Chapter 7: Membrane Structure and Function
Cholesterol can act as a
"fluidity buffer" because it slows the movement of the phospholipids
The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?
1.0 M
What would be least likely to diffuse through a plasma membrane without the help of a transport protein?
A large, polar molecule
glycoprotein
A protein with one or more carbohydrates covalently attached to it.
proton pump
An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.
electrogenic pump
An active transport protein that generates voltage across a membrane while pumping ions.
Which of the following correctly states the relationship between anabolic and catabolic pathways?
Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways
Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B, and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.
B; the diffusion gradient in cell B is steeper
Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?
Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall.
Which of the following molecules is most likely to passively diffuse across the plasma membrane?
Carbon dioxide
In which ways do the membranes of a eukaryotic cell vary?
Certain proteins are unique to each membrane.
osmosis
Diffusion of water through a selectively permeable membrane
Which of the following is not a function of membrane proteins?
Energy, carbon, and nitrogen storage
Active transport
Energy-requiring process that moves material across a cell membrane through a transport protein against a concentration difference
Which correctly describes some aspect of exocytosis or endocytosis?
Exocytosis and endocytosis change the surface area of the plasma membrane.
Cell-cell recognition proteins
Identification between cells. glyco-proteins that act as identification tags
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found?
In the interior of the membrane
What statement concerning carbohydrates associated with the plasma membrane is correct?
Membrane carbohydrates function primarily in cell-cell recognition
What function of membrane proteins is important in tissue formation during embryonic development in animals?
Membrane proteins with short sugar chains form identification tags that are recognized by other cells.
Which of the following is a major difference between prokaryotic and eukaryotic cells?
Most prokaryotic cells have no internal membranes; eukaryotic cells do.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found?
On the outside (external) surface of the membrane
Which of the following statements about passive transport is correct?
Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule.
How does the plasma membrane regulate inbound and outbound traffic?
Passive/Active Transport Exocytosis/Endocytosis
Which of the following enables a cell to pick up and concentrate a specific kind of molecule?
Receptor-mediated endocytosis
what enables a cell to pick up and concentrate a specific kind of molecule
Receptor-mediated endocytosis only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, endocytosis does not proceed.
hypertonic
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
hypotonic
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
cotransport
The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.
electrochemical gradient
The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).
Which of the following statements best describes how unsaturated fatty acids increase membrane fluidity at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
The plasma membrane is referred to as a "fluid mosaic" structure. What is a true statements about that model?
The fluid aspect of the membrane is due to the mobility of phospholipids, and embedded proteins account for the mosaic aspect.
Celery stalks that are immersed in fresh water for several hours become stiff. Which of the following statements best explains the observation that similar stalks left in a 0.15 M salt solution become limp?
The fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true?
The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.
Receptor-mediated endocytosis
The uptake of specific molecules based on a cell's receptor proteins
membrane potential
The voltage across a cell's plasma membrane.
What are some of the functions of membrane proteins?
Transport, enzymatic activity, signal, cell to cell recognition, intercellular joining, attachment to the cytoskeleton and ECM
What happens when two solutions separated by a selectively permeable membrane reach osmotic equilibrium?
Water molecules move between the two solutions, but there is no net movement of water across the membrane.
A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?
Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease.
membrane potential acts like
a battery
sodium-potassium pump
a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell
aquaporin
a channel protein in a cellular membrane that specifically facilitates osmosis
signal transduction proteins
a membrane receptor that has specific binding sites that fit a specific shape of a chemical messenger
The sodium-potassium pump hydrolyzes ATP and results in
a net positive change outside the cell membrane.
Enzymatic membrane protein
a protein built into the membrane may be an enzyme with its active site exposed to substances acts in the metabolic pathway
peripheral protein
a protein loosely bound to the surface of a membrane or to part on an integral protein and not embedded in the lipid bilayer
transport membrane proteins
a protein that spans the membrane that may provide a hydrophilic channel that selective solutes my shuttle through
concentration gradient
a region along which the density of a chemical substance increases or decreases
transport protein
a transmembrane protein that helps a certain substance or class of closely related substance to crosse the membrane
transmembrane proteins
a type of integral protein that spans the entire membrane
active transport moves
against the concentration gradient
Like phospholipids, most membrane proteins are
amphipathic
In a hypotonic solution a plant cell will
become turgid/firm
non polar molecules such as hydrocarbons
can easily dissolve in the lipid bilayer and cross it easily with out the aid of proteins
Which of the following factors is a primary contributor underlying cause of familial hypercholesterolemia?
defective LDL receptors on the cell membranes
A decrease in entropy is associated with which of the following types of reaction?
dehydration
The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is
determined as the membrane is being constructed.
