Membrane Structure Flashcards
Describe the structure of a phospholipid
Phosphate ‘head’; polar so hydrophilic, 1 glycerol, 2 fatty acid tails; hydrophobic
How do phospholipids form in aqueous solutions?
Bilayer, with hydrophilic phosphate heads facing the outside and hydrophobic fatty acid tails facing inwards
What are the main functions of membranes in cells?
~ separate organelles from cytoplasm so metabolic reactions can occur
~ control entry and exit of materials in organelles
~ provide internal support system
~ isolate enzymes which may damage cells
~ provide surface for reactions
Why is the cell membrane called the fluid mosaic model?
Fluid describes the constantly moving phospholipids, mosaic describes the randomly scattered proteins, glycoproteins and glycolipids
Which molecules can pass through the phospholipid bilayer without channel proteins ?
Small and non-polar
How do large and polar molecules enter the cell?
Through facilitated diffusion, using channel or carrier proteins
e.g. glucose uses the GLUT transporter protein, potassium and sodium use protein pump, large amounts of water use aquaporin
What are glycoproteins and glycolipids?
Glycoproteins = protein with carbohydrate attached
Glycolipids = Lipid with carbohydrate attached
What is the role of cholesterol in the cell membrane?
Found between phospholipids, provides stability by restricting movement of molecules; binds to tails of phospholipids and makes them pack closely together
Define osmosis
Movement of molecules from an area of low solute concentration to high solute concentration (movement of water from high to low conc.), still passive transport
Define simple diffusion
Movement of particles from high concentration to low concentration along the concentration gradient, requires no energy
Define facilitated diffusion
Movement of particles from an area of high to low concentration using the help of transport proteins, does not require energy
Define active transport
Movement of particles from an area of low to high concentration against the concentration gradient; requires energy from the ATP molecule which releases energy after hydrolysis
Describe the processes of endocytosis and exocytosis
Endocytosis = Particles are enclosed in vesicles made from cell surface membrane and transported into the cell
Exocytosis = Vesicles containing substance fuse with the cell surface membrane and release the contents
Do smaller organisms have lower or higher SA:V?
Higher
How is SA:V calculated?
Surface area / Volume
