CHAPTER 2
The different substances that make up the cell are collectively called protoplasm.
Protoplasm is composed mainly of five basic substances—
water, electrolytes, proteins, lipids, and carbohydrates.
Important ions in the cell include potassium, magnesium, phosphate, sulfate, bicarbonate, and
smaller quantities of sodium, chloride, and calcium.
Proteins can be divided into two types:
1. structural proteins- Structural proteins are present in the cell mainly in the form of long
filaments that are polymers of many individual protein molecules.
2. functional proteins- The functional proteins are usually composed of combinations of a
few molecules in tubular-globular form. These proteins are mainly the enzymes of the cell
and are often mobile in the cell fluid.
Neutral fats contain large quantities of triglycerides
The lipids in membranes provide a barrier that impedes movement of water and water-soluble
substances from one cell compartment to another.
approximate composition in cell membrane (7.5 to 10 nanometers thick) is 55% proteins, 25%
phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates.
The basic lipid bilayer is composed of three main types of lipids—phospholipids, sphingolipids,
and cholesterol.
Complex sphingolipids in cell membranes are thought to serve several functions, including:
-protection from harmful environmental factors,
-signal transmission
-adhesion sites for extracellular proteins
two types of cell membrane proteins:
1. integral proteins (carriers, channels, enzymes, receptors)- protrude all the way through
the membrane
2. peripheral proteins (enzymes, controllers of transport of substances through cell
membrane pores)- which are attached only to one surface of the membrane and do not
penetrate all the way through.
, The carbohydrate moieties attached to the outer surface of the cell have several important
functions:
1. Many of them have a negative electrical charge, which gives most cells an overall negative
surface charge that repels other negatively charged objects.
2. The glycocalyx of some cells attaches to the glycocalyx of other cells, thus attaching cells to
one another.
3. Many of the carbohydrates act as receptors for binding hormones, such as insulin. When
bound, this combination activates attached internal proteins that
in turn activate a cascade of intracellular enzymes.
4. Some carbohydrate moieties enter into immune reactions
cytosol contains mainly dissolved proteins, electrolytes, and glucose.
Dispersed in the cytoplasm are neutral fat globules, glycogen granules, ribosomes, secretory
vesicles, endoplasmic reticulum, the Golgi apparatus, mitochondria, lysosomes, and
peroxisomes.
endoplasmic reticulum (a network of tubular structures called cisternae and flat vesicular
structures in the cytoplasm):
– This organelle helps process molecules made by the cell and transports them to their
specific destinations inside or outside the cell.
– The space inside the tubules and vesicles is filled with endoplasmic matrix
– The ribosomes are composed of a mixture of RNA and proteins; they function to
synthesize new protein molecules in the cell
– smooth reticulum functions for the synthesis of lipid substances (phospholipids &
cholesterol) and for other processes of the cells promoted by intrareticular enzymes.
– Functions:
– 1. It provides the enzymes that control glycogen breakdown when glycogen is to be used
for energy.
– 2. It provides a vast number of enzymes that are capable of detoxifying substances, It
achieves detoxification by processes such as coagulation, oxidation, hydrolysis, and
conjugation with glycuronic acid.
The different substances that make up the cell are collectively called protoplasm.
Protoplasm is composed mainly of five basic substances—
water, electrolytes, proteins, lipids, and carbohydrates.
Important ions in the cell include potassium, magnesium, phosphate, sulfate, bicarbonate, and
smaller quantities of sodium, chloride, and calcium.
Proteins can be divided into two types:
1. structural proteins- Structural proteins are present in the cell mainly in the form of long
filaments that are polymers of many individual protein molecules.
2. functional proteins- The functional proteins are usually composed of combinations of a
few molecules in tubular-globular form. These proteins are mainly the enzymes of the cell
and are often mobile in the cell fluid.
Neutral fats contain large quantities of triglycerides
The lipids in membranes provide a barrier that impedes movement of water and water-soluble
substances from one cell compartment to another.
approximate composition in cell membrane (7.5 to 10 nanometers thick) is 55% proteins, 25%
phospholipids, 13% cholesterol, 4% other lipids, and 3% carbohydrates.
The basic lipid bilayer is composed of three main types of lipids—phospholipids, sphingolipids,
and cholesterol.
Complex sphingolipids in cell membranes are thought to serve several functions, including:
-protection from harmful environmental factors,
-signal transmission
-adhesion sites for extracellular proteins
two types of cell membrane proteins:
1. integral proteins (carriers, channels, enzymes, receptors)- protrude all the way through
the membrane
2. peripheral proteins (enzymes, controllers of transport of substances through cell
membrane pores)- which are attached only to one surface of the membrane and do not
penetrate all the way through.
, The carbohydrate moieties attached to the outer surface of the cell have several important
functions:
1. Many of them have a negative electrical charge, which gives most cells an overall negative
surface charge that repels other negatively charged objects.
2. The glycocalyx of some cells attaches to the glycocalyx of other cells, thus attaching cells to
one another.
3. Many of the carbohydrates act as receptors for binding hormones, such as insulin. When
bound, this combination activates attached internal proteins that
in turn activate a cascade of intracellular enzymes.
4. Some carbohydrate moieties enter into immune reactions
cytosol contains mainly dissolved proteins, electrolytes, and glucose.
Dispersed in the cytoplasm are neutral fat globules, glycogen granules, ribosomes, secretory
vesicles, endoplasmic reticulum, the Golgi apparatus, mitochondria, lysosomes, and
peroxisomes.
endoplasmic reticulum (a network of tubular structures called cisternae and flat vesicular
structures in the cytoplasm):
– This organelle helps process molecules made by the cell and transports them to their
specific destinations inside or outside the cell.
– The space inside the tubules and vesicles is filled with endoplasmic matrix
– The ribosomes are composed of a mixture of RNA and proteins; they function to
synthesize new protein molecules in the cell
– smooth reticulum functions for the synthesis of lipid substances (phospholipids &
cholesterol) and for other processes of the cells promoted by intrareticular enzymes.
– Functions:
– 1. It provides the enzymes that control glycogen breakdown when glycogen is to be used
for energy.
– 2. It provides a vast number of enzymes that are capable of detoxifying substances, It
achieves detoxification by processes such as coagulation, oxidation, hydrolysis, and
conjugation with glycuronic acid.
