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Cell > Membrane Transport > Flashcards

Membrane Transport Flashcards

1
Q

The body’s internal water is ditributed into two large components

A

Intracellular Fluid and Extracellular Fluid

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2
Q

Majority of cells are in this compartment

A

Intracellular Fluid

􏰅 Majority is in cells as ICF, the remaining 20% are interstitial fluid
and plasma
􏰅 Two-thirds of total body water

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3
Q

Functions of Intracellular Fluid

A

􏰀 Make, store, and utilize energy
􏰀 Repair itself
􏰀 Replicate
􏰀 Perform cell-specific functions

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4
Q

Brings to the cell nutrients (e.g., glucose, fatty acids (FAs), amino
acids (AAs)), oxygen, various ions and trace chemicals, and
hormones
􏰅 Removes CO2, waste products, and toxic or detoxified materials
from immediate cellular environment

A

Extracellular fluid

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5
Q

ECF is charactereized by ___ and ____ content, ____ as major anion

A

Na+, Ca2+, Cl-

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6
Q

Most common extracellular ion

A

Sodium

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7
Q

Most common intracellular ion

A

Potassium

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8
Q

Differences in concentrations forms what

A

forms gradients that drives pumps to maintain homeostasis between the extracellular and intracellular environments

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9
Q

Backbone is glycerol and Amphipathic: nonpolar FA tails, and polar head due to presence of
charged phosphate group

A

Phospholipids

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10
Q

Forms when polar head groups are larger than the hydrophobic tails
􏰁 Relatively small and consequently limited in their potential to form membranes

A

Micelle

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11
Q

Key structure in biological membranes

A

Bilayer

Polar heads oriented outwards the aqueous environment with the hydrophobic fatty acid chains hidden in between
Impermeable to most ater-soluble molecules

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12
Q

What happens when the number of heads is almost equal to tails?

A

tails associate with other tails and expose polar head groups to aqueous environment and form a sandwich of phospholipid bilayer.

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13
Q

The bilayer is driven by this

A

Hydrophobic Effect

(the tendency of nonpolar molecules
to self-associate in an aqueous environment, while in the process
excluding water))

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14
Q

Sometimes the bilayer can engulf the environment forming this with the polar heads oriented inside and non-polar tails still hidden away from water

A

Liposome

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15
Q

Amphiphagic behavior of lipids allow membranes to perform this

A

Compartmentalization

(Compartmentalization increases the efficiency of many subcellular processes by concentrating the required components to a confined space within the cell.)

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16
Q

Molecules that can pass from extracellular to intracellular environment

A

Small nonpolar hydrophobic & Small uncharged polar molecules

− Small nonpolar hydrophobic (e.g. O2, CO2 and steroids)
􏰅 Can easily permeate through the non-polar layer of phospholipid bilayer, thus can pass easily from the extracellular to intracellular
environment
− Small uncharged polar molecules (e.g. water, glycerol, urea and ethanol)
􏰅 May pass even if they are polar because of their small size

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17
Q

Molecules that can not pass from extracellular to intracellular environment

A

charged ions and large uncharged molecules

− Charged ions
􏰅 Cannot pass through the hydrophobic tails of the bilayer − Large uncharged molecules
􏰅 Cannot pass through bilayer due to size

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18
Q

Glycerol-phosphate backbone attached to two FAs via ester linkages and an alcohol

A

Phosphoglyceride

FA constituents are usually even-numbered carbon molecules (most common: 16 or 18C)
􏰁 Unbranched
􏰁 Can be saturated or unsaturated with one or more double bonds

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19
Q

Difference between Sphingomyelin and Phosopglyceride

A

Phospholipid that contains a sphingosine rather than a glycerol backbone

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20
Q

FA of Sphingomyelins are attached by an _____ to the amino group of spingosines, forming ____

A

amide; ceramide

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21
Q

Formed when primary hydroxyl group of sphingosines is esterified to
phosphorylcholine

A

Sphingomyelin

  • prominent in myelin sheaths
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22
Q

􏰁Mainly located in the plasma membrane displaying their sugar
components to the cell exterior

