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SFM > Cell Membranes And Transport > Flashcards

Cell Membranes And Transport Flashcards

1
Q

Physiological Role of Membranes

A

Protective barrier for cells and organelles
Cell characteristic shape
Separates intracellular environment from external medium
Allow selective permeability of various metabolites
Transport - nutrition, oxygen, waste, ions
Compartmentalization of organelles
Cell recognition
Anchoring site of cytoskeletal elements
Binding site for hormones and enzymes
Electrochemical potential - membrane excitability
Interlocking surfaces bind cells together )tissue gap jxns

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2
Q

Structure and Composition

A

Composed of lipids, proteins, and carbohydrates
Asymmetric bilayer arrangement
Semipermeable (small molecules can diffuse through)
Primary Components - Phospholipids
Amphipathic - hydrophilic head hydrophobic tail

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3
Q

Hydrophilic Head groups

A

Face aqueous environment outside and inside the cell and form the outer and inner surface of the cell membrane

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4
Q

Hydrophobic tails

A

Face the interior and form the hydrophobic core of the membrane

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5
Q

Lipid bilayer

A

Foundation for lipids or rosins to be embedded, attached, or anchored

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6
Q

Carbohydrate molecules

A

Can be covalently attached to membrane lipids or proteins

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7
Q

Phospholipids PL

A

most abundant lipids in membranes

Classified by backbone

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8
Q

Glycerophospholipids

A

Glycerol backbone + phosphate + 2FA esterfied

Phosphatidyl serine/choline/inositol

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9
Q

Sphingolipids SL

A

Sphingosine backbone + Long chain FA and phosphorylcholine

Sphingomyelin - most common SL

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10
Q

Glycolipids

A

Sphingosine backbone + Carbohydrate (oligosaccharide) residues
Found in outer leaflet of lipid bilayer

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11
Q

CHL

A

Embedded in lipid Bilayer

Steroid nucleus with OH and Hydrocarbon side chain

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12
Q

Lipid Rafts

A

Specialized sterol enriched microdomains in the PM

Very important for cell signaling

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13
Q

Outer sheet Ex

A

Phosphatidylcholine
Sphingomyelin
Glycolipids

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14
Q

Inner Sheet Intra

A

Phosphatidylinositol/serine/ethanolamine

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15
Q

Membrane Protiens

A

Integral embedded
Peripheral attached
Lipid anchored tethered

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16
Q

Integral Membrane Proteins

A

Firming embedded in the membrane

Stabilized by hydrophobic interactions with lipids

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17
Q

Polytopic transmembrane proteins

A

Span entire LB, weave in and out of membrane several times
Interact with Ex and In environment
Include - transporters, ion channels, and receptors that regulate molecule movement across the membrane and receive/transmit signals from ex environment of cell

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18
Q

Peripheral proteins

A

Loosely bound to membrane through electrostatic interactions what lipids or proteins

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19
Q

Lipid Anchored Proteins

A

Tethered to membranes via covalent attachment to a lipid

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20
Q

Carbohydrates

A

Covalently attached to coms lipids and proteins facing ex surface
Outer cover sheet of many membranes is covered with a carbohydrate shell - glycocalx

21
Q

Glycocalax function

A

Protection - protects membrane components from mechanical injury or enzyme degradation
Cell Adhesion - make more stable contact with other cells, tissue formation and fertilization
Cell Identification - differentiate own healthy cells from foreign or diseased cells, very important in RBC

22
Q

Membrane Fluidity

A

Proteins and Lipids rotate and move laterally in membranes
Fluid like quality
Fluid Mosaic Model - crucial for fxn
Allows proteins and lipids to undergo conformational changes and/or to move to specific areas to carry out their fxn

23
Q

Factors that influence membrane fluidity

A

Temperature
Lipid Composition
CHL

24
Q

Temperature

A

Fluid to rigid state - melting temp

25
Q

Below melting temp

Temp < MT

A

Ordered packing and rigid

26
Q

Above melting temp

A

Fluid membranes

Temp»>MT

27
Q

Lipid Composition Saturated FA

A

DECREASE membrane fluidity - rigid, tighter packing, reduces mobility

28
Q

Lipid Composition - Unsaturated FA

A

INCREASE membrane fluidity

Kinks in FA chain don’t allow tight packing

29
Q

If membrane too rigid (High SFA or below MT) CHL…

A

CHL intercalates membrane and increases fluidity to prevent packing

30
Q

If membrane too fluid (High USFA or above MT) CHL…

A

CHL stabilizes fluidity by fitting in gaps created by kinks

31
Q

Membrane Transport

A

PM semipermeable
Permeable to lipophillic molecules - steroids
Impermeable to hydrophilic/polar molecules - needs transport mechanism
Membrane proteins facilitate this transport across membrane
IMP Integral embedded in PM fxn as transporter proteins
Regulate flow of biomolecules in and out of cell

