3.2 The Cell Surface

Question 1

plasma membrane

Answer 1

defines the boundaries of the cell, governs its interactions with other cells, and controls the passage of materials into and out of the cell

Question 2

intracellular face

Answer 2

the side of the plasma membrane that faces the cytoplasm

Question 3

extracellular face

Answer 3

the side of the plasma membrane that faces outward from the cell

Question 4

molecular structure of the plasma membrane

Answer 4

98% lipids (75% phospholipids, 20% cholesterol molecules, 5% glycolipids) + 2% proteins

Question 5

glycocalyx

Answer 5

carbohydrate coating on the cell surface with multiple functions

Question 6

transmembrane proteins

Answer 6

proteins that pass completely through the phospholipid bilayer and either drift in the phospholipid film or are anchored to the cytoskeleton

Question 7

peripheral proteins

Answer 7

proteins that adhere to either the inner or outer face of the membrane

Question 8

receptors

Answer 8

surface proteins to which chemical signals bind for the purpose of cell communication

Question 9

enzymes

Answer 9

carry out the final stages of starch and protein digestion in the small intestine, help produce second messengers, and break down hormones and other signaling molecules whose job is done

Question 10

channel proteins

Answer 10

passages that allow water and hydrophilic solutes to move through the plasma membrane

Question 11

leak channels

Answer 11

channels that are always open and allow materials to pass through continuously

Question 12

gated channels

Answer 12

channels that open and close under different circumstances; play a role in the timing of nerve stimulation and muscle contraction

Question 13

ligand-gated channels

Answer 13

channels that respond to chemical messengers

Question 14

voltage-gated channels

Answer 14

channels that respond to changes in electrical potential across the plasma membrane

Question 15

mechanically gated channels

Answer 15

channels that respond to physical stress on a cell, such as stretch or pressure

Question 16

channelopathies

Answer 16

diseases caused by defects in channel proteins

Question 17

carriers

Answer 17

transmembrane proteins that bind to glucose, electrolytes, and other solutes and transfer them to the other side of the membrane

Question 18

pumps

Answer 18

carriers that consume ATP in the process of transferring solutes across the plasma membrane

Question 19

cell-adhesion molecules

Answer 19

membrane proteins through which cells adhere to one another and to extracellular material

Question 20

calcium channel blockers

Answer 20

a class of drugs that show the therapeutic relevance of understanding gated membrane channels

Question 21

glycocalyx

Answer 21

a fuzzy coat external to the plasma membrane composed of the carbohydrate moieties of membrane glycolipids and glycoproteins that is chemically unique in each individual (except identical twins) and acts like an identification tag that enables the body to distinguish its own healthy cells from transplanted tissues, invading organisms, and diseased cells

Question 22

microvilli

Answer 22

extensions of the plasma membrane that increase a cell’s surface area; best developed in cells specialized for absorption (e.g. epithelial cells of intestines and kidneys)

Question 23

brush border

Answer 23

a fringe of microvilli on the apical surface of an epithelial cell, serving to enhance surface area and promote absorption

Question 24

terminal web

Answer 24

a protein mesh to which microvilli are anchored by actin filaments

Question 25

cilia

Answer 25

hairlike processes with functions include sense, balance, and fluid flow monitoring

Question 26

ciliopathies

Answer 26

birth defects and hereditary diseases caused by defects in the development, structure, or function of the cilia

Question 27

power stroke

Answer 27

movement of the cilium that pushes along mucus or other matter

Question 28

recovery stroke

Answer 28

movement of the cilium that restores it to the upright position, ready to flex again

Question 29

chloride pumps

Answer 29

pumps that produce a saline layer at the cell surface by pumping Cl- into the extracellular fluid so that cilia can beat freely

Question 30

axoneme

Answer 30

the structural basis for ciliary movement, consisting of an array of thin protein cylinders called microtubules

Question 31

basal body

Answer 31

peripheral microtubules anchoring the cilium

Question 32

dynein arms

Answer 32

a motor protein on a microtubule

Question 33

flagellum

Answer 33

beats in an undulating, snakelike, corkscrew fashion

Question 34

pseudopod

Answer 34

cytoplasm-filled extensions of the cell that have different shapes and change continuously