(DSA2) Cell Membranes and Transport Flashcards
What is a glycocalyx and what is its function? DSA2 S19
Carbohydrate shell formed by glycoproteins and glycolipids in the outer leaflet. Functions: -protection -cell adhesion -cell identification (eg. RBCs)
What factors affect membrane fluidity and how do changes in these factors affect fluidity? DSA2 S25-26;28 LO3
Temperature: -increase in temp -> increase in fluidity -decrease in temp -> decrease in fluidity
Lipid composition: -long, saturated FAs -> decrease fluidity -short, unsaturated FAs -> increase fluidity
Cholesterol: -dampens fluidity due to temperature changes -increases fluidity when added to rigid, saturated FA membrane -decreases fluidity when added to fluid, unsaturated FA membrane
What are the main classifications of primary active transporters and what are examples of each? DSA2 S47 LO6
P-type: -hydrolyzes ATP and is phosphorylated at an ASPARTATE -examples: – Na+/K+-ATPase –Ca++-ATPase
ABC Transporter: -hydrolyzes ATP but is not phosphorylated -example: –P glycoprotein
What type of transporter is SGLT1 and what does it transport? DSA2 S57 LO6
Sodium-glucose transporter 1 2 Na+ and 1 glucose Unidirectional, secondary active transporter
What type of transporter is NCX and what does it transport? DSA2 S57 LO6
Sodium-calcium exchanger 3 Na+ and 1 Ca++ Secondary active antiporter
What is Invokana? DSA2 S59
SGLT2 inhibitor used to lower blood sugar and blood pressure by increasing urine output
How are dietary monosaccharides uptaken in the gut? DSA2 S63-65 LO7
Polysaccharides are broken down into monosaccharides (glucose, galactose, and sucrose) Across apical membrane of enterocyte: -glucose and galactose –SGLT1 via secondary active transport -sucrose –GLUT5 via facilitated diffusion Across basolateral membrane of enterocyte: -all transported by GLUT2 via facilitated diffusion
Phospholipids are
They are amphipatihic and contain: hydroppillic head group and hyrdophobic tail
The lipid bilayer serves as what?
A foundation in which a variety of lipids and proteins are embedded, attached or anchored. Carbs are covalety attached to lipids or proteins on the membrane.
Phospholipids (PLs)
Glycerophospholipids: glycerol backbone, with a phosphate and two fatty acids esterified to backbone. (examples are phosptadyl choline, phsopatidyl serine, and phospotidylinositol)
Sphingolipids (SL): sphingosine backbone, with a long chain fatty acid and phosphorylcholine (spingomylin)
What is a sphingomylenase
cuts a spingolipid: make s phosporyl choline and a ceramide
What is a Glycolipid
Glycolipids: Sphingosine backbone with carbohydrate (oligosaccharide) residue(s). Found in outer leaflet of the lipid bilayer.
Cholesterol
: Embedded in lipid bilayer. Steroid nucleus with a hydroxyl group and hydrocarbon side-chain. The latter interacts with hydrophobic tails of membrane lipids.
What are lipid rafts
- Specialized cholesterol-enriched microdomains in the PM. Look like “rafts floating in a sea of phospholipids”!
- Very important for cell signaling
What are the three membrane proteins
- integral membrane proteins
- peripheral proteins
- lipid anchored
- Integral membrane proteins
- firmly embedded in the membrane and stabilized by hydrophobic interactions with lipids.
- Polytopic Transmembrane proteins are integral membrane proteins that span the entire lipid bilayer, weave in and out of the membrane several times and interact with both the internal and external environment.
- Include transporters, ion channels and receptors
. Peripheral proteins
loosely bound to membrane through electrostatic interactions with lipids or proteins.
Lipid-anchored proteins
tethered to membranes via covalent attachment to a lipid.
- Integral membrane protein
- Peripheral protein
- Lipid anchored protein
(embedded)
(attached)
(tethered)
What is the Plasma membrane perimable to and what it is imerbale to?
It is semi permeable:
- Permeable to lipophilic molecules, move easily via diffusion e.g., steroid hormones
- Impermeable to hydrophilic/polar molecules – need a specific transport mechanism
- Membrane proteins facilitate the transport of specific molecules across the plasma membrane
NA
k
cl
ca
145/15 in
4/150 im
50/10 in
2/10 in*** 10k gradient
Simple Diffusion
- Occurs unaided
- Molecules that are small, non-polar and uncharged polar diffuse freely across the membrane
- Steeper the gradient, faster the diffusion
Facilated diffusion
–Needs the assistance of transmembrane proteins
–Molecules that are large and charged unable to cross the membrane
–Need a facilitator, i.e., proteins that can help in the movement
–Proteins function as ion channels or transporters
–Greatly increase the rate of transport
Ion channels have
high trhouput (trasnport millions of molecules per second)
Ligand-gated ion channels example:
•Antagonist of Glutamate receptor used to treat Alzheimer’s disease (Mimantine/Namenda)
P type
- ATP breaks into ADP and phosphate.
- Transporter forms a covalent bond with the phosphate to form an enzyme-phosphate intermediate.
- Phosphorylation occurs on a conserved aspartate residue.
- Undergo drastic conformational changes that facilitates the transport of ions from one side of the membrane to the other side.
Secondary active transport
•This mechanism also moves molecules against concentration gradient in an energy-dependent, protein-assisted manner.
-examples SGLT-1 or NCX
NCX
- The NCX is an antiporter.
- Functions to maintain low levels of intracellular calcium in cells.
- Imports 3Na+ down their concentration gradient and exports 1 Ca2+ against its gradient.
- Uses the energy stored in the Na+ gradient.
