Cell Membranes Flashcards
What are the components of a cell surface membrane? Clue= there are 4
Phospholipid bilayer, proteins, carbohydrates, cholesterol
What is a cell surface membrane?
The barrier between a cell and its environment. It controls the entry and exit of substances and is partially permeable meaning it only lets some molecules through.
Why is the arrangement of molecules described as the fluid mosaic model?
The phospholipids in the membrane are in constant motion (fluid) and there is a mosaic pattern of proteins throughout the membrane.
What do receptor proteins do?
Detective chemicals released from other cells.
Describe the phospholipid bilayer
Hydrophilic head - attracts water (faces out towards water on either side of membrane)
Hydrophobic tail - repels water (centre of membrane to stop water-soluble substances through it
Acts as a barrier
What does cholesterol do in a cell membrane?
Attached to tails between phospholipids causing them to pack closer together which restricts moment making less fluid and more rigid. Helps to maintain shape of animal cells where there is no cell wall.
What is diffusion?
Net movement of particles from an area of high to low concentration. It is passive so no energy is required.
What is simple diffusion?
When small and non polar particles diffuse directly through a membrane, down a concentration gradient.
What is facilitated diffusion?
Uses carrier or channel proteins in the membrane to speed up larger and charged particles.
Moves particles down a conc gradient, high to low.
Passive - doesn’t require energy
What kind of molecules do carrier proteins transport? Give an example too.
Large molecules e.g glucose and amino acids
What kind of molecules do channel proteins transport?
Charged particles e.g ions.
What are the factors affecting simple diffusion?
• The concentration gradient - higher = faster. During diffusion the difference in concentration between the two sides decreases into it reaches equilibrium.
• thickness of the exchange surface. Thinner = faster rate.
• surface area = larger = faster rate of diffusion.
Give an example of how an increase in surface area results in faster diffusion rate
Microvilli in epithelial cells in this small intestine. Microvilli are projections formed by the cell surface membrane folding up. It gives the cell a larger surface area and so more particles can be exchanged in the same amount of time increasing the rate of diffusion.
What are the factors affecting facilitated diffusion? (2)
• the concentration gradient. Higher concentration gradient result in a faster rate of diffusion.
• the number of channel or carrier proteins. The greater number of proteins result in a faster rate. Once all are in use it can’t happen any faster.
What is osmosis?
The diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential
What is water potential?
The likelihood of water molecules to diffuse out of or into a solution. Higher water potential means a higher concentration of water molecules.
What is an isotonic solution?
A solution with the same water potential
Why does pure water have the highest water potential?
There are no solids to restrict movement. Solutes lower the kinetic energy and therefore water potential.
What is a hypotonic solution? What direction is the net movement?
Solution has a higher water potential compared to the inside of the cell. Net movement is into the cell.
What is a hypertonic solution? What direction is the net movement?
Solution has lower water potential and ban the cell so net movement is out of the cell.
Factors affecting osmosis (3)
• water potential gradient. The higher the water potential gradient; the faster the rate.
• thickness of the exchange surface. Thinner = faster rate.
• surface area of the exchange surface. Larger = faster
How is active transport different to facilitated diffusion?
A.T moves solutes from a low to high concentration, F.D moves from high to low.
A.T requires energy, unlike f.d
Which molecule provides the energy for active transport?
ATP
Describe the process by which energy is released by the cell for active transport
Energy is released by the hydro lists of ATP into ADP and Pi
Describe how carrier proteins actively transport substances across the cell membrane
A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.
What are co-transporters?
A type of carrier protein that bind two molecules at a time. The conc gradient of one is used to move the other molecule against its own concentration gradient. Using a carrier protien
Factors affecting rate of active transport
•speed of individual carrier proteins.
•number of carrier proteins present.
•the rate of respiration in the cell and availability of ATP. If respiration is inhibited, a.t can’t take place.
How is glucose absorbed?
By co-transport into the bloodstream in the small intestine in the ileum (final part of the small intestine)
What transporter proteins are in an epithelial cell?
Sodium-glucose co-transporter protein
Sodium - potassium pump
Protein channel
What does the protein channel in the epithelial cell do?
Glucose diffuses through into the blood out of the cell, down its conc gradient by facilitated diffusion
What does the sodium glucose do transporter protein do?
Carries glucose into the cell with sodium.
Sodium gets actively transported OUT of the cell into the lumen of ileum but diffuses into the cell.
Explain the effect of a higher percentage of cholesterol would have on a fluid mosaic model
It would make the phospholipid by layer less able to move so less fluid and more rigid
Explain two ways the cell surface membranes of the epithelial cells in the mammalian ileum might be adapted to their function.
• villi - for larger surface area to maximise rate of absorption
• higher proportion of carrier and channel proteins to carry nutrients by facilitated diffusion or active transport.
How does temperature (0-45 degrees) affect membrane permeability?
From 0-45 degrees C, the phospholipids can move and aren’t packed as tightly together. the membrane is partially permeable.
As temperature increases, the phospholipids move more because they have more energy. This increases the permeability of the membrane.
How does temperature above 45°C affect membrane permeability?
The phospholipid bilayer starts to break down and the membrane becomes more permeable. Channel proteins and carrier proteins deformed so they can’t control into leaves the cell – this increases the permeability of the membrane
How does active transport happen across a cell membrane?
Using a carrier protein and ATP against a concentration gradient.
What is the water potential and unit of pure water?
0 KiloPascals
