Chapter 8: Biological Membranes Flashcards
Describe the cell membrane.
Semipermeability/selective permeability?
What molecules and compounds can diffuse across the membrane? Which need alternative entry?
What is the name for the theory that underlies the structure and function of the cell membrane?
The cell membrane is a plasma membrane composed of a phospholipid bilayer, the interior of which is nonpolar the cell and environment facing portions are polar.
The cell membrane is semi permeable as it chooses which particles can enter and leave the cell at any point in time.
The selective permeability of the cell membrane is due to its amphipathic nature as well as various transmembrane channels and carriers.
The cell membrane permits fat soluble compounds to cross easily.
Larger and water soluble compounds do not readily diffuse across the membrane and need alternative entry.
This is known as the fluid mosaic model.
Carbohydrates associated with membrane bound proteins are called what?
Carbohydrates associated with membrane-bound proteins, create a glycoprotein coat.
What is the main function of the cell membrane?
How does the cell membrane achieve this?
The main function of the cell membrane is to protect the interior of the cell from the external environment.
The cell membrane achieves this through its phospholipid and amphipathic nature along with embedded proteins that creates a selectively permeable environment.
Cellular membrane selectively regulate traffic into and out of the cell and are involved in both inter and intracellular communication and transport.
The cell membrane is in a constant state of flux on the molecular level.
What are lipid rafts (do they serve a role)?
Flippases (do lipids move between membrane layers)?
Phospholipids move rapidly in the plane of the membrane through simple diffusion.
Lipid rafts are collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules. Lipid rafts often serve roles in signaling. Lipid rafts move about within the plane of the membrane, but more slowly.
Proteins also travel within the plane of the membrane.
Lipids can also move between the membrane layers, but it is energetically unfavorable because of the polar head groups must be forced through the non-polar tail region.
Flippases facilitate this flipping between the layers (recalling that this is an enzyme, and therefore reduces the energy required for this to happen on its own)
MCAT concept check fluid mosaic model 8.1 page 296 question 1
Describe the role of flippases and lipid rafts in biological membranes.
Flippases are responsible for the movement of phospholipids between the layers of the plasma membrane because it is otherwise energetically unfavorable.
Lipid rafts are aggregate of specific lipids in the membrane that function as attachment points for other biomolecules and play roles and signaling.
MCAT concept check fluid mosaic model 8.1 page 296 question 2
List the following membrane components in order from most plentiful to least plentiful:
Carbohydrates, lipids, proteins, nucleic acids
Lipids, including phospholipids, cholesterol, and others are most plentiful.
Proteins, including transmembrane proteins, channels and receptors, membrane associated proteins, and embedded proteins are the next most plentiful.
Carbohydrates, including the glycoprotein coat, and signaling molecules, are the next most plentiful.
Nucleic acids are essentially absent in the cell membrane.
Many antidepressants increase levels of neurotransmitters in the brain, but the effects take longer to appear than the changes in neural chemistry. Why is that?
The reason for this delay is that the nervous system must still up regulate its post synaptic receptors to respond to the new levels of neurotransmitter.
What molecules lend fluidity and structural integrity to the cell membrane.
Within the cell membrane, there are a large number of phospholipids with very few free fatty acids.
Steroid molecules and cholesterol lend fluidity to the membrane.
Waxes provide membrane stability, help maintain the structural integrity of the cell.
What are fatty acids?
Fatty acids are carboxylic acids that contain a hydrocarbon chain and terminal carboxy group.
Fatty acids are the building blocks of fats in our bodies and food broken down during digestion and absorbed into the blood, forming triglycerides when joined together.
What are triacylglycerols? Whats another name for them?
Triacylglycerols (triglycerides) are storage lipids involved in human metabolism.
Three fatty acid chains esterified to a glycerol molecule.
What is a chylomicron?
Chylomicrons are transport molecules from the intestine that deliver food products to the blood stream to adipose and muscle tissue and liver etc.
What is a phospholipid?
What shape will phospholipids spontaneously assemble into (two answers)?
By substituting one of the fatty acids in triacylglycerol with a phosphate group, a glycerophospholipid is formed, commonly called a phospholipid.
Phospholipid spontaneously assemble into micelles (small mono layer vesicle) and liposomes (bilayered vesicle) due to its amphipathic nature.
