LESSON 2b: CELL MEMBRANE TRANSPORT Flashcards

1
Q
  • is the boundary between
    inside & outside…
    – separates cell from its environment
A

Cell membrane

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2
Q

Comes in …..

A

Food:
-carbohydrates
-sugars,
-proteins
-amino acids
-lipids
-salts, O2,H2O

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3
Q

Comes out…..

A

Waste:
- ammonia
-salts
-CO2
-H2O products

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4
Q

Can cell membrane be an impenetrable boundary?

A

NO!

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5
Q

Cell membrane permeability is ___________

A

Selective

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6
Q

– Allows some materials to pass.
àWater, oxygen, carbon
dioxide
– Prevents others from passing.
àProteins, carbohydrates

A

Differentially (selectively)
Permeable

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7
Q

Factors that determine how a
substance may be transported
across a plasma membrane:

A

– Size
– Polar or Nonpolar
– charge

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8
Q

-2nd Law of Thermodynamics
governs biological systems
– universe tends towards disorder
(entropy)

A

PASSIVE DIFFUSION

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9
Q

Movement of molecules in passive diffusion

A

High —-> low concentration

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10
Q

Only________, _________
molecules are able to
diffuse across a
phospholipid bilayer
at significant rates by
using passive
diffusion

A

small and relatively hydrophobic molecules

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11
Q

In passive diffusion, Molecules have to
dissolve in _______

A

lipid interior

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12
Q

Molecules that can pass through plasma membrane by passive diffusion

A
  • Gases (oxygen, carbon
    dioxide)
  • Water molecules (rate
    slow due to polarity)
  • Lipids (steroid
    hormones)
  • Lipid soluble molecules
    (hydrocarbons,
    alcohols, some
    vitamins)
  • Small noncharged
    molecules (NH3)
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13
Q

Why is diffusion important to cells
and humans?

A

Important in:
* Cell respiration
* Alveoli of lungs
* Capillaries
* Red Blood Cells
* Medications: time-release capsules

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14
Q
  • Diffusion through protein channels which do not
    interact with hydrophobic interior
    – For biological mol unable to dissolve in hydrophobic
    interior
    – no energy needed
A

Facilitated Diffusion

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15
Q

Facilitated =___________
Open Channel= ____________

A

-with help
-fast transport

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16
Q

Molecules that transport using facilitated diffusion

A
  • Ions (Na+, K+, Cl-)
  • Sugars (Glucose)
  • Amino Acids
  • Small water soluble molecules
  • Water (faster rate)
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17
Q

The passage of material in facilitated diffusion is aided both by ____________ and ___________

A

concentration gradient and transport protein

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18
Q

Two kinds of protein in facilitated diffusion

A

-Carrier Protein
-Channel Protein

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19
Q

-bind specific molecules, undergo conformational
change to release molecule
- ex. Glucose transporters

A

Carrier Proteins

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20
Q
  • form open pores for free diffusion
  • found in gap junctions
A

Channel Proteins

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21
Q

Molecules will
randomly move
through the pores
in ____________

A

Channel Proteins.

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22
Q

Some Carrier proteins ____________
through the membrane

A

do not extend

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23
Q

Some carrier protein _____________ molecules
through the lipid bilayer and release
them on the opposite side.

