Biology Chapter 7 (Membranes)

Active transport by the sodium-potassium pump follows this cycle.

1.corresponding to step one in a diagram below the text. Three Na+ ions from the cytosol bind to the pump. 2.corresponding to step two in the diagram below the text. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3.corresponding to step three in the diagram below the text. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4.corresponding to step four in the diagram below the text. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. 5. corresponding to step five in the diagram below the text. Release of the phosphate group causes another conformational change in the pump. 6. corresponding to step six in the diagram below the text. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.

Which of the following helps most to explain why water has a high specific heat?

A water molecule can make 4 hydrogen bonds.

The permeability of a biological membrane to a specific polar solute may depend on which of the following?

the types of transport proteins in the membrane ; The lipid bilayer will be impermeable or very poorly permeable to polar or charged solutes. The presence of the correct transport protein will determine the permeability.

BOTH channels and carriers

transport solutes DOWN a concentration gradient are integral membrane proteins provide a hydrophilic path across the membrane

The alpha and beta forms of glucose, found in starch and cellulose, differ in ...

how one of the -OH groups is oriented.

Water is a source of ______________ for chemical reactions in cells.

hydrogen atoms and oxygen atoms; Many reactions incorporate O and H from water into biological molecules. This happens when you digest starch and protein, for example.

Water has surface tension because ...

hydrogen bonds between surface water molecules resist being stretched.; The hydrogen bonds between surface water molecules are normally slightly stretched. Like a stretched sheet of rubber, the surface tends to contract and resists being penetrated.

Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.

hydrophobic molecules: Oxygen, carbon dioxide and nitrogen small uncharged polar molecules: water, urea, glycerol

Diffusion _____.

is a passive process in which molecules move from a region of higher concentration to a region of lower concentration

What name is given to the process by which water crosses a selectively permeable membrane?

osmosis; Osmosis is the passive transport of water.

Which of the following types of molecules are the major structural components of the cell membrane?

phospholipids and proteins

ONLY channels

provide a continuous path allow water molecules & small ions to flow quickly across the membrane

BOTH exocytosis & endocytosis

requires cellular energy transported substances never physically across the membrane

Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration outside the cell. What type of transport is used to move lactose into the cell?

Active transport; Under these conditions, lactose moves against its concentration gradient, so its transport will require energy.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature; Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are water-soluble.

Which complex carbohydrate contains only a-1,4-glycosidic linkages?

Amylose is formed from a-1,4-glycosidic linkages of glucose

Which of the following complex carbohydrates is listed with its correct function?

Cellulose: structural component of plant cell walls

Which of the following statements about cotransport of solutes across a membrane is correct?

Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.; The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different solutes using cotransport proteins.

True or false? Active transport differs from passive transport in that active transport does not require an input of energy.

False; Active transport requires the input of energy, whereas passive transport is primarily driven by the gradient.Active transport requires energy, whereas passive transport does not.

True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell for every two potassium ions pumped out of the cell.

False; The sodium-potassium pump maintains a state in which the concentration of sodium is low inside the cell relative to the outside and the concentration of potassium is high inside the cell relative to the outside; thus, three sodium ions are pumped out of the cell and two potassium ions are pumped into the cell against the electrochemical gradient.

A sugar can have ...

H covalently bound to the C of a C=O group.; This occurs in linear aldoses such as glucose.

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic; The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.

Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?

Ions, such as hydrogen ions, and hydrophilic molecules, such as water and glucose, cannot rapidly pass directly through the phospholipids of a plasma membrane. To move rapidly through the membrane, they must pass through membrane transport proteins.

Which statement is true of water's tensile strength?

It results from hydrogen bonding. It helps to pull water through plants. It involves both cohesion and adhesion.; Because of hydrogen bonding, water coheres to itself and adheres to cell walls. That makes it possible to pull water through plants without breaking the water column.

Which molecule is not a carbohydrate?

Lipid; A lipid is a hydrophobic polymer, not a carbohydrate.

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar.; Lipids are nonpolar molecules, whereas sugars are polar.

What distinguishes facilitated diffusion from simple diffusion?

Membrane proteins help move molecules across the membrane.

Which factor is important in making it possible to cool yourself by sweating? Think carefully!

Molecules collide with varied angles and speeds. Hydrogen bonds are relatively weak. Water has more energy at the body surface.; Random collisions allow some molecules to accumulate more energy than other molecules. The weakness of hydrogen bonds lets those molecules escape, leaving the cooler molecules behind.

Which of the following statements about monosaccharide structure is true?

Monosaccharides can be classified according to the spatial arrangement of their atoms

A molecule has the formula C n H2 n O n . What else does it need to be an unmodified monosaccharide?

O bound to every C.; If a monosaccharide has C without O attached, it's been modified.

