Steroids in Biology Structure Types and Functions

Steroids are biologically active organic compounds. They are made up of four rings that are arranged in a specific molecular configuration. The two main principle functions carried out by steroids include, it acts as an important component for the cell membrane where it alters the fluidity of the membrane. These also act as a signalling molecule. Hundreds of steroids can be found in animals, plants, and fungi. They are also called corticosteroids which can act as inflammatory medicines. In the cells, all the steroids are manufactured from the sterols such as lanosterols or cycloartenol. Due to the cyclization of triterpene squalene, these two sterols are derived.

The core structure of steroids consists of seventeen carbon atoms that are bonded in four fused rings of which three of them are six-membered cyclohexane rings, and one is a five-membered cyclopentane ring. The functional groups attached to the ring structure and the oxidation state of the rings, these two conditions make the steroids to be different from each other. The sterols are the form of steroids that have a hydroxyl group at the third position. By changing the ring structure, these steroids can also be modified radically. 

Steroid Hormone

These are man-made versions of chemicals that are produced to act like hormones. These hormones can be classified into two classes one is corticosteroids and another one is sex steroids. By the different receptors attached to the ring structures can vary these classes to form five different types of steroids: 

1. Glucocorticoids

2. Mineralocorticoids

3. Androgens

4. Estrogens

5. Progestogens

Steroid hormones are involved in the functioning of the control of metabolism, development of sex characters, inflammation, functions related to the immune system, and salt-water balance. The term steroid is used to describe both the hormones that are produced in the body and the hormones that are produced artificially to duplicate the functions of the natural ones. 

Nomenclature of Steroids

Steran which is also known as Gonane is the simplest one of all the steroids present and is considered as the nucleus of all the different steroids and sterols. It is made up of seventeen carbon atoms that have carbon-carbon bonding to form four fused rings; these rings are arranged in three-dimensional shapes. These three cyclohexane rings form the skeleton of the steroids. The remaining five carbon atoms are combined to form a cyclopentane structure that is attached to the skeleton. When the eight carbon-side chains and two methyl groups are attached to this skeleton it forms a cholestane framework. When a hydrogen atom is attached to the carbon-5 atom in the structure the difference occurs in the side of the large planar ring structure thus the two 5and 5stereoisomeric forms exist. 

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Examples of These Steroids Include:

• Cholic acid

• Lanosterol

• Medrogestone

• Testosterone

• Progesterone

In Addition to the Expansions, Contraction, and Cleavages, All These Variations That Occur to the Carbon-Carbon Bonds Can Vary the Steroids Framework Along With These:

• They can vary the bond orders in the ring structure.

• The number of methyl groups attached to the rings can also vary.

• The functional groups that are attached to the ring structure and the side chains can vary.

• The configuration of the groups that are attached to the ring structure and the side chains can vary.

Types of Steroids

The steroids are classified depending on the functions and structure:

By Function These are Classified as:

1. Corticosteroids: It includes two subclasses: 

• Glucocorticoids

• Mineralocorticoids

These steroid used for immunosuppression, regulating blood pressure, and maintaining the water-electrolyte balance. 

2. Sex Steroids: It helps to maintain the cyclical changes that occur in the uterus and to develop secondary sexual characteristics.

By Structure These are Classified as:

1. Intact Ring System: The classification that can be done by the chemical composition. Examples include cholanes with 24 carbon atoms, estranes with 18 carbon atoms, etc.

2. Cleaved, Expanded, and Contracted Rings: 

• Secosteroids are a subclass of these steroidal compounds that are formed by the biosynthetic or conceptual cleavage of the parent steroid rings. 

• Norsteroids and homosteroids are formed by biosynthetic steps. It is formed by the enzymic ring expansion-contraction reactions and ring closure of acyclic precursors with fewer or more ring atoms than that of the parent steroid framework. 

Biosynthesis and Metabolism

The various steroids that are found in fungi, plants, and animals are derived from the lanosterol or cycloartenol. The biosynthesis of steroids is an anabolic pathway where the production of steroids takes place from the simple precursors. Whereas the animals follow a unique biosynthetic pathway that provides a common target for the synthesis of antibiotics and anti-infection drugs. Statins are the cholesterol lower drug that is the target in humans by steroid metabolism. Humans and other animals follow the mevalonate pathway for the biosynthesis of steroids. In this pathway, they make use of acetyl-CoA as a building block for the DMAPP which is expanded as dimethylallyl pyrophosphate, and IPP that is expanded as isopentenyl pyrophosphate. By subsequent steps, these two join to form GPP, expanded as geranyl pyrophosphate which further synthesized as steroid lanosterol, and the modifications that are done to these are classified as steroidogenesis transformations.

1. Mevalonate pathway: It is also called the HMG-CoA reductase pathway, this pathway starts with the acetyl-CoA and ends with the IPP and DMAPP. The DMAPP and IPP donate the isoprene units which are assembled and modified further in the formation of terpenes and isoprenoids. The isoprene units are joined together to form squalene and are folded as a set of rings to form lanosterol, which is further converted into cholesterol and ergosterol. By using this pathway two classes of drugs are formed that are statins which are used to reduce cholesterol levels and bisphosphonates are used to treat degenerative bone disorders.

2. Steroidogenesis: The biological process through which the steroids are generated in the formation of cholesterol which is further changed to form other steroids. 

• Progesterone is the precursor of all other human steroids. All the tissue in the human body that produces steroids must first convert the cholesterol to pregnenolone. It occurs in the mitochondria as a rate-limiting step in the synthesis of steroids.

• The adrenal cortex produces aldosterone, testosterone, cortisol, and corticosterone.

• Estriol is formed in the placenta during pregnancy, testosterone is formed in the testes, and estrone, progesterone, and estradiol are formed in the ovary.

• By the primary pathway, DHEA-androstenedione-estrone or directly from the testosterone the estradiol is converted. 

Conclusion

According to steroids meaning, steroids are the chemicals that are produced naturally or artificially to duplicate the functions of certain hormones. Anabolic steroids are used as steroids bodybuilding. Even the Deca steroid is included in these anabolic steroids. These can enhance the strength of a muscle. Some steroids are used to provide relief to inflammatory conditions. There are some other benefits: the bone density can be improved, production of red blood cells can be improved, the decrease of fat content in the body can be seen and many more.