A

bond and drag

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24
Q

Other carrier proteins
___________to move
materials across the cell
membrane

A

change shape

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25
How do molecules move through the plasma membrane by facilitated diffusion?
* Channel and Carrier proteins are specific: * Channel Proteins allow ions, small solutes, and water to pass * Carrier Proteins move glucose and amino acids * Facilitated diffusion is rate limited, by the number of proteins channels/carriers present in the membrane.
26
Most cells, including _____________, are exposed to extracellular glucose concentrations that are higher than those inside the cell, so facilitated diffusion results in the net inward transport of glucose.
erythrocytes,
27
* Cells obtain food for ______ * __________ communicate * ____________ transport food to bloodstream * Muscle cells _____
-cell respiration -Neurons -Small intestine cells -contract
28
* Water Channels * Protein pores used during Osmosis * provide corridors allowing water molecules to cross the membrane. * Allow for fast transport * water channel proteins, make possible massive amounts of diffusion
Aquaporins
29
– is the diffusion of water across a differentially permeable membrane.
OSMOSIS
30
the pressure that develops in a system due to osmosis
Osmotic pressure
31
Concentrations of Water
1. Hypertonic 2. Hypotonic 3. Isotonic
32
Direction of osmosis is determined by comparing ___________
total solute concentrations
33
more solute, less water
Hypertonic
34
- less solute, more water
Hypotonic
35
equal solute, equal water
Isotonic
36
Cell survival depends on ___________
balancing water uptake & loss
37
Cell in Hypotonic Solution (Freshwater)
Animal Cell: Lysed Plant Cell: Turgid (Normal)
38
Cell in Isotonic Solution (Balanced)
Animal Cell: Normal Plant Cell: Flaccid
39
Cell in Hypertonic Solution (Saltwater)
Animal Cell: Shriveled Plant Cell: Plasmolyzed
40
When membrane permeable to both solute molecules and water, both solution have same osmolarity: _____________, even if one solution have lower osmolarity and the other have greater osmolarity.
Volume Unchanged
41
When membrane is impermeable to solute molecules but permeable to water. both solution have same osmolarity: _____________,
but volume move to area with greater solute because water is free to move.
42
Isotonic: animal cell immersed in ______ solution
mild salt
43
Example: Blood cell in plasma membrane in isotonic solution. Thus:
- no net movement of water, it flows across membrane equally, in both directions – volume of cell is stable
44
Example for hypotonic: Paramecium in Fresh water. Problem? Solution?
Problem: gains water, swell and can burst Solution: Contractile Vacuole (pumps water out of the cell using ATP)
45
Example of Hypertonic: Shellfish in Saltwater Problem? Solution?
Problem: Lose water and Die Solution: take up water or pump out salt
46
Non-lipid soluble substances diffuse through__________
membrane channels.
47
Why is osmosis important to cells and humans?
* Cells remove water produced by cell respiration. * Large intestine cells transport water to bloodstream * Kidney cells form urine
48
- Non lipid soluble passively diffuse ____________________ through channels that cross the lipid bilayer; some channels are open all the time whereas others are gated.
-down their electrochemical gradient
49
- The _____________ regulates the opening/closing of the channel
membrane potential (voltage)
50
Example of a specific stimulus:
-Voltage (Voltage-gated channel) -Ligand (ligand-gated channels) -Specific Stress (Stress-activated channels)
51
______ permit the free passage of ions and small polar molecules through the outer membranes of bacteria.
Porins
52
______ mediate the passage of ions across plasma membranes
Ion channels
53
__________ open in response to the binding of neurotransmitters or other signaling molecules.
Ligand-gated channels
54
___________ open in response to changes in electric potential across the plasma membrane.
Voltage-gated channels
55
* open or close depending on the presence or absence of a physical or chemical stimulus. * Ex. neurotransmitters bind to specific gated channels on the receiving neuron, these channels open. * This allows sodium ions into a nerve cell. * When the neurotransmitters are not present, the channels are closed
Gated Channels
56
example of voltage-gated channels
Membrane Potential - K+ voltage-gated channels -Na+ voltage-gated channels
57
regulates opening/closing of the channel.
membrane potential
58
exist as either open or close depending on the membrane voltage. It has only an activation gate.
K+ voltage-gated channels
59
-opens when the membrane potential depolarizes (i.e. becomes more positive). - It has activation and inactivation gates.
Na+ voltage gated channels
60
-a large family of cell surface proteins that respond to a variety of signals, including hormones, neurotransmitters, and light -a type of cell surface receptor that interacts with G proteins to initiate intracellular signaling pathways
G protein-linked receptor
61
-Cells may need to move molecules against concentration gradient – shape change transports solute from one side of membrane to other – protein “pump” – “costs” energy = ATP
Active Transport
62
The Importance of Active Transport
* Bring in essential molecules: ions, amino acids, glucose, nucleotides * Rid cell of unwanted molecules (Ex. sodium from urine in kidneys) * Maintain internal conditions different from the environment *Regulate the volume of cells by controlling osmotic potential *Control cellular pH *Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium- Potassium pump and Proton pumps)
63
Example of Active transport
Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients
64
Process of Sodium-Potassium Pump Action
1. binding of cytoplasmic Na+ to the protein stimulates phosphorylation by ATP 2. Phosphorylation causes the protein to change its conformation 3. The conformational change expels Na+ to the outside and extracellular K+ binds. 4. K+ binding triggers release of a phosphate group. 5. Loss of phosphate restores original conformation. 6. K+ released and Na+ sites are receptive again., the cycle repeats.
65
____________ move out of the cell and then _________ move into the cell
-3 Sodium ions -2 Potassium ions
66
Driven by the splitting of ATP to provide energy and conformational change to proteins by adding and then taking away a phosphate group
Sodium-Potassium Pump (Active Transport)
67
Sodium Potassium pump is used to establish an _______________ across neuron cell membranes
electrochemical gradient
68
