THE PLASMA MEMBRANE THE PLASMA MEMBRANE It has

THE PLASMA MEMBRANE

THE PLASMA MEMBRANE It has more roles than you know

The Plasma Membrane By the of this presentation you should: v Describe the chemical composition of the plasma membrane and relate it to its function.

The Plasma Membrane By the of this presentation you should: v Describe the chemical composition of the plasma membrane and relate it to its function. v Compare the structure and function of tight junctions, desmosomes and gap junctions

The Plasma Membrane By the of this presentation you should: v Describe the chemical composition of the plasma membrane and relate it to its function. v Compare the structure and function of tight junctions, desmosomes and gap junctions v Describe the types of membrane proteins and how they relate to membrane function

The Plasma Membrane The plasma membrane defines the extent of a cell.

The Plasma Membrane The plasma membrane defines the extent of a cell. It separates the inside (intracellular fluid ) from the outside (extracellular)

The Plasma Membrane The plasma membrane is composed of proteins and phospholipids.

The Plasma Membrane The plasma membrane is composed of proteins and phospholipids. The Fluid Mosaic Model states that the proteins float in a lipid bilayer.

The Plasma Membrane

Membrane Lipids The phospholipid molecule is bipolar with a hydrophobic , nonpolar portions & a hydrophilic, polar portion

Membrane Lipids

Membrane Glycolipids These are lipids with attached sugar groups. These are located on the outer membrane

Membrane Glycolipids These are lipids with attached sugar groups. These are located on the outer membrane They have multiple roles but can serve in cell attachment and recognition.

Membrane Glycolipids

Membrane Proteins Make up about 50% of the membrane's mass There are two types: Integral Proteins

Membrane Proteins Make up about 50% of the membrane's mass There are two types: Integral Proteins & Peripheral Proteins

Membrane Proteins Integral proteins are firmly inserted into the lipid bilayer.

Membrane Proteins Integral proteins are firmly inserted into the lipid bilayer. All contain hydrophobic and hydrophilic regions.

Membrane Proteins Integral proteins are firmly inserted into the lipid bilayer. All contain hydrophobic and hydrophilic regions. Most integral proteins are involved with transport.

Membrane Proteins

Membrane Proteins Peripheral proteins are loosely attached to integral proteins and are easily detached.

Membrane Proteins Peripheral proteins are loosely attached to integral proteins and are easily detached. They serve as: Enzymes § Motor functions (movement) § Link cells together (junctions) §

Membrane Proteins Many are glycoproteins, proteins with branching sugar groups.

Membrane Proteins Many are glycoproteins, proteins with branching sugar groups. The Glycocalyx is the fuzzy carbohydrate coat that covers the cell surface. These serve an important role in cell recognition.

(a) Transport A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane. Copyright © 2010 Pearson Education, Inc.

Signal Receptor Copyright © 2010 Pearson Education, Inc. (b) Receptors for signal transduction A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell.

(c) Attachment to the cytoskeleton and extracellular matrix (ECM) Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. Copyright © 2010 Pearson Education, Inc.

(d) Enzymatic activity Enzymes Copyright © 2010 Pearson Education, Inc. A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here.

(e) Intercellular joining Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs Copyright © 2010 Pearson Education, Inc.

(f) Cell-cell recognition Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells. Glycoprotein Copyright © 2010 Pearson Education, Inc.

Membrane Junctions Three factors act to bind cells together: Glycoproteins which act like an adhesive

Membrane Junctions Three factors act to bind cells together: Glycoproteins which act like an adhesive The contours of the adjacent membranes fit together like a puzzle

Membrane Junctions Three factors act to bind cells together: Glycoproteins which act like an adhesive The contours of the adjacent membranes fit together like a puzzle Special membrane junctions are formed

Membrane Junctions There are three types of membrane junctions. Each one has a specific purpose. They are: 1. Tight Junctions: These form an impermeable junction that encircles the cell. They are made of two classes of integral proteins occludins and claudins.

Membrane Proteins

Membrane Junctions There are three types of membrane junctions. Each one has a specific purpose. They are: 2. Desmosomes: are anchoring junctions. They are scattered along the cell membrane like rivets. They have a plaque on the cyctoplasmic face and proteins called cadherins which link the two plaques together.

Membrane Proteins

Membrane Junctions There are three types of membrane junctions. Each one has a specific purpose. They are: 3. Gap Junctions: These are communicating junctions between cells. The membranes are connected by hollow cylinders call connexons. These are usually found in excitable tissues.