What is very low density lipoprotein (VLDL)?
VLDL is a lipoprotein and acts as a lipid transporter.
Glycerophospholipids are used for lipid synthesis and can produce a hydrophilic surface layer on lipoproteins like VLDL.
VLDL, or very-low-density lipoprotein, is a type of lipoprotein, a combination of proteins and fats, that your liver produces and releases into the bloodstream to transport triglycerides (a type of fat) and cholesterol to your tissues.
The phosphate group can also acts as an attachment point for hydrophilic groups. What are some examples of this?
Choline can attach to phosphate groups (phosphatidylcholine aka lecithin)
Inisitol (phosphotidylinositol)
What are sphingolipids?
What differentiates them from glycerophospholipids?
What are the four kinds of sphingolipids?
Sphingolipids are important constituents of cell membranes.
Sphingolipids are similar in structure to glycerophospholipids but they do not contain glycerol, they contain a sphingosine or sphingoid compound rather than glycerol.
Ceramide: simple sphingolipid.
Sphingomyelin: phospholipid as it contains phosphocoline or phosphoethanolamine hydrophilic region.
Glucosphingolipis (CEREBROSIDE): glycolipid containing glucose or galactose as hydrophilic portion.
Gangliosides: glycolipid containing sialic acid (N-acetylneuraminic acid, NANA) linked to oligosaccharides.
What amino acid is important for making sphingolipids?
What are the types of sphingolipids?
What is cholesterol?
Cholesterol regulates membrane fluidity, and is necessary in the synthesis of all steroids.
Is amphipathic, makes up 20% of the cell membrane by mass. Makes up half of the cell membrane by mole fraction.
Cholesterol occupies space between phospholipids and stabilizes them. Cholesterol increases fluidity at lower temperature by preventing the formation of crystal structures in the membrane.
At high temperatures, it decreases the fluidity and helps hold the membrane intact.
What are waxes?
Waxes are a class of lipids that are extremely hydrophobic, rarely found in the cell membranes of animals, sometimes found in the cell membranes of plants.
Composed of long chain fatty acid and long chain alcohol, causing a high melting point.
Provide stability and rigidity within the non-polar tail region.
Waxes serve an extracellular function in protection and waterproofing.
What are the three types of membrane proteins?
Embedded, transmembrane, integral (transmembrane and embedded together), and peripheral.
Embedded proteins are associated with the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane.
Transmembrane proteins pass completely through the lipid bilayer (transporters, channels, receptors).
Embedded proteins and transmembrane proteins are collectively known as integral proteins.
Membrane associated (peripheral) proteins may be bound through electrostatic interactions with the lipid bilayer or to other transmembrane or embedded proteins like the G proteins found in G protein coupled receptors.
How do carbohydrates relate to the cell membrane?
What are important sphingolipids in the body?
Carbohydrates are attached to protein molecules on the extracellular surface of cells.
Carbohydrates are generally hydrophilic, interactions between glycol proteins and water can form a coat around the cell.
Carbohydrates connective signaling and recognition molecules.
Glycosphingolipids are responsible for ABO blood group antigens on red blood cells. Blood group antigens are sphingolipids connected to carbohydrates that differ only in their carbohydrate sequence.
Immune system and pathogens take advantage of these membrane, carbohydrates and membrane proteins to target particular cells.
What are membrane receptors?
Provide example.
Transporters for facilitated diffusion and active transport can be activated or deactivated by membrane receptors, which tend to be transmembrane proteins.
Ligand gated ion channels are membrane receptors that open a channel in response to binding of a specific ligand.
Other membrane receptors participate in bio signaling, such as G protein coupled receptors (GPCR) involved in several different signal transduction cascades.
Membrane receptors are generally proteins, although there are some carbohydrate and lipid receptors, especially in viruses.
What is a cell cell junction?
What is a cell adhesion molecule?
What are the two types of cell cell junctions?
Cells within tissues can form a cohesive layer via intercellular junctions that provide direct pathways of communication between neighboring cells or between cells and the extracellular matrix.
An important gap junction in myocardial cells are called intercalated discs. Intercalated discs allow the direct passage of ions and small molecules between myocardial cells, facilitating rapid and coordinated electrical conduction throughout the heart
Cell cell junctions are usually comprised of cell adhesion molecules (CAM), proteins that allow cells to recognize each other and contribute to proper cell differentiation and development.
