Gene Definition

Genes are the series of Nucleotides in DNA and RNA. Genes are considered as a unit of heredity that is responsible to carry traits and characteristics from parents to children. Genes are fragments of DNA (Deoxyribonucleic Acid). The body comprises of many cells which consist of structures known as Chromosomes. The Genes are contained in the Chromosomes that lie within the cell nucleus. A chromosome comprises of hundreds and thousands of Genes. 

Chromosomes

Chromosomes appear to be thread-like structures that are present inside the cell of animals and plants. A chromosome is made up of protein and DNA. The structure of the chromosome is capable to tightly wrap the DNA within the cell without which the DNA is too long to fit inside the cell. A human cell comprises 23 pairs of Chromosomes making a total of 46 chromosomes. The proteins apart from being the building block of the body are also responsible for the production of Enzymes. Enzymes are the responsible factors that carry out various functions and chemical reactions within the body. Thus the function of the body depends majorly upon the amount and type of protein the body is capable of synthesizing. Hence the genes play a vital role in protein synthesis and these genes are present on chromosomes. 

For proper growth and function of an organism cell division is necessary. New cells divide and replace the old worn-out cells. During the process of cell division, the DNA has to get distributed properly among the cells. Thus chromosomes are responsible to make sure that the DNA is properly copied and distributed accurately during cell divisions. If this process does not take place properly then the number and structure of the chromosome in the new cells will lead to other problems like leukemia and certain types of cancers in humans. Such problems are due to the defective chromosomes. When the person is suffering from hormonal problems, generally, the medical practitioner considers to take the history where he approaches the patient asking whether such an issue lies within either of the parents or whether anybody else has the same problem. It is due to these defective chromosomes certain disease are carried out in the children as well.

During the time of reproduction also it is necessary that the chromosomes of eggs and sperms are right in number or else it will lead to a defect in the offspring. For example, children born with downs syndrome have a defect in the number of chromosomes. Also, turners syndrome which happens in females where there is only one X chromosome present. This can result in a defect in the ovaries and also infertility. 

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Genes

The concept of ‘inheritance of traits’ was first discovered by Mendel but he could not describe it. The term ‘Genes’ was later coined in the year 1909 by Danish Botanist and Geneticist Wilhelm Johannsen. Genes consist of DNA. This DNA has a specific code for protein synthesis. Genes can vary in size. The complete set of chromosomes is called a Genome. The number of genes in a Genome is different in different species. For example, a human genome comprises of 22000 - 25000 Genes.

Organisms are divided into two types Eukaryotic and Prokaryotic. Eukaryotic organisms include the animals, plants, and certain fungi that have a definitive nucleus inside the cell membrane, thus genes are present in the nucleus of the cell. Prokaryotic organisms include certain bacteria where the nucleus is not present, the genes are present in a single chromosome that floats freely in the cytoplasm. Each individual is inherited with 2 copies of genes one from each parent. Almost all genes are the same in everyone except for a few genes called ‘Alleles’. These are a part of the same genes with a slight difference in the bases of DNA sequence, thus due to this, each individual has different physical features. Each chromosome has many genes and some genes are given abbreviated names as per the disorder trait.

Chemical Structure of Genes

All the organisms are constituted of DNA except for a few viruses who are composed of RNA (Ribonucleic Acid). The DNA looks much like a twisted ladder that is composed of Nucleotides. The sides of these ladders are made up of Sugars and Phosphates and the horizontal steps of this ladder which are called the rungs are made up of pairs of Nitrogenous bases. The bases are named as Adenine (A), Guanine (G), Thymine (T), Cytosine (C). The Adenine on one side of ladder binds with the Thymine on the other side of the ladder forming an A-T ladder rung. Similarly, the Cytosine binds with the Guanine forming a C-G ladder rung. If this bonds between the two bases are broken then the chain unwinds and results in the formation of identical DNA when the free Nucleotide within the cell align themselves according to the base pairing rule. This process leads to the passing of hereditary information from one generation of cells to next generation.

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Function of the Gene

Genes are required for the synthesis of proteins. However, there are certain other functions as well the Genes are responsible for. The Genes that do not synthesize protein form into mRNA. The micro RNA that do not undergo protein formation helps in the regulation of Gene instead. 

