Lecture 7: How does a cell maintain its internal environment Flashcards
What is the function of the plasma membrane?
Membrane provides a semi-permeable barrier. It controls the movement of substances.
Structure of plasma membrane:
Made out of phospholipids - hydrophilic heads & hydrophobic tails
Composition of hydrophobic fatty acids affects:
Membrane fluidity. Saturated tails pack together. Unsaturated tails prevent packing together. At moderate temps cholesterol reduces fluidity, at low temps increases fluidity
How do substances move across membranes?
Through Passive or Active transport
What is Passive transport?
Transport of lipid soluble molecules down their concentration gradient, no expenditure of ATP. Passive transport restricts the movement of water soluble & charged ions.
What is Facilitated diffusion?
Diffusion of substance down their concentration gradient either through channels or carrier proteins.
What is Active Transport?
Movement of specific substance against their concentration gradient “uphill” - forces particles across a membrane. Requires ATP input & involves pumps, endocytosis & exocytosis
What is a transport pump do?
Add definition
Why are Organelles important?
Keep incompatible processes apart. Provide special conditions for specific processes. From concentration gradients. Allow high concentrations of substances. Package for transport & export.
What is simple diffusion?
Substances diffuse directly through the phospholipid bilayer from and area of high conc to low once
What are membrane channels?
Channel structures in membrane which allow specific substances to diffuse through the membrane. They open & close in response to stimuli, membrane potential etc
What is carrier mediated transport? How does it work?
Substances diffuse by means of carrier structures in membrane. Substance binds to carrier on one side of membrane, inducing carrier to change shape and release substance on other side
