Cell Membranes Flashcards
Name the current model of the membrane.
Fluid mosaic.
Why is the cell membrane described as fluid?
The membrane moves as a result of individual phospholipid molecules that move relative to each other, therefore it is flexible.
Why is the membrane described like a mosaic?
Due to the components such as proteins embedded in it, it makes it look like a mosaic.
Name 3 ways substances can cross the cell membrane.
Diffusion
Osmosis
Active transport
Describe the structure of a phospholipid.
Name the bonds in a phospholipid.
Polar phosphate head attached to a glycerol which is bonded to 2 non polar fatty acids. The bond is called an ester bond.
How do phospholipids act in the presence of water?
The polar phosphate head is hydrophillic so it attracts to water.
The non polar fatty acid tails is hydrophobic so it repels water.
Describe how the cell membrane is arranged.
Arranged into a phospholipid bilayer where hydrophilic heads point outwards and hydrophobic tails point inwards.
Why can water diffuse through the cell membrane despite being polar?
It is very small.
Why is oxygen and carbon dioxide able to diffuse through the cell membrane?
They are small and uncharged.
Describe the solubility of phospholipids in water.
Phosphate head is soluble.
Fatty acid tails are insoluble.
How do phospholipids arrange when mixed/shaken in water?
They form micelles which are small lipid droplets where the hydrophilic heads point outwards and hydrophobic tails point inwards.
What is an intrinsic protein?
A protein embedded in the membrane.
What is an extrinsic protein?
A protein that is found on the inner or outer surface of the cell membrane.
What is a carrier protein?
A protein that spans across the membrane. The molecule binds to the protein which changes shape to push it across the membrane.
Active transport relies on which protein?
Carrier proteins.
Why do carrier proteins require ATP?
The ATP is needed to change the shape of the carrier protein.
Name 2 molecules that use carrier proteins.
Glucose
Amino acids.
What are channel proteins?
Proteins that span the whole membrane that create ‘channels’ for water soluble ions to move across.
What are channel proteins filled with?
Water.
Why are channel proteins selective to specific ions?
Due to their highly complex tertiary structure.
Facilitated diffusion relies on which 2 types of protein?
Carrier proteins
Channel proteins
How can channel proteins control how much of substance diffuses at a time?
The ends of the channel can open and close.
What do ions do to the channel protein before they can diffuse across the membrane?
They bind to the end of the channel protein.
What is a glycoprotein?
A protein molecule with a carbohydrate chain attached
Why are glycoproteins important for cell recognition?
Prevents our own cells from being attacked.
Describe how glycoproteins are involved with hormones and neurotransmitters.
Glycoproteins act as receptor sites.
How do glycoproteins allow tissues to be formed?
They help cells to attach to eachother.
What are glycolipids?
Lipids with a carbohydrate chain attached.
The carbohydrate on a glycolipid extends out into where?
The watery environment outside the cell.
How do glycolipids allow tissues to be formed?
They help cells to attach.
How are glycolipids similar to glycoproteins in terms of their function? (3 ways)
They act as recognition sites
They help cells to attach and form tissues.
They act as receptor sites for hormones and neurotransmitters.
Describe hydrophilic/hydrophobia in cholesterol.
Hydrophobic tails, hydrophilic heads.
Which type of organism are cholesterol molecules absent in?
Prokaryotes
How does cholesterol reduce the fluidity of the cell membrane?
They pull fatty acid tails of neighbouring phospholipids closer together which limits their movement.
How does cholesterol benefit the cell membrane at higher temperatures?
It reduces the rigidity of the membrane which stops it losing its structure.
Give 4 uses of cell membranes.
Keeps organelles inside the cell.
Site for biochemical reactions.
Allows the cytoplasm to split into compartments.
Allows cells to change shape.
