(DSA2) Cell Membranes and Transport

Question 1

What is a glycocalyx and what is its function? DSA2 S19

Answer 1

Carbohydrate shell formed by glycoproteins and glycolipids in the outer leaflet. Functions: -protection -cell adhesion -cell identification (eg. RBCs)

Question 2

What factors affect membrane fluidity and how do changes in these factors affect fluidity? DSA2 S25-26;28 LO3

Answer 2

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

Question 3

What are the main classifications of primary active transporters and what are examples of each? DSA2 S47 LO6

Answer 3

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

Question 4

What type of transporter is SGLT1 and what does it transport? DSA2 S57 LO6

Answer 4

Sodium-glucose transporter 1 2 Na+ and 1 glucose Unidirectional, secondary active transporter

Question 5

What type of transporter is NCX and what does it transport? DSA2 S57 LO6

Answer 5

Sodium-calcium exchanger 3 Na+ and 1 Ca++ Secondary active antiporter

Question 6

What is Invokana? DSA2 S59

Answer 6

SGLT2 inhibitor used to lower blood sugar and blood pressure by increasing urine output

Question 7

How are dietary monosaccharides uptaken in the gut? DSA2 S63-65 LO7

Answer 7

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

Question 8

Phospholipids are

Answer 8

They are amphipatihic and contain: hydroppillic head group and hyrdophobic tail

Question 9

The lipid bilayer serves as what?

Answer 9

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.

Question 10

Phospholipids (PLs)

Answer 10

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)

Question 11

What is a sphingomylenase

Answer 11

cuts a spingolipid: make s phosporyl choline and a ceramide

Question 12

What is a Glycolipid

Answer 12

Glycolipids: Sphingosine backbone with carbohydrate (oligosaccharide) residue(s). Found in outer leaflet of the lipid bilayer.

Question 13

Cholesterol

Answer 13

: Embedded in lipid bilayer. Steroid nucleus with a hydroxyl group and hydrocarbon side-chain. The latter interacts with hydrophobic tails of membrane lipids.

Question 14

What are lipid rafts

Answer 14

• Specialized cholesterol-enriched microdomains in the PM. Look like “rafts floating in a sea of phospholipids”!
• Very important for cell signaling

Question 15

What are the three membrane proteins

Answer 15

• integral membrane proteins
• peripheral proteins
• lipid anchored

Question 16

1. Integral membrane proteins

Answer 16

• 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

Question 17

. Peripheral proteins

Answer 17

loosely bound to membrane through electrostatic interactions with lipids or proteins.

Question 18

Lipid-anchored proteins

Answer 18

tethered to membranes via covalent attachment to a lipid.

Question 19

1. Integral membrane protein
2. Peripheral protein
3. Lipid anchored protein

Answer 19

(embedded)

(attached)

(tethered)

Question 20

What is the Plasma membrane perimable to and what it is imerbale to?

Answer 20

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

Question 21

NA

k

cl

ca

Answer 21

145/15 in

4/150 im

50/10 in

2/10 in*** 10k gradient

Question 22

Simple Diffusion

Answer 22

• Occurs unaided
• Molecules that are small, non-polar and uncharged polar diffuse freely across the membrane
• Steeper the gradient, faster the diffusion

Question 23

Facilated diffusion

Answer 23

–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

Question 24

Ion channels have

Answer 24

high trhouput (trasnport millions of molecules per second)

Question 25

Ligand-gated ion channels example:

Answer 25

•Antagonist of Glutamate receptor used to treat Alzheimer’s disease (Mimantine/Namenda)

Question 26

P type

Answer 26

• 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.

Question 27

Secondary active transport

Answer 27

•This mechanism also moves molecules against concentration gradient in an energy-dependent, protein-assisted manner.

-examples SGLT-1 or NCX

Question 28

NCX

Answer 28

• 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.