Biological Membranes [MCAT]
What are the 3 types of cell adhesion molecules (CAM)? what are their roles?
CAM are proteins 1) Gap Junctions (Connexons): permit movement of water and some solutes (not proteins) 2) Tight junctions: no water leakage; permeable enough to create a transepithelial voltage 3) Desmosomes: Connected by their cytoskeleton
What is another name for secondary active transport? What happens?
Coupled transport It also uses energy but there is no direct coupling to ATP hydrolysis. It harnesses the energy release by one particle going down its electrochemical gradient to drive a different particle up its electrochemical gradient.
What is a VLDL?
a lipid transporter
What are the two examples of passive transport?
1) Simple diffusion 2) osmosis
The resting membrane potential depends on...
1) The differential distribution of ions across the membrane 2) active transport process 3) selective permeability of the phospholipid bilayer
How is cholesterol similar to phospholipids? what happens at low and high temps?
1) They contain both a hydrophilic and a hydrophobic region 2) Membrane stability is derived from interactions with hydrophilic and hydrophobic interactions 3) Prevents crystal structures in the membrane 4) at low temps: increases fluidity 5) at high temps: decreases fluidity
In the fluid mosaic model, what are three common types of proteins?
1) Transmembrane protein: pass completely through the lipid bilayer 2) Embedded proteins: associated with only the interior (cytoplasmic) or exterior (extracellular surface) of the cell 3) Membrane-associated (Peripheral) proteins: They may be bound through electrostatic interactions, especially at lipid rafts, or to other transmembrane or embedded proteins.
What are waxes?
1) extremely hydrophobic 2) likely found in plants 3) long-chain fatty acid & long-chain alcohol 4) high melting point 5) provide stability and rigidity 6) serve as extracellular function as protection or waterproofing
How is a sphingolipid different from a phospholipid/ glycerophospholipid?
A sphingolipid does not contain glycerol
Types of lipids:
1) Fatty Acids 2) triacylglycerols/triglycerides 3) Lipids 4) Phospholipids Glycerophospholipids 5) sphingolipids Ceramide, sphingomyelins, cerebrosides, gangliosides 6) Cholesterol 7) Steroids 8) Waxes
What are two ways active transport can occur?
1) Primary active transport 2) Secondary active transport
What are two examples of facilitated diffusion?
1) Carriers 2) Channels
What are the two main functions of cholesterol?
1) Regulates membrane fluidity 2) Necessary in the synthesis of steroids
What happens in primary active transport?
ATP or some energy type of molecule is used to transport molecules across a membrane Enzyme transmembrane ATPase is also used
What do you call a transmembrane protein + an embedded protein?
An integral protein.
What is the role of Sodium-Potassium ATPase?
Maintain a low sodium concentration and high concentration of potassium ions intracellularly by pumping three sodium ions out for every two potassium ions pumped in
What is endocytosis? What are the two types and their function? How is this done?
Endocytosis: cell membrane invaginates and engulfs material Pinocytosis: fluids and dissolved particles Phagocytosis: ingestion of large solids such as bacteria Receptors embedded within the plasma membrane will initiate this process
What is the primary thermodynamic factor responsible for passive transport?
Entropy
Where do we find tight junctions?
Epithelial cells
What can pass more easily through the semipermeable phospholipid bilayer?
Fat-soluble compounds Large and water soluble compounds have to find other means
If we took a triacylglycerol and substituted one of the fatty acids with a phosphate group, a polar head group joins the nonpolar tails, what do we get?
Glycerophospholipid/ phospholipid
How are unsaturated fatty acids synthesized and transported in the human body?
Humans can only synthesize a few fatty acids. We attain many of our fatty acids through diet and it is transported as triacylglycerols from the intestine inside chylomicrons
In secondary active transport, when two particles move in the same direction, what do we call it? If they move in opposite directions, what do we call it?
Symport Antiport
In facilitated diffusion, what type of protein is necessary?