A

Glycospingolipids

Subtype of glycolipids that contain sugar lipids

Include galactosyl- and glucosyl-ceramides (cerebrosides) and the
gangliosides

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23
Q

Important in cell membrane fluidity

A

Cholesterol

Intercalates among the phospholipids of the membrane
− Hydrophilic hydroxyl group at aqueous interface, while remainder stays buried within the lipid bilayer leaflet
􏰁 Not present in plants
􏰁 Can be separated and quantified via column, thin-layer, and gas-liquid
chromatography

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24
Q

Majority of cholesterol resides in ____ but small amounts are found in ____

A

within plasma membrane; mitochondria, golgi complex, nuclear membrane

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25
Q

Difference between Glycolipids and Glycosphingolipids

A

Glycosphingolipid - cermaide backbone; act to modulate membrane-protein function, as well as playing a role in cell-cell communication.

Glycolipids - backbone is a sugar; serve a recognition function

26
Q

Major functional molecule of membranes

A

Proteins

Consist of enzymes, pumps and transporters, channels, structural components, antigens and receptors)

Interspersed along cell membrane, certain proteins can insinuate themselves
− Membrane phospholipids act as a solvent for membrane proteins

27
Q

Type of membrane proteins that interact extensively with phospholipids and span trhough the entire thickness of the bilayer

A

Integral Membrane Proteins

Mostly globular and amphipathic
􏰁 Asymmetrically distributed across the membrane bilayer
− Usually they serve as channels or for anchorage of the cell

28
Q

Formation of integtral membrane protein that serves as a receptor for recognition

A

Alpha helix

29
Q

Formation of integtral membrane protein that sServe as enzymes, transporter, or receptors

A

Helical bundles

30
Q

Formation of integtral membrane protein that Serve as channels between extracellular and intracellular environment

A

Beta barrel

31
Q

Specialized areas of the explasmic or outer leafle that is hypothesized to be involved in signal transfuction

A

Lipid rafts

− Enriched in cholesterol, sphingolipids, and certain proteins
− Lateral diffusion causes phospholipids (which may carry ligands and receptors) to move to other area
􏰁 Lipid rafts are stabilized through interactions with the actin cytoskeleton

32
Q

May derive from lipid rafts

A

Caveolae

The lipid rafts with ligands can invaginate and form caveolae
which pinch and enter cell to where it is needed (usually the

33
Q

− Often located below the apical surfaces of epithelial cells
− Prevent the diffusion of macromolecules between cells

A

Tight junctions

− Composed of various proteins, including occludin, various claudins, and junctional adhesion molecules
• Other specialized features: desmosomes, adherens junctions, and microvilli

34
Q

Passive Transporrt: Solutes move from ___ concentration to ____ concentration (up/down) electrochemical gradient)

A

high; low; down

35
Q

Type of passive transport where 􏰅 Solutes move down concentration gradient without the need for
receptors or channels

A

Simple diffusion

Limited by three factors:
􏰀 Thermal agitation of the specific molecule
􏰀 Concentration gradient across the membrane 􏰀 Solubility of the solute

36
Q

Type of passive transport where Materials travel down concentration gradient and have to pass a
channel of integral proteins

A

Passive diffusion

Ex. Aquaporins forming channels for water passage

37
Q

Type of passive transport that Involves either certain transporters or ion channels

A

Facilitated Diffusion

􏰅 Ligand must first activate the gated channel before it can move
down the concentration gradient

38
Q

Ping Pong Mechanism

A

􏰀 In the “ping” state, it is exposed to high concentrations of solute, and molecules of the solute bind to specific sites on carrier protein. Binding induces a conformational change that exposes the carrier to a lower concentration of solute (“pong” state) (Harper’s, p. 469)

39
Q

􏰀 Transport against concentration gradient but does not need help past carrier
􏰀 Moves one type of molecule bidirectionally
ligand must first activate the gated channel before it can move down the concentration gradient

A

Uniport

Ex. Ex. GLUT transporter in RBC for glucose to enter the RBC

40
Q

Materials are moved against a concentration gradien

A

active transport

41
Q

Type of active transport that entails pumps and energy from ATP is needed

A

Primary

Ex. Na+-K+-ATPase
􏰀 3 Sodium exits only if 2 ions of potassium are present 􏰀 Restores homeostasis

42
Q

type of active transport that Relies on concentration gradient generated by another system