Gap junctions and tight junctions are two types of cell cell junctions.
What is a gap junction?
What is connexin?
What passes through gap junctions, what does not pass through gap junctions?
What are gap junctions found in myocardial cells?
Gap junctions allow for direct cell cell communication and are often found in small bunches together.
Also called connexons and are formed by the alignment in the interaction of pores, composed of six molecules of connexin.
Connexin permit movement of water and some solute directly between cells. Proteins are generally not transferred through gap junctions.
Intercalated discs are gap junctions found in myocardial cells.
What are tight junctions?
Where are tight junctions found?
Tight junctions prevent solutes from leaking into the space between cells via a paracellular route.
Tight junctions form a watertight seal, preventing paracellular transport of water and solutes.
Tight junctions, which seal adjacent epithelial cells in a narrow band, are primarily found in epithelial and endothelial tissues. They are crucial for forming selective barriers and maintaining tissue homeostasis (and therefore found in the lining of renal tubules as well).
Think of tight junctions as a continuously sewed seam around the cell, functioning as a physical link between the cells as they form a single layer of tissue.
What are desmosomes?
Where are desmosomes typically found?
What are hemidesmosomes?
Desmosomes bind adjacent cells by anchoring to their cytoskeletons. Desmosomes are formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells.
Desmosomes are primarily found at the interface between two layers of epithelial tissues.
Hemidesmosomes have a similar function, but their main function is to attach epithelial cells to underlying structures, especially the basement membrane.
MCAT concept check membrane components 8.2 page 305 question 1
MCAT concept check membrane components 8.2 page 305 question 2
How does cholesterol play a role in the fluidity and stability of the plasma membrane?
MCAT concept check membrane components 8.2 page 305 question 3
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Contrast gap junctions and tight junctions.
What is a concentration gradient?
Relate concentration gradient to passive and active transport in the spontaneity of reaction.
What is the primary thermodynamic motivator in passive transport?
Will temperature impact transport?
Transport processes can be classified as active or passive defending on their thermodynamics.
Passive transport is spontaneous and does not require energy (negative deltaG)
Active transport is non-spontaneous and requires energy (positive deltaG)
The primary thermodynamic motivator and passive transport is an increase in entropy (deltaS).
Diffusion, facilitated diffusion, and osmosis, generally increase in rate as temperature increases.
Active transport may or may not be affected by temperature, depending on the enthalpy of the process (deltaH).
What is passive transport?
Is passive transport spontaneous?
Passive transport processes are those that do not require intercellular energy stores, but rather utilize the concentration gradient to supply the energy for particles to move.
Passive transport is spontaneous and therefore does not require an input of energy (negative deltaG).
What is simple diffusion?
Is this a spontaneous process?
What kind of molecules can undergo simple diffusion?
Simple diffusion is the most basic of all membrane traffic processes.
Simple diffusion is a spontaneous process, meaning there is no input of energy required, only a concentration gradient.
Substrates move down their concentration gradient directly across the membrane.
Only particles that are freely permeable to the membrane are able to undergo simple diffusion. In simple diffusion, small, nonpolar or uncharged molecules like oxygen, carbon dioxide, and water can directly pass through the cell membrane, moving from areas of high to low concentration without needing any transport proteins.
Speak about the potential energy in a chemical gradient and how it relates to simple diffusion.
There is potential energy in a chemical gradient; some of this energy is dissipated as the gradient is utilized during simple diffusion.
Liken this to the process of a ball rolling down a hill: there is potential energy in the ball when it sits at the top of the hill, and as the ball spontaneously rolls down the hill, some of the energy is dissipated.
What is osmosis?
What is hypotonic, isotonic, hypertonic solution?
Osmosis is a special kind of simple diffusion that concerns water.
Water will move from a region of lower solute concentration to one of higher solute concentration.
What is osmotic pressure?
Is osmotic pressure a colligative property?
What is the equation for osmotic pressure?
Osmotic pressure is the method of quantifying the driving force behind osmosis.
Osmotic pressure is a colligative property, a physical property of solutions that is dependent on the concentration of dissolved particles, but not on the chemical identity of those dissolved particles.