Integral membrane proteins to serve as transporters for these substrates
What is the role of Membrane-associated (peripheral) protein?
Involved in signaling or are recognition molecules on the extracellular surface
What does the enzyme flippase do? What thermodynamic process is involved?
It assist in the transition or "flip" between layers. They are able to move lipids between the membrane layers. For lipids to move on their own completely, this is energetically unfavorable because the polar head group of the phospholipid must be forced through the nonpolar tail region in the interior of the membrane.
What is a fatty acid?
It is a carboxylic acid that contain a hydrocarbon chain and terminal carboxyl group.
What is the result of active transport?
It results in the net movement of a solute against its concentration gradient. A ball rolling up a hill!
What uses primary active transport? What uses secondary active transport?
Neurons uses primary active transport Kidneys use secondary active transport
What are lipid rafts?
They are collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules; these rafts often serve roles in signaling.
What is exocytosis? Where is it important?
Secretory vesicles fuse with the membrane, releasing material Nervous system and intercellular environment
Simple diffusion Osmosis Facilitated Diffusion Active transport Concentration gradient of solute Membrane protein required Energy Required Example molecule
Simple diffusion: high to low No no o2 Osmosis: low to high no no water Facilitated diffusion: High to low Yes no Glucose/ions Active transport: Low to High Yes Yes Polar molecules/ions
Lipids (phospholipids, cholesterol,) > Proteins > Carbohydrates > nucleic acids
The abundance of membrane components
What is meant by the occluded state?
The carrier is not open to either side of the phospholipid bilayer
Where are desmosomes found?
They are found at the interface between two layers of epithelial tissue
What is the difference between the outer membrane and inner membrane of the mitochondria?
The outer membrane is highly permeable and porous which allows the passage of ions and small proteins The inner mitochondrial membrane is not as permeable. Involved in electro transport chain and ATP synthesis. no cholesterol involved with the inner mitochondrial membrane
What is the role of a hemidesmosome?
Their main function is to attach epithelial cells to underlying structures, especially the basement membrane.
Where would you find carbohydrates in a fluid mosaic model?
They are generally attached to protein molecules on the extracellular surface of the cells
What are triacylglycerols/triglycerides? How does it look?
They are storage lipids involved in human metabolic processes. They contain three fatty acids chains esterified to a glycerol molecule
What is the role of a membrane receptor?
They are transmembrane proteins and are able to activate or deactivate transporters They must have both an extracellular and intracellular domain and for this reason they are considered a transmembrane protein. At times, they can display enzymatic activity
What are glycerophospholipids used for?
They can produce a hydrophilic surface layer on lipoproteins such as very-low-density lipoprotein
What type of Dynamic do we see with the phospholipids?
They move rapidly in the plane of the membrane through simple diffusion
What is the role of membrane receptor like ligand-gated ion channels
They open channels in response to the binding of a specific ligands
What are the roles of phosphate groups for water-soluble groups?
They provide as attachment points
What is difference between a carrier and a channel?
Think of carriers as a revolving door Think of channels as tunnel. If it is open then it is open to both sides & if it is closed, it is closed to both sides.
What are considered transmembrane proteins?
Transporters, channels, and receptors
What is the different between an unsaturated fatty acid vs. fatty acid?
Unsaturated (more double bonds) which therefore exists as a liquid at room temperature. This ultimately creates fluidity to the membrane. Saturated (more single bonds) oil vs. butter
Can carbohydrates act as signaling and recognition molecules? if so, why?
Yes, because they are hydrophilic and its interaction with water form a coat around the cell.
What is the role of an embedded membrane protein?
catalytic behavior
What do phospholipids spontaneously assemble into?
micelles or liposomes note: do not confuse liposomes with lysosomes
What is the main function of the cell membrane?
protection
What is the role of phospholipids in signal transduction?
second messengers
The cell (plasma) membrane is often described as a...
semipermeable phospholipid bilayer
