DNA

• The nucleus of nearly every human cell contains 46 coiled structures known as chromosomes, which are bundled with DNA.
• The nucleus is located inside the cell.
• The list of instructions contained within DNA is represented by long, thin molecules, one for each chromosome, and each of these molecules forms a double-helix shape.
• Every double helix consists of two very long strands that wind themselves tightly around each other.
• These are linked by rungs, like a ladder. Adenine (A), Guanine (G), Thymine (T), and Cytosine (C) are all examples of bases, and they are paired with one another to form the rungs (C).
• Every time, A is paired with T, while G is always paired with C.
• The genetic code for the chromosome is stored in the order of the bases, and the method in which the bases link to one another is what allows DNA to replicate itself.

Nucleus

• Chromosomes are located within this organelle, which also serves as the cell's control center.

Chromosome

• DNA molecules form the building blocks of this structure.

Supercoiled DNA

• The double helix of DNA is wound into coils, which are then twisted together to form a supercoil.

Core unit

• Also known as a nucleosome, a nucleosome is a package consisting of eight proteins (histones) and approximately two twists of DNA looped around it.
• The combination of DNA and protein in this way is known as chromatin.

BASE PAIRS

• Due to the chemical properties of the four bases, pairings can only occur in two different combinations.
• Adenine and thymine are complementary to one another because they each have two potential sites for the formation of hydrogen bonds, whereas guanine and cytosine each have three potential sites for the formation of hydrogen bonds.

COILS AND SUPERCOILS

• The coiled shape of DNA makes it possible to cram an amazing length into a relatively small area.
• If a chromosome's DNA were unwound, it would stretch for around 5 cm (about 2 in) (5cm).
• In the nucleus of every cell (with the exception of mature red blood cells, which lack nuclei and DNA), there is a complete set of 46 chromosomes.
• When cells are not dividing, the DNA (which is wrapped around protein to form what is known as chromatin) is coiled much less tightly than it is during cell division.
• This makes it possible for some parts to be available for the assembly of proteins as well as other tasks.
• The DNA in a cell that is getting ready to split will unwind into supercoils as it does so.
• These supercoils are more compact, have a shorter length, and can be recognized by their characteristic "X" shape.

DNA backbone

• Having a structure that is made up of phosphate compounds and deoxyribose, which is a type of sugar, in alternating units

Helical repeat

• When there are 10.4 rungs of base pairs, the DNA helix will twist once.

DOUBLE HELIX

• Coiled and supercoiled forms of the DNA molecule can be found in chromosomes.
• The DNA molecule can alternatively be described as having loops and twists.
• It is accompanied by a number of proteins, the most prominent of which are the histones.

Adenine– thymine link

• Adenine always forms a base pair with thymine

Guanine– cytosine link

• Guanine and cytosine are the only two bases that can ever form a pair.

HOW DNA WORKS

• DNA's primary role is to act as a source of information that may be used to construct proteins.
• Some proteins serve as the primary building blocks of the body, whilst others can be converted into enzymes or hormones that regulate the chemical processes that occur within the body.
• The production of proteins can be broken down into its two primary stages: transcription and translation.
• During the process of transcription, information is extracted from DNA and replicated onto an intermediate form of molecule known as mRNA (messenger ribonucleic acid).
• The messenger RNA is transported out of the nucleus of the cell and into structures within the cell known as ribosomes.
• During the phase of translation, the mRNA serves as a template for the creation of the fundamental building blocks of proteins, which are called amino acids.
• There are approximately 20 distinct types of amino acids.
• The order in which they appear is determined by segments of mRNA that are three bases in length and are referred to as triplet codons.
• Because the order of the nucleotides in each codon determines the "code" for a certain amino acid, the phrase "genetic code" is often used.
• Instructions for constructing a particular protein from a given sequence of amino acids are stored in the mRNA.

TRANSCRIPTION

• In the nucleus of the cell, the strands of DNA momentarily separate, and one of these strands serves as a template for the production of messenger RNA (mRNA).
• The information contained in the DNA is replicated as a complementary copy by separate RNA nucleotides that contain the right bases and attach themselves to the exposed DNA bases in a cross-linked fashion.

TRANSLATION

• The attachment of the mRNA to the ribosome takes place in the cytoplasm of the cell. Individual tRNA (transfer ribonucleic acid) molecules have unique amino acids attached.
• They are only allowed to attach to the mRNA if the order of their bases is identical to that of the mRNA, which guarantees that they bring the appropriate amino acid.
• The right sequence of amino acids is brought to the ribosome by the tRNAs as the ribosome travels along the mRNA.
• This allows the amino acids to be assembled into a protein.

WHAT ARE GENES?

• Genes are typically understood to be the component of DNA that is essential for the production of a single protein.
• It is made up of all of the parts of the protein's DNA that contain the genetic code for all of the amino acids.
• In most cases, a single gene will be found on a single chromosome.
• On the other hand, it is possible for it to have multiple parts on various locations of the
• DNA molecule, each of which contains the code for a distinct piece of the protein.
• The formation of immature mRNA often involves the transcription of both introns and exons, which are lengths of DNA.
• After this, the molecular machinery of the cell removes the components of the mRNA that were created from the introns, leaving only the mature mRNA available for translation.
• There are also regulatory DNA sequences, which, in addition to encoding their own proteins and influencing the pace at which genes are transcribed, code for their own proteins.

PARTS OF A GENE

• Both the introns and the exons of a gene are transcribed in order to produce mRNAs that code for various parts of a protein.
• The lengths made from introns are then spliced off chemically, leaving regions that only contain exons.
• These exon-only portions are what are used to make the protein.

RANGE OF GENE SIZE

• The size of genes, which is often determined by the number of base pairs they contain, can vary greatly.
• The length of some genes is measured in thousands of base pairs, whereas the length of others might be measured in millions of base pairs.
• One of the tiniest genes is the one that codes for beta-globin.
• It is a code for a portion of the molecule that makes up hemoglobin.
• Right now, it is being contrasted with a larger gene.