Cell Membrane

Cell membrane

The outer boundary of a cell and separate cell contents from the outside environment

selectively permeable, allowing some substances to cross in and out of the cell more easily than others.

phospholipid bilayer, which means that it is made of two layers of phospholipid molecules.

Proteins and other molecules are embedded in the membrane. (such as cholesterol, channel, and carrier proteins)

Fluid mosaic model

The membrane is described as being both mosaic and fluid. The membrane is fluid because the proteins are molecules that can move laterally. It is a mosaic because it is composed of many different kinds of proteins and molecules.

Phospholipid bilayer

Lipid molecules containing a phosphate form of boundary to isolate contents from the environment. It has two layers known as the bilayer.

phospholipid molecule has a head that's hydrophilic head and a hydrophobic tail. The heads are on the outside and the tiles are on the inside

restricts the passage of hydrophilic substances across the membrane..

cell membrane (cholesteral and proteins)

Cholesterol and proteins are embedded in the bilayer.

Is important for the function, integrity and stability of the membrane.

Membrane transport (passive processes)

Simple diffusion

• Tendency of substances without energy to move from areas of high concentration to areas of low concentration

Osmosis

• The diffusion of water across the selectively permeable membrane

  • hypertonic: higher concentration of solute molecules

  • hypertonic: doesn’t have much solute in it

  • isotonic: at equilibrium. equal amount of solution and liquid

Membrane transport (facilitated diffusion; channel proteins)

Diffuse across a cell membrane, water soluble molecules must pass through protein channels in the membrane. These channels provide a pathway for the hydrophilic particles to travel through across the cell membrane without coming in contact with the hydrophobic tails. small molecules can easily pass through, but large molecules cannot.

Membrane transport (facilitated diffusion; carrier proteins)

Are only open on one side of the membrane at a time. When the specific substance binds to the binding site of the protein, the protein, then changes shape and opens on the other side. The substance is then released on the side opposite to where it ended.

Membrane transport (active transport)

Requires energy in the form of ATP, as substances are transported across the membrane against the concentration gradient

Substances moved from low concentration to high concentration

Membrane transport (vesicular transport)

Movement of substances across the cell membrane and sacks called vesicles

Endocytosis: takes liquids or solids into the cell

• phagocytosis: bring solids into a cell

• Pinocytosis: bringing liquids into a cell

• Both processes involve cells, absorbing large particles buying golfing them with their cell membrane to form a vehicle within the cytosol

Exocytosis: contents of vehicle inside the cell pass to the outside

• Migrates the membrane fuses with it and releases the contents to outside the cell