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Biology 202 > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

What is the boundary that separates living cells from its surroundings?

A

the plasma membrane

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2
Q

Selective permeability

A

allowing some substances to cross more easily than others

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3
Q

What is fundamental to life?

A

the ability of the cell to discriminate in its chemical exchanges with its environment

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4
Q

What is the most abundant lipid in the plasma membrane?

A

phospholipids

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5
Q

What are amphipathic molecules?

A

containing both hydrophobic and hydrophilic regions

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6
Q

What does the fluid mosaic model state?

A

that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

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7
Q

Who proposed the sandwich model?

A

Hugh Davson & James Danielli

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8
Q

What did the sandwich model propose? And what was the issue with this proposal?

A

-the phospholipid bilayer lies between 2 layers of globular proteins
-(issue)the placement of membrane proteins, which have hydrophilic and hydrophobic regions

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9
Q

Who proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water?

A

S.J. Singer & G. Nicolson

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10
Q

What is freeze-fracture?

A

a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer

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11
Q

What are membrane molecules held in place by?

A

weak hydrophobic interactions

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12
Q

How many times per second do adjacent phospholipids switch positions?

A

107

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13
Q

True or False: Flip-flopping across the membrane is not rare

A

False

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14
Q

Membranes rich in unsaturated fatty acids are

A

more fluid than those rich in saturated fatty acids

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15
Q

Cholesterol restrains movement of phospholipids

A

at warm temperatures

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16
Q

Cholesterol maintains fluidity by preventing tight packing

A

at cool temperatures

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17
Q

What occurs as temperatures cool?

A

membranes switch from fluid to a solid state

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18
Q

What do the membranes of fishes living in extreme cold temperatures have?

A

a high proportion of unsaturated hydrocarbon tails, enabling them to stay fluid

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19
Q

What do the membranes of bacteria and archaea living in thermal hot springs and geysers have?

A

unusual lipids that prevent excessive fluidity at such high temperatures

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20
Q

Adaptations to specific environments can be seen in?

A

variations in lipid composition of cell membranes
EXAMPLE: winter wheat increase the percentage of unsaturated phospholipids in their membranes in the autumn to prevent the membranes from solidifying during winter

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21
Q

What are the 2 major populations of membrane proteins?

A

integral and peripheral

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22
Q

What are peripheral proteins?

A

bound to the surface of the membrane

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23
Q

Integral proteins

A

penetrate the hydrophobic core

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24
Q

What are transmembrane proteins?

