Genes: Structure and Function

• Genes are the basic units of heredity, composed of DNA, and provide instructions for growth, development, function, and reproduction.

Structure of Genes

• Genes are made of DNA, which consists of two strands twisted into a double helix.
• Each DNA strand is composed of nucleotides, including a sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
• The sequence of nucleotides in DNA determines the specific genetic information.
• Genes are located on chromosomes, which are thread-like structures in the nucleus of cells.
• Humans have 23 pairs of chromosomes.

Gene Function

• Genes encode proteins, which are the building blocks of the body.
• Proteins catalyze biochemical reactions (enzymes), provide structural support (collagen), and regulate bodily processes (hormones).
• Gene expression involves transcription and translation.
• Transcription involves transcribing the DNA sequence of a gene into messenger RNA (mRNA) in the cell nucleus, guided by RNA polymerase.
• Translation involves transporting mRNA to the ribosome in the cytoplasm, where it is translated into a protein, with each codon corresponding to a specific amino acid.

Gene Types

• Protein-coding genes directly code for proteins and represent a small fraction of the human genome.
• Non-coding genes encode functional RNA molecules like ribosomal RNA (rRNA) and transfer RNA (tRNA), playing roles in protein synthesis and regulation.
• Regulatory sequences control when and how much a gene is expressed, including promoters, enhancers, and silencers.

Genetic Variation and Mutation

• Different forms of a gene are called alleles, which can be dominant or recessive, affecting inherited traits.
• Mutations are changes in the DNA sequence of a gene, occurring naturally or induced by external factors.
• Mutations can have beneficial, neutral, or harmful effects, potentially leading to genetic disorders or increased susceptibility to diseases like cancer.

Inheritance of Genes

• Traits are passed from parents to offspring according to Mendelian patterns (dominant and recessive).
• Autosomal genes are found on non-sex chromosomes, while sex-linked genes are on sex chromosomes (X or Y).
• Genetic recombination during sexual reproduction results in offspring with a mix of genetic material.

Gene Regulation

• Gene expression is tightly regulated to ensure proteins are produced at the right time, in the right cells, and in the correct amounts.
• Gene activity can be influenced by environmental factors through epigenetic changes, such as DNA methylation and histone modification.

Applications of Gene Research

• Understanding genes helps diagnose genetic disorders like cystic fibrosis, sickle cell anemia, and Huntington's disease.
• Gene therapy involves inserting, altering, or replacing genes to treat or prevent disease.
• Genetic engineering manipulates genes for agricultural, industrial, and medical purposes, using techniques like CRISPR-Cas9 to edit genes precisely.

Human Genome

• The human genome contains about 3 billion base pairs and approximately 20,000-25,000 genes.
• The Human Genome Project mapped all the genes in human DNA.
• A large part of the human genome is non-coding DNA, some of which regulates gene expression and maintains chromosome structure.

Epigenetic Influence on Genes

• Genes are affected by epigenetic factors, which change gene activity without altering the DNA code.
• Environmental factors like diet, stress, and toxins can influence epigenetic marks and gene expression, playing a role in development, aging, and disease onset.

Nucleic Acids

• Nucleic acids are essential biomolecules that govern genetic and hereditary properties.
• The two major types are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Structure of Nucleic Acids

• Nucleic acids are long polymers made of nucleotides.
• Each nucleotide contains a pentose sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base.
• Nitrogenous bases are classified into purines (adenine, guanine) and pyrimidines (cytosine, thymine (DNA), uracil (RNA)).
• Nucleotides are linked via phosphodiester bonds.
• The sequence of nitrogenous bases encodes genetic information.
• DNA is usually a double helix with two antiparallel strands.
• Adenine pairs with Thymine, and Guanine pairs with Cytosine through hydrogen bonds.
• RNA is typically single-stranded and can form secondary structures.
• In RNA, Uracil replaces Thymine and pairs with Adenine.

Types and Functions of Nucleic Acids

• DNA contains the genetic blueprint and is responsible for storing and transmitting hereditary information.
• DNA can replicate itself.
• Genes in the DNA contain instructions for synthesizing proteins.
• RNA plays a role in protein synthesis and gene expression.
• Messenger RNA (mRNA) carries genetic information from DNA to ribosomes.
• Ribosomal RNA (rRNA) forms the core structure of ribosomes and catalyzes protein synthesis.
• Transfer RNA (tRNA) transfers amino acids to the ribosome.
• Small nuclear RNA (snRNA) is involved in mRNA splicing.
• MicroRNA (miRNA) and small interfering RNA (siRNA) are involved in gene regulation.

Functions of Nucleic Acids

• DNA stores all the genetic instructions for the growth, development, functioning, and reproduction of organisms.
• DNA transmits hereditary information from one generation to the next.
• RNA translates genetic information into proteins.
• RNA molecules regulate gene expression and control cellular activities.

DNA Replication and RNA Transcription

• During DNA replication, each original DNA strand serves as a template for a new complementary strand.
• Helicase unwinds the DNA double helix.
• DNA polymerase adds nucleotides to the growing strand.
• Ligase joins Okazaki fragments on the lagging strand.
• RNA transcription copies a specific DNA sequence into RNA.
• RNA polymerase binds to DNA at the promoter region and synthesizes a complementary strand of RNA.
• Messenger RNA (mRNA) carries the genetic code from DNA to the ribosomes for protein synthesis.

Genetic Code and Translation

• The genetic code defines how the sequence of bases in mRNA is translated into the sequence of amino acids in proteins.
• A codon, a sequence of three bases in mRNA, specifies one amino acid.
• During translation, the ribosome reads mRNA and, with tRNA, assembles amino acids to form a polypeptide chain.

DNA and RNA in Biotechnology

• DNA is manipulated to produce desired traits in genetically modified organisms (GMOs).
• Gene therapy treats genetic disorders by introducing normal genes into cells.
• PCR (Polymerase Chain Reaction) amplifies DNA segments for research.
• CRISPR-Cas9 is a gene-editing technology used to alter DNA sequences.