Plasma Membrane

a&p 1

Plasma Membrane

• Outer boundary of the cell

• Separates Intracellular fluid from extracellular fluid

• Determines what goes into and out of the cell (selectively permeable)

Membrane Lipids (Phospholipids)

75% Phospholipids

• Arranged in a bilayer
• Hydrophilic (polar, charged) “head”
• Hydrophobic (nonpolar, uncharged) “tail”
• Modified triglyceride

Membrane Lipids (Cholesterol)

•20% of the membrane lipids

•Holds phospholipids still and can stiffen membrane

Membrane Lipids (Glycolipids)

•5% of the membrane lipids

•Phospholipids with short carbohydrate chains on extracellular face

•Contribute to glycocalyx—carbohydrate coating on cell surface

Membrane Protein (Integral)

Firmly inserted in lipid bilayer
Have hydrophobic and hydrophilic regions
Most are transmembrane

Membrane Protein (Peripheral)

Loosely attached to the outer or inner
surfaces of the integral proteins

Receptors

•bind chemical signals to trigger internal changes

•May cause production of a second messenger within cell receiving chemical message

Enzymes

catalyze reactions including digestion of molecules, production of second messengers

Channel proteins

allow hydrophilic solutes and water to pass through membrane (Some are always open, called leak channels, and some are gates (gated channels) that open only when triggered)

Ligand-gated channels (Channel Protein)

respond to chemical messengers

Voltage-gated channels (Channel Protein)

respond to charge changes

Mechanically gated channels (Channel Protein)

respond to physical stress on cell

Carriers

bind solutes and transfer them across membrane

Pumps

carriers that consume ATP (energy)

Cell-identity markers

glycoproteins acting as identification tags

Cell-adhesion molecules (CAMs)

mechanically link cell to another cell and to extracellular material

Second Messengers

stimulation of a cell by epinephrine

Glycocalyx

carbohydrate moieties of glycoproteins and glycolipids external to plasma membrane

Microvilli

extensions (1 to 2 μm) of the membrane that serve to increase surface area

Cilia

hair-like processes 7 to 10 μm long (move within saline layer at cell surface; mucus “floats” atop this layer)

Flagellum

whiplike structure (cell’s surface) Tail of a sperm is only functional flagellum in humans