Chapter 5: Membranes

Question 1

What are the two primary structures of membranes?

Answer 1

1. Phospholipids
2. Proteins

Question 2

What is the phospholipid bilayer?

Answer 2

The framework of the membrane; made up of two leaflets

Question 3

What is a leaflet?

Answer 3

A half of the phospholipid bilayer; lipids and proteins move laterally within a leaflet because membranes are semifluid

Question 4

What is the idea behind the fluid-mosaic model?

Answer 4

The membrane is a mosaic of lipid, protein, and carbohydrate molecules where the lipids and proteins can move relative to each other within the membrane; the membrane is made up of different components that are semifluid

Question 5

What are the three types of proteins associated with the membrane?

Answer 5

1. Transmembrane proteins
2. Lipid-anchored proteins
3. Peripheral membrane proteins

Question 6

What are transmembrane proteins?

Answer 6

Proteins that span one or both leaflets of the membrane

Question 7

What are lipid-anchored proteins?

Answer 7

Proteins that have their amino acid region covalently attached to a lipid

Question 8

What are peripheral membrane proteins?

Answer 8

Proteins that are noncovalently bound to regions of other membrane proteins or to the polar portions of phospholipids

Question 9

What are the properties of phospholipids that affect the fluidity of the membrane?

Answer 9

1. Length of nonpolar tails - shorter tails, greater fluidity
2. Presence of double bonds - more double bonds, greater fluidity
3. Presence of cholesterol (animal cells) - stabilizes membranes

Question 10

How do we know that membranes are semifluid?

Answer 10

An experiment conducted in 1970 verified the lateral movement of transmembrane proteins; at human body temperature, the mouse protein moved all over the fused cell

Question 11

Do proteins have the same range of movement in all cells?

Answer 11

No, depending on the cell type, 10%-70% of membrane proteins may be restricted in their movement

Question 12

What are the three general ways substances can cross the membrane?

Answer 12

1. Simple diffusion
2. Facilitated diffusion
3. Active transport

Question 13

What is simple diffusion?

Answer 13

A type of transport that does not require energy (passive transport); gases and small uncharged molecules are able to pass through the membrane

Question 14

What is facilitated diffusion?

Answer 14

A type of transport that does not require energy (passive transport); moderately sized molecules that are nonpolar/polar and uncharged/charged can pass through the membrane with assistance from a transmembrane protein channel

Question 15

What is active transport?

Answer 15

The movement of a solute across a membrane against its gradient; requires the import of energy

Question 16

What are the three attributes that determine how a solute can pass through the membrane?

Answer 16

1. Size
2. Polarity
3. Charge

Question 17

What is the transmembrane gradient?

Answer 17

Present when the concentration of a solute is higher on one side of a membrane than the other

Question 18

What is the electrochemical gradient?

Answer 18

A dual gradient with both electrical and chemical components

Question 19

What are the three ways solutions on different sides of a membrane relate to each other?

Answer 19

1. Isotonic (same solute)
2. Hypertonic (more solute)
3. Hypotonic (less solute)

Question 20

What is the relationship between solute concentration and water concentration?

Answer 20

They have an inverse relationship; more solute, less free water

Question 21

What is osmosis?

Answer 21

The diffusion of water across a membrane; moves down its concentration gradient

Question 22

What happens to an animal cell and a plant cell in a hypotonic solution?

Answer 22

Water will move to the inside of both cells; the animal cell will swell and undergo osmotic lysis, and the plant cell will only slightly swell due to its cell wall

Question 23

Why does osmotic lysis happen?

Answer 23

Water does not stop regardless of whether or not the animal cell’s membrane can stay intact; plant cells have cell walls to prevent this from happening

Question 24

What is a transport protein?

Answer 24

Transmembrane proteins that provide a passageway for the movement of ions and hydrophilic molecules across membranes

Question 25

What are membrane channels?

Answer 25

An open passageway that facilitate the diffusion of hydrophilic molecules or ions; do not have a specific binding site for solutes

Question 26

What are membrane protein transporters?

Answer 26

Carriers that bind their solutes in a hydrophilic pocket and undergo a conformational change that switches the exposure of the pocket from one side of the membrane to the other; provide the principal pathway for uptake of organic molecules, such as sugars, amino acids, and nucleotides; involved in expelling various waste materials out of cells

Question 27

What are the three different kinds of transporters?

