Slide 1

The Cell Cycle and MitosisRevision Draw and label an animal cellGive the function of nuclear pores, mitochondria, golgi apparatus, Endoplasmic reticulumWhat is the structure of DNA?How is DNA packaged?Chromosome StructureChromosomes are visible during cell division.Each chromosome consists of two chromatids joined somewhere along its length at the centromere.Genetic information (genes/alleles) carried on each chromatid is identical.CentromereChromatidChromosomeIdentify the gender and condition of the individual with the following karyotypes.Gender:Condition:Gender:Condition:12345678910111213141516171819202122231234567891011121314151617181920212223Gender: Male (XY)Condition:Gender: Female (XX)Condition:Gender: Male (XY)Condition: NormalGender: Female (XX)Condition: Trisomy 21The Cell CycleThe cell cycle describes the sequence of cell growth and cell division.It includes:Interphasecell growth synthesis of organelles DNA copying and checking of genetic informationMitosischromosomes divideCytokinesiscytoplasm divided between the daughter cells

5 The Cell CycleDNA replicationThis must happen at some time during interphaseThe cell cycle describes the events during one complete cycle of division, they are represented in the chart:Cytokinesiscompletes the cellular divisionNuclear divisionThis interphase and includes prophase, metaphase, anaphase and telophaseInterphase It is a period of intense activity to make new cellular structuresMitosis CellNucleusMitosis is the formationof two new IDENTICALdaughter cells from anoriginal cell.It is how organisms grow and is also the basis of simple Asexual reproduction.The interesting stuff happens In the nucleus.MitosisMitosis is a continuous sequence but is divided into four stages:prophasemetaphaseanaphasetelophaseEssentiallychromatids are separated by contraction of spindle fibres. chromatids are pulled to opposite poles of the cell.the cell then divides.Each chromatid contains identical genetic information so each daughter cell also contains identical information.8NucleusThe nucleus of all ordinary somatic (body) cells contains chromosomes.In diploid organisms (like us)there are two copies ofeach chromosome.In human body cells there are23 pairs of chromosomesmaking a total of 46 chromosomes.Early Prophase

During prophase the chromosomes become more distinctthey coil upshortenthickentake up stain more intenselyThe centriole divides Nucleolus becomes less prominent.

10Late Prophase

The chromosomes have become more distinct and are seen to consist of two chromatids joined by a centromere.The centrioles migrate to opposite poles of the cell.The nucleolus continues to shrink and disappears.The nuclear envelope disintegrates.

11Mitosis The following slides show stages in AlliumProphase (early)Chromosomes coil and condenseNuclear envelope presentNucleolus is evident

Prophase (late)Chromosome clearly visible as two chromatids joined at the centromereNuclear envelope disappearsNucleolus disappears12Metaphase

Each centriole is at a pole.Centrioles grow/produce spindle fibres.Spindle fibres attach to the centromere of the chromosomes.Each centromere is attached to both poles.Chromosomes pulled to the metaphase plate or equator.

13 Mitosis MetaphaseSpindle forms some fibres attach to the centromeres, others run from pole to pole.Chromosomes are pulled to the equator of the cell (metaphase plate) by contraction of the fibres.Centromere splits and cell then enters anaphase.

14Anaphase

Spindle fibres contract.The centromere divides. Chromatids (daughter chromosomes) are pulled to opposite poles of the cell.Pulled centromere first.Each half of the cell receives one chromatid from each chromosome.

15 Mitosis AnaphaseChromatids move to opposite poles of the cell.They are pulled centromere-first by the contracting spindle fibres.

16Telophase Chromatids reach the poles of the spindle.They begin to uncoil.They become less distinct.Nuclear envelope starts to reform.Q. What are the chromatids known as when they reach the poles of the spindle?Daughter chromosomes

17 Mitosis TelophaseChromatids (now often called daughter chromosomes) reach the poles of the spindle.Nuclear envelope reforms.Nucleolus reforms.Cell moves into cytokinesis or cell division.

