Week 4: Membranes Flashcards
What is the primary function of cell membranes?
To keep the inside in and the outside out
What surrounds the nucleus and mitochondria in eukaryotic cells?
A double membrane
What is the structure of the plasma membrane?
A lipid bilayer made of lipids and proteins
What are the two main components of biological membranes?
- Lipids
- Proteins
What is the role of cholesterol in the lipid bilayer?
Provides structural support
Define amphipathic molecules.
Molecules that are hydrophilic (water loving) and hydrophobic (water hating)
What do lipid bilayers spontaneously form in aqueous environments?
- Micelles
- Bilayers
- Spherical structures
What is the typical behavior of lipids in membranes?
- Fluidity
- Lateral diffusion
- Rotation
- Flexion
True or False: Flip-flopping of lipids in the membrane is common.
False
What are membrane proteins responsible for?
- Transport
- Structural links
- Receptors
How many proteins are there approximately per 50 lipids in a membrane?
1 protein
What type of protein can only be separated from the membrane with detergents?
Integral membrane proteins
Fill in the blank: The carbohydrate layer on the cell surface is called the _______.
glycocalyx
What is the purpose of the glycocalyx?
Involved in cell adhesion and protection
What types of molecules are typically transported across membranes?
- Small water-soluble molecules
- Ions
What do carrier proteins do?
Bind solutes and initiate a conformational change to transport them
How do channel proteins function?
Contain a pore through the membrane that is controlled for opening
What is the permeability of the lipid bilayer to hydrophilic molecules?
Barrier to most hydrophilic molecules
What types of molecules are mostly excluded by the lipid bilayer?
- Uncharged polar molecules
- Ions
What is the difference between integral and peripheral membrane proteins?
- Integral proteins: separated with detergents
- Peripheral proteins: separated with changes in pH or salt
What is the role of membrane proteins in cellular signaling?
They allow inside things to get out and outside things to get in
What type of protein is involved in membrane curvature in the ER?
Reticulons
What type of anchor do GPI-linked proteins have?
Glycosylphosphatidylinositol (GPI) anchor
What are the examples of membrane proteins that are involved in signal transduction?
- EGFR (epidermal growth factor receptor)
- Heterotrimeric G-proteins
What is the purpose of maintaining different solute concentrations inside and outside the cell?
To protect the cell and maintain the chemistry in organelles
Fill in the blank: Membranes act as a selective _______.
barrier
What initiates a conformational change in the protein during solute transport?
Solute binds on one side of the membrane
What is released on the other side after solute binding?
Solute
Give an example of a transporter that binds solute.
Glucose transporters (GLUTs)
How do channel proteins differ from transporters?
Channel proteins do not bind the solute but contain a ‘pore’ through the membrane
What type of transport moves molecules from high to low concentrations?
Passive transport
What type of transport moves molecules ‘uphill’?
Active transport
What do carrier proteins do in passive transport?
Bind molecules on the high concentration side and move them to the low concentration side
What influences the passive movement of charged ions?
Electrical and chemical gradient
What is a coupled carrier?
The transport of one molecule is ‘coupled’ with another
What is an example of a symport coupled carrier?
Na-glucose carrier
What do ATP-driven pumps use to drive active transport?
Hydrolysis of ATP
What is an example of an ATP-driven pump?
Na+-K+ pump
What is the function of the Na+-K+ pump?
Needed for muscle function and to maintain charge potential across the membrane
What do ion channels facilitate?
Passive transport of ions through hydrophilic pores
How many molecules can ion channels allow to pass per second?
10^8 molecules
What influences the opening/closing of ion channels?
Gating mechanisms
What is the selectivity of ion channels based on?
Narrow pore allowing contact between the ion and the pore wall
What types of cells are voltage-gated ion channels especially useful for?
Nerve cells (neurones) and skeletal muscle cells
What conditions can malfunctioning ion channels cause?
Epilepsy and neuromuscular conditions
What are the main components of cell membranes?
- Lipid bilayer
- Membrane proteins
- Sugar coat
Fill in the blank: The lipid bilayer is a _______ barrier.
selective
Name two ways small molecules cross the membrane barrier.
- Carrier proteins (passive or active transport)
- Channel proteins (ion channels - passive transport only)
