1.3 & 1.4 (Topic 1) Flashcards
Draw a simplified diagram of the structure of the phospholipid, including a phosphate-glycerol head and two fatty acid tails.
Head = phosphate and glycerol, Tails = fatty acids
Define hydrophilic and hydrophobic.
Hydrophilic: Polar and/or charged molecules (or regions of molecules) to which water can attract because they are “Water loving” substances.
Hydrophobic: Nonpolar molecules (or regions of molecules) to which water will not attract because they are “Water fearing” substances.
Define amphipathic and outline the amphipathic properties of phospholipids.
A molecule that contains both hydrophilic and hydrophobic regions. → i.e. a phospholipid
Amphipathic means there are both hydrophilic and hydrophobic regions in a single molecule. Phospholipids have a hydrophilic head region and hydrophobic tails.
Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.
There is water both outside and inside the cell. Phospholipids will arrange themselves in a bilayer so that the hydrophilic head associates with water and the hydrophobic tails face each other, away from the water.
State the primary function of the cell membrane.
It’s semi-permeable and controls the movement of substances into and out of the cell.
Contrast the structure of integral and peripheral proteins.
Peripheral proteins sit on one side of the surface of the cell membrane.
Integral proteins are embedded in the hydrophobic middle of the bilayer. Some integral proteins are “transmembrane” meaning they span both sides of the bilayer.
List at least four functions (with example) of membrane bound proteins.
- Receptor proteins receive extracellular signals.
- Transport proteins move ions and molecules across the bilayer.
- Enzymes catalyze reactions.
- Adhesion proteins anchor the cell to other cells.
- Recognition proteins identify the cell type in a multicellular organism.
Contrast the two types of transport proteins: pumps and channels
Channel proteins are used for passive transport of molecules as they move across the bilayer from higher to lower concentration.
Pump proteins are used for active transport of molecules as they move across the bilayer from lower to higher concentration.
Identify the structure of cholesterol in molecular diagrams.
Cholesterol is a lipid that can be distinguished by its characteristic four-ring structure.
Describe the structural placement of cholesterol within the cell membrane.
Cholesterol fits between phospholipids in the cell membrane, with its hydroxyl (-OH) group by the heads and the hydrophobic rings by the fatty acid tails.
Describe the function of cholesterol molecules in the cell membrane. Then, outline how temperature affects cell membrane fluidity.
Cholesterol acts as a regulator of membrane fluidity. At high temperatures if stabilizes the membrane and reduces melting. At low temperatures is prevents stiffening of the membrane. Membrane fluidity influences how permeable the structure is to solutes. Too fluid (higher temps) = too permeable Too stiff (lower temps) = not permeable enough
Describe the observations and conclusions drawn by Davson and Danielli in discovering the structure of cell membranes.
Davson and Danielli proposed the “protein-lipid sandwich” model of the cell membrane, in which a phospholipid bilayer was embedded between two layers of proteins.
Drawing of the fluid mosaic model
Phospholipid bilayer shown with heads facing in opposite directions
Phospholipids with labelled hydrophilic/phosphate head and hydrophobic/hydrocarbon tail
Peripheral protein, shown as globular structure at the surface of the membrane
Integral protein shown as embedded globular structure
Glycoprotein shown as embedded globular structure with protruding carbohydrate (shown as a branching, antenna-like structure)
Channel protein shown with a pore passing through it
Cholesterol shown in between adjacent phospholipids
Describe conclusions about cell membrane structure drawn from electron micrograph images of the cell membrane.
Cells are rapidly frozen and then fractured. Fracture occurs along lines of weakness, including between the two layers of phospholipids. Freeze-etched cell membranes provided evidence that the membrane was a bilayer with embedded proteins.
Describe conclusions about cell membrane structure drawn from cell fusion experiments.
Cell fusion experiments showed that protein molecules can move from place to place within the cell membrane; there is fluidity.
Describe conclusions about cell membrane structure drawn from improvements in techniques for determining the structure of membrane proteins.
- Improvements in tools and techniques allows scientists to extract membrane proteins and determine their chemical and physical properties.
- The membrane proteins were found to be varied in shape and size. Additionally, some proteins had hydrophobic regions.
- These findings did not match the model proposed by Davson and Danielli, in which proteins were uniform in shape and hydrophilic.