plasma membranes

Question 1

what is the structure of plasma membrane

Answer 1

• Membrane Lipids
• Membrane Proteins
• Membrane Carbohydrates
  Phospholipid
• 2 fatty acid chains
• Phosphoglycerates
• Phosphorylated alcohol: choline
• glycolipids - Contain a carbohydrate (sugar)
• glycoproteins
• cholesterol - 50% of the lipid membrane

Question 2

describe what consist in membrane proteins

Answer 2

Integral Membrane Proteins
• Single or multi-pass
• Partially embedded
(Prostaglandin H2 synthase)
• Non-covalent bonds
• Transmembrane helix

Peripheral Membrane Proteins
• Located outside or inside the cell
• Non-covalent bonds
• Interacts with integral proteins or polar head
groups

Lipid-anchored Membrane Proteins
• Covalent bonds to a lipid molecule
• Example of GPI (glycerophosphoinositol) e.g Alkaline
phosphatase, Glypican

Question 3

what consists of membrane carbohydrates?

Answer 3

endothelial layer

Carbohydrates associated with both
membrane lipids Glycolipids and proteins
Glycoproteins
• Carbohydrates are exclusively presented
on the extracellular side of the plasma
membrane (asymmetry)
• 2-10% of the membrane content (up to
8% in red blood cells)

Question 4

what is the fluid mosaic model?

Answer 4

-individual phospholipids and proteins can move side-to-side
within the layer
- Pattern produced by the lipids, scattered protein and carbohydrates
- Fatty acid composition and saturation influences fluidity
- Cholesterol modulates membrane fluidity

Question 5

what are the roles of cholestrol?

Answer 5

• regulates fluidity
• At low temperatures cholesterol prevents phospholipid tight packing and maintains fluidity

(increases membrane fluidity at low temperature)
- At warm temperatures cholesterol restricts phospholipid diffusion
(prevents membranes becoming too fluid at high temperature)

• sterols regulate O2 entry into eukaryotic cells and organelles
  • sterols act as O2 sensors across all eukaryotic life forms
  • sterols serve as a primitive cellular defence against O2 (including reactive oxygen species).
  Sterols may have evolved in eukaryotes as an adaptive response to the rise of terrestrial O2

Question 6

what are the functions of the plasma membranes

Answer 6

Lipids:
Establish semi-permeable barrier between external and internal aqueous environment
Provide environment in which proteins can dissolve and function.
Cell-Cell Recognition (Surface Identity Markers)

Proteins:
Cell-Cell Recognition (Identity)
Signal Transduction (Receptor)
Enzymatic activity
Attachment (cytoskeleton or extracellular matrix)
Intercellular junctions (Adhesion)

Question 7

how does cell-cell recognition work

Answer 7

• RBCs carry glycolipids that determine blood type : A, B, O or AB
• Play a key role in cell-cell recognition
  • Basis for rejection of foreign cells by immune system
  • Cells of the immune system express pattern recognition
  receptors (PRRs; e.g. toll-like receptors (TLRs), which
  recognize foreign lipoproteins, peptidoglycans, CpG-rich
  DNA, glycoproteins and phospholipids from bacteria,
  protozoan parasites and fungal spores.
  • Basis for innate immunity and defences against infection

Question 8

define all transport methods in plasma membrane in detail

Answer 8

simple diffusion

• no energy needed
• passive
• from high conc gradient to low conc gradient

facialted

• no energy needed
• passive
• from high conc gradient to low conc gradient
• through a channel protein or carrier

active transport
- ATP needed
- from low conc to high conc
- through channel proteins or carrier
- Protein conformational
changes
Na+ enters with Na+
-Glucose symporter (SLAC5A1/2) and is pumped out by Na+ -K +
-ATPase to maintain the Na+ concentration gradient

osmosis
- water diffuses across a membrane from the region of
lower solute concentration to the region of higher solute Concentration to balance the solute concentrations

Hypotonic solution : Solute concentration outside cell < inside the cell = Cell gains water - lyse

Isotonic solution : Solute concentration outside cell = inside cell = no net water movement

Hypertonic solution : Solute concentration outside cell > inside cell = Cell loses water - shrivels

Question 9

what is the the Clinical significance of the Plasma Membrane components

Answer 9

Disorders in ion transport can result in severe clinical consequences
Cystic Fibrosis is due to defect in the Cl- channel CFTR in epithelial cells
Lung congestion and infections
Dehydrated mucus leading to chronic
lung infections and inflammation, which
destroy pulmonary function)