p.12
Membrane Lipids and Fluidity
What distinguishes neutral lipids from polar lipids?
Neutral lipids are non-polar and hydrophobic, while polar lipids have a hydrophilic head and a hydrophobic tail.
p.59
Transport Mechanisms Across Cell Membranes
Why is phosphorylated glucose effectively locked into the cell?
Because it cannot bind the carrier protein any longer.
p.5
Surface Area to Volume Ratio
How does the volume of a cell increase relative to its length?
The volume of a cell increases with the cube of its length.
p.58
Transport Mechanisms Across Cell Membranes
Is transport by GLUT1 reversible?
Yes, transport by GLUT1 is reversible.
p.41
Transport Mechanisms Across Cell Membranes
What is osmosis?
The diffusion of water across a selectively permeable membrane.
p.14
Membrane Lipids and Fluidity
What adjustment is made to membrane lipids in hot temperatures to maintain fluidity?
Cells may increase the length of carbon chains in membrane lipids.
p.38
Diffusion Rates of Molecules
What happens to free energy as molecules move down their concentration gradients during diffusion?
Free energy is minimized.
p.23
Properties of Water in Biology
What are the sources of saturated fats?
Saturated fats are found in dairy products such as butter and cheese, as well as in meat and some fish, such as salmon.
p.53
Transport Mechanisms Across Cell Membranes
What is the function of channel proteins in cell membranes?
Channel proteins form hydrophilic channels through the membrane to provide a passage route for solutes.
p.13
Membrane Lipids and Fluidity
What factors affect the transition temperature (Tm) of a membrane?
The length of the fatty acids, the number of double bonds, and the proportion of sterols (e.g., cholesterol).
p.31
Structure and Function of Cell Membranes
Why are some membrane proteins constrained in their movement within the membrane?
They are anchored to protein complexes.
p.22
Properties of Water in Biology
What happens to most of the C=C double bonds during the partial hydrogenation of a typical plant oil?
Most of the C=C double bonds are removed.
p.9
Structure and Function of Cell Membranes
What is the primary function of cell membranes?
To define and control the content of cells by acting as a barrier between the inside and outside of the cell.
p.13
Membrane Lipids and Fluidity
What is the transition temperature (Tm) in the context of cell membranes?
The temperature at which a membrane changes between the fluid and gelled state.
p.33
Membrane Lipids and Fluidity
What are localized regions of membrane lipids in association with specific proteins called?
Lipid microdomains or lipid rafts.
p.4
Limitations on Cell Size
What is the major limit on cell size?
The need to maintain an adequate surface area/volume ratio.
p.53
Transport Mechanisms Across Cell Membranes
How do carrier proteins facilitate diffusion?
Carrier proteins bind solute molecules on one side of a membrane, undergo a conformation change, and release the solute on the other side of the membrane.
p.63
Active Transport vs. Passive Transport
What characteristic of active transport gives it an intrinsic directionality?
Active transport has an intrinsic directionality because it moves substances against their concentration gradient.
p.54
Transport Mechanisms Across Cell Membranes
What type of carrier is the glucose transporter in erythrocytes?
The glucose transporter is a uniport carrier for glucose.
p.22
Properties of Water in Biology
How does partial hydrogenation affect the melting point of the product?
It elevates the melting point of the product.
p.45
Transport Mechanisms Across Cell Membranes
What happens to a cell in a hypertonic solution?
It will shrink and shrivel.
p.31
Structure and Function of Cell Membranes
How do membrane proteins vary in their mobility within the membrane?
Some membrane proteins can move freely, while others are constrained because they are anchored to protein complexes.
p.16
Role of Cholesterol in Membrane Fluidity
What dual role does cholesterol play in membrane fluidity?
Cholesterol decreases fluidity by making the membrane more rigid but also prevents phospholipid hydrocarbon chains from packing tightly, reducing the tendency of membranes to gel upon cooling.
p.7
Properties of Water in Biology
What causes water molecules to be polar?
