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Biology 230 > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

molecules that can simply diffuse across the lipid bilayer

A

CO2 and O2

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2
Q

For molecules that cannot simply diffuse across the lipid bilayer, their transfer depends on specialized ______ than span the lipid bilayer, providing private passageways across the membrane for select substances.

A

membrane transport proteins

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3
Q

Two main classes of membrane proteins:

A

transporters & channels

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4
Q

What are transporters?

A

shift small organic or inorganic ions from one side of the membrane to the other by changing shape

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5
Q

What are channels?

A

form tiny hydrophilic pores across the membrane through which substances can pass by diffusion; discriminates on the basis of size and charge

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6
Q

Most channels only permit passage of inorganic ions and are therefore called ________.

A

ion channels

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7
Q

What are lipid bilayers impermeable to?

A

ions and most uncharged polar molecules

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8
Q

How easily can CO2 and O2 cross the membrane?

A

dissolve readily in lipid bilayers, diffuse rapidly across them

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9
Q

How easily do uncharged polar molecules cross the bilayer?

A

diffuse readily across a bilayer if they are small enough

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10
Q

How easily do charged molecules cross the bilayer?

A

lipid bilayers are highly impermeable to all inorganic ions, no mater how small

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11
Q

T or F: Most nutrients are too large or too polar to pass.

A

T

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12
Q

Na+ and K+ concentrations… Where is it higher? Lower?

A

Extracellular– more Na+

Intracellular– more K+

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13
Q

The high concentration of Na+ outside the cell is electrically balanced by extracellular ____.

A

Cl-

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14
Q

The high concentration of K+ inside the cell is balanced by what?

A

a variety of negatively charged organic and inorganic ions (anions) including nucleic acids, proteins, and many cell metabolites

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15
Q

electrical imbalances generate a voltage difference across the membrane

A

membrane potenial

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16
Q

When a cell is “unstimulated,” the exchange of anions and cations across the membrane will be precisely balanced. In these conditions, the voltage difference across the cell membrane– the ___________– holds steady. But it is not zero.

A

resting membrane potenial

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17
Q

What is the resting membrane potential in animal cells?

A

-20mV to -200mV

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18
Q

Passive vs active transport

A

Passive transport– molecules flow spontaneously “downhill” from a region of high concentration to a region of low concentration, transport protein doesn’t spend any energy, solutes follow gradient

Active transport– membrane protein has to expend energy, drives the flow “uphill” by coupling it to some other process that provides an input of energy, moves solutes against their concentration gradient

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19
Q

Active transport is carried out by special transporters called ______.

A

pumps

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20
Q

Two things that influence passive transport:

A

membrane potenial

concentration gradient

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21
Q

For an uncharged molecule, the direction of passive transport is determined solely by its ________.

A

concentration gradient

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22
Q

For an electrically charged molecule, what determines the direction of passive transport?

A

membrane potential and concentration gradient

net driving force is called electrochemical gradient

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23
Q

The cytosolic side of the plasma membrane is usually at a _______ potential relative to the extracellular side, so the membrane potential tends to pull positively charged solutes into the cell and drive negatively charged ones out.

A

negative

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24
Q

Why does water tend to move into a cell?

A

The total concentration of solutes inside the cell (osmolarity) exceeds solute concentration outside the cell. The resulting osmotic gradient tends to “pull” water into the cell.

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25
Q

the movement of water down its concentration gradient

A

osmosis

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26
Q

How do different cells cope will osmotic swelling?

A
  • Some eliminate excess water using contractile vacuoles.
  • Plant cells are prevented from swelling by their tough cell walls and so can tolerate a large osmotic difference across their plasma membrane.
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27
Q

responsible for the movement of small, water-soluble, organic molecules and some inorganic ions across cell membranes

A

transporters

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28
Q

Each cell membrane contains a characteristic set of different transporters. Examples?

A
  • Plasma membrane contains transporters that import nutrients such as sugars, amino acids, and nucleotides.
  • Lysozyme membrane contains an H+ transporter to acidify the interior and others that move digestion products out of the lysosome.
  • The inner membrane of the mitochondria contains transporters for importing the pyruvate that mitochondria use as fuel for generating ATP.
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29
Q

T or F: Passive transporters move a solute along its electrochemical gradient.

A

T

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30
Q

What is an example of a transporter that mediates passive transport? Explain.

