页数：36页文件大小：25.55 MB来源： 分子生物学基因Geneppt课件
本课件为《分子生物学》第3章有多少基因（How many genes are there?），依据 Gene VII 编排，讲解本章核心概念与分子机制，配逐页图示与文字版。
Chapter 3 How many genes are there?
3.1 Why are genomes so large? 3.2 Eukaryotic genomes contain both nonrepetitive and repetitive DNA sequences 3.3 Most structural genes lie in nonrepetitive DNA3.4 Total gene number is known for several organisms3.5 How many genes are essential? 3.6 How many genes are expressed?3.7 Organelles have DNA3.8 Organelle genomes are circular DNAs that code for organelle proteins 3.9 Mitochondrial DNA codes for few proteins3.10 The chloroplast genome codes for ~100 proteins and RNAs
Proteomeis the total number of proteins produced by an organism.
C-value is the quantity of DNA in the genome (per haploid set of chromosomes).
Nonrepetitive DNA shows reassoci at ion kinetics expected of unique sequences.
Repetitive DNA behaves in a reassoci at ion reaction as though many (related or identical) sequences are present in a component, allowing any pair of complementary sequences to reassociate.
Figure 3.1 DNA content of the haploid genome is related to the morphological complexity of lower eukaryotes, but varies extensively among the higher eukaryotes. The range of DNA values within a phylum is indicated by the shaded area.3.2 Why are genomes so large?.
Figure 3.2 The minimum genome size found in each phylum increases from prokaryotes to mammals.3.2 Why are genomes so large?.
Figure 3.3 The genome sizes of some common experimental animals.3.2 Why are genomes so large?.
Figure 3.4 A DNA reassoci at ion reaction is described by the C0t2/.
Figure 3.5 Rate of reassoci at ion is inversely proportional to the length of the reassociating DNA.
Figure 3.6 The reassoci at ion kinetics of eukaryotic DNA show 3 types of component (indicated by the shaded areas). The arrows identify the Cot1/2 values for each component.
Figure 3.7 The denatur at ion of reassociated nonrepetitive DNA takes place over a narrow temperature range close to that of native DNA, but reassociated repetitive DNA melts over a wide temperature range.
Figure 3.7 The denatur at ion of reassociated nonrepetitive DNA takes place over a narrow temperature range close to that of native DNA, but reassociated repetitive DNA melts over a wide temperature range.
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Figure 3.7 The denatur at ion of reassociated nonrepetitive DNA takes place over a narrow temperature range close to that of native DNA, but reassociated repetitive DNA melts over a wide temperature range.
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Figure 3.8 The proportions of different sequence components vary in eukaryotic genomes. The absolute content of nonrepetitive DNA increases with genome size, but reaches a plateau at ~2 109bp.
Figure 3.9 The hybridization of an mRNA tracer prepar at ion in a reassoci at ion curve shows that most mRNA sequences are derived from nonrepetitive DNA, the remainder from moderately repetitive DNA, and none from highly repetitive DNA.
Orthologs are corresponding proteins in two species as defined by sequence homologies.
Proteomeis the total number of proteins produced by an organism.
Figure 3.5 Genome sizes and gene numbers are known from complete sequences for several organisms (Arabidopsis, Drosophila, and man are estimated from partial data). Lethal loci are estimated from genetic data.
Figure 3.6 ~20% of Drosophila genes code for proteins concerned with maintaining or expressing genes, ~20% for enzymes, <10% for proteins concerned with the cell cycle or signal transduction. Half of the genes of Drosophila code for products of unknown function.
Figure 3.7 Because many genes are duplicated. the number of different gene families is much less than the total number of genes.
Figure 3.8 The fly genome can be divided into genes that are (probably) present in all eukaryotes, additional genes that are (probably) present in all multicellular eukaryotes, and genes that are more specific to subgroups of species that include flies.
