Molecular Genetics: DNA Structure & Function

Introduction to DNA

• DNA (Deoxyribonucleic acid) is a macromolecule that stores and copies information.
• DNA is made up of four building blocks: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).

Structure of DNA

• DNA is a double-stranded molecule consisting of two polynucleotide chains running in opposite directions.
• The bases are on the inside of the molecule, and the two chains are joined together by double hydrogen bonds between A and T and triple hydrogen bonds between C and G.
• The base pairing is very specific, making the two strands complementary to each other.

DNA Replication

• DNA replication is the process of creating a new DNA molecule from an existing one.
• Each strand of DNA serves as a template for the synthesis of a new complementary strand.
• DNA replication requires many enzymes that work coordinately, including DNA polymerases.

Nucleotides and Nucleic Acids

• Nucleotides are the unit structure of nucleic acids.
• A nucleotide is composed of three components: nitrogenous base, pentose sugar, and phosphate.
• Nucleic acids are linear polymers of nucleotides formed by phosphodiester bonds.

Base Pairing

• Complementary base pairing is the most important structural feature of nucleic acids.
• It connects bases of one polynucleotide chain with complementary bases of another chain.
• Double hydrogen bonds are formed between A and T (or A and U in RNA), and triple hydrogen bonds are formed between G and C.

Forms of DNA

• There are three main forms of DNA: B-form, A-form, and Z-form.
• B-form is the most common form of DNA, with a right-handed helix and 10 base pairs per turn.
• A-form is less common, with a right-handed helix and 11 base pairs per turn.
• Z-form is a radical change of B-form, with a left-handed helix and a zig-zag shape.

Denaturation and Annealing of DNA

• DNA double strands can be denatured by heat or chemicals.
• Denaturation is a reversible process, and denatured strands can be re-annealed again.
• The process of denaturation and annealing can be monitored using the hyperchromicity (melting profile).

Types of Nucleic Acids

• There are two types of nucleic acids: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).
• DNA has a deoxyribose sugar and uses the bases A, G, C, and T.
• RNA has a ribose sugar and uses the bases A, G, C, and U.

Function of DNA

• DNA is in action in all cells, and the same genetic information is used in different ways to create different cells.
• The control of gene expression occurs by regulating the flow of information from DNA to protein.
• The central dogma of molecular biology is the unidirectional flow of information from DNA to RNA to protein.

Gene Expression

• Gene expression is the process whereby the information contained in genes begins to have effects in the cell.
• Genes are DNA sequences that encode proteins, and gene expression refers to the process of creating a functional product.
• Transcription is a key step in gene expression, making an RNA copy of DNA.

Transcription

• Transcription is the process of creating an RNA copy of DNA.
• RNA polymerase acts as the enzyme to synthesize the RNA.
• The decision to transcribe a gene is the most important step in the control of gene expression.

Genetic Code

• The genetic code is written in 3-letter words, each of which codes for a particular amino acid.
• There are 20 different amino acids specified by the genetic code.
• The genetic code is biology's Rosetta Stone, using 4 letters (A, T, G, and C) to write 3-letter words.

Translation

• Translation is the process of reading the information in mRNA to synthesize a polypeptide.
• Translation requires ribosomes, mRNA, tRNA, and amino acids.
• The sequence of amino acids determines the structure and function of a protein.