A

Glucose transporter– because glucose is uncharged, the chemical component of its electrochemical gradient is zero. Thus, the direction in which it is transported is determined only by its concentration gradient.

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31
Q

How do solutes move against their concentration gradients?

A

pumps

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32
Q

Active transport is carried out in three main ways:

A
  • ATP-driven pumps: hydrolyze ATP to drive uphill transport
  • coupled pumps: link the uphill transport of one solute across a membrane to the downhill transport of another
  • light-driven pumps: use energy derived from sunlight to drive uphill transport (bacteriorhodopsin)
33
Q

Na+/K+ pump

A

uses energy from ATP hydrolysis to transport Na+ out of the cell and K+ into the cell

34
Q

One cycle of the Na+/K+ pump lasts how long?

A

10 milliseconds

35
Q

Inside the lumen of the sarcoplasmic reticulum is high concentrations of ____.

A

Ca2+

36
Q

How does a muscle cell contract?

A

When a cell is stimulated to contract, a single goes into the cell and Ca2+ floods out of the sarcoplasmic reticulum into the cytosol. This stimulates contraction. In order to stop contracting, the single is stopped and Ca2+ goes back into the sarcoplasmic reticulum.

37
Q

Is the concentration of Ca2+ high or low inside the cell?

A

low inside, high outside (like Na+)

38
Q

An influx of Ca2+ into the cytosol through Ca2+ channels is used by different cells for what?

A

as an intracellular signal to trigger various cell process, such as muscle contraction, fertilization, and nerve cell communication

39
Q

How is the high concentration of Ca2+ outside of the cell maintained?

A

ATP-driven Ca2+ pumps

40
Q

active transporters that use the movement of one solute down its electrochemical gradient to drive the uphill transport of another solute across the same membrane

A

coupled pumps

41
Q

Types of coupled pumps:

A

‣ symport– pump moves solutes in the same direction
‣ antiport– pump moves solutes in opposite directions
‣ uniport– transports only one type of solute across the membrane

42
Q

How do gut epithelial cells transport glucose?

A

These cells make use of the inward flow of Na+ down its steep concentration gradient.

The epithelial cells that line the gut posses a glucose-Na+ symport, which they can use to take up glucose from the gut lumen, even when the concentration of glucose is higher in the cell’s cytosol than it is in the gut lumen. Because the electrochemical gradient for Na+ is steep, when Na+ moves into the cell down its gradient, glucose is “dragged” into the cell with it.

43
Q

Gut epithelial cells have two types of glucose transporters located at opposite ends of the cell:

A

Apical domain: glucose-Na+ symporters that take up glucose actively, creating a high glucose concentration in the cytosol

Basal domain: cells have passive glucose uniports, which release glucose down its concentration gradient

44
Q

T or F: Plant cells, bacteria, and fungi have Na+ pumps in their plasma membrane.

A

F

Instead of an electrochemical Na+ gradient, they rely on an electrochemical gradient of H+ to import solutes into the cell. This gradient is created by H+ pumps in the plasma membrane that pump H+ out of the cell, thus creating an electrochemical proton gradient.

45
Q

What do H+ pumps in animal cells do?

A

actively transport H+ out of the cytosol into the organelle, thereby helping to keep the pH of the cytosol neutral and the pH of the interior of the organelle acidic

46
Q

proteins that form a hydrophilic pore across a membrane, through which selected small molecules or ions can passively diffuse

A

channels

47
Q

Two types of channels:

A

ion-selective

gated

48
Q

What are ion-selective channels?

A

Channels permit some inorganic ions to pass but not others. Each ion in aqueous solution is surrounded by a small shell of water molecules, most of which have to be shed for the ions to pass, in single file, through the selectivity filter in the narrowest part of the channel. Only those ions of the appropriate size and charge are able to pass.

49
Q

What are gated channels?

A

Ion channels are NOT continuously open. They open briefly and then close again. Most ion channels are gated, meaning a specific stimulus triggers then to switch between a closed an an open state by a change in their conformation.

50
Q

Which is faster? transporters or open ion channels

A

Open ion channels are 1000x faster than transporters because they do not need to undergo a conformational change for each ion that passes. More than a million ions can pass through an open ion channels each second.

51
Q

When there is an exact balance of charges on either side of the membrane, what is the membrane potential?

A

zero

52
Q

When ions of one type cross the membrane, they set up a charge difference between the two sides of the membrane. What is the membrane potential?

