2.5- Biological membranes Flashcards
What is the role of membranes? (name 3)
- To act as a partially a partially and sometimes selectively permeable membrane between cells and their environments
- Site of Chemical reactions
- Sites of cell communication and signalling
What is the function of phospholipids in a cell membrane
Phospholipids form the bilayer and are the main component of the surface area
What Is the function of Cholesterol in a cell mambrane?
It regulates membrane fluidity and flexibility
What is the function of proteins in cell membranes?
carrying out chemical reactions or regulating cross membrane transport
What are the 2 types of proteins in cell membranes?
Integral- span the entire membrane
Peripheral- embedded in half of a membrane
What is the function of glycoproteins and glycolipids in cell membranes?
can be antigens or receptor molecules
can bind with extracellular signalling molecules such as hormones
An increased temperature leads to the membrane increasing its……………..
Fluidity and permeability
Why does an increased temperature increase fluidity and permeability? (Phospholipids)
Phospholipids aquire more energy so they move around more
Why does an increased temperature increase fluidity and permeability? (Fatty acids)
fatty acids become less compressed
Why does an increased temperature increase fluidity and permeability? (Proteins)
proteins can denature at high temperatures reducing their ability to control transport across membranes
Which 3 factors can affect membrane permebility?
Increased temperature
Changes in PH - affect the function of proteins in the membrane
Organic solvents such as ethanol can damage a membrane by dissolving lipids held through it
Can you draw the fluid Mosic model?
Hmmmmmmmmm
What is the definition of diffusion?
The movement of molecules from a region of high concentration to a region of low concentration until the concentrations of the 2 regions are equal.
What 3 factors does the rate of diffusion depend on?
Surface area of cell
thickness of membrane
Temperature
i am a small non polar molecule. can i diffuse through a membrane?
yes, i can diffuse quickly
I am a small polar molecule. can i diffuse across a membrane?
yes, although it will be slower
I am an ion. Can i diffuse across a cell membrane?
Noooo, i have to be transported by other methods
I am a large polar molecule. Can i diffuse across a cell membrane??
nope, i have to be transported by other methods
Give 3 examples of molecules which can diffuse through a membrane.
Oxygen
CO2
Steroids
Fat soluble vitamins
What is the definition of osmosis?
the diffusion of water molecules from a region of high concentration to low concentration across a partially permeable membrane
Is osmosis a form of active transport
No, osmosis is a specialised form of diffusion.
What molecules can facilitated diffusion transport that normal diffusion cant?
large and polar molecuses
Give 4 examples of molecules that are transported by facilitated diffusion.
glucose
fructose
ions
urea
is facilitated diffusion an active process?
No, it is passive
What is needed for facilitated diffusion to occur?
Carrier proteins or Channel proteins
What are the 3 steps for facilitated diffusion through a carrier protein?
- Molecule binds with carrier proteins molecules on cell surface
- Protein changes shape and transports molecule through
- Molecule detaches and protein reverts to its original shape
What does the rate of facilitated diffusion depend on?
- Concentration gradient
- Number of channels or transporter proteins that are available
What are 3 passive processes which move molecules across membranes?
Diffusion
Facilitated diffusion
Osmosis
What are 3 active processes that are used to transport molecules across membranes?
Active transport
Endocytosis
Exocytosis
Why do active processes require energy?
They move molecules against their concentration gradient
What is endocytosis?
the bulk transport of substances into a cell
What is exocytosis?
The bulk transport of substances out of a cell
What to carrier proteins use to transport molecules across membranes?
ATP
What is endocytosis of liquids called?
pinocytosis
How does endocytosis work?
a vesicle forms around the molecules that have entered the cell, containing them
How does exocytosis work?
a membrane bound vesicle moves towards the membrane and then fuses together to release the contents of the vesicle into the extracellular environment
What is a hypotonic soloution?
A soloution where water potential outside the cell is higher than inside
What is an isotonic soloution?
a soloution where water potential is equal inside and outside the cell
What is a hypertonic soloution?
a soloution where water potential is higher on the inside of the cell than outside
Can plant cells burst?
no, they have a cell wall
What solution are animal cells put in to burst?
a hypotonic one
jimmy says that “in an isotonic soloution and a cucumber, no water is moving”
Explain why jimmy is stupid
Water will flow in and out at an equal rate
there is no net change in concentrations but water is still moving
When an animal cell shrinks, what is it called?
crenation
When a plant cell shrinks, it becomes……………..
plasmolysed
Why doesn’t a plant cell collapse when placed in a hyper tonic solution?
The cell wall keeps it rigid
I am a turgid cell that hasnt burst. What am i?
A plant cell in a hypotonic solution
How do membranes change when temperature is increased?
- The phospholipids require more energy and move around more so fluidity and permeability increase
- The way protiens are positioned may differ which can alter rates of reaction
How does a temperature decrease affect membrane permeability?
- Saturated fatty acids become compressed
- But unsaturated fatty acids become compressed and push adjacent phospholipid molecules away which maintains fluidity
What is the effect of solvents on cell membranes?
they damage cell membranes and dissolve lipids
What are the units of water potential?
kPa
What is the highest water potential?
0 kPa
What is a very low water potential example?
-100 kPa
