Chapter 5 Membranes: The Interface Between Cells & Their Environment

Select the two types of cell adhesion molecules (CAMs). -proteoglycans -cellulose -cadherins -glycosaminoglycans -integrins

-cadherins -integrins

Why is the phospholipid bilayer an effective barrier to hydrophilic or polar molecules?

Because of the hydrophobic interior of the bilayer

A key component of anchoring junctions are proteins called CAMs, which stands for

Cell Adhesion Molecules

The Na+/K+-ATPase pump establishes and maintains a gradient such that:

Na+ is higher outside the cell than inside, and K+ is higher inside the cell than outside

Cell ... are specialized structures within multicellular animals that physically adhere cells to each other.

junctions

Most phospholipids move freely within a semifluid membrane

laterally along the plane of the membrane in two dimensions

Transmembrane protein flip-flop does not occur spontaneously because it would be energetically

unfavorable

Endocytosis and exocytosis involve packaging substances into a membrane-enclosed

vesicle

In both endocytosis and exocytosis, the transported substance is packaged into a(n):

vesicle

Which of the following anchoring junctions bind to actin filaments in the cytoskeleton? -Hemidesmosomes -Desmosomes -Adherens junctions -Focal adhesions

-Adherens junctions -Focal adhesions

Which of the following anchoring junctions bind to actin filaments in the cytoskeleton? -Adherens junctions -Hemidesmosomes -Desmosomes -Focal adhesions

-Adherens junctions -Focal adhesions

Select all the functions of anchoring junctions. -Attach cells to each other -Provide a passageway for intercellular transport -Bond cells to the extracellular matrix -Anchor ER membranes of adjacent cells to each other

-Attach cells to each other -Bond cells to the extracellular matrix

What processes are used by eukaryotic cells to transport large molecules such as proteins and polysaccharides? -Primary active transport -Secondary active transport -Channel proteins -Endocytosis -Exocytosis

-Endocytosis -Exocytosis

What are likely binding sites for peripheral membrane proteins? -Fatty acid tails of phospholipids -Hydrophilic regions of integral membrane proteins -Hydrophobic regions of integral membrane proteins -Polar head groups of phospholipids

-Hydrophilic regions of integral membrane proteins -Polar head groups of phospholipids

Which of the following statements explain why the phospholipid bilayer is composed of two leaflets? -Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment. -Two leaflets result when membrane components secreted from inside the cell match up with membrane components gathered from the environment. -Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets. -Phospholipids are amphipathic and must interact with polar and nonpolar environments.

-Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment. -Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets. -Phospholipids are amphipathic and must interact with polar and nonpolar environments.

Why is it more appropriate to describe membranes as semifluid? -Molecules move laterally within the membrane leaflet. -Phospholipids spontaneously migrate between leaflets. -Phospholipids usually move in two dimensions. -Membrane proteins and lipids move freely in three dimensions.

-Molecules move laterally within the membrane leaflet. -Phospholipids usually move in two dimensions.

What processes are coupled across cell membranes? -The export of K+ ions -The import of K+ ions -The export of Na+ ions -The import of Na+ ions

-The import of K+ ions -The export of Na+ ions

What categories of proteins assist in the movement of molecules and ions across membranes? -channels -coenzymes -ligands -transporters

-channels -transporters

Which of the following statements regarding adherens junctions are true? -contain cadherins -bind to proteins in the extracellular matrix -bind to intermediate filaments in the cytosol -contain integrins -bind to actin filaments in the cytosol

-contain cadherins -bind to actin filaments in the cytosol

Which of the following statements regarding hemidesmosomes are true? -contain integrins -interact with intermediate filaments in the cytosol -interact with actin filaments in the cytosol -contain cadherins -interact with the extracellular matrix

-contain integrins -interact with intermediate filaments in the cytosol -interact with the extracellular matrix

Select the types of anchoring junctions found in animals. -focal adhesions -plasmodesmata -tight junctions -hemidesmosomes -adherens junctions -desmosomes

-focal adhesions -hemidesmosomes -adherens junctions -desmosomes

Which of the following proteins are integral membrane proteins? -peripheral membrane proteins -lipid-anchored proteins -transmembrane proteins -noncovalent helix proteins

