11遺傳的細(xì)胞與分子基礎(chǔ)英文版課件

1、The cellular and molecular basis in GeneticsThe cellular and molecular basThe CellBasic component of lifeTwo main categories, prokarytic and eukaryotic cellsDifferences in the nucleusThe CellBasic component of liProkaryotes lack a defined nucleus and have a simplified internal structureEukaryotes ha

2、ve membrane limited nucleus and more complicated internal structureThree branches of life(古細(xì)菌)(細(xì)菌)(真核生物界) Prokaryotes lack a defined nucBacterial cell（質(zhì)粒）Bacterial cell（質(zhì)粒）Prokaryotes: which include the archaea (古細(xì)菌) and bacteria, are the simplest, oldest, and most common organisms on the planet.(1)

3、 A typical prokaryote has a much smaller genome than a typical eukaryote.Nearly always, it is in the form of a simple loop of DNA.This loop is attached to the cell membrane.Prokaryotes: which include the(2) Even though the structure simple, there is a lot of DNA in a single bacterium. Stretched out,

4、 the DNA in an E. coli would be 500 times longer than the cell itself.(3) Prokaryotes do not have sexual reproduction, though they have several forms of gene exchange.These include swapping (交換的) plasmids (質(zhì)粒).(2) Even though the structure (4) The various genes, about 1200 in a typical bacterium, ar

5、e arranged along the length of the chromosome, like beads on a string.There is no particular functional grouping to their order, it is mostly evolutionary chance that determines their location.(5) In prokaryotes, the DNA loop replicates before fission (分裂), with both loops still attached to the cell

6、 membrane. During fission, as the cell membrane splits in two, one loop of DNA ends up in each new “daughter cell” (4) The various genes, aboutAnimal cellPlant cellThis is the basic structure of all living things. Animals, plants, and to some extent even bacteria (they are made up of cells too, but

7、the cells have a different structure,). The mitochondria (as well as chloroplasts in plants) are thought to be ancient bacteria that were somehow swallowed by the cell, and these mitochondria (including chloroplasts) carry some DNA of their own, but its the DNA in the nucleus of the cell well be foc

8、using on.Animal cellPlant cellThis is tEukaryotes: -including plants, animals, fungi, protists (原生生物), often multicellular.(1) Most eukaryotes have several orders of magnitude more DNA than a typical prokaryote. DNA is contained within a membrane-bound nucleus.Eukaryotes: (1) Most eukaryote(2) Like

9、prokaryotes, eukaryote genes are arranged along the length of a chromosome like beads on a string. There is no particular functional reason for their location, either within a chromosome, or with respect to what chromosome they are on, it is mostly an evolutionary accident.(2) Like prokaryotes, euka

10、ryot(3) Eukaryote DNA (except plastid 質(zhì)體DNA, which is very similar to bacterial DNA because of its evolutionary origin) is usually linear, not circular.These strands are long, and extended (thus, invisible to microscopes) during the normal life of the cell.These linear strands of DNA are called chro

11、mosomes and packed into a nucleus (or nuclei, in some cases).(3) Eukaryote DNA (except plas(4) In multicellular eukarotes, every cell has the same DNA, though in any given cell, only a fraction of the genes are active, others are permanently “turned off” during development. A careful division of chr

12、omosomes in cell division: mitosis and meiosis Sexual reproduction: 2 partners contribute equally to offspring life cycle: alternation of haploid and diploid phases (i.e. 1 vs. 2 copies of each gene and chromosome)(4) In multicellular eukarotesChromosomes:Chromosomes:(1) Chromosomes are where the ge

13、nes are located.(2) They are a complex of DNA and Proteins(3) Most of the time, chromosomes are not visible (chromatin).(4) Before cells divide, the chromatin compacts, or condenses, to form chromosomes, which can be stained and seen with a microscope(1) Chromosomes are where the (4)Chromosomes are

14、described by their general appearance.(5) At metaphase (when the chromosomes are easiest to see) each chromosome is actually a pair of sister chromatids, since the DNA has already been copied. (6) The chromosomes are grouped and individually identified based on the way they look at metaphase.(4)Chro

15、mosomes are described bTelomere regionsThe structure of a chromosome (著絲粒)A chromosome is made up of two identical chromatids, and it has a central region called the centromere where these two chromatids stick together. The ends of the chromosome are called telomeres. 染色單體端粒Telomere The structure of

