Membrane Structure and Function Flashcards
What regions of phospholipids are hydrophobic and which are hydrophilic?
Hydrophobic tails inside the membrane and hydrophilic heads exposed to water on either side
Phospholipids are amphipathic molecules, meaning what?
Contains hydrophobic and hydrophilic regions
What is the purpose of the fluid mosaic model of membrane structure?
To depict the membrane as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
Are proteins randomly distributed in the membrane?
No, they often form groups that carry out common functions
How does cholesterol reduce membrane fluidity at moderate temperatures?
By reducing phospholipid movement
How does cholesterol hinder solidification at low temperatures?
By disrupting packing
What are the two major types of membrane proteins?
Peripheral proteins, which are bound to the surface of the membrane, and Integral proteins that penetrate the hydrophobic core
What are transmembrane proteins?
Integral proteins that span the membrane
Hydrophobic regions of an integral protein consist of what type of amino acids?
Nonpolar, often coiled into α helices
What does the plasma membrane control?
The exchange of materials between the cell and its surroundings
Membranes exhibit selective permeability, meaning?
Some substances cross more easily than others
The fluid mosaic model explains what?
How membranes regulate molecular traffic across the membrane
What happens to the hydrophobic (nonpolar) molecules in the fluid mosaic model?
They dissolve in the lipid bilayer and pass through the membrane rapidly
What does the hydrophobic interior of the membrane do to the passage of hydrophilic (polar) molecules?
Blocks the passage
What is passive transport?
The diffusion of a substance across a membrane with no energy investment
What is diffusion?
The movement of particles of any substance so that they spread out evenly into the available space
The diffusion of a substance across a biological membrane is what type of transport?
Passive because no additional energy is required by the cell
What is osmosis?
The diffusion of free water across a selectively permeable membrane
How do water molecules diffuse across a membrane?
From the region of lower solute concentration to the region of higher solute until it is equal
What is active transport?
Transport requiring energy, typically in the form of ATP hydrolysis, to move substances against their concentration gradients
How do you know if a type of transportation is active?
If the transport proteins move solutes against their concentration gradients
All proteins involved in active transport are ____ proteins
Carrier
What does active transport enable cells to do?
To maintain solute concentrations that differ from the environment
Small molecules and water enter or leave the cell through?
The lipid bilayer or via transport proteins