The two lipid layers may
differ in specific lipid composition.
Variations in carbohydrate structure
distinguish one species from another, one individual from another, and even one cell type from another.
facilitated diffusion moves
down the concentration gradient
Passive transport can occur in either direction, but the direction of net diffusion is
down the concentration gradient of the solute.
integral proteins are
embedded into the phospholipid bilayer and may either extend all the way or partially through the bilayer.
Diffusion will continue until?
equilibrium is reached
Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also
exposed on the cytoplasmic side of the plasma membrane.
amphipathic
having both a hydrophilic region and a hydrophobic region
intercellular joining proteins
hook cells together - adhesion such as tight junctions or gap junctions
active transport enables a cell to maintain
internal concentrations of small solutes that differ from concentrations in its environment
Which of the following statements is true regarding potential energy?
it is the energy possessed by matter due to its location or structure
Exocytocis
large molecules are secreted when a vesicle fuses with the plasma membrane
Endocytocis
large molecules are taken in when the plasma membrane pinches inward forming a vesicle
What needs help to diffuse through the membrane?
large polar and uncharged molecules
What are the staple ingredients of membranes?
lipids and proteins
lipid rafts
lipids assembled in a defined patch in the cell membrane
Membrane carbohydrates are covalently bonded to ______ and extend out from_____
lipids or proteins the external side of the plasma membrane as a means of cell identification.
In a hypotonic solution, an animal cell will
lyse (burst)
Cell-cell recognition is an important function of ________, and this cell-cell recognition is important in tissue formation during embryo genesis.
membrane proteins
fluid mosaic model
model that describes the arrangement and movement of the molecules that make up a cell membrane
Passive trasport
movement of molecules without requirement of energy: 1) diffusion 2) osmosis (across a membrane) 3) facilitated diffusion (helped by transport proteins)
the cytoplasmic side of the membrane is
negatively charged
In an isotonic solution, an animal cell will
neither gain nor lose water
diffusion results in the
net movement of a substance from a region where it is more to a region where it is less concentrated
Are proteins randomly distributed in the membrane?
no they are often associated in long-lasting, specialized patches where they carry out common functions
In receptor-mediated endocytosis, membrane receptors bind to molecules outside of the cell. Immediately following endocytosis where will the membrane receptors be located?
on the inside surface of the vesicle
the hydrophobic region of an integral protein consists of
one or more stretches of nonpolar amino acids
Diffusion is a
passive and spontaneous process
The fluidity of a membrane affects its
permeability and the ability of the membrane proteins to function
What is an example of an amphipathic molecule?
phospholipids
The passageways for facilitated diffusion may be either
protein pores or carrier proteins.
Channel Proteins
provide corridors that allow a specific molecule or ion to cross the membrane
isotonic
referring to a solution that when surround a cell causes no net movement of water into or out of the cell
osmoregulation
regulation of solute concentrations and water balance by a cell or organism
In a hypertonic solution, an animal cell will
shrivel
What molecules can pass through the membrane through passive diffusion?
small uncharged or non-polar molecules hydrophobic
a transport protein is
specific for the substance it translocates allowing only a certain substance to cross the membrane
tonicity
the ability of a solution surrounding a cell to cause that cell to gain or lose water
Why are unsaturated fats liquid at room temperature?
the kind in the hydrocarbon tail keeps the molecules from packing as close together
facilitated diffusion
the passage of molecules or ions down a gradient across a membrane with assistance of specific transmembrane transport proteins requires no ATP
Pinocytosis:
the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane
are membranes static or fluid?
they are fluid b/c they are held together by weak bonds
In a hypertonic solution a plant cell will
undergo plasmolysis and the plasma membrane will shrink back from the cell wall
membrane carbohydrates are
usually short branched chains of carbs that may be covalently bonded to lipids or proteins
bulk transport across the plasma membrane usually occurs with
vesicles
all cells have
voltages across their plasma membranes due to a spearation fo opposite charges