Which of the following most accurately describes selective permeability?

Only certain molecules can cross a cell membrane.

Which of the following particles could diffuse easily through a cell membrane?

Oxygen; Small nonpolar molecules such as oxygen can diffuse across cell membranes

Which polysaccharide contains a modified monosaccharide?

Peptidoglycan; The N-acetylglucosamine and N-acetylmuramic acid units that make up peptidoglycan are composed of modified glucose monomers.

Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?

Polar groups attract one another. polar water molecules pull together, holding the polar parts of the amphipathic molecules and squeezing out the nonpolar parts. That leaves the nonpolar parts waving in the air.

Exocytosis

Secretes large molecules out of the cell Increases the surface area of the cell requires fusion of vesicles with the plasma membrane

The structure of the plasma membrane makes it selectively permeable, enabling it to regulate the transport of substances into and out of the cell.

Small, nonpolar molecules are hydrophobic, so they can easily cross the phospholipid bilayer of the plasma membrane. Polar molecules and ions are hydrophilic, so they cannot very easily cross the hydrophobic portion of the plasma membrane (formed by the phospholipid tails). Water is an unusual molecule because, despite the fact that it is polar, it is small enough to pass directly through the hydrophobic interior of the lipid bilayer, albeit slowly. Polar molecules and ions generally cross the plasma membrane with the help of transport proteins. For example, water crosses the bilayer rapidly via transport proteins called aquaporins.

Which of the following transporters does not use passive transport to move molecules across a membrane?

Sodium-potassium pump; This pump uses the energy provided by ATP hydrolysis to transport sodium and potassium ions across the membrane.

Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?

The charge on the other side of the membrane is generally the opposite of the ion's charge.; Ions tend to move toward regions of unlike charge.

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels?

The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.

What happens when glucose forms a ring?

The molecule loses its carbonyl group.; The C=O group becomes -O-C-OH.

What is the LEAST that two molecules can differ, and still be called different kinds of sugars?

The orientation of an OH group differs.; In the open-chain form, two sugars may differ in the orientation (right or left) of just one OH group.

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids; Phospholipids contain both a polar head and a nonpolar hydrocarbon tail, both of which are necessary for their ability to form membrane bilayers.

Which factors affect the rate of osmotic movement of water?

The rate of osmosis increases with increasing differences in solute concentrations between two solutions separated by a selectively permeable membrane.; The rate of osmosis varies with a number of factors, including temperature, pressure, and the difference in solute concentrations between two solutions separated by a selectively permeable membrane.

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.; This is how the sodium-potassium pump generates voltage across the cell membrane.

Which of the following statements about the sodium-potassium pump is correct?

The sodium-potassium pump moves Na+ and K+ in opposite directions, resulting in a net negative charge inside the cell.; An electrogenic pump creates a net movement of charge across a membrane. The sodium-potassium pump moves three Na+ out and two K+ in for a net transport of one positive charge out of the cell

Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?

The two sides of a cell membrane face different environments and carry out different functions.

Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside of the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. Which of the following statements about this mechanism is accurate?

To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.; The movement of sodium down its gradient drives glucose up its gradient, and because sodium is at different concentrations on either side of the membrane and as sodium has a +1 charge, an electrochemical gradient also exists.

Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration?

Transporter; The GLUT-1 transporter assists the diffusion of glucose through the membrane.

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True

true or false? Peptidoglycan is a polysaccharide found only in bacteria.

True

ONLY carriers

Undergo a change in shape to transport solutes across the membrane transport primarily small polar organic molecules

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. Water molecules are constantly in motion and will continually move across the membrane. However, becuase the solutions are in equilibrium, there is not net movement across the membrane.

Which of the following molecular movements is due to diffusion or osmosis?

When a plant cell is placed in concentrated salt water, water moves out of the cell.; If the salt water is hypertonic to the plant cell's contents, water moves out of the cell by osmosis, a form of diffusion.

Dissolving is best described as ...

When sugar dissolves in water, the sugar molecules remain intact but mingle with water molecules. When salt (NaCl) dissolves, its Na+ and Cl- ions separately mingle with water.

Which of the following allows water to move much faster across cell membranes?

aquaporins

Hydrogen bonds ...

can form between H and N.; They can also form between H and other highly electronegative atoms, such as O, if the atoms have strong partial charges.

The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?

cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis; Movement of most solutes against their concentration gradient couples the movement of one solute down its concentration gradient to the movement of another (glucose in this case) against its concentration gradient.

Endocytosis

decreases the surface area of the cell forms vescicles from inward folding of the plasma membrane

Based on Figure 7.18 in your textbook, which of these experimental treatments would increase the rate of sucrose transport into the cell?

decreasing extracellular pH

The process shown in this animation is referred to as _____

facilitated diffusion; Diffusion is occurring via a transport protein.