-lipid-anchored proteins -transmembrane proteins

What are the three molecular components of cellular membranes? -proteins -nucleic acids -phospholipids -minerals -carbohydrates

-proteins -phospholipids -carbohydrates

Which of the following are examples of endocytosis? -exocytosis -receptor-mediated endocytosis -ligand-enhanced endocytosis -phagocytosis -pinocytosis

-receptor-mediated endocytosis -phagocytosis -pinocytosis

Which of the following proteins are integral membrane proteins? -peripheral membrane proteins -noncovalent helix proteins -transmembrane proteins -lipid-anchored proteins

-transmembrane proteins -lipid-anchored proteins

Which of the following are pumped by the Na+/K+ -ATPase? -three Na+ into the cell -two ATP into the cell -two ATP out of the cell -three K+ into the cell -two K+ into the cell -three Na+ out of the cell

-two K+ into the cell -three Na+ out of the cell

Which of the following are pumped by the Na+/K+ -ATPase? -three Na+ into the cell -two K+ into the cell -three Na+ out of the cell -two ATP into the cell -two ATP out of the cell -three K+ into the cell

-two K+ into the cell -three Na+ out of the cell

Lipid-anchored protein

A lipid molecule is covalently attached to an amino acid side chain of the membrane protein.

Transmembrane protein

A segment of amino acids is inserted into the phospholipid bilayer.

A B C

A) Transmembrane protein B) Peripheral membrane protein C) Lipid-anchored protein

The sodium/potassium -ATPase transports Na+ and K+ ions against their gradients using the energy from ... hydrolysis

ATP

Why is the Na+/K+-ATPase pump considered an antiporter?

Because it moves two substances in opposite directions.

What process requires gap junctions?

Contraction of cardiac muscle cells

Which type of anchoring junction contains cadherins that connect cells to each other and to intermediate filaments in the cytosol?

Desmosome

What is osmosis?

Diffusion of water from an area of low solute concentration to an area of high solute concentration

What property of biological membranes describes the ability of individual molecules to move within the membrane?

Fluidity

Which of the following statements is correct about a biological membrane that is fluid?

Individual molecules can move within the membrane.

In the 1940s, studies of animal cells suggested that the import of ... is coupled to the export of ...

K+; Na+

Due to the Na+/K+ -ATPase, cells are able to maintain concentration gradients so that the concentration of ... ions is greater outside the cell than inside, and the concentration of ... ions is greater inside the cell than outside.

Na, K

Peripheral membrane protein

Noncovalent associations form with phospholipids or other membrane proteins

Which of the following best describes the process of active transport?

Particles moving across a membrane against a concentration gradient.

What separates the internal contents of a cell from the extracellular environment?

The plasma membrane

Isotonic solution

The solute concentration outside a cell is equal to the solute concentration inside the cell.

Hypertonic solution

The solute concentration outside a cell is higher than the solute concentration inside the cell.

Hypotonic solution

The solute concentration outside the cell is lower than the solute concentration inside the cell.

How do transporters differ from channel proteins?

Transporters must change conformation to allow solutes to cross the membrane.

An animal cell is placed in a hypertonic medium. Predict which way water will move.

Water will move from the inside of the cell to the outside.

Transporter proteins transport solutes across the membrane via:

a conformational change triggered by solute binding

What is the basic structure of the plasma membrane?

a phospholipid bilayer

A phospholipid molecule consists of:

a polar head and two nonpolar tails

Active transport is the movement of a solute across the membrane ... its concentration gradient.

against

The Na+/K+ -ATPase actively transports Na+ and K+ ions ... their gradients by using the energy from ATP hydrolysis.

against

In multicellular organisms, intercellular channels such as gap junctions in animals and plasmodesmata in plants

allow the movement of substances between adjacent cells.

Phospholipids have both hydrophobic and hydrophilic components. As such, they are said to be

amphipathic

The Na+/K+ -ATPase pump is considered a(n) ... because it binds both Na+ and K+ and transports them in opposite directions.

antiporter

In adherens junctions, proteins called ... connect cells to each other. In the cytosol, adherens junctions bind to ... filaments.

cadherins, actin

Cell adhesion molecules (CAMs) include the two integral membrane proteins ... and ...

cadherins, integrins

In a desmosome, proteins called ... connect cells to each other. In the cytosol, desmosomes are connected to ... filaments.

cadherins, intermediate

The three main types of macromolecules that comprise the plasma membrane are ... ... and ...

carbohydrate, phospholipid, and protein

The anchoring junction proteins that form the connections between cells are called:

cell adhesion molecules

In multicellular animals, cells are linked to one another by

cell junctions.

