Cell Mem Basics And Mem Proteins

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Overton

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1890 used hypertonic shrinkage of plat cells to estimate composition of plasma membrane. By assumption that adding permeable compounds would stop hypertonic shrinkage and like dissolves like, concluded that membrane is completely lipid (false)

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How does adding permeable compounds affect hypertonic shrinkage

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Permeable compounds prevent hypertonic shrinkage. Allows solute concentration to balance out so the cell will not shrink because adding any solute to water lowers the water concentration

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Plant cell in hypertonic solution

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SHRINKAGE

Higher [H2O] inside the cell than out so water moves out of the cell

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Plant cell in isotonic solution

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No swelling of shrinking. Water concentration is equal inside and outside of cell.

Ideal for RBCs

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Plant cell in hypotonic solution

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Cell expands but because of cell wall, plant cells do not show hypotonic swelling. Lower [H2O] inside of cell so water moves into cell.

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2 types of membrane proteins

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Soluble

Membrane bound (Peripheral or Integral)

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Integral membrane proteins

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Membrane- bound. Many are spanning proteins (go from outside to inside of cell)

Ends facing the polar heads have polar aa r groups, middle have nonpolar r groups

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(structurally) what determines if a membrane protein is spanning or integral?

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amino acid sequence - are side chains polar or nonpolar in in what parts

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Integral Non- Spanning membrane proteins

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Hydrophobic- completely within the membrane

Amphipathic- both in and out of mem

Held onto membrane by ionic bonds

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How to identify Integral Protein

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Does NOT come off the membrane with high salt after centrifugation

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Separate Integral membrane proteins from the membrane

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Detergents!

Detergent- solublized proteins are soluble in water and removed from the membrane

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Peripheral membrane

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Don't penetrate mem bilayer, associated to mem by ionic bonding

Can associate with another protein or with membrane lipids

If a protein in bound to a lipid, it must be positive because phosphates in the lipid bilayer are only negative

Protein bound to another protein can be + or -

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Identify a peripheral membrane

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Comes off of the membrane with high salt

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Add high salt to a bunch of membranes and proteins, centrifuge at 100,000g for 1 hour. How to the results indicate what types of proteins were on the membranes?

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Protein in pellet- Integral

Protein in supernatant- Peripheral

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Add detergent to a bunch of membranes and proteins, centrifuge at 100,000g for 1 hour. How do the results indicate what types of proteins were on the membranes?

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Protein in pellet- Peripheral

Protein in supernatant- Integral

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2 Types of membrane carbohydrates

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Membrane carbs are on but not in the membrane

1. Glycoprotien

2. Glycolipid

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Glycoprotein

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Protein with covalently attached sugars (type of mem carb)

When on membrane, sugars face outside of cell (can be associated with endomembrane system)

Most cell receptors are glycoproteins

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Glycolipid

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Lipid with covalently attached sugars (type of mem carb)

Sugars face outside of cell when on plasma membrane and can be cell receptors

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Is the composition of all cells the same or different

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Different depending on cell function. Looking at ratios of protein, lipid, and carbs can indicate the type of cell

Cell composition differ for different things in different organisms (liver cells in a cow are different from liver cells in a human)

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General idea: Why would a cell have more proteins than other cells (name cell function)

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ex. mitochondria membrane cells and chloroplast membranes have higher degrees of protein

Endosymbiont theory- these cells existed on their own at one point, require more protein to live independently

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General idea: Why would a cell have more lipids than other cells (name cell function)

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ex. nerve myelin cells are mostly lipid for electrical conductivity

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Are the strands of the lipid bilayer identical

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Usually not (inner monolayer differs from outer monolayer)

Depends on the proteins attracted by charged head groups