Active transport can be classed into 2 groups
1. PRIMARY ACTIVE TRANSPORT 2. SECONDARY ACTIVE TRANSPORT
69
- _____________ is directly used to move substances across the membrane against its concentration gradient (i.e. from an area of low concentration .to an area of high concentration)
Cellular energy (i.e. ATP)
70
A substance is actively transported using ATP through one channel. Then it diffuses back passively through a channel and its energy harnessed from transport is used to move another substance against it concentration gradient.
PRIMARY ACTIVE TRANSPORT
71
Active transport, a process in which energy is provided by another coupled reaction, is used to drive the uphill transport of molecules in the _______________
energetically unfavorable direction
72
Ion pumps responsible for maintaining gradients of ions across the plasma membrane, provide important examples of active transport driven directly by ______________.
ATP hydrolysis
73
Some molecules are transported against their concentration gradients using energy derived not from ATP hydrolysis, but from the ________________ in the energetically favorable direction.
coupled transport of a second molecule
74
The __________ of the intestine provide a good example of active transport drive by the Na+ gradient. (Na+ is coupled by glucose, where the energy harnessed by Na+ is used for transport)
epithelial cells lining
75
- Two substances are transported in the same direction across a plasma membrane. - One of the substance moves passively down its concentration gradient while the second substance uses ATP to move against its concentration gradient across the plasma membrane.
SECONDARY ACTIVE TRANSPORT:SYMPORTER
76
-Two substances are transported across the membrane in opposite directions across the plasma membrane. - One of the substance moves passively down its concentration gradient while the second substance uses ATP to move against its concentration gradient across the plasma membrane.
SECONDARY ACTIVE TRANSPORT: ANTIPORTER
77
A ____________ can transport only a single molecule using the facilitated diffusion of glucose.
Uniport
78
An _________ uses active transport to move two molecules in opposite direction
antiport
79
- moving things out. – Transport of large molecules – Requires energy – Keeps the macromolecule contained
Vesicle Formation
80
Vesicles form as a way to transport molecules out of a cell
Exocytosis
81
Exocytosis of Proteins
1. Vesicle formation: Proteins destined for export are enclosed in membrane vesicles by the trans Golgi. 2. Vesicle movement: The vesicles are transported to the plasma membrane. 3. Vesicle fusion: The vesicle fuses with the plasma membrane. 4. Content release: The contents of the vesicle are released into the extracellular space.
82
Vesicles form as a way to transport molecules into a cell
Endocytosis
83
Types of Endocytosis
-Phagocytosis -Pinocytosis -Receptor-Mediated Transport
84
-Cell eating - engulf Large, particulate matter (Bacteria, viruses, and aged or dead cells). -Example: Phagocytes
Phagocytosis
85
How insulin works in regulation of blood sugar level and how endocytosis take place when insulin level drops?
1. Glucose transporters are stored within the cell in membrane vesicles, 2. When insulin interacts with its receptor, this vesicles move to the surface to fuse with the plasma membrane, increasing the number of glucose transporters in the plasma membrane. 3. When insulin level drops, glucose transporters are removed from the plasma membrane by endocytosis, forming small vesicles. 4. The smaller vesicles fuse with larger endosomes. 5. Patches of the endosomes enriched for the glucose transporters bud off to become small vesicle, ready to return to the surface when insulin levels rise again,
86
-Most common form of endocytosis -* Cell forms an invagination * Materials dissolve in water to be brought into cell * Called “Cell Drinking” * Ex. Intestinal cells, Kidney cells, Plant root cells -Takes in dissolved molecules as vesicles
Pinocytosis
87
Best example for Pinocytosis
Plant Roots
88
Movement of very specific molecules into the cell with the use of vesicles coated with the ______________
Clathrin Protein
89
-a form of pinocytosis, provides a mechanism for the selective uptake of specific macromolecules. -Coated pits are specific locations coated with clathrin and receptors. When specific molecules (ligands) bind to the receptors, then this stimulates the molecules to be engulfed into a coated vesicle - Ex. Uptake of cholesterol (LDL) by animal cells
Receptor-Mediated Transport
90
Some integral proteins have receptors on their surface to _________________, hormones cholesterol, etc
recognize & take in
91
are specialized regions of the plasma membrane where specific cell surface receptors are found.
Clathrin-coated pits
92
a membrane associated GTP-binding protein, assists in the budding off of pits from the plasma membrane.
Dynamin
93
Clathrin assembles into a _____________-that distorts the membrane, forming invaginated pits.
basketlike structure
94
Clathrin coated pits occupy about ____ of the surface area of plasma membranes.
1-2%
95
are vesicles with tubular extensions, located at the periphery of the cell, that fuse with clathrin-coated vesicles which have shed their coats.
Endosomes
96
An important feature of early endosomes is that they maintain an ______________ as the result of the action of a membrane H+ pump.
acidic internal pH
97
Process of endocytosis from clathrin-coated pits.
1. Arrival of a nerve impulse at the terminus of a neuron triggers the fusion of synaptic vesicles with the plasma membrane, releasing neurotransmitters. 2. The synaptic vesicle membrane is retrieved by endocytosis from clathrin-coated pits. 3. The endocytosis vesicles fuse with early endosomes. 4. Synaptic vesicles are regenerated by budding from the endosome and refilled by the uptake of neurotransmitters from the cytosol.
98
_________________ is the major fate of membrane proteins taken up by receptor-mediated endocytosis.
Recycling to the plasma membrane
99
Ligands and membrane proteins destined for _____________________ are transported from early endosomes to late endosomes, which are located near the nucleus
degradation in lysosomes
100
a phenomenon where receptor-ligand complexes are removed from the plasma membrane, thereby terminating the response of the cell to growth factor stimulation.
Receptor down-regulation
101
are phagosomes fused to lysosomes, contain lysosomal acid hydrolases that digest the ingested material
Phagolysosomes
102
The ______________ by phagocytosis plays distinct roles in different kinds of cells
ingestion of large particles