11遗传的细胞与分子基础英文版课件.ppt

1、The cellular and molecular basis in GeneticsThe Cell Basic component of life Two main categories,p r o k a r y t i c a n d eukaryotic cells Differences in the nucleus Prokaryotes lack a defined nucleus and have a simplified internal structure Eukaryotes have membrane limited nucleus and more complic

2、ated internal structure Three branches of life(古细菌古细菌)(细菌细菌)(真核生物界真核生物界)Bacterial cell（质粒）（质粒）Prokaryotes:which include the archaea(古细菌古细菌)and bacteria,are the simplest,oldest,and most common organisms on the planet.(1)A typical prokaryote has a much smaller genome than a typical eukaryote.Nearly al

3、ways,it is in the form of a simple loop of DNA.This loop is attached to the cell membrane.(2)Even though the structure simple,there is a lot of DNA in a single bacterium.Stretched out,the DNA in an E.coli would be 500 times longer than the cell itself.(3)Prokaryotes do not have sexual reproduction,t

4、hough they have several forms of gene exchange.These include swapping(交换的)plasmids(质粒质粒).(4)The various genes,about 1200 in a typical bacterium,are 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 c

5、hance that determines their location.(5)In prokaryotes,the DNA loop replicates before fission(分裂),with both loops still attached to the cell membrane.During fission,as the cell membrane splits in two,one loop of DNA ends up in each new“daughter cell”Animal cellPlant cellThis is the basic structure o

6、f all living things.Animals,plants,and to some extent even bacteria(they are made up of cells too,but 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

7、chloroplasts)carry some DNA of their own,but its the DNA in the nucleus of the cell well be focusing on.Eukaryotes:-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 membr

8、ane-bound nucleus.(2)Like 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.(3)Eu

9、karyote DNA(except plastid 质体质体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 chromosomes and pack

10、ed into a nucleus(or nuclei,in some cases).(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 chromosomes in cell division:mitosis and meiosis Sexual rep

11、roduction: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)Chromosomes:(1)Chromosomes are where the genes are located.(2)They are a complex of DNA and Proteins(3)Most of the time,chromosomes are not visible(

12、chromatin).(4)Before cells divide,the chromatin compacts,or condenses,to form chromosomes,which can be stained and seen with a microscope(4)Chromosomes are described by their general appearance.(5)At metaphase(when the chromosomes are easiest to see)each chromosome is actually a pair of sister chrom

13、atids,since the DNA has already been copied.(6)The chromosomes are grouped and individually identified based on the way they look at metaphase.Telomere regionsThe structure of a chromosome (着丝粒着丝粒)A chromosome is made up of two identical chromatids,and it has a central region called the centromere w

14、here these two chromatids stick together.The ends of the chromosome are called telomeres.染色单体染色单体端粒端粒Other Chromosome Components Chromosomal DNA contains other things besides genes:centromere(where the mitotic spindle attaches)telomeres(special structures on the ends of chromosomes)origins of replic

15、ation(where copying of DNA starts)pseudogenes(non-functional,mutated copies of genes)transposable elements,transposons(intranuclear parasites)genes that make small RNAs and not proteins“junk”(?)Chromosome Number Homologous chromosomes(同源染色体同源染色体):a pair of chromosomes that contain similar informatio

16、n(1 from mom and 1 from dad)Chromosomes(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?Examples of Animal Chromosome NumbersAnimalsChromosome No.Fruit Fly8Mouse 40Dog78Chicken78Jap.Qu

17、ail(鹌鹑鹌鹑)78Turkey80Duck80Examples of Plant Chromosome NumbersPlantsChromosome No.Rice 24Pea 14Wheat 42Tomato 24Maize 20Largest number of chromosomes known in a eukaryote:630 pairs(1260 total per somatic cell)Ophioglossum reticulatum（瓶耳小草瓶耳小草）a fern（蕨（蕨）Chromosome Theory H o w d o w e k n o w t h a t

18、 chromosomes are the physical location of genes?Evidence from cytology in organisms with heteromorphic sex chromosomes(异形性染异形性染色体色体)suggests that it was possible to correlate cytology with the inheritance of sex-linked traits.Chromosome Theory:What do we mean when w e s a y s e x chromosomes are het

19、eromorphic(异形异形的的)?Chromosome Theory:Other features of chromosomes were also useful.e.g.Barbara McClintocks work in maizeEuchromatinChromatin that is actively expressed is called euchromatin.Chromatin that is not actively expressed is called eterochromatinThe nucleolus(核仁核仁)is the site of ribosomal

20、RNA transcription and ribosome assembly.Animals,plants and fungi have repeats of their ribosomal RNA genes.Chromosomes Staining can also be used to reveal physical features of chromosomes.Technologies like FISH(fluoresence in situ hybridization)are very useful if one wishes to correlate sequences wi

21、th physical features.-The satellite DNA image could have been produced by FISH instead of autoradiography.HeterochromatinConstitutive heterochromatin(which is always condensed and inactive)will be visible as a compact region of chromatin.e.g.,the chromocenter in DrosophilaPolytene chromosomes Dipter