The unequal distribution of electrons or charge.
p.62
Active Transport vs. Passive Transport
What does active transport allow in terms of cellular environment?
Active transport allows the creation and maintenance of an internal cellular environment that differs greatly from the surrounding environment.
p.14
Membrane Lipids and Fluidity
How do cells maintain membrane fluidity in cold temperatures?
By decreasing the length of carbon chains in membrane lipids.
p.48
Transport Mechanisms Across Cell Membranes
Why can't most substances in the cell cross membranes by simple diffusion?
Because they are too large or too polar.
p.23
Properties of Water in Biology
What is the health impact of eating more trans fats according to the latest research?
Eating more trans fats was linked to an increased risk of death or heart disease.
p.55
Transport Mechanisms Across Cell Membranes
How does the erythrocyte uptake glucose?
By facilitated diffusion because the level of blood glucose is much higher than that inside the cell.
p.38
Diffusion Rates of Molecules
In which direction do chemical reactions and physical processes proceed?
In the direction of decreasing free energy.
p.37
Transport Mechanisms Across Cell Membranes
What is simple diffusion?
The unassisted net movement of a solute from high to lower concentration.
p.54
Transport Mechanisms Across Cell Membranes
What type of carrier is the anion exchange protein in erythrocytes?
The anion exchange protein is an antiport anion carrier for Cl– and HCO3–.
p.29
Membrane Lipids and Fluidity
What is the behavior of membrane lipids in terms of asymmetry?
Membrane lipids exhibit little or no transverse diffusion (flip-flopping) from one lipid layer to the other.
p.61
Active Transport vs. Passive Transport
What are the three important cellular functions of active transport?
Uptake of essential nutrients, removal of wastes, and maintenance of nonequilibrium concentrations of certain ions.
p.33
Membrane Lipids and Fluidity
What characteristics do lipid rafts in the outer monolayer of animal cells have?
They have elevated levels of cholesterol and glycosphingolipids and are less fluid than the rest of the membrane.
p.7
Properties of Water in Biology
Why is water considered the universal solvent in biology?
Because it can dissolve a wide variety of substances.
p.63
Active Transport vs. Passive Transport
How does active transport differ from diffusion in terms of direction?
Active transport is unidirectional, while diffusion is nondirectional and proceeds as directed by the concentrations of the transported substances.
p.43
Transport Mechanisms Across Cell Membranes
What determines the osmotic movement into and out of a cell?
The relative osmolarity, or total solute concentrations inside versus outside of the cell.
p.5
Surface Area to Volume Ratio
Why do larger cells have proportionately smaller surface areas?
Because the surface area of the cell increases with the square of its length, while the volume increases with the cube of its length.
p.16
Membrane Lipids and Fluidity
How do sterols influence membrane fluidity?
Sterols, such as cholesterol, decrease membrane fluidity by intercalating into the membrane and increasing the Tm.
p.37
Transport Mechanisms Across Cell Membranes
What types of molecules typically undergo simple diffusion?
Gases, nonpolar molecules, or small polar molecules such as water, glycerol, or ethanol.
p.58
Transport Mechanisms Across Cell Membranes
What dictates the direction of transport facilitated by a carrier protein like GLUT1?
The relative solute concentrations outside and inside the cell.
p.68
Active Transport vs. Passive Transport
What powers indirect active transport?
Indirect active transport is not powered by ATP hydrolysis.
p.46
Limitations on Cell Size
How do cells without cell walls solve the osmolarity problem?
By pumping out inorganic ions, reducing the intracellular osmolarity.
p.42
Transport Mechanisms Across Cell Membranes
What is osmosis?
The movement of water toward the region of higher solute concentration across a selectively permeable membrane.
p.35
Transport Mechanisms Across Cell Membranes
What types of substances typically move across cell membranes?
Dissolved gases, ions, and small organic molecules, also known as solutes.
p.34
Structure and Function of Cell Membranes
How do lipid rafts contribute to the immune system?
