Chapter 5 Membrane transport and cell signaling

Question 1

Plasma Membrane

Answer 1

Seperates living cells from its surroundings.

controls traffic in and outside of the cell

Question 2

Selective permeability

Answer 2

The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others.

Question 3

amphipathic

Answer 3

Phospholipids are the most abundant lipid in most membranes

Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions

A phospholipid bilayer can exist as a stable boundary between two aqueous compartments

Question 4

Fluid mosaic model

Answer 4

Most membrane proteins are also amphipathic and reside in the bilayer with their hydrophilic portions protruding

The fluid mosaic model states that the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

Groups of certain proteins or certain lipids may associate in long-lasting, specialized patches

Question 5

Integral proteins

Answer 5

Integral proteins penetrate the hydrophobic interior of the lipid bilayer

Integral proteins that span the membrane are called transmembrane proteins

The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into a helices

Question 6

Peripheral proteins

Answer 6

Peripheral proteins are loosely bound to the surface of the membrane

Question 7

What are the six major functions of membrane proteins?

Answer 7

1. Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 8

The permability of the lipid bilayer

Answer 8

Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer of the membrane and cross it easily

Polar molecules, such as sugars, do not cross the membrane easily

Question 9

Transport proteins

Answer 9

allow passage of hydrophilic substances across the membrane

Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel

Question 10

Aquaporins

Answer 10

Channel proteins called aquaporins facilitate the passage of water

Question 11

Diffusion

Answer 11

is the tendency for molecules to spread out evenly into the available space

Although each molecule moves randomly, diffusion of a population of molecules may be directional

At dynamic equilibrium, as many molecules cross the membrane in one direction as in the other

Question 12

Concentration gradient

Answer 12

Substances diffuse down their concentration gradient, from where it is more concentrated to where it is less concentrated

No work must be done to move substances down the concentration gradient

Question 13

Passive transport

Answer 13

The diffusion of a substance across a biological membrane is passive transport because no energy is expended by the cell to make it happen

Question 14

Osmosis

Answer 14

is the diffusion of free water across a selectively permeable membrane

Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides

Question 15

Tonicity

Answer 15

is the ability of a surrounding solution to cause a cell to gain or lose water

Question 16

Isotonic solution

Answer 16

Solute concentration is the same as inside the cell; no net water movement across the plasma membrane

Question 17

Hypertonic solution

Answer 17

Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water

Question 18

Hypotonic

Answer 18

Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water

Question 19

Osmoregulation

Answer 19

Osmoregulation, the control of solute concentrations and water balance, is a necessary adaptation for life in such environments

example,

The protist Paramecium caudatum, which is hypertonic to its pondwater environment, has a contractile vacuole that can pump excess water out of the cell

Question 20

turgid

Answer 20

Cell walls help maintain water balance

A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (very firm)

Question 21

Flaccid

Answer 21

If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

Question 22

plasmolysis

Answer 22

In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis

Question 23

Facilitated diffusion

Answer 23

• In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane
• Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane

Question 24

Channel proteins include

Answer 24

Channel proteins include

• *Aquaporins**, for facilitated diffusion of water
• *Ion channels** that open or close in response to a stimulus (gated channels)

Question 25

Ion Channels

Answer 25

Ion channels that open or close in response to a stimulus (gated channels)

Question 26

Active transport

Answer 26

Active transport moves substances against their concentration gradients

Active transport requires energy, usually in the form of ATP

Active transport allows cells to maintain concentration gradients that differ from their surroundings

Question 27

Sodium potassium pump

Answer 27

is one type of active transport system

Exchanges Na+ for K+ across the plasma membrane of animal cells

Question 28

Membrane potential

Answer 28

Membrane potential is the voltage across a membrane

Voltage is created by differences in the distribution of positive and negative ions across a membrane

Question 29

Electrochemical gradient

Answer 29

Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane

A chemical force (the ion’s concentration gradient)

An electrical force (the effect of the membrane potential on the ion’s movement)

Question 30

Electrogenic pump

Answer 30

An electrogenic pump is a transport protein that generates voltage across a membrane.

Example:

The sodium-potassium pump is the major electrogenic pump of animal cells

Question 31

Proton pump

Answer 31

The main electrogenic pump of plants, fungi, and bacteria is a proton pump

Electrogenic pumps help store energy that can be used for cellular work

Most protein pumps are powered by ATP

Question 32

Cotransport

Answer 32

Cotransport occurs when active transport of a solute indirectly drives transport of other solutes

Plant cells use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

Question 33

Exocytosis

Answer 33

In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents

Many secretory cells use exocytosis to export products

Question 34

Endocytosis

Name the three types

Answer 34

In endocytosis, the cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane

Endocytosis is a reversal of exocytosis, involving different proteins

There are three types of endocytosis

1. Phagocytosis (“cellular eating”)
2. Pinocytosis (“cellular drinking”)
3. Receptor-mediated endocytosis

Question 35

local signaling

Answer 35

• Eukaryotic cells may communicate by direct contact
• Animal and plant cells have junctions that directly connect the cytoplasm of adjacent cells
• These are called gap junctions (animal cells) and plasmodesmata (plant cells)
• The free passage of substances in the cytosol from one cell to another is a type of local signaling

Question 36

paracrine signaling

Answer 36

In many other cases of local signaling, messenger molecules are secreted by a signaling cell

• These messenger molecules, called local regulators, travel only short distances
• One class of these, growth factors, stimulates nearby cells to grow and divide
• This type of local signaling in animal cells is called paracrine signaling

Question 37

Synpatic signaling

Answer 37

Another more specialized type of local signaling occurs in the animal nervous system

This synaptic signaling consists of an electrical signal moving along a nerve cell that triggers secretion of neurotransmitter molecules

These diffuse across the space between the nerve cell and its target, triggering a response in the target cell

Question 38

long-distance signaling

Answer 38

In long-distance signaling, plants and animals use chemicals called hormones

In hormonal signaling in animals (called endocrine signaling), specialized cells release hormone molecules that travel via the circulatory system

Hormones vary widely in size and shape

Question 39

What are the three stages of cell signaling?

Answer 39

1. Reception: target cells detection of a signaling molecule coming from outside of the cell. A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cells surface
2. Transduction: a step or series of steps that converts the signal to a form that can bring about a specific cellular response.
3. Response: transduced signal triggers cellular response. The response may be an imaginable cellular activity. such as catylist by enzyme, rearrangemnt of cytoskeleton.

Question 40

Submerging a red blood cell in distilled water will result in

Answer 40

Cell will become lysis (it will burst) hypotonic