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Biology 1406 > chapter 7 > Flashcards

chapter 7 Flashcards

1
Q

The plasma membrane is the boundary that

A

separates the living cell from its surroundings

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2
Q

The plasma membrane exhibits

A

selective permeability, allowing some substances to cross it more easily than others

  • it chooses. its picky.
  • not just anything gets in the cell. they decide what gets in cell. its like a bouncer at a club that decides who gets to go in or who doesnt.
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3
Q

Phospholipids are the most abundant

A

lipid in the plasma membrane

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4
Q

Phospholipids are

A

amphipathic molecules, containing hydrophobic and hydrophilic regions

-half like water, half doesnt like water

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5
Q

The fluid mosaic model states that

A

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

-fluid- dynamic, moving
-mosaic- a bunch of little pieces together
made of lots of different molecules/elements

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6
Q

Membranes have been chemically analyzed and found to be made of

A

proteins and lipids

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7
Q

Scientists studying the plasma membrane reasoned that it must be a

A

phospholipid bilayer

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8
Q

two main components of membranes

A

proteins and lipids (phospholipids)

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9
Q

In 1935, Hugh Davson and James Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins
Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions
In 1972, S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water

A

proteins are embedded across membrane

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10
Q

Freeze-fracture studies of the plasma membrane supported the fluid mosaic model.

A

Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer.

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11
Q

Phospholipids in the plasma membrane can move within the bilayer. (constantly moving)

A

Most of the lipids, and some proteins, drift laterally.(move left to right)
Rarely does a molecule flip-flop transversely across the membrane.

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12
Q

As temperatures cool, membranes

A

switch from a fluid state to a solid state

-this is bad. dont want a membrane to freeze up.

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13
Q

The temperature at which a membrane solidifies depends on the types of lipids

A

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

(unsaturated fatty acids- double bonds with kinks)
(saturated fatty acids- will stack much better)

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14
Q

Membranes must be fluid to

A

work properly

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15
Q

The steroid cholesterol has different effects on membrane fluidity at different temperatures
(does different jobs at different times)

A
  • At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
  • At cool temperatures, it maintains fluidity by preventing tight packing. and keeps things moving so it doesnt pack or go too slow.

normal body temperature- keep things moving but it restrains it so it doesnt go too fast

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16
Q

Some proteins in the plasma membrane can

A

drift within the bilayer

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17
Q

Proteins are much larger than lipids and

A

move more slowly

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18
Q

Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions.

A

Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary.

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19
Q

A membrane is a

A

collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayer

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20
Q

Proteins determine

A

most of the membrane’s specific functions

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21
Q

The two sides of a membrane have

A

different protein and lipid compositions

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22
Q

phospholipids

A

most common lipid in a membrane

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23
Q

Peripheral proteins

A

are bound to the surface of the membrane

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24
Q

Integral proteins penetrate the hydrophobic core (across the membrane).

