Cell and Molecular Biology Exam 1 Click Questions

What cellular structures do biomembranes define in eukaryotic cells?

Plasma membrane, nucleus, vesicles (-somes), ER, golgi, mitochondria

What cellular structures do biomembranes define in prokaryotic cells?

Plasma membrane defines the cell

What are some of the functions of biomembranes?

1. Defines cell structure and compartmentalizes organelles and their functions (e.g. transcription confined to nucleus)

2. Connects to cytoskeleton to support cell structure and movement

3. Mediates exchange of biomolecules between the cell/organelle and the surrounding environment (i.e. cell-cell, cell-ECM, organelle-cytoplasm)

4. Transduces extracellular stimuli signaling

5. Site for cellular reactions (e.g. electron transport chain

Why do biomembranes form an enclosed biolayer?

Cells and organelles surround and are surrounded by aqueous solutions and membrane lipids are amphipathic. The polar head groups interact with polar water and the nonpolar tails, which cannot interact with water, interact with each other – this forms a bilayer with the head groups facing outward. The nonpolar tails cannot be exposed to water, therefore they form an enclosed structure.

What are the 3 classes of biomembrane lipids?

Phosphoglycerides, sphingolipids, sterols

Why aren’t sterols phospholipids?

Sterols do not have a phosphate group linking the nonpolar hydrophobic hydrocarbon rings to a polar hydrophilic head group

Why aren’t sphingolipids phosphoglycerides?

Glycerol 3-phosphate (glycerol) does not link the polar head group to the hydrocarbon tails

What is the most abundant type of lipid in the biomembrane?

Phospholipids or phosphoglycerides

What makes plasmalogen different from other phosphoglycerides?

Plasmalogens have an ether and ester linkage linking the fatty acid tails to glycerol. Other phosphoglycerides have two ester linkages.

What physical property of biomembranes does membrane lipid asymmetry affect? How?

Curvature. Shape of lipids (cylindrical (PC) versus cone (PE))

What physical properties of biomembranes does lipid composition affect? How?

Curvature – PC (cylindrical), PE (cone).

Thickness – cholesterol orders fatty acid tails, make them elongated, increasing thickness. Disorder fatty acid tails are shorter, decreasing thickness.

Fluidity – low cholesterol disrupts van der Waals interactions between fatty acid tails, increasing fluidity. Short and/or unsaturated (kinks) FA tails have reduced van der Waals interaction, increases fluidity. Long and/or saturated (straight) FA tails are ordered, tightly packed, decreasing fluidity.

What are examples of the functional consequences of lipid composition and asymmetry that we discussed in the class today?

Relatively high exoplasmic SM to protect intestinal cells from harsh environment; high cholesterol in myelin sheath to insulate axons; PS externalization to mark apoptotic cells for phagocytosis.

What cytosolic molecule is the major precursor in lipid biosynthesis?

Acetyl CoA

Where are most lipids synthesized?

Endoplasmic Reticulum

What are the 3 types of membrane proteins?

Transmembrane (integral), lipid anchored, peripheral

How do these 3 types of membrane proteins associate with the membrane?

1. Transmembrane – hydrophobic portion (often an alpha helix) spans the lipid bilayer. Hydrophilic portions extend extracellularly into the aqueous ECM and intracellularly into the aqueous cytoplasm. Polar residues of the hydrophilic portions can also interact with polar head groups of the lipid bilayer.

2. Lipid anchored proteins are anchored to the membrane by covalent attachment to a GPI anchor or to a fatty acid (myristate, palmitate, farnesyl or geranylgeranyl) imbedded in the membrane.

3. Peripheral membrane proteins interact directly with the polar head groups of the lipid bilayer or interact with a transmembrane or lipid-anchored protein.

Give an examples of how you could exploit biomembrane properties for drug delivery?

1) Incorporate hydrophobic drug into liposome bilayer to mediate transport through blood.
2) Load hydrophilic drugs into the core of liposome that is engineered to target specific exoplasmic peripheral or transmembrane protein of target cell type.

What is the advantage of having biomembranes function as permeability barriers?

1) Keep biomolecules partitioned
2) Can use biomolecule partitioning to regulate cellular processes.

What does lipophilic mean?

Soluble in lipid

How does the lipophilicity of a molecule affect the membrane permeability and diffusion?

The more lipophilic, the easier it permeates and faster it diffuses across a lipid bilayer.

How can lipophilicity be measured?

Partition coefficient = [x] lipid/ [x] water

Which of these molecules is lipophilic and why?

EtOH, hydrophobic.

How do large hydrophilic molecules get across a biomembrane?

Transmembrane transport proteins

Which direction do molecules naturally want to flow across a membrane?

Down their concentration gradient.

What does it take for molecules to flow against their gradient?

Energy

What types of gradients are established across membranes?

Chemical (solute concentration), elelctrochemical

What are the 3 main types of transport proteins?

ATPase, channel, transporters

Which transporter uses ATP hydrolysis to transport ions and which direction do the ions flow?

ATPase; against the electrochemical gradient

Which transporters do not use energy to transport biomolecules and why is energy not required?

Channels and Uniport Transporters. Energy is not required because molecules are transported down the concentration gradient.

Define uniporter

Transport molecules down electrochemical gradient. Does not require energy.

Define antiporter

Two molecules transported through the same transporter, but in different directions. One molecule is transported down its electrochemical gradient, providing energy for the other molecule to be transported against its electrochemical gradient.

Define symporter

Two molecules transported through the same transporter in the same direction. One molecule is transported down its electrochemical gradient, providing energy for the other molecule to be transported against its electrochemical gradient.