A

Secondary (Cotransport)

43
Q

typeof active transport where Both substances must be present for carrier to be activated and transported to the same direction

A

Symport

Ex. SGLT1 in intestines which needs glucose and sodium for carrier to transport both into the cell

44
Q

type of active transport where Both substances have to be present however they will be transported in an opposite manner

A

Antiport

Ex. Sodium Calcium exchanger - during muscle contraction, calcium is released from muscle endoplasmic reticulum. To prevent calcium excess, exchanger brings calcium out of cell when sodium is delivered in

45
Q

Composed of transmamebrane protein subunits, most are highly selective for one ion; allow impermeable ions to cross membranes at rates approaching diffusion limits

A

Transporters

46
Q

Type of transporter permeases bind solute and undergo conformational changes, transferring solute across the membrane

A

Carriers

􏰁 Involved in passive and active transport
􏰁 Transport is significantly slower than via ion channels
• Examples: Symporters, uniporters, and antiporters

47
Q

Ion channels can be activated

A

− Voltage-gated:
􏰅 Voltage change in exterior or interior via concentration changes of
Na+, K+, Cl-
− Ligand-gated:
􏰅 Ligand attached to receptor in or near ion channel can trigger
opening
− Mechanically-gated:
􏰅 Stress/physical stimuli ex. In the inner ear

48
Q

T/F: Ion channels can require activation (i.e. non-gated)

A

False:
− Some channels are not gated
− E.g. Aquaporins, K+ Leak Channels

49
Q

Process by which cells take up large molecules

A

Endocytosis

Provides a mechanism for regulating the content of certain membrane
components (e.g. hormones)

50
Q

Type of Endocytosis that ingests large particles such as viruses, bacteria, cells, or cellular debris

A

Phagocytosis

  • Plasma membrane engulfs solid particle and brings it to interior of cell as a phagosome
    − Phagosome contains part of the cell membrane and ingested materials
  • Occurs only in specialized cells such as macrophages and granulocytes
51
Q

− “Cell drinking”

− Cell membrane Invaginates water and other substances − Transport inside the cell via vesicles

A

Pinocytosis

52
Q

Uptake of a solute by formation of small vesicles is proportionate to its concentration in the surrounding extracellular fluid

A

Fluid-phase pinocytosis

It’s a nonselective process (Harper’s, p. 1161

53
Q

aka Receptor-mediated endocytosis
􏰀 Primarily responsible for the uptake of specific
macromolecules where there are binding sites on the plasma membrane

A

Absorptive pinocytosis

Requires attachment of ligand on cell receptor surface

Ligand on receptor moves through lipid rafts to clathrin-coated pit, the cell membrane then invaginates and endocytosis takes place
􏰀 Clathrin will travel where needed and when reached, clathrin is returned to the surface to await new complex
􏰀 Receptors and ligand separate where receptors are reused at the surface and ligands are transported to lysosome or golgi complex

54
Q

Process of releasing macromolecules outside of the cell 􏰁 Also involved in membrane remodeling

A

Exocytosis

55
Q

3 fates of molecules released by exocytosis

A

− They remain associated with the cell surface (membrane proteins)
− They become part of the extracellular matrix (ex. collagen and
glycosaminoglycans)
− They can enter the extracellular fluid and signal other cells

56
Q

Structures that permit direct transfer of small molecules between adjacent cell membranes

A

Gap Junctions

57
Q

Connect cells that are within 2-4mm of each other

A

Connexins

Connexins form connexons (6 connexin molecules make 1
hemiconnexon; 2 hemiconnexons make 1 connexon)
􏰅 One gap junction contains several connexons
􏰅 Open channels enable the diffusion of small solutes thus providing
a direct mechanism of cell to cell communication

58
Q

Extracellular vesicles are generated by at least two distinct mechanisms

A

microvesicles and

exosomes

59
Q

Generated by budding from the plasma membrane of a source cell

A

Microvesicles

60
Q

Generated from the multivesicular body (MVB)

− Secreted from the source cell upon fusion of the MVB with the plasma membrane

A

Exosomes

61
Q

Microvesicles and exosomes ultimately fuse to their target cell to deliver a distinct “payload” T/F

A

True

Cell (6 decks)

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