Lipid rafts help bind activated immune system cells to their microbial targets.
p.67
Transport Mechanisms Across Cell Membranes
What is required for cotransport to occur in the cell?
Both H+ and another molecule are needed for cotransport.
p.12
Membrane Lipids and Fluidity
What are the two main types of lipids based on polarity?
Neutral lipids and polar lipids.
p.27
Structure and Function of Cell Membranes
What are the main classes of membrane proteins?
Integral membrane proteins, peripheral membrane proteins, and lipid-anchored proteins.
p.66
Active Transport vs. Passive Transport
What does indirect active transport depend on?
The simultaneous transport of two solutes.
p.64
Active Transport vs. Passive Transport
How can active transport mechanisms be divided?
Based on the sources of energy and whether or not two solutes are transported at the same time.
p.25
Structure and Function of Cell Membranes
What does the 'mosaic' in the Fluid Mosaic Model refer to?
A mosaic of proteins in a fluid lipid bilayer.
p.45
Transport Mechanisms Across Cell Membranes
What occurs to a cell in a very hypotonic solution?
It will swell and perhaps burst (or lyse).
p.77
Structure and Function of Cell Membranes
How do cell membranes contribute to cellular communication?
Cell membranes contain receptors that allow cells to communicate with each other and respond to external signals.
p.8
Membrane Lipids and Fluidity
What are the main functions of lipids?
Energy storage, membrane structure, and specific biological functions.
p.30
Structure and Function of Cell Membranes
What forms glycolipids and glycoproteins in cell membranes?
Oligosaccharides covalently bound to lipids and proteins.
p.72
Transport Mechanisms Across Cell Membranes
Which cells use a Na+/glucose symporter to take up glucose and amino acids?
The cells lining the intestine.
p.27
Structure and Function of Cell Membranes
What does freeze fracture microscopy reveal about membrane proteins?
It shows that proteins are embedded or 'floating' in and on the lipid bilayer of cell membranes.
p.4
Surface Area to Volume Ratio
Why is surface area important for a cell?
Because exchanges between the cell and its surroundings take place at the cell surface.
p.60
Active Transport vs. Passive Transport
What is the purpose of active transport in cellular processes?
To move solutes up a concentration gradient, away from equilibrium.
p.19
Membrane Lipids and Fluidity
How does Micrococcus adapt to cool temperatures?
Micrococcus uses an enzyme to cut two carbons off the 18 carbon fatty acids to produce 16 carbon fatty acids.
p.66
Active Transport vs. Passive Transport
How does the favorable movement of one solute affect the movement of another in indirect active transport?
The favorable movement of one solute down its gradient drives the unfavorable movement of the other up its gradient.
p.29
Membrane Lipids and Fluidity
What role do flippases play in membrane lipid behavior?
Flippases are enzymes that can facilitate the transverse diffusion of lipids under special conditions.
p.49
Active Transport vs. Passive Transport
Is energy input required for facilitated diffusion?
No, energy input is not needed in facilitated diffusion.
p.49
Transport Mechanisms Across Cell Membranes
What role do transport proteins play in facilitated diffusion?
Transport proteins provide a path through the lipid bilayer, allowing the 'downhill' movement of a polar or charged solute.
p.36
Transport Mechanisms Across Cell Membranes
How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion is protein-mediated (involving carrier and/or channel proteins) and does not require cellular energy, moving substances down the gradient toward equilibrium.
p.74
Transport Mechanisms Across Cell Membranes
What is the first step in the mechanism of the Na+/Glucose symporter?
Two external Na+ ions bind their sites on the symporter, which is open to the exterior.
p.62
Active Transport vs. Passive Transport
Why are many membrane proteins involved in active transport called pumps?
Because energy is required to move substances against their concentration gradients.
p.77
Structure and Function of Cell Membranes
What is one primary function of cell membranes?
Cell membranes act as a barrier to protect the cell from its surroundings.
p.56
Transport Mechanisms Across Cell Membranes
How does GLUT1 transport glucose through the membrane?
