There are three main types of DNA structures: A-DNA, B-DNA, and Z-DNA. A-DNA and B-DNA are both right-handed double helices while Z-DNA has a left-handed zigzag structure. DNA replication involves the separation of the DNA strands to serve as templates for synthesis of new complementary strands. There are three main types of RNA: tRNA transfers amino acids to the ribosome during protein synthesis, rRNA is a component of ribosomes, and mRNA carries genetic instructions from DNA to the ribosome. Gene expression involves transcription of DNA into mRNA followed by translation of mRNA into proteins with the help of tRNA and rRNA in the ribosome. The central dogma states that DNA

1. DNA and RNA

2. • Glycosidic Linkage
• Phosphodiester bond
• Nucleotide
• Nucleoside

4. Packaging of DNA helix

5. DNA Types
• There are three different DNA types:
• A-DNA: It is a right-handed double helix similar to the B-DNA form. Dehydrated DNA takes
an A form that protects the DNA during extreme conditions such as desiccation. Protein
binding also removes the solvent from DNA, and the DNA takes an A form. there is a slight
increase in the number of base pairs (bp) per turn. This results in a smaller twist angle. A-
DNA is broader and more compressed along its axis than B-DNA.
• B-DNA: This is the most common DNA conformation and is a right-handed helix. The
majority of DNA has a B type conformation under normal physiological conditions.
• Z-DNA: Z-DNA is a left-handed DNA where the double helix winds to the left in a zig-zag
pattern. It was discovered by Andres Wang and Alexander Rich. It is found ahead of the start
site of a gene and hence, is believed to play some role in gene regulation.

6. Replication
• The two strands would separate and act as a
template for the synthesis of new
complementary strands. After the completion
of replication, each DNA molecule would have
one parental and one newly synthesised strand.
This scheme was termed as semiconservative
DNA replication

7. Types of RNA
• tRNA – Transfer RNA
• The transfer RNA is held responsible for choosing the correct protein or the amino acids required by the
body in-turn helping the ribosomes. It is located at the endpoints of each amino acid. This is also called as
soluble RNA and it forms a link between the messenger RNA and the amino acid.
• rRNA-Ribosomal RNA
• The rRNA is the component of the ribosome and are located within the in the cytoplasm of a cell, where
ribosomes are found. In all living cells, the ribosomal RNA plays a fundamental role in the synthesis
and translation of mRNA into proteins. The rRNA is mainly composed of cellular RNA and are the
most predominant RNA within the cells of all living beings.
• mRNA – Messenger RNA.
• This type of RNA functions by transferring the genetic material into the ribosomes and pass the
instructions about the type of proteins, required by the body cells. Based on the functions, these types of
RNA is called the messenger RNA. Therefore, the mRNA plays a vital role in the process of transcription
or during the protein synthesis process

8. Gene expression
• Gene expression is the process by which the instructions in our DNA are
converted into a functional product, such as a protein.
• Transcription and translation.
• Transcription is when the DNA in a gene is copied to produce
an RNA transcript called messenger RNA (mRNA).
• This is carried out by an enzyme called RNA polymerase which uses available
bases from the nucleus of the cell to form the mRNA.

9. • Translation occurs after the messenger RNA (mRNA) has carried the transcribed
‘message’ from the DNA to protein-making factories in the cell, called ribosomes.
• The message carried by the mRNA is read by a carrier molecule called transfer
RNA (tRNA).
• The mRNA is read three letters (a codon) at a time.
• Each amino acid is attached specifically to its own tRNA molecule.
• When the mRNA sequence is read, each tRNA molecule delivers its amino acid to the
ribosome and binds temporarily to the corresponding codon on the mRNA molecule.
• Once the tRNA is bound, it releases its amino acid and the adjacent amino acids all
join together into a long chain called a polypeptide.
• This process continues until a protein is formed.

11. Central Dogma
• The central dogma of molecular biology
states that DNA contains instructions
for making a protein, which are copied
by RNA.
• RNA then uses the instructions to make
a protein.
• In short: DNA → RNA → Protein, or
DNA to RNA to Protein.

12. Mutation
• Mutation is the change in our DNA base pair sequence due to various
environmental factors such as UV light, or mistakes during DNA replication.
• It is a heritable change. Mutations can affect genotype as well as phenotype.
• Mutagen.
• Sickle cell anemia