A

not zero

53
Q

Explain why K+ is the predominant intracellular ion and how it creates a membrane potential.

A
  1. ) K+ is pumped into the cell (via Na+ pump)
  2. ) generates a K+ gradient
  3. ) K+ leak channels allow free flow of ion
  4. ) flow out of cell (due to concentration gradient)
  5. ) leave unbalanced negative charges inside
  6. ) membrane potential created
54
Q

What happens when the K+ leak channels are closed?

A

membrane potenial equals zero

55
Q

What happens when the K+ leak channels are open?

A

K+ ions flow out of the cell creating a membrane potential (unbalanced negative charge inside the cell).

56
Q

The membrane potential in which the flow of positive and negative ions across the plasma membrane is precisely balanced, so that no further difference in charge accumulates across the membrane is called the __________.

A

resting membrane potential

57
Q

used to calculate the theoretical resting membrane potential

A

Nerst equation

58
Q

Nerst equation

A

V= 62 log 10 (C0/Ci)

59
Q

What is the resting membrane potential inside animal cells?

A

between -20 and -200mV

60
Q

measures the electric current going through a single channel molecule

A

patch-clamp recording

61
Q

Types of gated ion channels:

A

◦ voltage-gated: controlled by membrane potential
◦ ligand-gated: controlled by the binding of some molecule (the ligand) to the channel
◦ mechanically-gated: controlled by mechanical force applied to the channel

62
Q

Ex of a mechanically gated ion channel:

A

The auditory hair cells in the ear are an example of cells that depend on mechanically-gated channels. Sound vibrations pull the channels open, causing ions to flow into the hair cells; this ion flow sets up an electrical signal that is transmitted from the hair cell to the auditory nerve, which conveys the signal to the brain.

63
Q

This organism respond to both mechanically-gated and voltage-gated ion channels.

A

Mimosa pudica

  • A mechanical stimulus opens a mechanically-gated channel.
  • A change in membrane potential opens voltage-gated channels.
64
Q

Zones of a neuron:

A

◦ input zone– dendrites and cell body
◦ trigger zone– where electrical signals originate
◦ conducting zone– where electrical signals travel along
◦ output zone– release signaling molecules

65
Q

a traveling wave of electrical excitation caused by rapid, transient, self-propagating depolarization of the plasma membrane in a neuron or other excitable cell

A

action potenital

66
Q

an “all-or-nothing” event

A

action potenial

67
Q

organism that was used to study action potential because of its giant axon

A

squid Loligo pealei

68
Q

What triggers an action potential?

A

a depolarization (becoming less negative) of a neuron’s plasma membrane

69
Q

How does a neuron work?

A

The resting membrane potential is -60 mV. The stimulus that depolarizes the plasma membrane to about -40mV opens voltage-gated Na+ channels in the membrane and triggers an action potential. The membrane rapidly depolarizes further, and the membrane reaches +40mV before it returns to its resting negative value as the action potential terminates.

70
Q

ions crucial to the action potential

A

Na+

K+

71
Q

Explain how depolarization and repolarization.

A

Resting membrane potential is -60mV. Voltage-gated channels open at -40mV, causing Na+ to rush into the cell. At +40mV, Na+ channels close and K+ channels open. K+ flows out of the cell until it reaches below resting membrane potential. The Na+/K+ pump brings it back to -60mV.

72
Q

Why are myelinated axons faster than unmyelinated?

A

jumping from node to node increases signal speed (100 m/s)

73
Q

T or F: Action potentials cannot pass directly from a neuron to another cell.

A

T

74
Q

region where a neuron’s axons terminals transmit signals to another cell through a fluid-filled synaptic cleft

A

synapse

75
Q

Voltage-gated Ca2+ channels in nerve terminals convert an _______ signal into a _______ signal.

A

electrical / chemical

76
Q

Steps of the release of a NT:

A
  1. ) AP depolarizes terminal plasma membrane
  2. ) Opens voltage-gated Ca2+ channels
  3. ) Ca2+ rushes into nerve terminal
  4. ) Synaptic vesicles fuse with plasma membrane
  5. ) Release of NT into synaptic cleft
77
Q

convert the chemical signal back into an electrical signal

A

transmitter-gated ion channels

78
Q

Where is an example of a transmitter-gated ion channel found?

A

neuromuscular junction

Biology 230 (2 decks)

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