U4 Cell Membrane Flashcards
(36 cards)
1
Q
Cell membranes are composed of
A
Phospholipids, proteins, glycolipid, and cholesterol
2
Q
Phospholipids compose the cell membrane
A
- half of the cell membrane is a bilayer of phospholipids
- bilayer is stable with hydrophobic “tails”, of each layer pointing inwards or hydrophilic “head” pointing out
- other components ‘float’ in the bilayer
because they also have hydrophobic regions - phospholipids have a low viscosity, meaning
that the membrane behaves like a fluid
3
Q
List three proteins that compose half the membrane
A
channel proteins - create a passage for materials to move passively through the cell membrane carrier proteins - actively ‘pump’ materials through the membrane glycoproteins - proteins with attached carbohydrates, used in cell-to-cell communication
4
Q
minor components of the cell membrane?
A
glycolipid - lipids with attached carbohydrates, act as receptors and anchors for other structures cholesterol - regulates the fluidity of the bilayer, preventing it from becoming too viscous or too fluid
5
Q
What is a fluid-mosaic modeL?
A
- membrane is a fluid in which the lipids and proteins are able to move around freely in one plane
- membrane components are not held together by bonds, but by their reaction to water
- membrane components distribute evenly over fluid surface to form mix mosaic
6
Q
what does permeable mean?
A
can be passed through
7
Q
What permeable is the membrane?
A
- selectively permeable because hydrophobic inner layer is permeable to non-polar molecules (lipids) and small molecule (gases, water)
- but is impermeable to polar molecules (ions, glucose, amino acids) and large molecules (polysaccharides, protein)
8
Q
how are substances permeable to membrane transported
A
the physical process of diffusion
9
Q
how are substances impermeable to membrane transported
A
active transportation (using ATP) by proteins or movement by the cells
10
Q
what is concentration
A
how much of a substance is
mixed with another substance
11
Q
what is solution
A
a mixture where one or more
substances are dissolved in another
12
Q
what is solute
A
substance that is dissolved in the
solvent, e.g. gases, ions
13
Q
what is solvent
A
fluid in which the solute is dissolved,
always water
14
Q
What is passive transport?
A
- requires no energy input
- occurs when there is an inequality in the distribution of a substance in a solution (concentration gradient)
- substances always diffuse down concentration gradient from high to low concentration gradient
15
Q
what is Diffusion?
A
- no energy required
- small non-polar molecules such as lipids and gases
- acts down concentration gradient
- takes place directly through phospholipid bilayer bc it permeable to these materials
16
Q
Factors that affect the rate of diffusion
A
temperature - higher temperature speeds up
the molecules, increasing the rate of diffusion
molecule size - smaller molecules pass
through the bilayer more easily, increasing the
rate of diffusion
molecule charge - charged or polar molecules
are obstructed by the bilayer, decreasing the
rate of diffusion
concentration gradient - stronger the gradient,
higher the rate of diffusion
17
Q
What is osmosis?
A
- diffusion of water (the solvent) across a selectively permeable membrane
- acts down the concentration gradient
- takes place directly through the bilayer (bc small)
- no energy required
18
Q
what is tonicity?
A
relative concentrations of solute in a
solution compared to another solution
19
Q
What is isotonic condition?
A
- solute concentrations are equal in the two
solutions - there is no concentration gradient, and so
osmosis is equal between the two solutions - a cell placed in isotonic solution will stay the
same
20
Q
What is Hypertonic condition?
A
- solute concentration relatively higher in the
solution under comparison - osmosis will always cause water to enter the
hypertonic solution - a cell placed in a hypertonic solution will lose
water and shrink
21
Q
What is hypotonic condition?
A
- solute concentration relatively lower in the
solution under comparison - osmosis will always cause water to move into
the hypertonic solution - a cell placed in a hypotonic solution will gain
water and swell and burst (lysis)
22
Q
What is osmotic pressure?
