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Bio 217 > Topic 7 > Flashcards

Topic 7 Flashcards

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Biology 101 flashcards
1
Q

Plasma Membranes

A

The boundary that separates the living cell from its surroundings
* Plasma membrane is a dynamic structure
* Exhibits selective permeability

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2
Q

selective permeability

A

Some substances cross more easily than others

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3
Q

Transport proteins

A

can control passage across cellular membranes

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4
Q

most abundant lipid in the PM

A

Phospholipids

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5
Q

Phospholipids are

A

amphipathic (Contains both hydrophobic and
hydrophilic components)

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6
Q

Forming bilayer means

A

it can create a boundary between two aqueous compartments

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7
Q

The PM is a containing

A

dynamic structure
* Phospholipid heads
* Phospholipid tails
* Water molecules
* Transmembrane channel

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8
Q

Cellular membranes are

A

fluid mosaics of lipids

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9
Q

Fluid mosaic model:

A
  • Membrane made up of many protein molecules bobbing in a fluid bilayer of phospholipids
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10
Q

Membrane Fluidity
Membranes are held together mainly by

A

weak hydrophobic interactions
* Most lipids and some proteins can move sideways within a membrane
* Rarely, a lipid may flip-flop from one phospholipid layer to the other

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11
Q

What affects membrane fluidity?

A
  • as temp drops, fluidity of emmbrane decreases
  • reduction in fluidity affects function of membranes
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12
Q

reduction in fluidity affects

A

function of membranes

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13
Q

temperature when membrane solidifies depends on

A

composition of lipids

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14
Q

Saturated and unsaturated fatty acids in membranes

A

Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids

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15
Q

Unsaturated fats

A

the kinks in the tails prevent packing
* Stays fluid at lower temp

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16
Q

Saturated fats

A

straight tails allow tight packing
* Becomes solid at lower temp

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17
Q

Role of cholesterol as a buffer for membrane fluidity

A

The steroid cholesterol has different effects on the membrane fluidity of animal cells at different temperatures
- at warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
- at cool temps it maintains fluidity by preventing tight packing

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18
Q

Evolution of differences in membrane lipid composition

A

Some species have variations in lipid composition of cell membranes
* Appear to be adaptations to specific environmental conditions
* Ability to change the lipid compositions in response to temperature changes
* Evolved in organisms that live where temperatures vary

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19
Q

Fluid mosaic model: What makes it mosaic?

A
  • Collection of multiple different proteins, embedded in the lipid bilayer
  • Phospholipids form the bulk of the membrane
  • Proteins determine most of the membrane’s
    functions
  • Structural and function mosaic
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20
Q

2 major types of membrane proteins:

A

1) Integral proteins
2) Peripheral proteins

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21
Q

Integral proteins

A

Enters into hydrophobic region of lipid bilayer
* Includes transmembrane proteins
* Hydrophobic core made of nonpolar amino acids, coiled into α-helices

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22
Q

Peripheral proteins

A
  • BOUND TO THE SURFACE OF THE MEMbrane (not embeded
  • do not pass through the hydrophobic core of the bilayer
  • membrane associated proteins
  • on cytoplasmic side : can be attached to cytoskeleton components
  • on extra celluar side: cell recognition
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23
Q

Cell-surface membrane proteins can carry out several functions

A

1 transport
2 enzymatic activity
3 signal transduction
4 cell-cell recognition
5 intercellular joining
6 attachment to the cytoskeleton and extracellualr matrix

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24
Q

Cell-cell recognition by membrane carbohydrates

A
  • Cells can recognize each other by surface molecules
  • On extracellular surface of PM
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25
Q

Glycocalyx

A

Carbohydrates outside the cell, can be covalently bound to:
* Lipids > forming glycolipids
* Proteins > forming glycoproteins

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26
Q

Lipids > forming

A

glycolipids

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27
Q

Proteins > forming

A

glycoproteins

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28
Q

Membranes have a sidedness to them

A
  • Membranes have distinct inside and outside faces
  • Distribution of proteins, lipids, and associated carbohydrates in the PM is asymmetrical
  • Determined when the membrane is built by the ER and Golgi apparatus
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29
Q

Membrane structure results in selective permeability

A
  • Emergent Properties of membrane:
  • Properties of membrane is vastly different and broader than properties of individual components
  • Plasma membranes are selectively permeable
  • Regulates the cell’s molecular traffic and exchange of materials with surroundings
30
Q

The Selective Permeability of the Lipid Bilayer

A
  • Hydrophobic molecules can dissolve in the lipid bilayer and pass through the membrane rapidly
  • Hydrophilic molecules including ions and polar molecules do not cross the membrane easily
  • Proteins built into the membrane play key roles in regulating transport
31
Q

Transport proteins includes

A
  • Allow passage of hydrophilic
    substances across the membrane
  • Channel proteins
  • Carrier proteins
32
Q

Channel proteins:

A
  • Hydrophilic channel that certain molecules or ions can use as a tunnel
  • Ie) Aquaporin - facilitates the passage of water molecules
33
Q

Carrier proteins:

A
  • Bind to molecules and change shape
    to shuttle them across the membrane
34
Q

A transport protein is specific for

A

the substance it moves
* Ie) Glucose transporter, Na+/K+ pump

35
Q

Diffusion

A

is molecules spreading out evenly into the available space
* Ie)perfumeinair,dyeinwater
* Each molecule moves randomly, but overall population of molecules moves down concentration gradient

