[A&P] Cell Membranes

Main function of the cell membrane

Also known as the plasma membrane, this separates the inner contents of a cell from its eterior environment.

General structure of the cell membrane

Pliable structure composed primarily of back-to-back phospholipids (a “bilayer”). Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions.

hydrophilic molecule

“water loving”

Are phosphate heads hydrophilic? Why or why not?

• The phosphate group is negatively charged, making the head polar and hydrophilic

• The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments.

• Can dissolve in water

• Some the tail is positively charged, making it an amphipathic molecule

hydrophobic molecule

Molecule that repels and is repelled by water.

The cell membrane consists of __ layers of phospholipids

Two adjacent layers: The lipid tails of one layer face the lipid tails of the other layer, meeting at the interface of the two layers.

Intracellular fluid (ICF)

the fluid interior of the cell.

Extracellular fluid (ECF)

The fluid environment outside the enclosure of the cell membrane.

Interstitial fluid (IF)

The term given to extracellular fluid not contained within blood vessels.

Membrane Proteins

• The lipid bilayer forms the basis of the cell membrane, but it is peppered throughout with various proteins.

• Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein

integral protein

Protein that is embedded in the membrane.

channel protein

Example of an integral protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell.

Cell recognition proteins,

Serve to mark a cell’s identity so that it can be recognized by other cells.

Receptor

type of recognition protein that can selectively bind a specific molecule outside the cell, and this binding induces a chemical reaction within the cell.

ligand

• The specific molecule that binds to and activates a receptor. Some integral proteins serve dual roles as both a receptor and an ion channel.

• One example of a receptor-ligand interaction is the receptors on nerve cells that bind neurotransmitters, such as dopamine.

  • When a dopamine molecule binds to a dopamine receptor protein, a channel within the transmembrane protein opens to allow certain ions to flow into the cell.

glycoprotein

A protein that has carbohydrate molecules attached, which extend into the extracellular matrix.

glycocalyx

• Is a fuzzy-appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane.

• The glycocalyces found in a person’s body are products of that person’s genetic makeup.

  • They give each of the individual’s trillions of cells the “identity” of belonging in the person’s body.

    • This identity is the primary way that a person’s immune defense cells “know” not to attack the person’s own body cells,

    • but it also is the reason organs donated by another person might be rejected.

The role(s) of glocalyx

• It may gave molecules that allow the cell to bind another cell

• May have molecules that allow the cell to bind to another cell

• It may contain receptors for hormones

• It might have enztmes t break down nutrients

Peripheral proteins

• Typically found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein

  • Some peripheral proteins on the surface of intestinal cells, for example, act as digestive enzymes to break down nutrients to sizes that can pass through the cells and into the bloodstream.

True or false: the cell membrane can regulate the concentration of substances inside the cell.

True

Passive transport is

the movement of substances across the membrane without the expenditure of cellular energy.

Active transport

The movement of substances across the membrane using energy from adenosine triphosphate (ATP).

Concentration gradient

• The difference in concentration of a substance across a space.

• Molecules (or ions) will spread/diffuse from where they are more concentrated to where they are less concentrated until they are equally distributed in that space.

Diffusion

• The movement of particles from an area of higher concentration to an area of lower concentration.

• Whenever a substance exists in greater concentration on one side of a semipermeable membrane, such as the cell membranes, any substance that can move down its concentration gradient across the membrane will do so.

Simple diffusion

The mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated is a form of passive transport