Chapter 5 - Plasma Membrane

6 Different types of functions of proteins in a plasma membrane:

- Attachment to the cytoskeleton and ECM - Signal Reception and relay - Enzymatic activity - Cell-cell recognition - Intercellular joining - Transport

2 Types of Transport Proteins

1) Channel proteins - passageway 2) Carrier proteins - Binds passageway, changes shape and releases transported molecule inside cell.

Active Transport

A cell expends energy to move solute against its concentration gradient. ATP supplies the energy for most active transport. Why? Na-K pump Allows cell to maintain internal solute concentration different from that of external fluid extracellular.

Phospholipid

A lipid made up of glycerol joined to 2 fatty acids and a phosphate group, giving the molecule two non polar hydrophobic tails and a polar hydrophilic head. Phospholipids form bilayers that function as biological membranes.

"Down the concentration gradient"

A net movement from the side of the membrane where molecules are more concentrated to the side where they are less concentrated. High solute to low solute concentration

Selectively permeable

Allows smaller molecules to pass (non polar), while not allowing other larger ones (Ions, large mol).

Osmosis

Diffusion of water across a selectively permeable membrane. Low concentration of solute to High concentration of solute OR Area with more water to less water.

Glycoprotein

Glycoproteins may serve as ID tags that are recognized by membrane proteins of other cells.

"Against the concentration gradient"

Low solute concentration to high solute concentration.

Junction protein

Membrane proteins may form intercellular junctions that attach adjacent cells.

Hypotonic (less)

Outside solute < Inside solute Flow from outside to inside *Solute concentration inside the cell is HIGHER*

Hypertonic (more)

Outside solute > Inside solute Flow from inside to outside *Solute concentration inside the cell is LOWER*

Attachment Protein

Proteins that attach to the extracellular matrix and cytoskeleton help support the membrane and can coordinate external and internal changes.

Transport Protein

Provides a channel for the diffusion of specific solute across a membrane. A type of passive transport.

Isotonic

Same concentration in and out of the cell. When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell.

Receptor Proteins

Signaling molecules bind to receptor proteins which relay the message by activating other molecules inside the cell.

Tonicity

The ability of a surrounding cell to cause a cell to gain or lose water. Depends on the concentration of solutes outside related to inside the cell.

cell membrane

The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. Small, non polar molecules may pass through (CO2 and O2). The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded proteins.

cell membrane function

The main functions of the cell membrane are: 1- To maintain the physical integrity of the cell - that is to mechanically enclose the contents of the cell. 2- To control the movement of particles e.g. ions or molecules, into and out of the cell.

Facilitated Diffusion

The passage of a substance (polar or ionic/charged) through a specific transport protein across a membrane down its concentration gradient. A type of passive transport. Type that use facilitated diffusion: sugars, amino acids, ions, even water (aquaporins = protein channel).

Phospholipid Bilayer

The phospholipids in the plasma membrane are arranged in two layers, called a phospholipid bilayer. Each phospholipid molecule has a head and two tails. The head "loves" water (hydrophilic) and the tails "hate" water (hydrophobic). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outwards, toward either the cytoplasm or the fluid that surrounds the cell. Molecules that are hydrophobic can easily pass through the plasma membrane, if they are small enough, because they are water-hating like the interior of the membrane. Molecules that are hydrophilic, on the other hand, cannot pass through the plasma membrane—at least not without help—because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane. hydrophobic tails hydrophilic heads

Diffusion

The tendency of particles of any substances to spread out into the available space. Example: CO2 and O2, small, non polar.

Active Transport protein

Transport proteins allow specific ions or molecules to enter or exit the cell. Use of energy (ATP)

Passive Transport

a movement of ions and other atomic or molecular substances across cell membranes without need of energy input. Cell does not have to expend energy to diffuse across its membrane.

Channel Protein

a protein that allows the transport of specific substances across a cell membrane.

Enzymes in membrane

proteins grouped to carry out sequential reactions.

Hydrophilic heads

water loving (phosphate part - non polar)

Hydrophobic tails

water-fearing (fatty acid part - polar)