01 Replication and Division of Nuclei and Cells

CELL AND NUCLEAR CELL AND NUCLEAR DIVISIONDIVISION

Replication and division of nuclei Replication and division of nuclei and cellsand cells

ALBIO9700/2006JK

Haploid and diploid cellsHaploid and diploid cells

• nn – number of chromosomes in one – number of chromosomes in one set of chromosomesset of chromosomes

• DiploidDiploid – cells that contain 2 sets of – cells that contain 2 sets of chromosomes (chromosomes (2n2n))

• HaploidHaploid – cells that contain 1 set of – cells that contain 1 set of chromosomes (chromosomes (nn))

• Humans: a 2n body cell has 46 Humans: a 2n body cell has 46 chromosomes and a gamete has 23chromosomes and a gamete has 23

ALBIO9700/2006JK

Two types of nuclear Two types of nuclear divisiondivision

• GrowthGrowth – when diploid zygote grows – when diploid zygote grows into a multicellular diploid adult the into a multicellular diploid adult the daughter cells must keep the same daughter cells must keep the same number of chromosomes as the parent number of chromosomes as the parent cell: cell: MitosisMitosis

• Sexual reproductionSexual reproduction – there must be a – there must be a point when the number of chromosomes point when the number of chromosomes is halved. If there was no point in the life is halved. If there was no point in the life cycle when the number of chromosomes cycle when the number of chromosomes halved then it would double every halved then it would double every generation: generation: MeiosisMeiosis

ALBIO9700/2006JK

ALBIO9700/2006JK

Biological importance of Biological importance of mitosismitosis

• MitosisMitosis – nuclear division that produces 2 – nuclear division that produces 2 genetically identical daughter nuclei, each genetically identical daughter nuclei, each containing the same number of chromosomes as containing the same number of chromosomes as the parent nucleusthe parent nucleus

• Allows Allows growthgrowth of multicellular organisms from of multicellular organisms from unicellular zygotes. Growth may occur over the unicellular zygotes. Growth may occur over the entire body (animals) or be confined to certain entire body (animals) or be confined to certain regions (meristems of plants)regions (meristems of plants)

• Replacement of cells and Replacement of cells and repairrepair of tissues. Dead of tissues. Dead cells replaced by identical ones (skin, lining of the cells replaced by identical ones (skin, lining of the gut and even whole parts of the body)gut and even whole parts of the body)

• Basis of Basis of asexual reproductionasexual reproduction (production of new (production of new individuals of a species by one parent organism). individuals of a species by one parent organism). The ability to generate whole organisms from single The ability to generate whole organisms from single cells is becoming important in biotechnology and cells is becoming important in biotechnology and genetic engineeringgenetic engineering

ALBIO9700/2006JK

ChromosomesChromosomes

• ChromoChromo means ‘coloured’; means ‘coloured’; somessomes means ‘bodies’ means ‘bodies’• Chromosomes are matched in pairs (Chromosomes are matched in pairs (homologous homologous

pairspairs). In the original zygote, one of each pair came ). In the original zygote, one of each pair came from the mother and one from the father.from the mother and one from the father.

• Accurate and precise nuclear division during growth Accurate and precise nuclear division during growth results in all cells of the body containing the two results in all cells of the body containing the two sets of chromosomes.sets of chromosomes.

• The pairs of chromosomes can be distinguished The pairs of chromosomes can be distinguished because each pair has a distinctive banding pattern because each pair has a distinctive banding pattern when stained.when stained.

• 2 chromosomes are displayed to one side (2 chromosomes are displayed to one side (sex sex chromosomeschromosomes) which determine the sex. All other ) which determine the sex. All other chromosomes are called chromosomes are called autosomesautosomes..

