both
sides
_______ is the ability of a surrounding solution to cause cells to gain or lose water
Tonicity
What happens to a cell in an isotonic, hypotonic and hypertonic solution?
no net water movement across the plasma
membrane, cell gains
water, cell loses water
Define Osmotic concentration
total solute concentration of a
solution
Which three terms are used to describe an animal cell in the three types of tonicity? What kind of solution do they prefer?
Shrivelled, normal and lysed
Prefer isotonic
Which three terms are used to describe a plant cell in the three types of tonicity? Which do they prefer?
Plasmolyzed, turgid, flaccid
Prefer hypotonic
Define Osmoregulation
the control of solute concentrations and
water balance
In __________ ___________, transport proteins aid the passive movement of molecules across the plasma membrane
facilitated diffusion
___ channels are a type of channel protein which facilitate the diffusion of ions
ion
Some ion channels are _________ _________, which open or close in response to a stimulus
gated channels
_______ proteins undergo a subtle change in shape
(___________)
that translocate the solute-binding site across the membrane
Carrier, conformation
Active transport requires _______, usually in the form of ________
energy, ATP
________ ___________ is the voltage difference across a membrane
Membrane potential
What is membrane potential caused by?
Voltage is created by differences in the distribution of positively and negatively charged ions across a membrane
Two combined forces, collectively called electrochemical gradient, drive diffusion of ions across a membrane. What are they?
A chemical force, An electrical force
An ___________ ______ is a transport protein that generates voltage
across a membrane. The sodium-potassium pump is the major __________
______ of
animal cells
electrogenic pump, electrogenic pump
The main electrogenic pump of plants, fungi, and bacteria is a _________ pump
proton
Electrogenic pumps help store energy that can be used for ___________ ______
cellular work
________ occurs when active transport of a solute indirectly drives transport of other solutes
Cotransport
Large molecules, such as polysaccharides and proteins, cross membrane via __________
vesicles
Does bulk transport require energy?
Yes
Describe exocytosis
transport vesicles migrate to the membrane, fuse
with it, and
release their contents to the outside of the cell
Describe endocytosis
cell takes in macromolecules by forming
vesicles from the
plasma membrane
What are the three types of endocytosis?
Phagocytosis, Pinocytosis, Receptor-mediated endocytosis
In Phagocytosis what fuses to the newly made vesicle to digest its contents?
lysosome
In receptor-mediated endocytosis, binding of ________ to receptors triggers vesicle formation
ligands
Human cells use receptor-mediated endocytosis to take in __________ for synthesis of membranes and other steroids
cholesterol