Chapter 5: Structure and Function of Plasma Membranes
Fluid mosaic model:describes the plasma membrane’s structure as a mosaic of
components including phospholipids, cholesterol, proteins, glycoproteins, and
glycolipids, resulting in a fluid character.
Glycoprotein: combination of carbohydrates and proteins.
Glycolipids: Combination of carbohydrates and lipids.
A phospholipid is a molecule consisting of glycerol, two fatty acids, and a
phosphate-linked head group.
❖ A phospholipid molecule consists of a three-carbon glycerol backbone
with two fatty acid molecules attached to carbons 1 and 2, and a
phosphate- containing group attached to the third carbon.
❖ The head can form hydrogen bonds, but the tail cannot.
❖ Amphiphilic: molecule possessing a polar or charged area and a
nonpolar or uncharged area capable of interacting with both hydrophilic
and hydrophobic environments. “ dual- loving”
❖ Hydrophilic: molecule with the ability to bond with water, “water-loving”
➢ Areas of these molecules are in contact with the aqueous fluid both
inside and outside the cell.
❖ Hydrophobic: molecule that does not have the ability to bond with water.
“ water-hating”
➢ They interact with other nonpolar molecules in chemical reactions,
but generally do not interact with polar molecules.
➢ When placed in water hydrophobic molecules tend to form a ball or
cluster
Interior is hydrophobic and exterior is hydrophilic.
Integral proteins: protein integrated into the membrane structure that
interacts extensively with the membrane lipids hydrocarbon chains and
often spans the membrane.
Peripheral proteins: protein at the plasma membrane’s surface either on
its exterior or interior side.
❖ Peripheral proteins, along with integral proteins, may serve as
enzymes, as structural attachments for the cytoskeleton fibers, or
as part of the cell’s recognition sites.
, Component Location
Phospholipids Main Membrane Fabric
Cholesterol Attached between phospholipids and
between the two phospholipid layers
Integral proteins Embedded within the phospholipid layers;
may or may not penetrate through both
layers
Peripheral proteins On the phospholipid bilayer inner or outer
surface; not embedded within the
phospholipids
Carbohydrates Generally attached to protein on the
outside membrane layer
Carbohydrates
❖ They are always on the cells’ exterior surface and are bound either to proteins (
forming glycoproteins) or to lipids ( forming glycolipids)
❖ Along with peripheral proteins, carbohydrates form specialized sites o n the cell
surface that allow cells to recognize each other.
❖ If carbohydrates components of both glycoproteins and glycolipids it's know as
the glycocalyx ( meaning sugar coating)
➢ The glycocalyx is highly hydrophilic and attracts large amounts of water to
the cell’s surface.
Selectively permeable: membrane characteristic that allows some substances through.
Passive transport: method of transporting material through a membrane that does
NOT require energy.
❖ Oxygen and water can get in easily
❖ Substances move from an area of higher concentration to an area of lower
concentration
Fluid mosaic model:describes the plasma membrane’s structure as a mosaic of
components including phospholipids, cholesterol, proteins, glycoproteins, and
glycolipids, resulting in a fluid character.
Glycoprotein: combination of carbohydrates and proteins.
Glycolipids: Combination of carbohydrates and lipids.
A phospholipid is a molecule consisting of glycerol, two fatty acids, and a
phosphate-linked head group.
❖ A phospholipid molecule consists of a three-carbon glycerol backbone
with two fatty acid molecules attached to carbons 1 and 2, and a
phosphate- containing group attached to the third carbon.
❖ The head can form hydrogen bonds, but the tail cannot.
❖ Amphiphilic: molecule possessing a polar or charged area and a
nonpolar or uncharged area capable of interacting with both hydrophilic
and hydrophobic environments. “ dual- loving”
❖ Hydrophilic: molecule with the ability to bond with water, “water-loving”
➢ Areas of these molecules are in contact with the aqueous fluid both
inside and outside the cell.
❖ Hydrophobic: molecule that does not have the ability to bond with water.
“ water-hating”
➢ They interact with other nonpolar molecules in chemical reactions,
but generally do not interact with polar molecules.
➢ When placed in water hydrophobic molecules tend to form a ball or
cluster
Interior is hydrophobic and exterior is hydrophilic.
Integral proteins: protein integrated into the membrane structure that
interacts extensively with the membrane lipids hydrocarbon chains and
often spans the membrane.
Peripheral proteins: protein at the plasma membrane’s surface either on
its exterior or interior side.
❖ Peripheral proteins, along with integral proteins, may serve as
enzymes, as structural attachments for the cytoskeleton fibers, or
as part of the cell’s recognition sites.
, Component Location
Phospholipids Main Membrane Fabric
Cholesterol Attached between phospholipids and
between the two phospholipid layers
Integral proteins Embedded within the phospholipid layers;
may or may not penetrate through both
layers
Peripheral proteins On the phospholipid bilayer inner or outer
surface; not embedded within the
phospholipids
Carbohydrates Generally attached to protein on the
outside membrane layer
Carbohydrates
❖ They are always on the cells’ exterior surface and are bound either to proteins (
forming glycoproteins) or to lipids ( forming glycolipids)
❖ Along with peripheral proteins, carbohydrates form specialized sites o n the cell
surface that allow cells to recognize each other.
❖ If carbohydrates components of both glycoproteins and glycolipids it's know as
the glycocalyx ( meaning sugar coating)
➢ The glycocalyx is highly hydrophilic and attracts large amounts of water to
the cell’s surface.
Selectively permeable: membrane characteristic that allows some substances through.
Passive transport: method of transporting material through a membrane that does
NOT require energy.
❖ Oxygen and water can get in easily
❖ Substances move from an area of higher concentration to an area of lower
concentration
