Molecular Biology: Gene Expression

• Molecular biology is the study of the molecular basis of biological activity.

Gene Expression

• Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product.
• These products are often proteins, but can also be functional RNA molecules like tRNA or rRNA.
• The central dogma of molecular biology describes the flow of genetic information: DNA -> RNA -> Protein.
• Transcription is the process of synthesizing RNA from a DNA template.
• Translation is the process of synthesizing protein from an RNA template.
• Gene expression is carefully regulated to control the amount and timing of gene products.
• Regulation can occur at various stages, including transcription, RNA processing, translation, and protein modification.
• Transcription factors are proteins that bind to DNA and regulate transcription.
• Activators enhance transcription, while repressors inhibit transcription.
• RNA processing includes capping, splicing, and polyadenylation.
• Splicing removes introns and joins exons to create a mature mRNA molecule.
• mRNA stability can also be regulated to control gene expression.
• Translation can be regulated by initiation factors, elongation factors, and termination factors.
• Post-translational modifications, such as phosphorylation and glycosylation, can affect protein activity and stability.
• Epigenetics, such as DNA methylation and histone modification, can also affect gene expression.

DNA Replication

• DNA replication is the process of copying a DNA molecule.
• It is essential for cell division and inheritance.
• DNA replication is semi-conservative, meaning that each new DNA molecule consists of one original strand and one newly synthesized strand.
• DNA replication begins at specific sites called origins of replication.
• DNA polymerase is the enzyme that synthesizes new DNA strands.
• DNA polymerase requires a template strand and a primer to begin synthesis.
• DNA is synthesized in the 5' to 3' direction.
• The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments called Okazaki fragments.
• Okazaki fragments are joined together by DNA ligase.
• Helicase unwinds the DNA double helix.
• Topoisomerase relieves the tension created by unwinding.
• Primase synthesizes RNA primers to initiate DNA synthesis.
• Proofreading mechanisms correct errors during DNA replication.
• Telomeres are repetitive sequences at the ends of chromosomes that protect against DNA degradation during replication.
• Telomerase is an enzyme that maintains telomere length.

Molecular Genetics

• Molecular genetics is the field of biology that studies the structure and function of genes at the molecular level.
• It involves the study of DNA, RNA, and proteins, and their roles in heredity and gene expression.
• A gene is a unit of heredity that encodes a functional product, such as a protein or RNA molecule.
• Genes are located on chromosomes, which are made up of DNA.
• The genome is the complete set of genetic material in an organism.
• Mutations are changes in the DNA sequence that can alter gene function.
• Mutations can be spontaneous or induced by mutagens.
• Point mutations are changes in a single nucleotide base.
• Frameshift mutations are insertions or deletions of nucleotides that alter the reading frame of a gene.
• Chromosomal mutations are changes in the structure or number of chromosomes.
• Genetic engineering involves manipulating genes to alter the characteristics of an organism.
• Recombinant DNA technology involves combining DNA from different sources.
• Gene therapy involves introducing genes into cells to treat disease.
• Genomics is the study of entire genomes, including their structure, function, and evolution.
• Proteomics is the study of the complete set of proteins in an organism.
• Bioinformatics combines biology and computer science to analyze large datasets of biological information.

Protein Synthesis

• Protein synthesis, also known as translation, is the process of creating proteins from an mRNA template.
• It occurs in ribosomes, which are complex molecular machines found in the cytoplasm.
• The mRNA molecule contains the genetic code that specifies the amino acid sequence of the protein.
• Each codon, a sequence of three nucleotides, corresponds to a specific amino acid.
• tRNA molecules carry amino acids to the ribosome and match them to the appropriate codon on the mRNA.
• Ribosomes move along the mRNA molecule, reading the codons and adding amino acids to the growing polypeptide chain.
• Translation begins at a start codon (usually AUG) and ends at a stop codon (UAA, UAG, or UGA).
• Once the protein is synthesized, it folds into a specific three-dimensional structure that determines its function.
• Chaperone proteins assist in the folding process.
• Post-translational modifications, such as phosphorylation, glycosylation, and ubiquitination, can alter protein structure and function.
• Proteins can be targeted to specific locations within the cell or secreted outside the cell.
• The signal sequence directs proteins to the endoplasmic reticulum for secretion or membrane localization.
• Protein degradation is the process of breaking down proteins into their constituent amino acids.
• The ubiquitin-proteasome system is a major pathway for protein degradation.
• Protein misfolding and aggregation can lead to disease.