Topic 2B - Cell Membranes Flashcards
What is the role of the cell-surface membrane?
They are a partially-permeable barrier between a cell and it’s environment, controlling which substances enter and leave the cell.
What are cell membranes composed of?
Lipids (phospholipids), proteins, and carbohydrates.
Give three properties of the cell membrane.
Bilayer, fluid because phospholipids constantly moving. Proteins scattered through the bilayer like tiles in a mosaic. Some can move sideways, others are fixed in position. Cholesterol.
Describe proteins in the membrane and their features.
Channel proteins and carrier proteins allow large molecules and ions to pass through the membrane. Receptor proteins on the membrane allow the cell to detect chemicals released from other cells.
What can’t enter through the membrane and why?
Water-soluble substances like ions can’t enter because the centre of the bilayer is hydrophobic, so it acts like a barrier.
What is cholesterol? Describe its purpose in the cell membrane.
A type of lipid. It is present in all membranes except bacterial cell membranes. They fit between the phospholipids, binding to the tails and causing them to pack closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid. They also help to maintain the shape of animal cells as they don’t have cell walls.
How do you calibrate a colorimeter?
Using pure water.
Name some control variables in the experiment about the permeability of membranes.
Equally sized beetroot/same mass.
Same volume of water.
Same length of time for beetroot in water.
What is the permeability of a cell membrane like below 0° and why?
The phospholipids don’t have much energy and can’t move, so they’re packed close together and make the membrane rigid. However, channel proteins and carrier proteins deform, increasing the permeability. Ice crystals form, and pierce the membrane.
What is the cell membrane permeability like between 0 and 45° and why?
Phospholipids have more energy and can move, so they aren’t as packed together. Membrane is partially permeable. As temp increases, phospholipids move more due to more energy, so increases permeability.
What is the permeability of the cell membrane like above 45° and why?
Phospholipid bilayer melts. Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins deform, increasing permeability.
What is diffusion?
Net movement of particles from an area of higher concentration to an area of lower concentration.
Name two molecules that can easily diffuse through cell membranes and why.
Oxygen and carbon dioxide. They’re small, so they can pass through spaces between the phospholipids. They’re also non-polar, so they are soluble in the hydrophobic lipid bilayer.
Name two large molecules and two charged particles.
Amino acids and glucose are large. Ions and polar molecules are charged.
Why can’t charged particles diffuse quickly through the cell membrane?
They’re water soluble, and the centre of the bilayer is hydrophobic.
Describe how carrier proteins work.
They move large molecules across membranes, down their conc gradients. A large molecule attached to the binding site of the protein, and the protein changes shape. This releases the molecule on the opposite side of the membrane.
Why do we say that carrier proteins and channel proteins are specific.
Different carrier proteins facilitate the diffusion of different molecules. Same with channel proteins.