Cell Membranes And Transport - DSA

Question 1

Role of Cell Membranes

Answer 1

• Protective barrier
• selective permeability
• transport

Question 2

Membrane composition

Answer 2

• Lipid Bilayer. Hydrophobic core hydrophilic surfaces
• Carbohydrates are covalently attached to some membrane lipids
• has lipds and proteins attached.

Question 3

Phospholipids

Answer 3

• Most abundant lipids in biological membranes

Question 4

Describe the two types of phospholipids and give examples of each.

Answer 4

1. Glycerophospholipids: glycerol backbone + phosphate + 2 FA’s
   - Phosphatidylserine, phosphatidylcholine.
2. Sphingolipids: sphingosine backbone + long chain FA + phosphorylcholine.
   - Sphingomyelin

Question 5

Function and products of sphingomyelinase

Answer 5

• cleaves sphingomyelin

- cleavage results in phosphorylcholine + Ceramide

Question 6

Describe the structure of glycolipids. Where are they found?

Answer 6

• Sphingosine backbone with carbohydrate residues

- found in the outer leaflet

Question 7

Location of Membrane Lipids. What is found in the inner sheet vs. outer sheet?

Answer 7

1. Inner: phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine.
2. Outer: Phosphatidylcholine, sphingomyelin, glycolipids.

Question 8

What are the three types of membrane proteins and how are they held to the membrane?

Answer 8

1. Integral membrane proteins: hydrophobic interactions
2. Peripheral proteins: electrostatic interactions w/ lipids or proteins
3. Lipid-anchored proteins: covalently tethered to lipid.

Question 9

What is the glycocalyx and what are its 3 functions?

Answer 9

Carbohydrate molecules covalently attached to proteins and lipids that face extracellular space

1. Protection
2. Cell adhesion
3. Cell identification.

Question 10

Factors that influence fluidity:

Answer 10

1. Higher temperature = higher fluidity
2. Saturated lipids decrease fluidity. Shorter chains increase fluidity
3. Cholesterol: makes stiff membranes fluid and fluid membranes stiff.

Question 11

Ion Gradients of Na, K, and Cl. Which is higher inside or outside of the cell?

Answer 11

• Na = higher outside cell
• K = higher inside cell
• Cl = higher outside of the cell

Question 12

Types of Passive transport:

Answer 12

• Simple Diffusion = unaided. Small non-polar molecules diffuse freely across the membrane.
• Facilitated diffusion = needs a facilitator like channel or transporter

Question 13

Types of Active Transport

Answer 13

• Primary: uses ATP directly

- Secondary: uses energy stored in concentration gradient.

Question 14

Describe a P type ATPase

Answer 14

• Type of primary active transport.

- atp is hydrolyzed, protein gets phosphorylated

Question 15

Describe ABC transporters

Answer 15

• atp is hydrolyzed, does NOT phosphorylate the transporter

Question 16

Describe Secondary Active Transport

Answer 16

• energy dependent, moves molecules against concentration gradient.
• source of energy is not ATP hydrolysis.
• unfavorable flow of 1 species tied to favorable flow of another species.
• EX: SGLT, NCX

Question 17

Describe Sodium Glucose Transporter 1

Location, function, molecule it moves

Answer 17

• located in epithelial cells of intestine and renal tubules
• mediates unidirectional movement of Na+ (favorable) and glucose (unfavorable) across small intestine and renal tubule.
• Na+ gradient is reset by Na+/K+-atpase.
• type of secondary active transport.

Question 18

Na+/Ca+ exchanger (NCX) function, location,etc.

Answer 18

• Antiporter
• imports 3 Sodium down their gradient and exports 1 calcium against its gradient.
• Type of Secondary active transport

Question 19

Describe transport of glucose from lumen of intestines to blood.

Answer 19

• Glucose & galactose move against their gradient with sodium into the enterocyte using SGLT1.
• Sodium is returned to blood via Na/KATPase
• glucose, galactose, and fructose (brought in by glut5 via facilitated diff) are transferred to blood via GLUT2 (facilitated diffusion)