Natural selection is the force that ensures that useful genes are retained in the genome. Mutations occur at random, and their most common effect in an open reading frame will be to damage the protein product. An organism with a damaging mutation will be at a disadvantage in evolution, and ultimately the mutation will be eliminated by the competitive failure of organisms carrying it. The frequency of a disadvantageous allele in the popul at ion is balanced between the gener at ion of new mutations and the elimin at ion of old mutations. Reversing this argument, whenever we see an intact open reading frame in the genome, we assume that its product plays a useful role in the organism. Natural selection must have prevented mutations from accumulating in the gene. The ultimate fate of a gene that ceases to be useful is to accumulate mutations until it is no longer recognizable.
Figure 3.5 Genome sizes and gene numbers are known from complete sequences for several organisms (Arabidopsis, Drosophila, and man are estimated from partial data). Lethal loci are estimated from genetic data.3.4 How many genes are essential?.
Abundance of an mRNA is the average number of molecules per cell.
Figure 3.9 Hybridization between excess mRNA and cDNA identifies several components in chick oviduct cells, each characterized by the Rot? of reaction.3.5 How many genes are expressed?.
Figure 3.10 HDA analysis allows change in expression of each gene to be measured. Each square represents one gene (top left is first gene on chromosome I, bottom right is last gene on chromosome XVI). Change in expression relative to wild type is indicated by red (reducti on), whte (no change) or blue (increase). Photograph kindly provide3.5 How many genes are expressed?.
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ctDNAis chloroplast DNA.mtDNAis mitochondrial DNA.
Figure 3.01 Over view:mitochondrial protein aggregates are assembled from the products of expression of nuclear genes and mitochondrial genes.
Figure 3. 02 The Organelle ATPase consists of 2 pairs, the F0 membrane factor and the F1 ATPase, whose subunits have various origins in different species and organelles.
Figure 3.11 Mitochondrial genomes have genes coding for (mostly complex 1-4) proteins, rRNAs, and tRNAs.
Figure 3.13 The mitochondrial genome of S. cerevisiae contains both interrupted and uninterrupted protein-coding genes, rRNA genes, and tRNA genes (positions not indicated). Arrows indicate direction of transcription.
Figure 3.12 Human mitochondrial DNA has 22 tRNA genes, 2 rRNA genes, and 13 protein-coding regions. 14 of the 15 protein-coding or rRNA-coding regions are transcribed in the same direction. 14 of the tRNA genes are expressed in the clockwise direction and 8 are read counter clockwise.
Figure 3.14 The chloroplast genome codes for 4 rRNAs, 30 tRNAs, and ~50 proteins.3.9 The chloroplast genome codes for ~100 proteins and RNAs.
1.The sequences comprising a eukaryotic genome can be classified in three groups: nonrepetitive sequences are unique; moderately repetitive sequences are dispersed and repeated a small number of times in the form of related but not identical copies; and highly repetitive sequences are short and usually repeated as a tandem array. 2.Most structural genes are located in nonrepetitive DNA.3.The total number of genes is <1000 for Mycoplasma and intr a cellular para sites, 20004000 for bacteria, >6000 for yeast, >12,000 for insects, and >100,000 for mammals.4.Genes are expressed at widely varying levels.
It is likely that not all genes are essential (defining lethal genes by the existence of devastating effects when they are mutated). The numbers of nonessential genes and essential genes could be comparable.
5.Non Mendeli an inheritance is explained by the presence of DNA in organelles in the cytoplasm. Mitochondria and chloroplasts both represent membrane-bounded systems in which some proteins are synthesized within the organelle, while others are imported. The organelle genome is usually a circular DNA that codes for all of the RNAs and for some of the proteins that are required.6.Mitochondrial genomes vary greatly in size from the 16 kb minim a list mammalian genome to the 570 kb genome of higher plants.7.Mammalian mtDNAs are transcribed into a single transcript from the major coding strand, and individual products are generated by RNA processing. Rearrangements occur in mitochondrial DNA rather frequently in yeast; and recombination between mitochondrial or between chloroplast genomes has been found. There are some tantalizing homologies between mitochondrial and chloroplast genomes.
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