Poland Liceum ogólnokształcące, klasa III Biology

Chapters: 6

1. VI. Expression of genetic information in human cells

From gene to protein

Molecular Basis of Inheritance – DNA is the genetic material in most living things (some viruses use RNA). It is a double helix: two antiparallel strands of nucleotides, A pairs with T by 2 hydrogen bonds and G with C by 3. Long DNA is packed on histones into nucleosomes and then chromatin. DNA copies itself semi-conservatively (Meselson–Stahl). The central dogma says DNA → RNA → protein. Transcription makes RNA from one strand; in eukaryotes the hnRNA is capped, tailed and spliced. The genetic code is a triplet, has 64 codons (61 for amino acids, 3 stops), starts with AUG, is nearly universal and degenerate. Ribosomes translate mRNA into protein with tRNA adaptors. Genes are switched on and off; the lac operon is the classic example. The Human and Rice Genome Projects read whole genomes, and DNA fingerprinting uses repeat DNA (VNTRs) to identify people.

Inheritance of traits · Variation and mutation

Principles of Inheritance and Variation – Genes come in pairs (alleles). Each parent passes one allele of each pair to the child. Mendel showed dominance (3 : 1), segregation and independent assortment (9 : 3 : 3 : 1). Real life has twists: incomplete dominance (1 : 2 : 1), co-dominance (AB blood), multiple alleles, pleiotropy (one gene, many effects) and polygenic traits (many genes, one trait). Genes sit on chromosomes, so genes on the same chromosome are linked and are separated only by crossing over. Sex chromosomes decide sex (XX-XY in humans, ZW in birds, haplo-diploid in honeybees) and carry sex-linked genes (haemophilia, colour blindness). Mistakes in genes cause Mendelian disorders (thalassemia, sickle-cell) and mistakes in chromosome number cause Down, Turner and Klinefelter syndromes.
Mutations – A mutation is a sudden, lasting change in the DNA. Gene (point) mutations change one or a few bases: substitution, insertion or deletion. Insertions and deletions shift the reading frame. Chromosome mutations change big pieces or the number of chromosomes. Mutations happen by chance or because of mutagens such as UV light, X-rays and some chemicals. They can be harmful, neutral or useful, and they are the first source of all genetic variation.

Traditional and molecular biotechnology · GMOs, gene therapy and ethics

Biotechnology: Principles and Processes (Recombinant DNA Technology) – Genetic engineering means changing the genes of a living thing on purpose. We cut the gene we want with restriction enzymes (molecular scissors), paste it into a carrier DNA called a vector using DNA ligase (molecular glue), put it into a host cell, pick out the cells that took it, and grow them in big tanks (bioreactors) to collect the product. PCR makes millions of copies of a gene, and gel electrophoresis sorts DNA pieces by size.
Biotechnology and its Applications – The tools of genetic engineering are used in medicine, farming and research. Bacteria make human insulin; yeast makes safe vaccine proteins. Stem cells can become many cell types. Gene therapy puts a correct gene into a patient's cells. GM crops like Bt cotton carry a gene for a protein that kills pests. Transgenic animals carry foreign genes to help study disease or make medicines. Because these are powerful, India controls them through GEAC, and laws guard against biopiracy and unfair patents.

Mechanisms of evolution · Human origins

Evolution: Origin of Life, Mechanisms and Human Evolution – Life began on the early Earth from simple chemicals: Oparin and Haldane proposed it and Miller made amino acids in a flask. Evidence of evolution comes from fossils, homologous and analogous organs, embryos, molecules and changes we can watch (industrial melanism, drug resistance). Darwin explained it by natural selection acting on variation in populations; the modern synthetic theory adds genes: mutation, recombination, gene flow, genetic drift and natural selection change allele frequencies. If none of these act, frequencies stay constant: Hardy–Weinberg, p² + 2pq + q² = 1. Selection can be stabilising, directional or disruptive. One ancestor spreading into many habitats gives adaptive radiation (Darwin’s finches, Australian marsupials). Humans evolved from Dryopithecus-like apes through Australopithecus, Homo habilis, Homo erectus and Neanderthals to Homo sapiens.

Organisms and their environment · Interactions and ecosystems

The Ecological Niche – Every organism lives in a habitat (its address) and has a niche (its role: what it eats, where and when it is active, and how it affects others). Its life is shaped by abiotic factors (temperature, light, water, pH) and biotic factors (food, predators, competitors). For each factor it has a range of tolerance with an optimum in the middle. The potential (fundamental) niche is everything it could use; the realised niche is the smaller part it actually uses when competitors and predators are present. When two species' niches overlap fully, one pushes the other out (competitive exclusion); partly overlapping species can coexist by sharing resources. Species with narrow tolerance can act as bioindicators.
Ecosystem: Structure, Productivity, Energy Flow and Pyramids – An ecosystem is a working unit of nature where living things (biotic) and non-living things (abiotic) interact. Plants make food at a rate called productivity: gross (GPP) minus respiration gives net (NPP = GPP − R). Dead matter is broken down in five steps: fragmentation, leaching, catabolism, humification and mineralisation. Energy enters as sunlight, flows one way through trophic levels and only about 10% passes on each time. Ecological pyramids of number, biomass and energy show this; number and biomass pyramids can be inverted, but the energy pyramid is always upright.

Biodiversity and its protection

Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).