Polar, hydrophilic substancescannotpass directly through the lipid bilayer.

Simple diffusion does not require the use of transport proteins.

Nonpolar, hydrophobic molecules diffuse directly through the lipid bilayer.

Diffusion - net movement of substances from an area of high concentration to low concentration.

In passive transport substances cross the membrane by diffusion.

Transport of Substances Across the Plasma Membrane (PM)

The cell expends energy to transport water soluble substances against their concentration gradient.

allow water soluble substances (small polar molecules and ions) to pass through the membrane without any energy cost.

Example: The binding of insulin to insulin receptors causes the cell to put glucose transport proteins into the membrane.

Binding triggers a change inside the cell.

Signal transduction (receptor) proteinsbind hormones and other substances on the outside of the cell.

This is especially important on the membranes of organelles.

Intercellular junction proteins - help like cells stick together to form tissues.

The cytoskeleton attaches to integrins on the cytoplasmic side of the membrane.

Integrins are a type of integral protein Glycolipids also play a role in cell recognition.Carbohydrate chains vary between species, individuals, and even between cell types in a given individual.5-1a Glycolipid Integrin Phospholipid Microfilaments of cytoskeleton CholesterolĬell-cell recognition proteins - identify type of cell and identify a cell as “self” versus foreign Glycoproteins and glycolipids are proteins/lipids with short chain carbohydrates attached on the extracellular side of the membrane.Ĭarbohydrate of glycoprotein Glycoprotein Fig.Peripheral proteins are on one side or the other of the membrane.Most of the membrane’s functions are accomplished by the embedded proteins.Phospholipid Bilayer Label the: Hydrophilic heads Hydrophobic tails Membrane Structure All membranes are phospholipid bilayers with embedded proteins.

Membrane Structure Phospholipid Phospholipids are the major structural component of membranes. Most protein and phospholipid molecules can move laterally.Proteins and other molecules are embedded in a framework of phospholipids.Internal membranes provide structural order for metabolism.Controls traffic of molecules in and out.forms a boundary between a living cell and its surroundings.Membranes organize the chemical activities of cells.

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