Chapter 1 – The Foundations of Biochemistry1.4 Genetic Foundations- Deoxyribonucleic acid , DNA – the genetic materialo Sequence of nucleotides encodes instructions for forming all other cellular components- The perpetuation of a biological species requires that its genetic information be:o Maintained in a stable formo Expressed accuratelyo Reproduced with a minimum of errorsGenetic Continuity Is Vested in Single DNA MoleculesThe Structure of DNA Allows for Its Replication and Repair with Near-Perfect Fidelity- Deoxyribonucleotides – four different monomeric subunits- If one strand is damaged, continuity of information is assured by the information in the other strand, which can act as a template for repairThe Linear Sequence in DNA Encodes Proteins with Three-Dimensional Structure- A linear sequence of deoxyribonucleotides in DNA codes, through RNA, for the production of a protein with a corresponding linear sequence of amino acids- The protein then folds into a particular three-dimensional shape, determinedby its sequence and stabilized primarily by noncovalent interactions- Native conformation – the precise three-dimensional structure of a proteino Crucial to function- Chromosomes, ribosomes, and membranes are supramolecular complexes formed by noncovalent association of proteins with other macromolecules- Accurate folding requires the right:o pHo Ionic strengtho Metal ion concentrations1.5 Evolutionary FoundationsChanges in the Hereditary Instructions Allow Evolution- Mutation – a change in the nucleotide sequence of DNAo Changes instructions for a cellular componento Can also be caused by incorrectly repaired damageo Can be harmful or lethalo Occasionally beneficial- Wild-type – unmutate cellso Eliminated in natural selectionBiomolecules First Arose by Chemical Evolution- It is hypothesized that organic building blocks were produced through ultraviolet irradiation, lightning, or volcanic eruptions, acting on the gases in the prebiotic Earth’s atmosphere or on inorganic solutes in superheated thermal vents deep in the ocean- RNA can act as a catalystRNA or Related Precursors May Have Been the First Genes and Catalysts- DNA and protein may have appeared simultaneously, and RNA preceded bothBiological Evolution Began More Than Three and a Half Billion Years AgoThe First Cell Probably Used Inorganic Fuels- The earliest cells arose in a reducing, anaerobic atmosphere and probably obtained energy from inorganic fuels- An alternative source of organic compounds could have been extraterrestrial space- A significant evolutionary event was the development of pigments capable of capturing energy from light, which could be used to reduce CO2 to form more complex, organic compounds- Cyanobacteria are the modern descendants of early photosynthetic oxygen-producers- Earliest cells were anaerobico The transfer of electrons from organic molecules to O2 releases a lot ofenergy, so organisms that could do this had an advantageEukaryotic Cells Evolved from Simpler Precursors in Several Stages- Three major changes must have occurred:o As cells acquired more DNA, the mechanisms required to fold it compactly into discrete complexes with specific proteins and to divideit equally between daughter cells at cell division became more elaborate Specialized proteins were requiredo As cells became larger, a system of intracellular membranes developed, segregating processeso Endosymbiotic associations – enveloping of aerobic bacteria or photosynthetic bacteria by early eukaryotic cells that eventually became permanent- Clustering was advantageous and led to cellular differentiationMolecular Anatomy Reveals Evolutionary Relationships- Genome – the complete genetic endowment of an organism- Homologs – two genes that share readily detectable sequence similarities- Paralogs – two homologous genes that occur in the same specieso Usually have different functions- Orthologs – two homologous genes found in different specieso Usually have the same function- Annotated genome – a description of the likely function of each gene product accompanying the sequenceFunctional Genomics Shows the Allocations of Genes to Specific Cellular Processes- The more complex an organism, the greater the proportion of its genome thatencodes genes involved in the regulation of cellular processesGenomic Comparisons Have Increasing Importance in Human Biology and
View Full Document
Unlocking...