What is the equation for osmotic pressure?
What is the vant hoff factor for glucose? NaCl? Sulfuric acid?
What is facilitated diffusion?
What is a carrier protein? channel protein?
Facilitated diffusion is simple diffusion for molecules that are impermeable to the membrane (large, polar, or charged).
The energy barrier is too high for these molecules to cross freely, so facilitated diffusion requires integral membrane proteins to service transporters or channels for these substrates.
Carriers are only open to one side of the cell membrane at any given point, think of carriers as a revolving door.
Channels are viable transporters that may be in an open or closed confirmation.
What is active transport?
Does active transport require energy?
Active transport results in the net movement of a solute against its concentration gradient (rolling a ball up a hill).
Active transport always requires energy (non-spontaneous positive deltaG)
What is primary active transport? Example.
Secondary active transport? Is there other name for secondary active transport? Example.
Primary active transport uses ATP (or other energy molecules) to directly power, the transport of molecules across the membrane. TRANSMEMBRANE ATPASE is a primary active transport enzyme.
Secondary active transport, also known as coupled transport, harnesses the energy released by one particle going down its electrochemical gradient to drive a different particle up its gradient.
Does secondary active transport require direct coupling of energetic molecules, such as ATP hydrolysis?
Secondary transport, or coupled transport, uses energy to transport particles across the membrane, but does not directly couple to ATP hydrolysis.
Secondary transport (coupled transport) harnesses the energy released by one particle going down its electrochemical gradient to drive a different particle up its electrochemical gradient.
What is symport?
What is antiport?
Regarding secondary active transport:
Symport: both particles flow the same direction across the membrane.
Antiport: the particles flow in opposite directions across the membrane.
Give biologically relevant examples for primary active transport and secondary active transport.
Primary active transport maintains the membrane potential of neurons in the nervous system.
The kidneys use secondary active transport, usually driven by sodium, to reabsorb and secrete various solute into and out of the filtrate.
Table 8.10 page 312 showing simple, diffusion, facilitated diffusion, and active transport summaries.
What is endocytosis?
Pinocytosis?
Phagocytosis?
What triggers the process of endocytosis?
What are vesicle coating proteins?
Endocytosis occurs when the cell membrane invaginate and engulf material to bring it into the cell.
The material is encased in a vesicle, separating the environment of the cell and the environment of the engulfed material.
Pinocytosis is the endocytosis of fluids and dissolved particles.
Phagocytosis is the ingestion of large solids, such as bacteria.
Substrate binding to specific receptors embedded within the plasma membrane will initiate the process of endocytosis.
Invagination is initiated and carried out by vesicle coating proteins (most notably Clatrhin).
What is exocytosis?
Give a biologically relevant example of exocytosis.
Exocytosis occurs when secondary vesicle fuse with the membrane, releasing material from inside the cell to the extracellular environment.
Exocytosis is important in the nervous system and intercellular signaling.
Exocytosis of neurotransmitters from synaptic vesicles is a crucial aspect of neuron physiology.
MCAT concept check membrane transport 8.3 page 313 question 1
What is the primary thermodynamic factor responsible for passive transport?
The primary thermal dynamic factor responsible for passive transport is entropy.
MCAT concept check membrane transport 8.3 page 313 question 2
What is the relationship between osmotic pressure and the direction of osmosis through a semi permeable membrane?
As osmotic pressure increases, more water will tend to flow into the compartment to decrease solute concentration.
Osmotic pressure is often considered a “sucking” pressure because water will move toward the compartment with the highest osmotic pressure.
MCAT concept check membrane transport 8.3 page 313 question 3
Compare the two types of active transport.
What is the difference between symport and antiport.
Primary active transport uses ATP as an energy source for the movement of molecules against their concentration gradient.
Secondary active transport (or couple transport) uses an electrochemical gradient to power the transport.
Symport moves both particles in secondary active transport across the membrane in the same direction.
Antiport moves particles across the cell membrane in opposite directions.
Give biologically relevant examples of antiport secondary active transport.
Antiport Examples:
Sodium-Calcium Exchanger (NCX):
This protein, found in excitable cells like heart muscle cells, transports sodium ions into the cell and calcium ions out of the cell, effectively removing calcium after an action potential.