32
Q

Ion Gradients

A

Greatest energy requirements Na+, K+, Cl-

Ca2+ 10,000 fold gradient

33
Q

Passive Transport

A

Energy independent

Down concentration gradients high —> low

34
Q

Active Transport

A

Energy dependent
Against concentration mechanism low —> high
Energy from ATP hydrolysis used to pump ions

35
Q

Simple Diffusion

A

Unaided
Molecules — small, nonpolar, uncharged diffuse freely across
Steeper gradient, faster diffusion
O2, H2, ethanol, diethylether, benzene NONPOLAR
H2O, CO2, NH3, Urea POLAR

36
Q

Facilitated Diffusion

A

Needs the assistance of transmembrane proteins to facilitate
Molecules large and charged that cant cross
Ion channels or transporters greatly increases rate of transport
H2O aquaporin, Na+K+Cl- symporter, Cl-/HCO3 exchange protein, glucose transporter GLUT1

37
Q

Ion channels

A

Pores or gates in the membrane which allow charged and polar molecules (ions and water) to move across membranes down gradients - open in response to different stimuli
HIGH THROUGHPUT millions of molecules/sec

38
Q

Ligand Gated Ion Channels

A

Responsive to Uganda
Binding of NT or hormone causes conformational changes on protein, facilitate opening of channel, rapid transport of ions down gradient
Disassociation of ligand closes channel
Glutamate receptor - Antagonist of glutamate receptor used to treat Alzheimer’s
Resting, open, desensitized

39
Q

Voltage gated ion channels

A

Responsive to membrane potential
Electrical voltage across LB large excess of - charge inside cell
Depolarization (Membrane potential goes up due to influx of + ions) triggers opening of VGIC permitting specific ions to cross down gradient
Found in excitable cells - NEURONS
Na+ channel
Topical Anesthetics - clinic to block pain - blocks Na channel to inhibit neurotransmission
Puffer Fish

40
Q

Active Transport

A

Energy dependent, protein assisted movement against concentration gradient
IMP polytopic TPT
Bind to molecule on one side of membrane and release it to other side

41
Q

Primary Active Transport

A

Uses ATP directly

42
Q

Secondary Active Transport

A

Use energy stored in a concentration gradient - coupled to primary transport system
Against gradient, protein assisted manner
Unfavorable flow of one species of ion against a gradient coupled to favorable flow of another species down a gradient
Sodium-glucose Transporters SGLT
Sodium Calcium Exchanger NCX
Antiporter
Symporter
Uniporter

43
Q

P type ATPases

A

ATP hydrolyzed, protein gets phosphorylated
Use ATP hydrolysis energy to drive against
ATP —> ADP + Phosphate
Transporters forms a COVALENT bond with the Phosphate to form enzyme-phosphate intermediate
Phosphorylation occurs on aspartate residue
Conformational changes
Na+/K+ATPase and Ca2+ATPase

44
Q

ABC Transporters

A

ATP is hydrolyzed but does not phosphorylate the transporter
Pump wide range of small molecules against gradient
Glycoproteins

45
Q

ABC Transporters and Drugs

A

Since many pathogens upregulate ABC transporters expression, many transport drugs outside the cell, so cells don’t respond to effect of drugs, leading to drug resistance
Antibiotic resistance

46
Q

Sodium Glucose Transporter 1

A

SGLT1 epithelial cells that line the SI and renal tubules
Unidirectional movement of Na+ and glucose across SI and renal tubules
Na+ goes down its gradient —> provides energy to move glucose uphill
Then set by Na+/K+ATPase

47
Q

SGLT Drugs - Invokana

A

if inhibit the SGLT it wont send glucose through the transporter into blood and will stay in the kidneys to be excreted in the urine, to lower blood sugar
Lower A1C, cause weight loss because increase ursine output

48
Q

Na+Ca2+ Exchanger NCX

A

Antiporter
Fxn - maintain low levels of intracellular Ca2+
Imports 3Na+ down gradient and exports 1 Ca2+ against gradient
Uses energy stored in Na+ gradient

49
Q

Transport Mechanisms in uptake of Dietary Monosaccharides

A

Once digested, monosaccharides derived from starch, sucrose, and lactose need to be transported from intestinal lumen to blood stream across enterocyte
Facilitated diffusion and Active transport occur here
D - Glucose and Galactose enter lumen along with Na+ by SAT by SGLT1, transported across enterocyte not blood via FD using GLUT2
Fructose only by FD down gradient using GLUT5 on apical side and GLUT2 on basal side
Na+ in by SGLT1 delivered to blood stream using PAT by Na+/K+ATPase

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