A
- pressure created by osmotic movement of water
- can be strong if if a cell is placed in solution
with very different tonicity, e.g. strong enough
to burst the cell in a hypotonic solution
23
Q
Transport by protein is
A
- passive, and active
- down/up concentration gradient
- requires channel or carrier protein in cell membrane
- allows cell to absorb substances that cannot ordinarily pass through bilayer
24
Q
Facilitated transport is
A
- small polar substances (glucose, amino acids and ions)
- acts down concentration gradient
- no energy required (passive)
- occurs through channel and carrier proteins bc substances can’t pass through the bilayer
25
Example of facilitated transport
the sodium ion channel
- nerve cells have an inequality of ions across their membranes, creating a net voltage
- sodium ion channel proteins open when the charge is negative and allow Na + ions to diffuse into the cell
- charge, small size of channel within protein
26
Active transport is
- small polar substances (glucose, amino acids)
- acts up or down the concentration gradient
- occurs through the carrier proteins because substances cannot pass through bilayer
- ATP is required
27
Example of active transport
sodium potassium pump
cells usually contain high concentrations of
K+, but low concentrations of Na+
- this relationship is maintained by a carrier
protein which moves three Na+ out of the cell,
and two K+ into the cell
- each ‘pumping’ also requires the use of a
single ATP molecule
28
Endocytosis, Exocytosis
- large molecules (proteins) or liquids
- can be up/down concentration gradient
- membrane must physically move
- ATP energy is required
- solid is phagocytosis (cell eating)
- liquid is pinocytosis (cell drinking)
- transporting IN is endocytosis
- transporting OUT is exocytosis
29
what is the surface area-to-volume ratio?
- cell volume increases more quickly than surface area as the cell gets bigger
- this means that as cell size increases the surface area-to-volume decreases
30
why are cells so small?
- cells transport nutrients and wastes across
their membrane, which is the surface area
- the cell contents, which need the nutrients
and produce the waste, represent the cell’s
volume
- there is a minimum ratio between surface
area and volume, below which the cell cannot
transport enough materials to maintain life
31
describe pinocytosis and phagocytosis
Pinocytosis and phagocytosis are processes that allow cells to consume very large molecules or food particles. Pinocytosis involves the formation of a vacuole around
substances dissolved in the environment, as though the cell is ‘drinking.’ Phagocytosis
involves the formation of a vacuole around large food particles, such as whole cells, as though the cell is ‘eating.’
32
How are the surface area of a cell and its volume related? What is the significance of this
relationship?
- cells transport nutrients and and wastes across their membrane, which is surface area
- the cell contents, which need the nutrients and produce the waste which represent the cells volume
- there is a minimum ratio between the surface area and volume, below which the cell cannot transport enough materials to maintain life
33
Distinguish between Endocytosis and Exocytosis
Endocytosis is the engulfing of materials outside the cell by the cell membrane, forming vacuoles
within the cytoplasm. Exocytosis is the fusion of vacuoles with the cell membrane and the
release of the substances contained inside.
34
Describe the functioning of the sodium potassium pump.
The sodium potassium pump is an example of a carrier protein involved in active transport.
Three Na + ions from the cytoplasm bind to the protein; the energy from a molecule of ATP
changes the shape of the protein, causing the ions to be exposed outside the cell and released.
Two K + ions are then bound to the protein, causing it to revert to its original shape and release
the K + ions inside the cytoplasm.
35
Distinguish between diffusion and facilitated transport.
Both processes are passive and result from the random motion of particles. Some particles will
not diffuse through the cell membrane, however and so pass through special channel proteins as
part of facilitated transport.
36
Distinguish between facilitated transport and active transport.
Facilitated transport is a passive process that occurs due to diffusion of substances through
transmembrane channel proteins. Active transport is an active process that occurs due to the
movement of substances by carrier proteins, consuming ATP, either with or against the
concentration gradient. Facilitated transport generally carries ions and other small, polar,
hydrophilic substances.
