Chapter 3: Membrane structure and function Flashcards
What is the function of biological membranes?
Membranes are selectively permeable barriers that separate the inside of a cell from the
outside (intracellular and extracellular)
* Membranes also surround organelles and separate the inside of an organelle (the lumen)
from the outside (the cytosol)
What is the plasma membrane and what is its function?
The plasma membrane surrounds the cell controls what gets into and out of the cell.
* It is selectively permeable: only some substances can pass
What is the plasma membrane made of?
phospholipids and proteins (True for all membranes)
Are membranes fluid?
Yes proteins and lipids move
How do proteins and lipids move within the membrane?
- Phospholipids are not fixed in position, they are always moving
o They can move from side to side (lateral diffusion)
o They can move from inside to outside (flip-flop- happens less often) - Proteins in the membrane also move freely by lateral diffusion
What is the fluid mosaic model?
Models membranes as being fluid and made of different components
What are the two types of membrane proteins?
- Peripheral (lacks hydrophobic sequences)
- Integral (hydrophobic regions interact with the interior of the membrane)
Do integral proteins have a hydrophobic and hydrophilic region?
Yes
What are the functions of membrane proteins?
- Transport
- Enzymatic reactions
- Signal transduction
- Cell-Cell recognition
- Intercellular joining
- Stabilization of membranes
What are some other important features of membranes?
- Glycoproteins (membrane proteins with carbohydrate groups attached to them)
- Glycolipids (membrane lipids with carbohydrate groups attached to them)
- Cholesterol (part of the phospholipid bilayer)
- Asymmetry ( the inner layer is not the same as the outer layer)
Does heat increase or decrease membrane fluidity?
Increase
What type of phospholipids increase fluidity?
shorter and unsaturated ones
How does cholesterol affect membrane fluidity?
Fluidity buffer:
– Keeps membranes from becoming too fluid when
temp. increases
– Keeps membranes from becoming too rigid when
temp. decrease
What is membrane sideness?
They have an inside and an outside
What are the 4 types of membrane transport?
- Diffusion
- Facilitated diffusion
- Active transport
- Bulk transport
What is diffusion?
- Passive transport (No energy required)
- substances move down their concentration gradient
(from high concentration to low concentration)
What is facilitated diffusion?
- Does not require energy
- Requires a channel or carrier (integral proteins)
- solute moves down its concentration gradient
What is facilitated transport used to transport?
polar or ionic compounds such as glucose
How is water transported in and out of the cell?
Aquaporin
What is simple diffusion used to transport?
hydrophobic molecules (non-polar)
What is active transport?
Solutes move from low to HIGH concentration
(UP the concentration gradient)
* An integral membrane protein is required
* Energy is required
How is active transport different from simple and facilitated diffusion?
energy is required
What is active transport used to transport?
polar and charged/ionic molecules
What is osmosis?
Osmosis is the diffusion of water across a
semi-permeable membrane (only water can
pass!)
* Depends on the concentration of solutes
* Water will move to the area of higher
solute concentration
