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