16、 a chOther Chromosome ComponentsChromosomal DNA contains other things besides genes:centromere (where the mitotic spindle attaches)telomeres (special structures on the ends of chromosomes)origins of replication (where copying of DNA starts)pseudogenes (non-functional, mutated copies of genes)transpo

17、sable elements, transposons (intranuclear parasites)genes that make small RNAs and not proteins“junk” (?)Other Chromosome ComponentsChrChromosome NumberHomologous chromosomes(同源染色體): a pair of chromosomes that contain similar information (1 from mom and 1 from dad)Chromosome NumberHomologous chChrom

18、osomes (1) How many chromosomes are present in an animals or plants cell ? 1,10, 50.(2) Does the animals or plants physical size relate to the number of chromosomes it contains? Chromosomes (1) How many chromExamples of Animal Chromosome NumbersAnimalsChromosome No.Fruit Fly8Mouse 40Dog78Chicken78Ja

19、p. Quail (鵪鶉) 78Turkey80Duck80Examples of Animal Chromosome Examples of Plant Chromosome NumbersPlantsChromosome No.Rice 24Pea 14Wheat 42Tomato 24Maize 20Examples of Plant Chromosome NLargest number of chromosomes known in a eukaryote: 630 pairs (1260 total per somatic cell)Ophioglossum reticulatum（

20、瓶耳小草 ） a fern（蕨 ）Largest number of chromosomes Chromosome Theory How do we know that chromosomes are the physical location of genes? Evidence from cytology in organisms with heteromorphic sex chromosomes (異形性染色體) suggests that it was possible to correlate cytology with the inheritance of sex-linked

21、traits.Chromosome TheoryChromosome Theory:What do we mean when we say sex chromosomes are heteromorphic (異形的)?Chromosome Theory: Chromosome Theory: Other features of chromosomes were also useful. e.g. Barbara McClintocks work in maize Chromosome Theory: OtherEuchromatinChromatin that is actively exp

22、ressed is called euchromatin. Chromatin that is not actively expressed is called eterochromatinThe nucleolus (核仁) is the site of ribosomal RNA transcription and ribosome assembly.Animals, plants and fungi have repeats of their ribosomal RNA genes.EuchromatinChromosomes Staining can also be used to r

23、eveal physical features of chromosomes. Technologies like FISH (fluoresence in situ hybridization) are very useful if one wishes to correlate sequences with physical features.- The satellite DNA image could have been produced by FISH instead of autoradiography.Chromosomes HeterochromatinConstitutive

24、 heterochromatin (which is always condensed and inactive) will be visible as a compact region of chromatin.e.g., the chromocenter in Drosophila HeterochromatinPolytene chromosomes Diptera (雙翅目) replicate chromosomes in their salivary glands, but the replicated chromosomes stay together. These are ca

25、lled polytene chromosomes.Puffs (疏松部) on these polytene hromosomes will be apparent if specific genes are activated.-e.g., heat shock puffs, ecdysterone(蛻皮激素) puffs.Polytene chromosomesPuffs (疏松部“Lampbrush” Chromosomes: This shows “l(fā)ampbrush” chromosomes (often seen in amphibians) which illustrate t

26、he physical orientation of chromosomes.“Lampbrush” Chromosomes:How is Chromatin CompactedEukaryote-specific proteins called histones form a structure called the nucleosome (核小體), and DNA wraps around nucleosomes. How is Chromatin CompactedDNA (dideoxynucleic acid) the double helixThis picture here i

27、s to show you what DNA is. Its a double helix, it was first defined by Watson and Crick in 1953 in a famous article in Nature. They got the Nobel prize for this in 1962.DNA (dideoxynucleic acid)This ChromosomeA chromosome is a lump (一團(tuán)) of very tightly packed DNA strands. You see the double helix an

28、d how it is wrapped around the histone proteins and then coiled up more and more to make up the chromosomes. These chromosomes are all inside the nucleus. Packing of DNAChromosomeA chromosome is a luDNAchromatinchromatin fibersfibers connected to chromosome scaffoldCondenced scaffoldChromosome腳手架 DN

29、Achromatinchromatin fibersfiThe increased amount of DNA necessitates a means of condensing these long strands into compact structures that can be sorted into separate daughter cells during cell division.Histones are important and very evolutionarily conservative proteins. Loops of DNA are wrapped ar

30、ound one histone (like thread around a spool線軸), and locked in by a second, forming a structure called a nucleosome (核小體).These structures further supercoil into a condensed configuration, to form the familiar shapes that scientists have viewed under light microscopes.The increased amount of DNA neH