A

integral proteins that span the membrane

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25
Alpha helices
one or more stretches of coiled nonpolar amino acids along the hydrophobic regions of an integral protein
26
What are the 6 major functions of membrane proteins?
-transport of specific solutes into or out of cells -enzymatic activity, sometimes catalyzing one of a number of steps of metabolic pathway -signal transduction, relaying hormonal messages to the cell -cell-cell recognition, allowing other proteins to attach 2 adjacent cells together -intercellular joining of adjacent cells with gap or tight junctions -attachment to the cytoskeleton and extracellular matrix, maintaining cell shape and stabilizing the location of certain membrane proteins
27
What is the name of white blood cells that are am essential part of the human immune system?
CD4+ T helper cells
28
Why are CD4+ T helper cells called helper cells?
one of their main roles is to send signals to other types of immune cells
29
What is CCR5 or CD195?
a protein on the surface of white blood cells that is involved in the immune system as it acts as a receptor for chemokines
30
Cell-cell recognition
-recognize each other by binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane -important in the sorting and organizing of cells into tissues and organs during development -basis for the rejection of foreign cells by the immune system
31
Membrane carbohydrates may be covalently bonded to both
lipids(forming glycolipids) or proteins (forming glycoproteins)
32
Where do carbohydrates vary among species?
on the external side of the plasma membrane
33
What is an example of variation seen in the carbohydrate part of glycoproteins on the membranes of red blood cells?
Blood types (A, B, AB, and O)
34
When is the asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane determined?
when the membrane is built by the ER and golgi apparatus
35
Which molecules can dissolve in the lipid bilayer and pass through the membrane rapidly?
hydrophobic(nonpolar) molecules, such as hydrocarbons and CO2, and O2
36
Which molecules do not cross the membrane easily?
polar molecules, such as sugars, and their surrounding shell of water
37
What do transport proteins allow?
passage of hydrophilic substances across the membrane
38
Examples of transport proteins
channel proteins: have a hydrophilic channel that certain molecules or ions can use as a tunnel carrier proteins: bind to molecules and change shape to shuttle them across the membrane
39
Aquaporins
channel proteins that facilitate the passage of water
40
Diffusion
the tendency for molecules to spread out evenly into the available space; may be directional; at dynamic equilibrium(cross the membrane in one direction as in the other)
41
Concentration gradient
the region along which the density of a chemical substance increases or decreases
42
True or False: no work must be done to move substances down the concentration gradient
True
43
Passive transport
the diffusion of a substance across a biological membrane that requires no energy from the cell to make it happen
44
What is osmosis?
the diffusion of water across a selectively permeable membrane
45
How does water diffuse?
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
46
Tonicity
the ability of a surrounding solution to cause a cell to gain or lose water
47
Isotonic solution
solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
48
Hypertonic solution
solute concentration is greater than that inside the cell; cell loses water
49
Hypotonic solution
solute concentration is less than that inside the cell; cell gains water
50
What helps maintain water balance?
cell walls
51
How does a plant cell become turgid(firm)?
in a hypotonic solution; swells until the wall opposes uptake
52
How does a plant cell become flaccid(limp)?
if it and it's surroundings are isotonic; no net movement of water into the cell; plant may wilt
53
What causes plasmolysis?
plant cells lose water in a hypertonic environment, the membrane pulls away from the wall resulting in plasmolysis
54
Osmoregulation
the control of solute concentrations and water balance
55
The protist Paramecium
hypertonic to its pond water environment; has a contractile vacuole that acts as a pump
56
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 -solute moves down concentration gradient & transport requires no energy
57
Channel proteins include
aquaporins and ion channels
58
Aquaporins
facilitated diffusion of water
59
Ion channels
open or close in response to a stimulus
60
Some diseases are caused by malfunctions in specific transport systems, what's an example of this?
the kidney disease cystinuria -absence of a carrier protein that transports cysteine and other amino acids across the membranes of kidney cells -painful kidney stones as amino acids accumulate and crystallize in the kidneys
61
Active transport
moves substances against their concentration gradient -requires energy, usually in the form of ATP -performed by specific proteins embedded in the membranes -allows cells to maintain concentration gradients that differ from their surroundings - [K+] - high inside the cells and low outside; [Na+] - low inside, high outside
62
Sodium-potassium pump
uses between 20 to 40% of the body energy
63
How is voltage created?
by differences in the distribution of positive or negative ions across a membrane
64
Membrane potential
the voltage difference across a membrane: cytoplasm(-); extracellular(+)
65
Electrochemical gradient
two combined forces drive the diffusion of ions across a membrane
66
Chemical force
the ion's concentration gradient
67
Electrical force
the effect of the membrane potential on the ion's movement
68
What is an electrogenic pump?
a transport protein that generates voltage across a membrane (sodium-potassium in animal cells)
69
What is the main electrogenic pump of plants, fungi, and bacteria?
proton pump
70
What do electrogenic pumps help with?
store energy that can be used for cellular work
71
Cotransport
occurs when active transport of a solute indirectly drives transport of other solutes -plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell EXAMPLE: diffusion of H+ into the cell and the transport of sucrose into the cell
72
How do small molecules and water enter or leave the cell?
through the lipid bilayer or via transport proteins
73
How do large molecules, such as polysaccharides and proteins cross the membrane?
in bulk via vesicles(requires energy)
74
Exocytosis
-transport vesicles migrate to the membrane, fuse with it, and release their contents -many secretory cells use exocytosis to export their products
75
Examples of secretory cells using exocytosis
-pancreatic cells: secrete insulin into the blood -neurons: release neurotransmitters that signal other neurons or muscle cells -plant cells: delivers proteins and certain carbohydrates from golgi vesicles to the outside of the cell
76
Endocytosis
the cell takes in macromolecules by forming vesicles from the plasma membrane; reversal of exocytosis, involving different proteins
77
What are the 3 types of endocytosis?
-phagocytosis("cellular eating") -pinocytosis("cellular drinking") -receptor-mediated endocytosis
78
What occurs in phagocytosis?
a cell engulfs a particle in a vacuole -vacuole fuses with a lysosome to digest the particle
79
What occurs during pinocytosis?
molecules are taken up when extracellular fluid is "gulped" into tiny vesicles
80
What occurs during receptor-mediated endocytosis?
binding of ligands to receptors triggers vesicle formation
81
What is a ligand?
any molecules that binds specifically to a receptor site of another molecule

Biology 202 (5 decks)

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