22、a(双翅目)replicate chromosomes in their salivary glands,but the replicated chromosomes stay together.These are called polytene chromosomes.Puffs(疏松部疏松部)on these polytene hromosomes will be apparent if specific genes are activated.-e.g.,heat shock puffs,ecdysterone(蜕皮激素)puffs.“Lampbrush”Chromosomes:This

23、 shows“lampbrush”chromosomes(often seen in amphibians)which illustrate the physical orientation of chromosomes.How is Chromatin CompactedEukaryote-specific proteins called histones form a structure called the nucleosome(核小体核小体),and DNA wraps around nucleosomes.DNA(dideoxynucleic acid)the double heli

24、xThis picture here is 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.ChromosomeA chromosome is a lump(一团)of very tightly packed DNA strands.You see the double helix and how it is wrap

25、ped 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 DNADNAchromatinchromatin fibersfibers connected to chromosome scaffoldCondenced scaffoldChromosome脚手架 The increased amount of DNA necessitates a means o

26、f 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 around one histone(like thread around a spool线轴),and locked in by a second,formin

27、g a structure called a nucleosome(核小体核小体).These structures further supercoil into a condensed configuration,to form the familiar shapes that scientists have viewed under light microscopes.How is Chromatin CompactedChromatin can be further compacted to form the 30 nm solenoid.This involves linker his

28、tones.The activation of genes can reflect the acetylation of histones(many transcriptional activators recruit histone acetyltransferases(组蛋白乙酰转移酶)or act as acetyltransferases)How is Chromatin CompactedThe solenoid can be further compacted on a protein scaffold.The structure of the scaffold is not co

29、mpletely clear,and there is evidence that DNA may hold chromosomes together in a compact form.The Physical Nature of ChromosomesNot all of the DNA on chromosomes encodes proteins(or RNAs).This shows the location of satellite DNA on mouse chromosomes.What are Genes?Genes(1)Genes are the tiny,basic un

30、its of inheritance found in DNA.(2)Genes determine color,size,and make-up for every 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.What are

31、Loci?Loci(位点位点)are numbered.This depicts a chromosome half.When geneticists 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.Loci(1)The

32、 different points or markers along 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 c

33、an be two Alleles.What are Alleles(等位基因等位基因)?(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 mothe

34、r and one from your father.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.LociAllelesActual photoHow Many Loci are There?Bacteria have about 1,200

35、genes Yeast have about 5,000,Drosophila melanogaster have about 10,000 Human beings have approximately 29,000.Do all loci have multiple alleles(复等位基因复等位基因)?No,only a small percentage of loci have multiple alleles,perhaps 1-5%or less,depending upon the species.Gene Differences Genes often have severa

36、l 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 an individual diploid organism can have 2 alleles at most:one from each

37、 parent.Diploid=having 2 copies of each gene and each chromosome.Structure of a geneRegulatory regionRegion that acts as a template forthe production of proteinsThis is the basic elements of a gene.Its made up of the region that is the template for a protein,as well as a regulatory region.This regio

38、n defines when,where,and in how many copies RNA is going to be made.The Physical Nature of GenesGenome projects have allowed us to establish the physical nature of genes in great detail.e.g.,Prokaryotes do not have introns and exons;animals,fungi and plants have different gene structures.The Physica

39、l Nature of GenesGraphically,these differences would look like this:Gene ExpressionGenes are expressed 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 polypeptid

40、e.the genetic code is a list of which 3 base DNA or RNA sequence(codon)encodes which amino acid.The same genetic code is used in(almost)all organisms.DNAGeneTranscriptionTranslationRNA(messenger RNA)Protein(sequence ofamino acids)Functioning of proteins within living cells influences an organisms tr

41、aits.Central dogma of information flow in geneticsAll cells in the body have the same DNA,but different genes are expressed in different cells and u n d e r d i ff e r e n t conditions.The number and localisation of RNA molecules is going to influence how much protein is made and in which part of th

42、e 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 because the two cells have decided to use different parts of their DNA or at different timepoints.The muscle cell has everyt

43、hing needed to make a nerve cell and vice versa(发过来也一样发过来也一样).Pigmentation gene,dark allelePigmentation gene,light alleleTranscriptionand translationHighly functionalpigmentation enzymePoorly functionalpigmentation enzymeMolecular levelMutation&Phenotypic VariationWing cellsLots of pigment madeLittl

44、e pigment madePigmentmolecule(b)Cellular levelPigmentation gene,dark allelePigmentation gene,light alleleTranscriptionand translationHighly functionalpigmentation enzymePoorly functionalpigmentation enzyme(a)Molecular levelMutation&Phenotypic VariationDark butterflyLight butterfly Organismal levelMu

45、tation&Phenotypic VariationDark butterflies are usuallyin forested regions.Light butterflies are usually in unforested regions.Populational levelThe“Take Home”Messages(1)It was possible to establish that chromosomes are the physical location of genes by correlating visible aspects of the chromosomes

46、 with patterns of inheritance(sex chromosomes).(2)Prokaryotic genomes are very gene-rich(90%protein coding,in many cases)Eukaryotic genomes may have a majority of DNA that is non-coding(regulatory,structural,selfish?).Eukaryotic chromosomes can be divided into two broad types of chromatin-heterochromatin and euchromatin.The latter is the location of functional genes.