Cells(membrane) Dla

Question 1

What are the3 major classes of lipids?

Answer 1

• phospholipids
• cholesterol
• glycerolipids

Question 2

What are the types of lipids?

Answer 2

About 50% membrane mass

• amphipathic
  
  • hydrophilic
    
    • water-loving (polar head)
  • hydrophobic (water-fearing) nonpolar tail

Question 3

What are the classifications of proteins in the cell membrane ?

Answer 3

About. 50% membrane mass

2 major classes:

• integral membrane
  
  • embedded in or pass through the lipid bilayer

Peripheral membrane
- associate with integral membrane proteins

Question 4

What are phospholipids?

Answer 4

Most abundant membrane lipid

• phosphatidyl serine
• phosphatidylethanolamine

Question 5

What is the effect of cholesterol on the membrane?

Answer 5

Intercalates between phospholipids

Affects membrane fluidity in temperature dependent manner

Question 6

What is the effect of glycolipids in the membrane?

Answer 6

• constitute ~5% of lipid molecules
• Sugar containing lipid molecules
• found exclusively in outer monolayer

Question 7

What are the types of membrane proteins?

Answer 7

1. Integral membrand proteins
   Transmembrane
   -single and multi passAnchored
   • alpha helix
   • lipid chain
   • oligosaccharide linker
2. Peripheral membrane proteins
   • noncovalent association with integral membrane proteins

Question 8

What are the 6 general categories of integral membrane proteins?

Answer 8

1. Pumps/carriers/ transporters
   Transport specific ions across the membrane
   -sodium
   -potassium

Transport metabolic precursors

• amino acids
• sugars

2. Channels
   - transport of ions, small molecules and water
   
   • passive diffusion

• aqua porins
  
  • water
• gap junctions
  
  • passage of ions, small molecules between adjacent cells

3. Receptors
4. Linkers
5. Enzymes
6. Structural proteins

Question 9

What is a glycocalyx?

Answer 9

Card rich zone on the cell surface

• glycolipids
• glycoproteins
• proteoglycans

Question 10

What are the functions of the glycocalyx ?

Answer 10

-Helps establish the micro environment at cell surface

• protection
  
  • mechanical storage
  • chemical storage

-cell recognition

• cell to cell interaction
  
  • lectins
    
    • carbohydrate binding proteins

Question 11

Describe the lipid bilayer

Answer 11

• hydrophilic head ground face exterior and cytosol

- fatty acid tails create a hydrophobic core

Question 12

Described the asymmetry of the membrane

Answer 12

• specific phospholipids localize to outer and inner leaflets
• phosphatidylserine localized to the inner leaflet
  
  • eznymatically transferred to the outer leaflet during programmed cell death
  • triggers phagocytic removal of dying cells

Question 13

Summarize the fluid mosaic model

Answer 13

-lipids and proteins have ability to move within the plane of the membrane

Question 14

Describe the fluidity of the membrane

Answer 14

-membrane lipids and proteins are mobile

• cholesterol serves to stabilize the membrane
  
  • reduce membrane fluidity

Question 15

Describe the selective permeability of the membrane

Answer 15

Permeable

• hydrophobic, non-polar, uncharged
  
  • oxygen, carbon dioxide

Less permeable

• small, polar, uncharged
• water

Highly impermeable

• charged (ions)
• polar
• charged

Question 16

Summarize Transmembrane proteins

Answer 16

• channels & transporters

- increase the permeability of the membrane to molecules that cannot cross the lipid bilayer

Question 17

What is exocytosis?

Answer 17

Substance exits the cell by the fusion of a vesicle with the plasma membrane

Question 18

What is endocytosis ?

Answer 18

Substance enters the cell by a vesicle formed from the plasma membrane

Question 19

Contrast the 3 types of endocytosis

Answer 19

1. Receptor mediated
   - cargo-specific
   - Clathrin dependent
2. Pinocytosis
   - non-specific
   - clathrin-independent
3. Phagocytosis
   - clathrin-independent
   - actin-dependent

Question 20

Contrast the types of exocytosis

Answer 20

Regulated

• secretory cells
  
  • endocrine
  • exocrine
  • neurons
• stimulus
• CA2+ influx
• fusion of secretory cvesicles with plasma membrane

Constitutive- substance for export continuously delivered to plasma membrane

Question 21

Describe the functioning of receptor mediated endocytosis

Answer 21

• selective uptake of large molecules and particles
• clathrin-dependent
• Clathrin costed pits
  
  • Clathrin molecules interact with cargo receptors via Adaptin
  • Clathrin forms a basket-like cage
    
    • drives vesicle formation
  • Dynamin mediates the vesiclepinching off from the plasma membrane
    
    • GTPase

Question 22

In receptor mediated endocytosis, in what cases are receptors recyc’ed, with the ligand degraded ?

Answer 22

• low density lipoprotein (LDL) receptor
• insulin-glucose transporter
• other peptide hormone & their receptors

Question 23

In receptor mediated endocytosis, in what cases are receptor and ligand recycled?

Answer 23

• iron, transferrin& transferrin receptor

- major histocompatibility complex I & II

Question 24

In receptor mediated endocytosis, in what cases are receptor and ligand degraded?

Answer 24

-epidermal growth factor (EGF) & receptor

Question 25

In receptor mediated endocytosis, in what cases are receptor & ligand transcytosis?

Answer 25

• secretion of immunoglobin (secretory IgA) into saliva

- secretion of maternal IgG into milk

Question 26

What is vesicle targeting?

Answer 26

-Rab-GTPase interaction with tethering proteins

• docking complex
  
  • Rab-GTPaseand receptor immobilize the vesicle near target membrane
• Accurate targeting
  
  • vesicle specific membrane protein= v-SNARE
  -target-specific membrane protein= t-SNARE

Question 27

What is an endosome ?

Answer 27

Membrane-enclosed structure associated with endocytosis pathway

Question 28

Contrast the early and late endosome pathway

Answer 28

Early endosome
- functions to sort and recycle proteins

Late endosome
-receives proteins for degradation

• receives newly synthesized lysosomal enzymes from the Golgi
• matures into a lysosome

Question 29

Explain the functioning of pinocytosis

Answer 29

• cell drinking
• non-specific ingestion by small vesicles -constitutive
• invagination of plasma membrane
  
  • no receptor proteins
  • Clathrin-independent
• vesicle pinches-off
• fusion with lysosome

Question 30

Explaine the functioning of phagocytosis

Answer 30

Ingestion of large particles

• microorganisms
• apoptotic cells
• non-biological materials

Generally performed by specialized phagocytes

• macrophage
• neutrophil

Particle binds to plasma membrane receptor (e.g. antibodies)

Extension of pseudopods
-dependent on actin microfilament polymerization

Phagosome fuses with lysosome
-digestion

Residual body-indigestible substances