Topic 2B: Cell Membranes Flashcards
What is the definition of diffusion?
Net movement of particles from an area of high concentration to an area of low concentration.
What type of process is diffusion?
Passive process, no energy needed
When does diffusion stop?
When an equlibrium is reached
What 3 things affect diffusion- explain?
Concentration gradient- Higher means its faster
Thickness of exchange surface- Thinner means faster
Surface area- Larger means faster
Why is facilitated diffusion needed?
Some larger molecules would diffuse extremely slowly through the phospholipid bilayer as they are so big
What do the large/charged particles diffuse through in facilitated diffusion?
Carrier or channel proteins
What type of process is facilitated diffusion?
Passive process, no energy needed
How does a carrier protein work?
First a large molecule attatches to carrier proteins and the protein changes shape, this releases molecules on opposite side
Where do channel proteins form?
In pores
What are the 2 things that affect facilitated diffusion?
Concentration gradient- Increased faster until equlibrium reached
Number of proteins- Once all proteins are used, FD can’t occur any quicker even with increased conc gradient
How do you work out gradient from a graph?
Change in y/change in x
What the definition of osmosis?
Diffusion of water molecules across partially permeable, from an area of high to low water potential
What is the definition of water potential?
Potential of water molecules to diffuse in/out a solution
What’s the water potential of water?
Zero (0)
What’s meant by isotonic?
2 Solutions with the same water potential
What’s meant by hypotonic?
Solutions with higher water potential compared with inside cell
What’s meant by hypertonic?
Solutions with lower water potential compared with inside cell
What 3 factors affect osmosis?
Water potential (Increased WP)
Thickness of exchange surface (Thinner=faster)
Surface area (Increased SA=faster)
Is energy needed for active transports?
Energy is needed
Whats the definition of active transport?
Net movement of particles from an area of low concentration to an higher concentration
What protein is needed for active transport, how does it work?
Carrier protein, molecules attatches to carrier proteins, it changes moving the molecules across the membrane
What type of protein are co-transports?
Carrier protein
How do co-transporters work?
But they bind 2 molecules at a time, the conc gradient of one is used to transport the other, gradient their conc gradient
How do co-transporters work to move glucose into the blood? (step one)
Sodium ions are actively transported out of the epithelial cells in the ileum into the blood sodium-potassium pump creating the conc gradient of Na
What’s step 2+3 of the process of glucose being transported into the blood via co-transporters?
This cause sodium ions to diffuse from the lumen of the ileum into the cells. Down the conc gradient via sodium glucose co-transporter proteins
Glucose diffues out of the cell, into the blood through a protein channel by FD
What 3 things affect active transport?
Speed of individual carrier protein (Faster= Faster Rate of AT)
Rate of respiration (If respiration inhibited AT doesn’t occur)
Numbers of carrier proteins (More= Faster)
How permeable is a cell membrane?
Partially permeable
What model best describes cell membranes and when was it created?
Fluid mosaic model (1972)
Why is the bilayer ‘fluid’?
Constantly moving
What is it called when a carb is attached to a protein?
Glycoprotein
Which part of the phospholipid is hydrophobic?
Tail, repels water
What part of the phospholipid is hydrophilic?
Head, attracts water
What does cholesterol give to a membrane and how?
Stability, fits into hydrophobic tails and packs them closely together restricting movement and makes them less fluid and more rigid
Whats another characteristic of cholesterol?
Also has hydrophobic regions so its able to create a further barrier to polar substances moving through the membrane
How does the cell membrane act at 0 degrees?
Phospholipids don’t have much energy, so they can’t move very much.
They’re packed closely together and membrane is rigid
Channel and carrier proteins in the membrane denature increasing permeability of the membrane
How does the cell membrane act above 45 degrees?
Phospholipid starts to melt and the membrane becomes more permeable.
Water inside the cell expands, putting pressure on the membrane.
Protein denature so can’t control what enters or leaves
How does the cell membrane act between 0-45 degrees?
Phospholipids can move around aren’t packed as tightly together, membrane is partially permeable
As the temp increases they move more increasing permeabilty
