Cell Membranes Flashcards
What is the cell membranes role?
Cell surface membranes surround the cell controlling what comes in and what comes out. They’re partially permeable meaning some molecules can come through but not all.
How can molecules enter and leave the cell?
Molecules can enter and leave by diffusion, osmosis, and active transport.
What is meant by the fluid mosaic model?
The fluid mosaic model is used to describe the arrangement of molecules in the membrane - ‘fluid’ because the phospholipids are constantly moving around and ‘mosaic’ because protein molecules are scattered throughout the phospholipids like tiles in a mosaic.
How does temperature effect the phospholipid membrane bilayer?
Below 0 - Phospholipids do not have enough energy making membrane rigid. Carrier and channel proteins denature.
Between 0-45 - Phospholipids have more energy, increase permeability.
Above 45 - Bilayer melts, water in the cell expands putting pressure on, channel and carrier proteins denature.
What is diffusion?
Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.
What factors effect diffusion?
Concentration Gradient – The higher it is, the faster the rate of diffusion.
Surface Area – The larger the surface area, the faster the rate of diffusion.
Diffusion Pathway – The shorter is it, the faster the rate of diffusion.
What is facilitated diffusion?
Some larger or charged molecules would diffuse extremely slowly through the phospholipid bilayer because they are too big or because they are water soluble. So, to speed things up carrier and channel proteins are used
How do carrier proteins work?
Moving larger molecules down the concentration gradient
1. A large molecule attaches to a carrier protein on the membrane.
2. Then, the protein changes shape.
3. This releases the molecule on the opposite side of the membrane
How do channel proteins work?
Channel proteins form pores in the membrane for charged particles to diffuse through. Different channel proteins diffuse different charged particles.
What factors affect facilitated diffusion?
Concentration gradient – The higher the gradient the faster the rate of diffusion
Amount of proteins – Once all proteins are in use, facilitated diffusion can’t happen any faster.
What is osmosis?
Osmosis is 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 are factors affecting osmosis?
Water potential gradient – The higher the gradient, the faster the diffusion.
Exchange pathway – The thinner the exchange surface, the faster the diffusion.
Surface area – The larger the surface areas, the faster the diffusion.
What is active transport?
Active transport uses energy to move molecules and ions across the plasma membrane down the concentration gradient using carrier proteins and co-transporters.
What is the difference between diffusion and active transport?
Active transport moves molecules from a low to high concentration and requires energy.
What is co-transport?
A type of carrier protein, they bind to molecules together at a time. The concentration gradient of one is used to move the other molecule against its own concentration gradient.
- e.g. Sodium and glucose