A
  • 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 alpha helices
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25
Six major functions of membrane proteins
1. Transport 2. Enzymatic activity (speed up reactions) 3. Signal transduction 4. Cell-cell recognition 5. Intercellular joining 6. Attachment to the cytoskeleton and extracellular matrix (ECM) -Membranes are structural and functional mosaics
26
Cells recognize each other by
binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
27
Membrane carbohydrates may be covalently bonded to
lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
28
Carbohydrates on the external side of the plasma membrane vary among
species, individuals, and even cell types in an individual | Example – Blood types
29
Membranes have
distinct inside and outside faces
30
The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when
the membrane is built by the ER and Golgi apparatus
31
Molecules that start out on the inside face of the ER end up
on the outside face of the plasma membrane
32
A cell must exchange materials with its surroundings, a process controlled by the
plasma membrane
33
Plasma membranes are selectively permeable, regulating the cell’s molecular traffic. Three things that influence whether something will get in the membrane or not:
- Size of molecule - Polarity of molecule (hydrophobic or hydrophilic) - Presence/absence of transport proteins in the membrane
34
Hydrophobic (nonpolar) molecules, such as hydrocarbons, can
dissolve in the lipid bilayer and pass through the membrane rapidly -Hydrocarbons, CO2 and O2
35
Polar molecules, such as sugars, do not
cross the membrane easily (hydrophilic molecules) | -C6H12O6, or charged molecules
36
its easy to get in the membrane if it is
hydrophobic
37
Transport proteins allow
passage of hydrophilic substances across the membrane
38
Some transport proteins, called channel proteins, have a
hydrophilic channel that certain molecules or ions can use as a tunnel
39
Channel proteins called aquaporins facilitate
the passage of water
40
Other transport proteins, called carrier proteins, bind to
molecules and change shape to shuttle them across the membrane
41
A transport protein is
specific for the substance it moves
42
Diffusion is
the tendency for molecules to spread out evenly into the available space
43
Although each molecule moves randomly, diffusion of a
population of molecules may be directional
44
At dynamic equilibrium,
as many molecules cross the membrane in one direction as in the other
45
Types of passive transport
diffusion osmosis facilitated diffusion
46
Substances diffuse down their
concentration gradient, the region along which the density of a chemical substance increases or decreases. No work must be done to move substances down the concentration gradient -Oxygen gets into cells this way for cellular respiration
47
The diffusion of a substance across a biological membrane is
passive transport because no energy is expended by the cell to make it happen
48
in diffusion, the concentration of one molecule has
no effect on the movement of other molecules
49
passive transport-
requires no energy to do anything to make it happen. it just happens
50
diffusion
movement of molecules from an area of [high mol (high concentration)] to---> [low mol (low concentration)] "down" the concentration gradient
51
osmosis
movement of water across a selectively permeable membrane | water will move from an area of [low solute] to ---> an area of [high solute]
52
Osmosis is the
diffusion of 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 -water moves from where there is less stuff to more stuff.
53
Tonicity is the
ability of a surrounding solution to cause a cell to gain or lose water (its always a comparison) (how cells gain or lose water)
54
Isotonic solution:
Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane its the exact same thing water vs. water x vs. x
55
Hypertonic solution:
Solute concentration is greater than that inside the cell; cell loses water have more solute than what it is being compared to
56
Hypotonic solution:
Solute concentration is less than that inside the cell; cell gains water have less solute than what comparing it to
57
Hypertonic or hypotonic environments create
osmotic problems for organisms
58
Osmoregulation,
the control of solute concentrations and water balance, is a necessary adaptation for life in such environments (Adapt H2O concentrations)
59
The protist Paramecium,
which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump
60
in a hypotonic solution in animal cells
it fills with water until it lyses (explodes)
61
in a isotonic solution in animal cells
its normal an equal amount of water goes in and out we want cells in isotonic enviornemnt
62
in a hypertonic solution in animal cells
it becomes crenate/shriveled
63
in a hypotonic solution in a plant cell
it is turgid, normal. | plant cells love to be turgid in hypotonic solution
64
in a isotonic solution in a plant cell
it is flaccid, water goes in and out
65
in a hypertonic solution in a plant cell
it is plasmolyzed, the plasma membrane rips off edges of plasma membrane, this is bad
66
Cell walls help
maintain water balance
67
plant cells like to be in
hypotonic solutions
68
animal cells like to be in
isotonic solutions
69
A plant cell in a hypotonic solution
swells until the wall opposes uptake; the cell is now turgid (firm)
70
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
71
In a hypertonic environment, plant cells
lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis -cant be fixed. bad.
72
In facilitated diffusion,
transport proteins speed the passive movement of molecules across the plasma membrane - Most transport proteins are very specific - 2 types of transport proteins: - -Channel proteins and carrier proteins
73
Channel proteins provide
corridors that allow a specific molecule or ion to cross the membrane
74
Channel proteins include
- Aquaporins for facilitated diffusion of water (help move water) - Ion channels that open or close in response to a stimulus (gated channels)
75
Carrier proteins undergo a
subtle change in shape that translocates the solute-binding site across the membrane (move things down concentration gradient)
76
Some diseases are caused by
malfunctions in specific transport systems, for example the kidney disease cystinuria
77
Facilitated diffusion is still passive
because the solute moves down its concentration gradient, and the transport requires no energy -Channel proteins and carrier proteins
78
Some transport proteins, however, can move
solutes against their concentration gradients | -this requires energy
79
Active transport
moves substances against their concentration gradients
80
Active transport requires
energy, usually in the form of ATP
81
Active transport is performed by
specific proteins embedded in the membranes
82
Active transport allows
cells to maintain concentration gradients that differ from their surroundings
83
The sodium-potassium pump
is one type of active transport system
84
Membrane potential is the
voltage difference across a membrane
85
Voltage is created by
differences in the distribution of positive and negative ions across a membrane
86
Cells have a
net negative internal charge
87
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)
88
An electrogenic pump is a
transport protein that generates voltage across a membrane | ex. sodium potassium pump
89
The sodium-potassium pump is the major electrogenic pump of animals
3 Na+ out, 2K+ in = overall 1 positive charge to the extracellular fluid
90
The main electrogenic pump of plants, fungi, and bacteria is a
proton pump
91
Electrogenic pumps help
store energy that can be used for cellular work
92
Cotransport occurs when
active transport of a solute indirectly drives transport of other solutes
93
Plants commonly use
the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
94
Small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins
Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles
95
Bulk transport requires energy
- exocytosis | - endocytosis
96
In exocytosis,
transport vesicles migrate to the membrane, fuse with it, and release their contents
97
Many secretory cells use exocytosis to export their products
- Pancreatic beta cells releasing insulin - Neurons releasing neurotransmitters - Plants making cell walls
98
exocytosis
taking things out of the cell
99
In endocytosis,
the cell takes in macromolecules by forming vesicles from the plasma membrane
100
Endocytosis is a
reversal of exocytosis, involving different proteins
101
There are three types of endocytosis
Phagocytosis (“cellular eating”) Pinocytosis (“cellular drinking”) Receptor-mediated endocytosis (“picky eater”)
102
endocytosis
bring things into the cell
103
In phagocytosis a cell engulfs a particle in a vacuole
The vacuole fuses with a lysosome to digest the particle
104
In pinocytosis,
molecules are taken up when extracellular fluid is “gulped” into tiny vesicles
105
In receptor-mediated endocytosis,
binding of ligands to receptors triggers vesicle formation
106
A ligand is
any molecule that binds specifically to a receptor site of another molecule

Biology 1406 (53 decks)

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