biology 1115 chapter 7
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biology 1115 chapter 7
Membrane structure and function
What is selective permeability?
Allowing some substances to cross it more easily than others.
What is the cell membranes composed of?
Composed of a fluid-mosaics of
Phospholipids are the most common lipid.
What type of molecules are phospholipids? what does it mean?
molecules which means they contain
Can phospholipids in the plasma membrane move within the bilayer? If so, how?
Yes they can. Most of the lipids and some protein drift
. Rarely do they flip-fop.
What may cause a flip-flop to occur?
Membranes rich in ___________ are more fluid than those rich in ___________ .
unsaturated fatty acids, saturated fatty acids.
What are the different effects that
has on membrane fluidity at different temperatures?
At warm temperatures,
cholesterol retains movement of phospholipids
At cool temperatures, it
by preventing tight packing of phospholipids
-cholesterol (only in animal cells) acts as a buffer
What determines most of the membrane's specific functions?
Define peripheral proteins.
They are bound to the surface of the membrane. (more hydrophobic)
Define integral proteins.
penetrate the hydrophobic core.
embedded through the bilayer.
What functions do membrane proteins perform? (6)
attachment to the cytoskeleton and the ECM
What function does carbohydrates play in the plasma membrane?
each other by binding to carbohydrates on the plasma membrane.
What are the two membrane carbohydrates and how are they bonded?
Membrane carbohydrates may be
bonded to lipids (forming
) or more commonly to proteins (forming
What types of substances would you expect to easily pass through the lipid bilayer?
molecules such as
polar molecules DO NOT cross
What is passive transport?
of a substance across a membrane with
What is diffusion?
It's the tendency for molecules to
spread out evenly
into the available space.
moves from an area of high concentration to low concentration
What are the movements of substances in passive transport?
, from an area where its MORE concentrated to where it's LESS concentrated with no energy.
Define Osmosis. (2)
It's the diffusion of
selectively permeable membrane
diffuses from the region of
lower solute concentration
to the region of
higher solute concentration.
What is tonicity?
It's the ability of a solution to cause a cell to gain or lose water.
what is hypertonic?
It's when a solution has a higher solute concentration than cell
causes cell to lose water and shrivel
What is hypotonic?
Solution has a lower solute concentration than the cell
causes cell to gain water and burst
What is isotonic?
Solution and cell have equal solute concentrations.
When animal cell bursts from a hypotonic solution, what is it called?
What happens to a plant cell when it's in a hypotonic solution?
swells until the walls opposes uptake
cell is now
What happens to a plant cell when it's in a isotonic solution?
no net movement of water into the cell
cell becomes flaccid (limp) and plant may wilt
What happens to a plant cell when it's in a hypertonic solution?
plant cells lose water
eventually membrane pulls away from the wall, an effect called
What happens in facilitated diffusion?
when transport proteins speed the
movement of molecules across the plasma membrane.
What are transport proteins?
that allow passage of
across the membrane.
What are channel proteins?
that certain molecules or ions can use as a tunnel.
What facilitated transport/diffusion?
Its a passive transport aided by proteins.
What are ion channels?
Channels that open and close in response to stimulus. (
What are carrier proteins?
These proteins bind to molecules and
to shuttle them across the membrane.
What is active transport?
their concentration gradient
, usually in the form of
What is the sodium-potassium pump? (3)
one type of active transport system
shuttles 3 Na+ OUT and 2 K+ INTO the cell
both move against their gradients
Define membrane potential.
voltage difference across a membrane
What is a electrogenic pump?
a transport protein that
across a membrane
What is the major electrogenic pump in plant, fungi, bacteria and animal cells?
Plant, fungi, and bacteria cells
Occurs when active transport of a solute
transport of another solute.
What is bulk transport? (2)
It's the crossing of a membrane in a bulk
big molecules like macromolecules
Transport vesicles migrate to the membrane, fuse with it, and
release their contents
to the outside of the cell.
Define endocytosis. what are the three types?
takes in macromolecules
from the plasma membrane. It includes:
Define pinocytosis. (2)
Molecules are taken up when extracellular fluid is "gulped" into
for small molecules
Cell engulfs a particle in a
for big molecules
What is endosome?
Vesicle that's formed from the membrane.
Define receptor-mediated endocytosis.
(any molecule that binds specifically to a receptor site) to
triggers vesicle formation
for specific molecules