• Each chromosome has a characteristic set of genes Each chromosome has a characteristic set of genes which code for different featureswhich code for different features

ALBIO9700/2006JK

Banding pattern of human Banding pattern of human chromosomeschromosomes

ALBIO9700/2006JK

ALBIO9700/2006JK

Structure of chromosomesStructure of chromosomes

• A double structure made of 2 identical structures A double structure made of 2 identical structures ((chromatidschromatids))

• 2 chromatids are held together by a narrow region 2 chromatids are held together by a narrow region ((centromerecentromere))

• Centromere position is characteristic for a Centromere position is characteristic for a particular chromosomeparticular chromosome

• Each chromatid contains one DNA moleculeEach chromatid contains one DNA molecule• The fact that the 2 DNA molecules in sister The fact that the 2 DNA molecules in sister

chromatids, and hence their genes, are identical is chromatids, and hence their genes, are identical is the key to precise nuclear divisionthe key to precise nuclear division

• The gene for a particular characteristic is always The gene for a particular characteristic is always found on the same position (found on the same position (locus/locilocus/loci) on a ) on a chromosomechromosome

ALBIO9700/2006JK

• Homologous chromosomesHomologous chromosomes – a pair of – a pair of chromosomes in a diploid cell that have chromosomes in a diploid cell that have the same structure as each other, with the same structure as each other, with the same genes (but not necessarily the the same genes (but not necessarily the same alleles of those genes) at the same same alleles of those genes) at the same lociloci

• Each member of a pair possesses genes Each member of a pair possesses genes for the same characteristics but differing for the same characteristics but differing in how they code for those characteristicsin how they code for those characteristics

• AllelesAlleles – a particular variety of a gene – a particular variety of a gene

ALBIO9700/2006JK

CancerCancer

• Cancer shows the importance of controlling cell division precisely – result of uncontrolled mitosis

• Cancerous cells divide repeatedly, out of control, and a tumour develops which is an irregular mass of cells. The cells usually show abnormal changes in shape.

ALBIO9700/2006JK

Carcinogens Carcinogens

• Starts when changes occur in the genes Starts when changes occur in the genes that control cell divisionthat control cell division

• OncogeneOncogene – mutated gene that causes – mutated gene that causes cancercancer

• MutationMutation – a change in the gene – a change in the gene• Cancerous cells manage to escape early Cancerous cells manage to escape early

death and being destroyed by the body’s death and being destroyed by the body’s immune system. The mutation is passed on immune system. The mutation is passed on to all that cell’s descendents.to all that cell’s descendents.

• MutagenMutagen – factor which brings about any – factor which brings about any mutationmutation

• CarcinogenCarcinogen – agent that causes cancer – agent that causes cancer

ALBIO9700/2006JK

• Ionising radiationIonising radiation– X-rays, gamma rays, UV light and particles from X-rays, gamma rays, UV light and particles from

the decay of radioactive elements. Cause the the decay of radioactive elements. Cause the formation of damaging ions inside cells which formation of damaging ions inside cells which can break DNA strandscan break DNA strands

• ChemicalsChemicals– Tar of tobacco smoke, certain dyes (aniline Tar of tobacco smoke, certain dyes (aniline

dyes), Etidium bromide (EtBr)dyes), Etidium bromide (EtBr)• Virus infectionVirus infection

– Burkitt’s lymphoma, leukaemia, papilloma Burkitt’s lymphoma, leukaemia, papilloma viruses (cervical cancer)viruses (cervical cancer)

– Viruses that cause cancer usually carry Viruses that cause cancer usually carry oncogenes or regulatory genes that can become oncogenes or regulatory genes that can become oncogenesoncogenes

• Hereditary predispositionHereditary predisposition– Susceptibility to the factors that cause the Susceptibility to the factors that cause the

disease is inherited or inheritance of a single disease is inherited or inheritance of a single faulty genefaulty gene

– Retinoblastoma (error on chromosome 13)Retinoblastoma (error on chromosome 13)ALBIO9700/2006JK

ALBIO9700/2006JK

• Primary growthPrimary growth – a small group of tumour – a small group of tumour cellscells

• BenignBenign tumours – do not spread from their tumours – do not spread from their site of origin, but can compress and site of origin, but can compress and displace surrounding tissues (warts, ovarian displace surrounding tissues (warts, ovarian cysts and some brain tumours)cysts and some brain tumours)

• MalignantMalignant (cancerous) tumours – spread (cancerous) tumours – spread throughout body, invade other tissues and throughout body, invade other tissues and eventually destroy themeventually destroy them

• Cells can break off and spread through Cells can break off and spread through blood and lymphatic system to other parts blood and lymphatic system to other parts of the body (of the body (secondary growthssecondary growths) – ) – metastasismetastasis

ALBIO9700/2006JK

ALBIO9700/2006JK

ALBIO9700/2006JK