Answer 27

1. Uniporter 2. Symporter 3. Antiporter

Question 28

What is primary active transport?

Answer 28

The direct use of energy to transport a solute against its gradient

Question 29

What is secondary active transport?

Answer 29

The use of energy stored in a pre-existing gradient to drive the active transport of another solute

Question 30

What is the sodium-potassium (Na+/K+-ATPase) pump?

Answer 30

An ion pump that involves an antiporter that actively transports NA+ and K+ against their gradients using the energy from ATP hydrolysis

Question 31

What are ion pumps?

Answer 31

The transportation of ions to maintain gradients that drive many important cellular processes; a large percentage (70%) of cellular energy is invested into ion pumping

Question 32

What are intercellular channels?

Answer 32

Channels that allow direct movement of substances between adjacent cells

Question 33

What are gap junctions?

Answer 33

Intercellular junctions that exist in animal cells and are abundant in tissues where cells need to communicate with each other; made up of proteins called connexins that form a connexon; allow the passage of ions and small molecules

Question 34

What are plasmodesmata?

Answer 34

Intercellular junctions that exist in plant cells; the plasma membrane of one cell is continuous with the plasma membrane of an adjacent cell, forming a pore that permits diffusion of small molecules between cells

Question 35

What are the two different types of vesicular transport?

Answer 35

1. Endocytosis 2. Exocytosis

Question 36

What is exocytosis?

Answer 36

Materials inside the cell are packaged into vesicles and excreted to the extracellular environment

Question 37

What is endocytosis?

Answer 37

The plasma membrane invaginates to form a vesicle that brings substances into the cell

Question 38

What are the three different types of endocytosis?

Answer 38

1. Receptor-mediated endocytosis 2. Pinocytosis 3. Phagocytosis

Question 39

What is receptor-mediated endocytosis?

Answer 39

A type of endocytosis that uses receptor proteins to bring in specific cargo

Question 40

What is pinocytosis?

Answer 40

A type of endocytosis that primarily brings in fluid, allowing cells to sample the extracellular environment

Question 41

What is phagocytosis?

Answer 41

A type of endocytosis that involves bringing in very large particles; only some cells have phagocytes

Question 42

What is a uniporter?

Answer 42

A protein transporter that only moves one ion or molecule across the membrane

Question 43

What is a symporter?

Answer 43

A protein transporter that moves two ions or molecules across the membrane

Question 44

What is an antiporter?

Answer 44

A protein transporter that moves two ions or molecules in the opposite directions

Question 45

What are anchoring junctions?

Answer 45

Junctions that link cells to each other and to the extracellular membrane; formed by cell adhesion molecules like cadherins and integrins

Question 46

What are the four types of anchoring junctions?

Answer 46

1. Adherens junctions 2. Desmosomes 3. Hemidesmosomes 4. Focal adhesions

Question 47

What are adherens junctions?

Answer 47

Anchoring junctions that connect cells to each other, use cadherins, and bind actin filaments

Question 48

What are desmosomes?

Answer 48

Anchoring junctions that connect cells to each other, use cadherins, and bind intermediate filaments

Question 49

What are hemidesmosomes?

Answer 49

Anchoring junctions that connect cells to the extracellular membrane, use integrins, and bind intermediate filaments

Question 50

What are focal adhesions?

Answer 50

Anchoring junctions that connect cells to the extracellular membrane, use integrins, and bind actin

Question 51

What are tight junctions?

Answer 51

Junctions that form a tight seal between cells and prevent material from leaking between adjacent cells

Question 52

What are the different functions of biological membranes?

Answer 52

1. Selective uptake and export of ions and molecules 2. Cell compartmentalization 3. Protein sorting 4. Anchoring of the cytoskeleton 5. Production of energy intermediates such as ATP 6. Cell signaling 7. Cell and nuclear division 8. Adhesion of cells to each other and to the ECM

Question 53

What is passive transport?

Answer 53

The diffusion of a solute across a membrane in a process that is energetically favorable and does not require an input of energy

Question 54

What happens to an animal cell and a plant cell in a hypertonic solution?

Answer 54

Water will move out of both cells; the animal cell will undergo crenation and the plant cell will undergo plasmolysis

Question 55

What happens to an animal cell and a plant cell in an isotonic solution?

Answer 55

There is no net movement of water in both cells