Cell Physiology Flashcards
Describe the structure of the cell surface membrane
Phospholipids bilayer with cholesterol molecules occurring among the hydrocarbon tails ( mostly in animal cells ) and proteins in the bilayer, intrinsic proteins span both layers whereas extrinsic proteins are attached to the membrane surface. Phospholipids in the cell membrane are constantly moving while the proteins are scattered amongst them. This structure is called the fluid-mosaic model
Describe what the glycocalyx is
A fringe formed on the outer membrane by polysaccharides bound to either proteins or lipids
State the factors that effect the fluidity of a membrane
The more phospholipids with unsaturated hydrocarbon chains there are the more fluid is in the membrane ( the kinks in the tails prevent them from packing close together so more move men is possible
Phosphoplipids with longer hydrocarbon tails decrease the fluidity ( attractive forces among the tails will be greater)
Higher temp causes a higher fluidity, low temp causes the bilayer to freeze into a solid like state
Cholesterol acts as a temp buffer, at higher temp cholesterol provides additional binding forces therefore decreasing the fluidity. At low temp cholesterol prevents the membrane from becoming frozen by preventing the phosopholipids from packing too close
What role does the glycocalyx play
Allows cells to recognise each other and group together to form tissues.
Glycoprotein receptors and signalling molecules fit together as they have complimentary shapes
What does the mode of transport through a membrane depend on?
The size of the molecule - large molecules can only move in and out by cytosis
The polarity- non-polar molecules move through the phospholipid bilayer, polar substances move via proteins
The conc. of the substance on either side of the membrane- substances move from a high to low conc. by diffusion, if movement against the gradient is necessary then active transport is used
Outline diffusion
Non-polar molecules, respiratory gases oxygen and carbon dioxide, very small polar molecules such as water and urea all move through the phospholipid bilayer down their conc. gradients
Outline facilitated diffusion
Ions and charged groups can’t move through the phospholipid bilayer so there movement is facilitated by particular membrane proteins, no metabolic energy is used and movement is down the conc. gradient
What are channel proteins
They have a specific shape to allow only one type of ion through. Gated channels can be opened and closed. Most water molecules diffuse through specific water channel proteins called aquaporins
( they have a hydrophilic core )
What are carrier proteins
They can selectively transport medium-sized molecules such as glucose and amino acids.
Molecules bind to a site on the protein, which changes shape to bring the molecule through the membrane
What is osmosis
The diffusion of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential
What is water potential?
A measure of the free energy of the water molecules in a system
Why can a cell never have a water potential of 0
There is always some solute in a cell
Equation for water potential
Water potential of cell= solute potential + pressure potential
What happens to water in solutions
Some of the water molecules form shells around the solutes becoming no longer free
This lowers water potential
What happens to cells in hypotonic solutions
Animal cells will swell up and lose
Plants will become turgid as their cell walls prevent bursting
What happened to cells in hypertonic solutions
Red blood cells will become crenated
Plant cells will undergo plasmolysis the point where the cytoplasm loses contact with the cell walls is incipient plasmolysis
Outline active transport
Substances move across the membrane form a low concentration to low concentration AGAINST the concentration gradient this requires ATP from respiration. The carrier proteins are known as pumps and there is a specific protein for each type of ion or molecule
The protein changes shape and moves the substance through the membrane
What is cytosis
The bulk transport into (endocytosis) or out of (exocytosis) the cell without passing through the cell surface membrane (substances too large to be carried by protein carriers)
Outline endocytosis
The cell surface membrane invaginates and the membrane folds around the substance like a vacuole or vesicle
Two types
Phagocytosis- uptake of solid particles within vacuoles. E.g ingestion of bacteria by polymorphs
Pinocytosis- uptake of solutes and large molecules within vesicles
Outline exocytosis
Secretory vesicles move towards and fuse with the cell surface membrane, reading their protein contents out of the cell
Involved in the removing of waste products from the cell