18CytokinesisThe cell divides!In animal cells:starts by constriction from the edges of the cell (invagination).In plant cells: a cell wall is laid down.Daughter cells have the same chromosome number and genetic makeup as each other and the parent cell DNA replication precedes mitosis.19 Mitosis CytokinesisAs shown here, in plant cells a cell wall is laid down in the position of the metaphase plate.

20InterphaseThis stage comes between successive cell divisions. It is not really part of mitosis, but mitosis couldnt happen without it.DNA replication occurs (allowing for the double stranded chromosome which later divides).Cellular structures are made (subsequently divided between the two daughter cells).A significant proportion of time is spent checking genetic information.

21Mitosis

Telophase

Prophase

Interphase

Metaphase

Anaphase22The chromosomes condense into visible, shorter and thicker threads. The chromosomes appear as two strands or chromatids joined by the centromere. During prophase in animal cells the two centrioles move towards opposite poles of the nucleus. Centrioles are absent in plant cells. At the end of prophase the double chromosomes start to move towards the middle (equator) of the nucleus The nuclear membrane fragments and disappears. Prophase

This is a brief phase The chromosomes are arranged in the equatorial plane of the cell with their centromeres attached to the spindle fibres. In side view they appear as a line across the middle of the spindle.Metaphase

This is a brief phase The chromosomes are arranged in the equatorial plane with their centromeres attached byspindle fibres to the microtubule ends. In side view they appear as a line across the middle of the spindle.Metaphase

The double stranded chromosomes are pulled apart separating each chromatid.They are drawn towards the poles by the contracting spindles by their centromeres. By late anaphase the cell contains two equal groups of chromosomes each near the respective pole of the spindle.Anaphase

The double stranded chromosomes are pulled apart separating each chromatid.They are drawn towards the poles by the contracting spindles by their centromeres. By late anaphase the cell contains two equal groups of chromosomes each near the respective pole of the spindle.Anaphase

The double stranded chromosomes are pulled apart separating each chromatid.They are drawn towards the poles by the contracting spindles by their centromeres. By late anaphase the cell contains two equal groups of chromosomes each near the respective pole of the spindle.Anaphase

The two sets of chromosomes (now just single chromatids) reach new poles and become enclosed in new nuclear membranes The chromosomes become longer and thinner and return to their interphase form Cytokinesis occurs- a cleavage furrow develops, deepens and eventually cuts the cell in two. The two new genetically identical cells then pass into the G1 phase of the cell cycle.Telophase

The two sets of chromosomes (now just single chromatids) reach new poles and become enclosed in new nuclear membranes The chromosomes become longer and thinner and return to their interphase form and the nucleoli reappear. Cytokinesis occurs- a cleavage furrow develops, deepens and eventually cuts the cell in two. The two new genetically identical cells then pass into the G1 phase of the cell cycle.Telophase

Cytokinesis occurs- a cleavage furrow develops, deepens and eventually cuts the cell in two. The two new genetically identical cells then pass into the G1 phase of the cell cycle.Cytokinesis

Cytokinesis occurs- a cleavage furrow develops, deepens and eventually cuts the cell in two. The two new genetically identical cells then pass into the G1 phase of the cell cycle.CytokinesisIdentify the stage of mitotic division that the cells indicated by guidelines are in . State a reason for your identification.ECDFBAG

BACHFDEG A = Cytokinesis B = Prophase (late) C = Prophase (early) D = Anaphase (late) E = Anaphase (early) F = Metaphase G = InterphaseAnd the correct order of the stages is: And the correct order of the stages is: (G) C B F E D H A (G)H H = TelophaseKey points:

DNA is copied during Interphase NOT prophase!

The four stages are VERY basically;a. Prophase nuclear membrane disintegrates and doubled chromosomes condense, shorten and BEGIN to move to the equator. b. Metaphase the chromosomes line up alongthe equator attached to spindles by their centromeres

c. Anaphase the chromatids of each replicated double chromosome are ripped apart at the centromere andpulled towards different poles.

d. Telophase chromosomes (chromatids) arrive at the poles and new nuclear membranes form followed by cytokinesis actual cytoplasm splitting to form twonew IDENTICAL daughter cells

Mitosis

An overview