Cell Membranes And Transport

Question 1

Physiological Role of Membranes

Answer 1

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

Question 2

Structure and Composition

Answer 2

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

Question 3

Hydrophilic Head groups

Answer 3

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

Question 4

Hydrophobic tails

Answer 4

Face the interior and form the hydrophobic core of the membrane

Question 5

Lipid bilayer

Answer 5

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

Question 6

Carbohydrate molecules

Answer 6

Can be covalently attached to membrane lipids or proteins

Question 7

Phospholipids PL

Answer 7

most abundant lipids in membranes

Classified by backbone

Question 8

Glycerophospholipids

Answer 8

Glycerol backbone + phosphate + 2FA esterfied

Phosphatidyl serine/choline/inositol

Question 9

Sphingolipids SL

Answer 9

Sphingosine backbone + Long chain FA and phosphorylcholine

Sphingomyelin - most common SL

Question 10

Glycolipids

Answer 10

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

Question 11

CHL

Answer 11

Embedded in lipid Bilayer

Steroid nucleus with OH and Hydrocarbon side chain

Question 12

Lipid Rafts

Answer 12

Specialized sterol enriched microdomains in the PM

Very important for cell signaling

Question 13

Outer sheet Ex

Answer 13

Phosphatidylcholine
Sphingomyelin
Glycolipids

Question 14

Inner Sheet Intra

Answer 14

Phosphatidylinositol/serine/ethanolamine

Question 15

Membrane Protiens

Answer 15

Integral embedded
Peripheral attached
Lipid anchored tethered

Question 16

Integral Membrane Proteins

Answer 16

Firming embedded in the membrane

Stabilized by hydrophobic interactions with lipids

Question 17

Polytopic transmembrane proteins

Answer 17

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

Question 18

Peripheral proteins

Answer 18

Loosely bound to membrane through electrostatic interactions what lipids or proteins

Question 19

Lipid Anchored Proteins

Answer 19

Tethered to membranes via covalent attachment to a lipid

Question 20

Carbohydrates

Answer 20

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

Question 21

Glycocalax function

Answer 21

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

Question 22

Membrane Fluidity

Answer 22

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

Question 23

Factors that influence membrane fluidity

Answer 23

Temperature
Lipid Composition
CHL

Question 24

Temperature

Answer 24

Fluid to rigid state - melting temp

Question 25

Below melting temp | Temp < MT

Answer 25

Ordered packing and rigid

Question 26

Above melting temp

Answer 26

Fluid membranes | Temp>>>MT

Question 27

Lipid Composition Saturated FA

Answer 27

DECREASE membrane fluidity - rigid, tighter packing, reduces mobility

Question 28

Lipid Composition - Unsaturated FA

Answer 28

INCREASE membrane fluidity | Kinks in FA chain don’t allow tight packing

Question 29

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

Answer 29

CHL intercalates membrane and increases fluidity to prevent packing

Question 30

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

Answer 30

CHL stabilizes fluidity by fitting in gaps created by kinks

Question 31

Membrane Transport

Answer 31

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

Question 32

Ion Gradients

Answer 32

Greatest energy requirements Na+, K+, Cl- | Ca2+ 10,000 fold gradient

Question 33

Passive Transport

Answer 33

Energy independent | Down concentration gradients high —> low

Question 34

Active Transport

Answer 34

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

Question 35

Simple Diffusion

Answer 35

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

Question 36

Facilitated Diffusion

Answer 36

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

Question 37

Ion channels

Answer 37

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

Question 38

Ligand Gated Ion Channels

Answer 38

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

Question 39

Voltage gated ion channels

Answer 39

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

Question 40

Active Transport

Answer 40

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

Question 41

Primary Active Transport

Answer 41

Uses ATP directly

Question 42

Secondary Active Transport

Answer 42

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

Question 43

P type ATPases

Answer 43

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

Question 44

ABC Transporters

Answer 44

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

Question 45

ABC Transporters and Drugs

Answer 45

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

Question 46

Sodium Glucose Transporter 1

Answer 46

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

Question 47

SGLT Drugs - Invokana

Answer 47

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

Question 48

Na+Ca2+ Exchanger NCX

Answer 48

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

Question 49

Transport Mechanisms in uptake of Dietary Monosaccharides

Answer 49

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