By the alternating conformation mechanism.
p.65
Active Transport vs. Passive Transport
What is direct active transport?
The accumulation of solute molecules on one side of the membrane coupled directly to an exergonic chemical reaction.
p.15
Membrane Lipids and Fluidity
How do saturated fatty acids affect membrane packing?
Saturated fatty acids pack together well in the membrane.
p.50
Active Transport vs. Passive Transport
Why do most cells have an excess of negatively charged solutes inside the cell?
This charge difference favors the inward movement of cations such as Na+ and outward movement of anions such as Cl-.
p.11
Membrane Lipids and Fluidity
What is a key characteristic of amphipathic molecules in membrane lipids?
They have hydrophobic fatty acid tails and a hydrophilic polar head.
p.24
Role of Cholesterol in Membrane Fluidity
What are low-density lipoproteins (LDLs) commonly known as?
LDLs are commonly known as 'bad cholesterol'.
p.69
Transport Mechanisms Across Cell Membranes
What do most cells continuously pump out of the cell in symport mechanisms of indirect active transport?
Most cells continuously pump either sodium ions or protons out of the cell.
p.9
Membrane Lipids and Fluidity
What characteristic do membrane lipids and proteins share?
They are amphipathic, having both hydrophilic and hydrophobic regions.
p.70
Active Transport vs. Passive Transport
How do fungi and plants uptake organic solutes?
They use proton symport, with ATP driving the proton pump that creates and maintains the proton electrochemical potential.
p.41
Transport Mechanisms Across Cell Membranes
Why do water molecules move across membranes in response to differences in solute concentration?
Because the solutes themselves often do not readily cross the membranes.
p.10
Structure and Function of Cell Membranes
How do proteins typically transverse the lipid bilayer in cell membranes?
Via alpha helices; these are known as integral proteins.
p.3
Diffusion Rates of Molecules
How do many molecules move through the cytoplasm?
By diffusion, the unassisted movement of a substance from a region of high concentration to a region of low concentration.
p.34
Structure and Function of Cell Membranes
What roles do lipid rafts play in cellular function?
Lipid rafts are involved in detecting and responding to extracellular signals, transporting nutrients and ions across membranes, binding activated immune system cells to microbial targets, and transporting cholera toxin into intestinal cells.
p.50
Active Transport vs. Passive Transport
What is the result of active transport of ions across the plasma membrane in all organisms?
It results in an asymmetric distribution of ions inside and outside the cell.
p.69
Transport Mechanisms Across Cell Membranes
How is the uptake of sugars and amino acids driven in symport mechanisms of indirect active transport?
The high extracellular concentration of Na+ is a driving force for the uptake of sugars and amino acids.
p.47
Structure and Function of Cell Membranes
What types of cells have cell walls that prevent them from swelling and bursting in a hypotonic solution?
Cells of plants, algae, fungi, and many bacteria.
p.48
Transport Mechanisms Across Cell Membranes
What is facilitated diffusion?
It is the exergonic process where solutes move across cell membranes with the assistance of transport proteins, following their concentration gradient.
p.8
Membrane Lipids and Fluidity
What are lipids polymers of?
Various monomers including fatty acids.
p.46
Limitations on Cell Size
What is the effect of reducing intracellular osmolarity in cells without cell walls?
It minimizes the intracellular osmolarity and the difference in solute concentration between the cell and the surroundings.
p.30
Structure and Function of Cell Membranes
What is the glycocalyx and where is it located?
The glycocalyx is a loose carbohydrate layer on the outer surface of the cell.
p.67
Transport Mechanisms Across Cell Membranes
How is a low concentration of H+ maintained inside the cell?
Through cotransport mechanisms that transport H+ out of the cell.
p.39
Transport Mechanisms Across Cell Membranes
Where do erythrocytes take up and release oxygen?
Erythrocytes take up oxygen in the lungs and release it in the body tissues.
p.19
Membrane Lipids and Fluidity
What role does the desaturase enzyme play in E. coli at cool temperatures?