Sodium-Hydrogen Exchanger (NHE):
This antiporter transports sodium into the cell and hydrogen out of the cell, helping to regulate pH.
Sodium-Potassium Pump (Na+/K+ ATPase):
While primarily a primary active transport pump, it also functions as an antiporter, moving three sodium ions out of the cell and two potassium ions into the cell.
Give biologically relevant examples of symport secondary active transport.
Symport Examples:
Sodium-Glucose Symporter (SGLT1):
This protein in the small intestine and kidneys facilitates the co-transport of sodium ions and glucose molecules into cells, both moving in the same direction.
Sucrose Transport in Plants:
Plants use a proton-sucrose symporter to co-transport sucrose into cells, with protons moving down their concentration gradient and sucrose moving against its gradient.
What are some instances of specialized biological membranes?
Sarcolemma of muscle cells must maintain a membrane potential for muscle contraction to occur.
Mitochondrial membranes facilitate oxidative phosphorylation to produce ATP by oxidative respiration.
Sodium potassium pumps in nerve cell membranes are essential for action, potentials and signal transduction.
The permeability of the cell membrane to ions and the selectivity of ion channels both lead to an electrochemical gradient between the exterior and the interior of cells.
What is the membrane potential?
What is the resting membrane potential?
What are leak channels?
What are sodium potassium pumps?
The difference in electrical potential across cell membrane is called the membrane potential, Vm.
The resting potential for most cells is between -40 and -80 mV, depolarization can raise the member in potential as high as +35 mV.
Maintaining membrane potential requires energy because ions may passively diffuse through the cell membrane over time using leak channels.
An ion or transporter pump, such as sodium potassium pump (Na+/K+ ATPase) regulates the concentration of intracellular and extracellular sodium and potassium ions.
Chloride ions also participate in establishing membrane potential.
What is the Nernst equation?
How can it be used to determine the membrane potential from the intra- and extracellular concentrations of the various ions?
The Nernst equation is a thermodynamic equation in electrochemistry that relates a cell’s potential to its temperature and reaction quotient. It’s derived from the reaction’s Gibbs free energy and can be used to calculate a cell’s potential under non-standard conditions (or standard conditions such as body temperature.
What is the Nernst equation for membrane potential from intra and extracellular concentrations of various ions?
Note: inside the body so standard body condition equation, which is what T in K and C?
Z is the charge of the ion.
Again. Nurnst equation. Both for nonstandard conditions and simplified for body temperature.
What is it?
What is body temp in K?
What are units of volts?
The Nernst equation is a chemical thermodynamic relationship that calculates the reduction potential of a reaction (half-cell or full cell reaction) under non-standard conditions based on the standard electrode potential, temperature, the number of electrons involved, and the activities or concentrations of the reactants and products.
Z is the charge if the ion.
For fun. What is the Nernst equation under standard temperature and pressure of 1 atm (10^4 pascals or 101.3 kPa), 1 mol concentration, 25° C (298K)
Z is the charge of the ion.
What is the Goldman-Hodgkin-Katz voltage equation?
What does P represent?
Why is Cl- inverted relative to the other ions?
The Goldman-Hodgkin-Katz voltage equation flows from the Nernst equation, taking into account the relative contribution of each major ion to the membrane potential.
What is the Goldman-Hodgkin-Katz VOLTAGE equation?
The Goldman-Hodgkin-Katz voltage equation calculates the voltage potential across a cell membrane while taking into account the concentrations and permeability of each major ion to the membrane potential.
More ions outside is higher voltage.
More ions inside is lower voltage.
What is the importance of understanding the Goldman-Hodgkin-Katz voltage equation?
The Goldman-Hodgkin-Katz voltage equation is all about the amount of ions on the inside of the cell and on the outside of the cell.
Concentration of potassium is low on the outside and high on the inside.
Concentration of sodium is high on the outside and low on the inside.
Therefore, looking at the equation, sodium contributes to a positive membrane potential and potassium contributes to a negative membrane potential.
Think about the resting membrane potential of -70 mV. When resting potential is achieved, the contributions of potassium on the inside outweigh the contributions of sodium on the outside, giving a total negative voltage potential.
What is the sodium potassium pump?
What enzyme facilitates the sodium potassium pump?