36
Q

Dynamic equilibrium:

A

equal number of molecules cross the membrane in each

37
Q

Substances diffuse down their

A

concentration gradient
-No work is done to move substances down the concentration gradient

38
Q

Passive transport: Diffusion

A

The diffusion of a substance across a biological membrane is passive transport as no energy is expended by the cell
* Each substance moves down its own concentration gradient

39
Q

Osmosis:

A

The diffusion of water across a sleectively permable membrane
permeable membrane
* Water diffuses across a membrane moving from a lower to a higher solute concentration
* Water is trying to dilute a concentrated solution
* Until the solute concentration is equal on both sides

40
Q

Water diffuses across a membrane moving from

A

a lower to a higher solute concentration
- High free water (low solute)&raquo_space; low free water (high solute)

41
Q

The behaviour of a cell in a solution depends on

A

solute concentration and membrane permability

42
Q

Tonicity:

A

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

43
Q

tonicity of a solution depends on

A

its concentration of solutes that cannot cross the mmebrane, relative to that inside the cell

44
Q

Osmoregulation

A

the control of solute concentrations and water balance

45
Q

Isotonic solution:

A

Solute concentration is the same as that
inside the cell
* No net water movement across the plasma membrane

46
Q

Hypertonic solution:

A
  • Solute concentration in solution is greater than
    inside the cell; cell loses water
  • Water wants to dilute the higher solute concentration outside of cell
47
Q

Hypotonic solution:

A
  • Solute concentration in solution is less than inside the
    cell; cell gains water
  • Water wants to dilute the higher solute concentration inside of cell
    Cells without cell walls will shrivel in hypertonic solution and lyse (burst) in a hypotonic solution
48
Q

Water balance of cells with cell walls

A
  • Cell walls help maintain water balance
49
Q

Isotonic solution:

A
  • There is no net movement of water into the cell
  • The cell becomes flaccid (limp)
49
Q

Hypertonic solution:

A
  • In a hypertonic environment, plant
    cells lose water
  • The membrane pulls away from the cell wall, causing the plant to wilt, a potentially lethal effect called plasmolysis
50
Q

Hypotonic solution

A
  • A plant cell in a hypotonic solution swells
    until the wall opposes uptake
  • The cell is now turgid (firm)
  • Turgor pressure provides non-woody plants mechanical support
51
Q

facilitated diffusion

A

transport proteins speed the passive movement of molecules across the plasma membrane
- no energy needed, passive
- molecules still moving down concentration gradient
- channel and carrier proteins involved

52
Q

Channel Proteins

A
  • Provide corridors to allow a specific molecule or ion to cross the membrane
    -ex aquaporins (facillitate diffusion of water)
53
Q

Ion channels

A

facilitate the transport of ions

54
Q

gated channels

A

open or close in response to a stimulus
- ex in nerve cells ion channels open in response to electrical stimulus

55
Q

Carrier Proteins

A

Undergo a change in shape that translocates the solute-binding site across the membrane
- ex glucose transporter
The change in shape can be triggered by the binding and release of the transported molecule

56
Q

Active transport uses

A

energy to move solutes against their gradients

57
Q

Active transport

A

requires energy
- usually in the form of atp hydrolysis to move substrances against their concentration gradient
- terminal phosphate group from atp is transferred to the transport protein
* Active transport allows cells to maintain concentration gradients that differ from their surroundings
* All proteins involved in active transport are carrier proteins

58
Q

All proteins involved in active transport are

A

carrier proteins

59
Q

sodium-potassium pump

A

a transport protein that is energized by transfer of a phosphate group from the hydrolysis of ATP

60
Q

Electrochemical gradient

A

the combined forces that drives diffusion of ions across a membrane
- chemical and electrical

61
Q

Membrane potential

A

voltage across membrane, due to differences in distribution of ions across a membrane
- cytoplasm side, negative
- extracellular side, positive

62
Q

Cotransport

A

occurs when active transport of a solute indirectly drives transport of other substances
- secondary active transport

Diffusion of first substance down concentration gradient is coupled to transport of second substance against own concentration gradient

63
Q

Bulk transport across the plasma membrane

A
  • Small molecules and water pass through the lipid bilayer or via transport proteins
  • Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles
  • Bulk transport occurs via endocytosis or exocytosis and requires energy
  • Can also recycle and remodel plasma membrane
64
Q

Exocytosis

A
  • In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell
  • Many secretory cells use exocytosis to export their products
  • Sidedness of membranes
  • Exo - expelling
65
Q

Endocytosis

A
  • The cell takes in macromolecules by forming vesicles from the plasma membrane
  • Endocytosis is a reversal of exocytosis, involving different proteins
  • There are three types of endocytosis
66
Q

There are three types of endocytosis

A
  • phagocytosis (cellular eating)
  • pinocytosis (cellular drinking)
  • receptor-mediated endocytosis
67
Q

phagocytosis

A

a cell engulfs a particle in a vacuole
* Extends pseudopodia to engulf particle
* The vacuole fuses with a lysosome to digest the particle

68
Q

pinocytosis

A

molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles
* Cellular drinking

69
Q

Endocytosis: Receptor mediated

A
  • In receptor-mediated endocytosis, binding of specific solutes to receptors triggers vesicle formation
  • Receptor proteins, receptors, and other molecules from the extracellular fluid are transported in the vesicles
  • Emptied receptors are recycled to the plasma membrane

Bio 217 (14 decks)

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