The desaturase enzyme increases the number of double bonds in fatty acids.
p.71
Active Transport vs. Passive Transport
What is a well-understood example of direct active transport by a P-type ATPase in animal cells?
The Na+/K+ ATPase (or pump).
p.71
Active Transport vs. Passive Transport
What is an example of indirect active transport?
The Na+/glucose symporter.
p.20
Role of Cholesterol in Membrane Fluidity
How do sterols like cholesterol act in cell membranes?
Sterols moderate membrane fluidity in both directions, acting as a buffer.
p.75
Transport Mechanisms Across Cell Membranes
What causes the Na+/Glucose symporter to lock in its inward-facing conformation?
The dissociation of two Na+ ions in response to the low internal Na+ concentration.
p.68
Active Transport vs. Passive Transport
How is the inward transport of molecules up their electrochemical gradients achieved in indirect active transport?
It is coupled to and driven by the simultaneous inward movement of Na+ (in animals) or protons (in plants, fungi, bacteria) down their gradients.
p.11
Membrane Lipids and Fluidity
What are the three classes of membrane lipids?
Phospholipids, glycolipids, and sterols.
p.36
Transport Mechanisms Across Cell Membranes
What is simple diffusion and how does it work?
Simple diffusion is the movement of substances via lipids without the expenditure of cellular energy, moving down the gradient toward equilibrium.
p.26
Membrane Lipids and Fluidity
How is lateral diffusion within the lipid layer demonstrated experimentally?
By fluorescence recovery after photobleaching (FRAP).
p.18
Role of Cholesterol in Membrane Fluidity
How do sterols affect the permeability of membranes?
Sterols decrease the permeability of membranes to ions and small polar molecules.
p.18
Role of Cholesterol in Membrane Fluidity
Why do sterols decrease membrane permeability?
Sterols fill spaces between the hydrocarbon chains of phospholipids, blocking routes that ions and small molecules would take through the membrane.
p.52
Transport Mechanisms Across Cell Membranes
What is the role of transport proteins in the erythrocyte plasma membrane?
They are among the best understood of all transport proteins and facilitate various transport mechanisms.
p.26
Membrane Lipids and Fluidity
What are the two types of movements that contribute to membrane fluidity?
Rotational movement and lateral diffusion within the lipid layer.
p.76
Transport Mechanisms Across Cell Membranes
What mechanism uses Na+ to transport glucose into the cell?
Sodium-glucose co-transport (or symport).
p.56
Transport Mechanisms Across Cell Membranes
What are the two conformational states of GLUT1?
T1, with the binding site open on the outside of the cell, and T2, with the binding site open to the inside of the cell.
p.2
Limitations on Cell Size
What are the three main factors that limit cell size?
The requirement for adequate surface area relative to volume, the rates at which molecules can diffuse, and the need to maintain adequate local concentrations of substances required for necessary cellular functions.
p.2
Limitations on Cell Size
Why is the surface area to volume ratio important for cell size?
Because it ensures that the cell has enough surface area to adequately exchange materials with its environment relative to its volume.
p.24
Role of Cholesterol in Membrane Fluidity
How do high-density lipoproteins (HDLs) affect cholesterol levels in the body?
HDLs carry cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile, hence they are called 'good cholesterol'.
p.74
Transport Mechanisms Across Cell Membranes
What happens after the Na+ ions bind to the Na+/Glucose symporter?
This allows one molecule of glucose to bind.
p.15
Membrane Lipids and Fluidity
Why are unsaturated fatty acids more fluid than saturated fatty acids?
Unsaturated fatty acids have bends in the chains due to one or more double bonds, preventing them from packing together neatly.
p.52
Active Transport vs. Passive Transport
How is the membrane potential of erythrocytes maintained?
By active transport of potassium ions inward and sodium ions outward.
p.20
Membrane Lipids and Fluidity
How do organisms regulate membrane fluidity in cooler temperatures?
By shortening fatty acid chains and increasing the number of double bonds.