31、ow is Chromatin CompactedChromatin can be further compacted to form the 30 nm solenoid. This involves linker histones.The activation of genes can reflect the acetylation of histones (many transcriptional activators recruit histone acetyltransferases (組蛋白乙酰轉(zhuǎn)移酶 )or act as acetyltransferases)How is Chr

32、omatin CompactedHow is Chromatin CompactedThe solenoid can be further compacted on a protein scaffold.The structure of the scaffold is not completely clear, and there is evidence that DNA may hold chromosomes together in a compact form.How is Chromatin CompactedThe Physical Nature of ChromosomesNot

33、all of the DNA on chromosomes encodes proteins (or RNAs).This shows the location of satellite DNA on mouse chromosomes.The Physical Nature of ChromosWhat are Genes?What are Genes?Genes(1) Genes are the tiny, basic units of inheritance found in DNA.(2) Genes determine color, size, and make-up for eve

34、ry living species.(3) Each equine species receives half of their genes from their sire (father) and half from their dam (mother).(4) Physically, genes are linked together like a strand of pearls to form a chromosome.GenesWhat are Loci ?Loci(位點(diǎn))are numbered. This depicts a chromosome half.When geneti

35、cists speak about genes, they prefer to use the word locus. The two are virtual synonyms, but locus means location, and it refers to the place where variation can occur. Using the word gene emphasizes its information content.What are Loci ?Loci(位點(diǎn))are numLoci(1) The different points or markers along

36、 a chromosome.(2) Loci are like street signs in a busy city, allowing us to find our way along a complex chromosome.(3) At a specific locus, scientists can locate certain genes. These genes appear at that locus for every individual of that species.(4) At one locus there can be two Alleles.LociWhat a

37、re Alleles (等位基因) ?(1)Two alleles are found at each loci on a chromosome.(2)Alleles code for the different ways a gene can be expressed.(3) For example, consider your eye color. You have a loci on a chromosome for eye color. At that loci there are two allelesone from your mother and one from your fa

38、ther. The dominant of the two alleles is the eye color that you display. This is your phenotype (the eye color seen). The genetic classification (what we cant see but what is on the loci) is called the genotype.What are Alleles (等位基因) ?(1)TwLociAllelesActual photoLociAllelesActual photoHow Many Loci

39、 are There?Bacteria have about 1,200 genesYeast have about 5,000, Drosophila melanogaster have about 10,000Human beings have approximately 29,000.Do all loci have multiple alleles (復(fù)等位基因) ?No, only a small percentage of loci have multiple alleles, perhaps 1-5% or less, depending upon the species.How

40、 Many Loci are There?BacterGene DifferencesGenes often have several alleles: the same gene in the same chromosomal location, but with minor nucleotide changes that yield slightly different proteins.For a given gene, many different alleles can exist in a population (members of the same species), but

41、an individual diploid organism can have 2 alleles at most: one from each parent. Diploid = having 2 copies of each gene and each chromosome.Gene DifferencesGenes often ha1Structure of a geneRegulatory regionRegion that acts as a template forthe production of proteinsThis is the basic elements of a g

42、ene. Its made up of the region that is the template for a protein, as well as a regulatory region. This region defines when, where, and in how many copies RNA is going to be made. Structure of a geneRegulatory The Physical Nature of GenesGenome projects have allowed us to establish the physical natu

43、re of genes in great detail.e.g., Prokaryotes do not have introns and exons; animals, fungi and plants have different gene structures.The Physical Nature of GenesThe Physical Nature of GenesGraphically, these differences would look like this:The Physical Nature of GenesGene ExpressionGenes are expre

44、ssed in a 2 step process: First, an RNA copy of a single gene is made (transcription). Then, the nucleotide sequence of the RNA copy (messenger RNA) is translated into the amino acid sequence of the polypeptide.the genetic code is a list of which 3 base DNA or RNA sequence (codon) encodes which amin

45、o acid. The same genetic code is used in (almost) all organisms.Gene ExpressionGenes are expreDNAGeneTranscriptionTranslationRNA (messenger RNA)Protein(sequence ofamino acids)Functioning of proteins within living cells influences an organisms traits.Central dogma of information flow in geneticsAll c

46、ells in the body have the same DNA, but different genes are expressed in different cells and under different conditions.DNAGeneTranscriptionTranslatio The number and localisation of RNA molecules is going to influence how much protein is made and in which part of the body. This is the reason two cells that carry the exact same DNA in their nucleus can be totally different. One of them can be a muscle cell, the other one a nerve cell. This is becaus