Transcription

Transcription is nothing but making and RNA copy of the Gene. This is called as the messenger RNA (mRNA). RNA also is a long chain just like DNA but in RNA, base Thymine is replaced by base Uracil (U). 

When the unwinding process of the double helix strand of DNA is taking place, one of the unwinded strands form into the complimentary strand of RNA. This new strand formed is called as the messengerRNA or mRNA. The mRNA further leaves the nucleus by separating itself from DNA. The mRNA travels into the cytoplasm of the cell and attaches itself to the Ribosome. Here the protein synthesis starts taking place.

Translation

The mRNA is the responsible factor to make sure which amino acids need to link together. The mRNA code guides the ribosome the type of amino acids and in which order they need to link together. Another smaller type of RNA known a tRNA (tranfer RNA) brings the amino acids to the Ribosomes. This is how the chain of protein keeps growing. Then it is further folded into a three dimensional structure influenced by the nearby molecules. These nearby molecules are called as the Chaperone molecules. Chaperone molecules are the proteins that are responsible for the assembling and disintegration of the macromolecular structures.

Gene Expression

Our body comprises of numerous cells like liver cells, lungs cells, etc that combine to form organs. All these cells of the organs of the body perform different functions and release different chemical substances but they are derived from a single fertilized cell that contains the same DNA. Their appearances and functions differ because different genes are expressed in different cells. When and how a Gene is expressed is already coded in the DNA. The expression of Gene depends on various factors that include the age and sex of the individual, the type of tissue of the organ and what chemical substance it releases, etc. The transcription and translation process can get interrupted due to the various chemical substances around the DNA.

Replication and Mutation

The growth and reproduction of an organism depends upon cell division. The cell divides in to two identical cells that are called as the daughter cells. This happens when every Gene in the Genome makes a duplicate copy and this process is called as DNA replication. These copies are made by the enzyme known as DNA polymerase. DNA is a double helix model. The enzyme reads from one strand of this double helix known as the template strand and then it further synthesizes into a complementary strand. This is how the process of replication takes place. At the end of this phase we have two identical double stranded DNA.  

There is a possibility that mistakes happen at the time of replication therefore, to avoid this mistake the cells have proofreading capability that makes sure the bases of the double helix model pair properly. DNA replication with minor variations is not a problem and it occurs frequently but mistakes that are duplicated in the next identical strand formed will create an issue. This duplication of mistakes in the next strand formed is called as Mutation.

FAQ (Frequently Asked Questions)

1. What are the Functions of Genes?

Ans: There are two main functions of DNA 

  • It passes the genetic material from parents to offsprings.

  • It also plays an important role in the synthesis of proteins.

2. What is Genetic Inheritance?

Ans: The genetic material is passed on from parents to offsprings in the form of DNA. All the organisms undergo the process of growth and reproduction. The information that is required for the reproduction and survival of these organisms is encoded in the DNA that is passed on from one generation to another. This is how the Genetic inheritance takes place.

3. What is the Importance of Genes?

Ans: Genes are the unit of heredity in any living organism like plants, animals, bacteria, fungi etc. Every cell in the body is subjected to growth and replication. Genes contains the information required for building, multiplying and maintaining cells. The reason we carry certain physical appearances, habits and certain diseases from parents is because of these genes who are responsible for passing genetic information from parents to offsprings.

4. What are Genetic Tests Used for?

Ans: Genetic tests in todays world are used for the diagnosis of certain disorders like Polycystic Kidney Disease, Turners Syndrome, Sickle cell Anemia, Cystic Fibrosis, etc. Genetic tests also are helpful in predicting which disease a person is likely to develop. 

The technology is so advanced that these Gene defects can be corrected by Gene therapy and certain diseases can be avoided to occur in an individual. Scientists are researching for the same which may allow the doctors to insert a Gene for the rectification of disease than subjecting an individual to drugs and surgeries. The research is still going on for the same.

5. What are the Types of DNA Mutations?

Ans: Mutation is the permanent alteration in the sequence of the DNA that makes up a Gene. There are three types of DNA mutation that are:

  • Base substitutions

  • Deletions 

  • insertions