Cell membranes and transport Flashcards
What does the term hydrophobic mean?
When molecules are insoluble to water
What does the term hydrophilic mean?
When molecules are soluble to water
Which part of a phospholipid molecule is hydrophobic?
The fatty acid tails
Which part of a phospholipid molecule is hydrophilic?
The phosphate head
Are phosphate heads polar or non-polar?
Polar
Are fatty acid tails polar or non-polar?
Non-polar
What is the function of a phospholipid bilayer?
Allow diffusion of lipid soluble substances, non-polar molecules e.g. CO2 and O2.
Acts as a barrier to polar molecules as cannot pass through hydrophobic tails unless very small (water)
What is the role of plasma membranes within cells?
Compartmentalisation (separate cell components from cytoplasm)
Hold components of metabolic pathways in place e.g. mitochondria
What is the role of plasma membranes at the surface of cells?
Separate cell contents from outside environment
Cell recognition and signalling
Regulate transport of materials in or out of cells
Which model did Singer and Nicholson present about the structure of the plasma membrane?
The fluid mosaic model.
Fluid = phospholipids and proteins move around each other
Mosaic = Proteins are scattered within the phospholipid and do not form a continuous layer as suggested by earlier models
How does active transport work?
Uses energy to move molecules and ions across plasma membranes against a conc gradient. Involves carrier proteins.
What is the function of endo and exocytosis?
Enable the cell to take up or release large molecules, or lots of molecules at once
How is endocytosis carried out?
The cell surrounds the substance with a section of its plasma membrane.
Membrane pinches off to form a vesicle containing the substance
Requires energy
How is exocytosis carried out?
Vesicles containing substances to be released pinch off from golgi apparatus and move towards plasma membrane.
Vesicles fuse with plasma membrane and release their contents outside the cell.
Requires ATP
What happens in passive transport?
Doesn’t require energy.
Molecules move down a conc gradient (high to low)
Which transport methods are passive?
Simple Diffusion
Osmosis
Facilitated diffusion
What happens in simple diffusion?
Movement of molecules/ions from a region of high conc to a region of low conc until an equilibrium is reached
Diffusion through the spaces between phospholipids
What happens in facilitated diffusion?
Larger molecules/ions and polar molecules cannot diffuse directly through phospholipid bilayer.
Use carrier or channel proteins
What happens in osmosis?
Water molecules move down a conc gradient from high water potential to low water potential through a partially permeable membrane
What is a partially permeable membrane?
Membrane with holes to allow small molecules to fit through e.g. water
What factors affect the rate of difffusion?
Conc gradient - steeper = faster
Thickness of exchange surface - thinner = faster
Surface area - bigger = faster
Temperature - higher = faster
Size of molecule - small = faster
Lipid solubility - more soluble = easier movement across membrane
What do channel proteins do?
Channel proteins form a pore through which polar particles can diffuse down the conc gradient
What do carrier proteins do?
Carrier proteins move large molecules into cell by changing shape to allow release onto the other side of the membrane
What is the function of glycolipids and glycoproteins in a plasma membrane?
Cell signalling/recognition
Sites for drug, hormone and antibody binding
Provide antigens during the immune response