Unlike transporters, ... proteins provide an open passageway all the way across the plasma membrane.

channel

Proteins that assist in the movement of substances across membranes can be classified into two types based on how they move solutes across a membrane: ... and ...

channels, transporters

Eukaryotic cells can transport large molecules such as proteins and polysaccharides via ... and ... . Both of these mechanisms involve membrane vesicles or vacuoles.

endocytosis, exocytosis

Vesicular movement of large molecules into cells is called ... , and vesicular movement of large molecules out of cells is called ...

endocytosis, exocytosis

In animals, anchoring junctions attach adjacent cells to each other and to the ... matrix.

extracellular

When the concentration of a solute is higher on one side of membrane than the other, a(n) transmembrane ... is established.

gradient

Membrane fluidity is increased when membrane lipids

have shorter nonpolar tails.

The four types of anchoring junctions in humans are adherens junctions, desmosomes, ... and ... adhesions.

hemidesmosomes, focal

The two types of anchoring junctions that connect cells to the extracellular matrix are ... and ... ...

hemidesmosomes, focal adhesions

Transmembrane proteins do not flip flop across bilayer leaflets because

hydrophilic protein regions would pass through the hydrophobic bilayer interior.

Phospholipid bilayers are an effective barrier to many charged or polar solutes because of their ... interior region.

hydrophobic

When the concentration of solutes outside the cell is higher than that intra-cellularly, the solution is said to be ... relative to the inside of the cell.

hypertonic

A solution whose solute concentration is higher than the concentration of solutes inside a cell is

hypertonic.

When the concentration of solutes outside the cell is lower than that intra-cellularly, the solution is said to be ... relative to the inside of the cell.

hypotonic

A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ... membrane protein.

integral

While individual cells have many types of transport proteins in their membranes, the cells of multicellular organisms also may have ... that allow the movement of substances between adjacent cells.

intercellular channels

Passage of ... through gap junctions allows the coordinated contraction of cardiac muscle cells.

ions

When the concentrations of dissolved particles (solutes) on both sides of the plasma membrane are equal, the two solutions are said to be

isotonic

The internal and external environments of a cell are separated by a structure known as the plasma

membrane

Shorter nonpolar tails make the membrane ... fluid.

more

The fatty acid tails of phospholipids are ... and are found in the ... of the phospholipid bilayer.

nonpolar. interior

Proteins that associate with the plasma membrane through non-covalent interactions with phospholipids or transmembrane proteins are called ... membrane proteins.

peripheral

The plasma membrane consists of a(n) ... bilayer.

phospholipid

The three types of endocytosis are receptor-mediated endocytosis, ... and ...

pinocytosis, phagocytosis

In a plasmodesma, the ... of one cell is continuous with that of another cell.

plasma membrane

The intercellular channels that connect plant cells to one another are called

plasmodesmata

What type of cell junctions form channels between adjacent plant cells?

plasmodesmata

Phospholipids have a ... head region that will interact with aqueous environments.

polar

The plasma membrane of a cell is considered to be

selectively permeable

All cells are surrounded by a ... permeable plasma membrane, meaning that the membrane allows the passage of some molecules and ions but not others.

semi

Transporter proteins bind their solutes in a hydrophilic pocket and then undergo a(n) ... change that switches the exposure of the pocket from one side of the membrane to the other.

shape

What organelle in adjacent cells is connected by the central tubules in plasmodesmata?

smooth endoplasmic reticulum

The primary difference between endocytosis and exocytosis is

the direction of transport.

The two leaflets of a lipid bilayer are formed because

the polar head groups of phospholipids can interact with the polar interior and exterior of the cell.

The Na+/K+ -ATPase pumps ... Na+ ions out of the cell and ... K+ ions into the cell.

three; two

Which of the following cell junctions prevent material from passing between adjacent cells of animals?

tight junctions

A term that describes a situation in which the concentration of a solute is higher on one side of a membrane than the other is

transmembrane gradient.