There is a steady state resting relationship between ion diffusion and the sodium potassium ATPase (Na+/K+ ATPase).
Na+/K+ ATPase maintains a low concentration of sodium ions and high concentration of potassium ions a intracellularly by pumping three sodium ions out for every two potassium ions pumped in.
The movement of three sodium ions pumped out for every two potassium ions pumped in has a net effect of removing one positive charge from the intracellular space of the cell, this maintains the negative resting potential of the cell (-70 mV).
The combination of what two membrane transport processes maintains the resting potential of the cell?
Na+/K+ ATPase: pumps sodium out and potassium in, leaving net positive outside, negative resting potential of cell.
Leak channels that allow sodium and potassium to passively diffuse into or out of the cell down their concentration gradients.
Cell membranes are more permeable to potassium ions than sodium ions at rest because there are more potassium leak channels than sodium leak channels.
What do mitochondria do?
How many membranes do mitochondria have?
Mitochondria produce ATP through oxidative phosphorylation, also called oxidative respiration.
Mitochondria contain two membranes: the inner and outer mitochondrial membranes with the presence of a small inter membrane space in between the two layers.
Describe the outer mitochondrial membrane.
The outer mitochondrial membrane is highly permeable due to large pores that allow the passage of ions and small proteins.
The outer mitochondrial membrane does not allow large proteins or macromolecules into the inner mitochondrial space.
The outer membrane completely surrounds the inner mitochondrial membrane, with the presence of a small membrane space in between the two layers.
Describe the inner mitochondrial membrane.
The inner mitochondrial membrane has a much more restricted permeability compared to the outer mitochondrial membrane.
Contains numerous infoldings called cristae (kris-tay) which increase the available surface area for the integral proteins associated with the membrane.
The integral proteins in the inner mitochondrial membrane are involved in the electron transport chain in ATP synthesis.
The inner membrane also encloses the mitochondrial matrix, where the citric acid cycle produces high energy electron carriers used in the electron transport chain.
Where are the proteins involved with the electron transport chain in ATP synthesis located?
The integral proteins associated with the inner mitochondrial membrane are the site of oxidative phosphorylation (the electron transport chain and ATP synthesis).
What is the mitochondrial matrix?
What happens in the mitochondrial matrix?
The mitochondrial matrix is enclosed by the inner mitochondrial membrane.
The mitochondrial matrix is the site of the citric acid cycle, which produces high energy electron carriers used in the electron transport chain.
Does the mitochondrial membrane contain cholesterol?
The reminder about chore membrane does not contain cholesterol, but rather a high-level of cardiolipin.
What is cardiolipin?
Cardiolipin (CL) is a unique, dimeric phospholipid primarily found in the inner mitochondrial membrane (IMM), playing a crucial role in mitochondrial function, dynamics, and bioenergetics, as well as being involved in processes like mitophagy and apoptosis.
MCAT concept check specialized membranes 8.4 page 315 question 1
How is the resting membrane potential maintained?
The membrane potential, which results from a difference in the number of positive and negative charges on either side of the membrane, is maintained primarily by the sodium potassium pump which moves three sodium ions out of the cell for every two potassium ions pumped in, and to a minor extent by leak channels that allow the passive transport of ions.
MCAT concept check specialized membranes 8.4 page 315 question 2
Exact value is -64 mV
MCAT concept check specialized membranes 8.4 page 315 question 3
What distinguishes the inner mitochondrial membrane from other biological membranes?
What is the pH gradient between the cytoplasm and the inter membrane space?
The inner mitochondrial membrane lacks cholesterol, which differentiates it from most other biological membranes. It contains cardiolipin, a unique feature of the inner mitochondrial membrane.
There is no pH gradient between the cytoplasm and the inter membrane space because the outer mitochondrial membrane has such high permeability to biomolecules.
The proton motive force of the mitochondria is across the inner mitochondrial membrane, not the outer mitochondrial membrane.
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Lecithin is a phospholipid, a key component of cell membranes.
Phosphatidylinositol (PI) is a type of phospholipid, a key component of cell membranes, that serves as a precursor for phosphoinositides, which are crucial in cell signaling and membrane dynamics.
Cholesterol is a type of steroid, specifically a sterol, belonging to the family of lipids that share a four-ring chemical structure.
