Presentation on theme: "Introduction to Biology"— Presentation transcript:
1Introduction to Biology The Cell CycleIntroduction to Biology
2The Key Roles of Cell Division The ability to reproduce is one of the key features that separates life from non-life.All cells have the ability to reproduce, by making exact copies of themselves.
3In multicellular organisms, cell division is needed for: In unicellular organisms, division of one cell reproduces the entire organismIn multicellular organisms, cell division is needed for:Development of an embryo from a sperm/eggGrowthRepair
4LE 12-2 Reproduction Growth and development Tissue renewal 100 µm
5Asexual ReproductionAsexual reproduction is reproduction that involves a single parent producing an offspring.The offspring produced are, in most cases, genetically identical to the single cell that produced them.Asexual reproduction is a simple, efficient, and effective way for an organism to produce a large number of offspring.Prokaryotic organisms (like bacteria) reproduce asexually, as do some eukaryotes (like sponges)
6Sexual ReproductionIn sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow.The offspring produced inherit some genetic information from both parents.Most animals and plants, and many single-celled organisms, reproduce sexually.
8Cell DivisionCells duplicate their genetic material before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA.A dividing cell duplicates its DNA, allocates the two copies to opposite ends of the cell, and only then splits into daughter cells.
9Cellular Organization of the Genetic Material A cell’s endowment of DNA (its genetic information) is called its genome.DNA molecules in a cell are packaged into chromosomes.
10ChromosomesThe genetic information that is passed on from one generation of cells to the next is carried by chromosomes.Every cell must copy its genetic information before cell division begins.Each daughter cell gets its own copy of that genetic information.Cells of every organism have a specific number of chromosomes.
11Prokaryotic Chromosomes Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm.Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.
12Eukaryotic Chromosomes In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin.
13Chromatin is composed of DNA and histone proteins.
14DNA coils around histone proteins to form nucleosomes.
15The nucleosomes interact with one another to form coils and supercoils that make up chromosomes.
16Chromosomes During Cell Division In preparation for cell division, DNA is replicated and the chromosomes condenseEach duplicated chromosome has two sister chromatids, which separate during cell divisionThe centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached
18Phases of the Cell Cycle The cell cycle consists ofMitotic (M) phase (mitosis and cytokinesis)Interphase (cell growth and copying of chromosomes in preparation for cell division)Interphase (about 90% of the cell cycle) can be divided into subphases:G1 phase (“first gap”)S phase (“synthesis”)G2 phase (“second gap”)
19INTERPHASE S (DNA synthesis) LE 12-5INTERPHASES(DNA synthesis)G1CytokinesisMitosisG2MITOTIC(M) PHASE
20G1 Phase: Cell GrowthIn the G1 phase, cells increase in size and synthesize new proteins and organelles.
21S Phase: DNA Replication In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.
22G2 Phase: Preparing for Cell Division In the G2 phase, many of the organelles and molecules required for cell division are produced.
23M Phase: Cell DivisionIn eukaryotes, cell division occurs in two stages: mitosis and cytokinesis.Mitosis is the division of the cell nucleus.Cytokinesis is the division of the cytoplasm.
24Important Cell Structures Involved in Mitosis Chromatid – each strand of a duplicated chromosomeCentromere – the area where each pair of chromatids is joinedCentrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindleSpindle – long proteins (part of the cytoskeleton) that the centrioles produceHelps move the chromosomes into place.
26ProphaseDuring prophase, the first phase of mitosis, the duplicated chromosome condenses and becomes visible.
27ProphaseThe centrioles move to opposite sides of nucleus and help organize the spindle.
28ProphaseThe spindle forms and DNA strands attach at a point called their centromere.
29ProphaseThe nucleolus disappears and nuclear envelope breaks down.
30MetaphaseDuring metaphase, the second phase of mitosis, the centromeres of the duplicated chromosomes line up across the center of the cell.
31MetaphaseThe spindle fibers connect the centromere of each chromosome to the two poles of the spindle.
32AnaphaseDuring anaphase, the third phase of mitosis, the centromeres are pulled apart and the chromatids separate to become individual chromosomes.
33AnaphaseThe chromosomes separate into two groups near the poles of the spindle.
34TelophaseDuring telophase, the fourth and final phase of mitosis, the chromosomes spread out into a tangle of chromatin.
35TelophaseA nuclear envelope re-forms around each cluster of chromosomes.
36TelophaseThe spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.
37Cytokinesis Cytokinesis is the division of the cytoplasm. The process of cytokinesis is different in animal and plant cells.
38Cytokinesis in Animal Cells The cell membrane is drawn in until the cytoplasm is pinched into two equal parts.Each part contains its own nucleus and organelles.
39LE 12-9a100 µmCleavage furrowContractile ring ofmicrofilamentsDaughter cellsCleavage of an animal cell (SEM)
40Cytokinesis in Animal Cells In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall.Instead, a cell plate forms between the divided nuclei that develops into cell membranes.A cell wall then forms in between the two new membranes.
41LE 12-9bVesiclesformingcell plateWall ofparent cell1 µmCell plateNew cell wallDaughter cellsCell plate formation in a plant cell (TEM)
42LE 12-10 Chromatin condensing Nucleus Chromosomes Cell plate 10 µm NucleolusProphase. Thechromatin is condensing.The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is starting to form.Prometaphase. Wenow see discrete chromosomes; eachconsists of two identical sister chromatids. Laterin prometaphase, thenuclear envelope will fragment.Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all atthe metaphase plate.Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro-tubules shorten.Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.
46LE 12-6da10 µmMETAPHASEANAPHASETELOPHASE AND CYTOKINESIS
47LE 12-6da10 µmMETAPHASEANAPHASETELOPHASE AND CYTOKINESIS
48LE 12-6da10 µmMETAPHASEANAPHASETELOPHASE AND CYTOKINESIS
49Virtual Onion Root Tip Mitosis Lab Click here to start
50Binary FissionProkaryotes (bacteria and archaea) reproduce by a type of cell division called binary fissionIn binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes actively move apart
51Chromosome replication begins. Soon thereafter, LE 12-11_1Cell wallOrigin ofreplicationPlasmamembraneE. coli cellBacterialchromosomeChromosome replication begins. Soon thereafter,one copy of the origin moves rapidly toward the other end of the cell.Two copiesof origin
52Chromosome replication begins. Soon thereafter, LE 12-11_2Cell wallOrigin ofreplicationPlasmamembraneE. coli cellBacterialchromosomeChromosome replication begins. Soon thereafter,one copy of the origin moves rapidly toward the other end of the cell.Two copiesof originOriginOriginReplication continues. One copy of the origin is now at each end of the cell.
53LE 12-11_3 Cell wall Origin of replication Plasma membrane E. coli cellBacterialchromosomeChromosome replication begins.Soon thereafter,one copy of the origin moves rapidly toward the other end of the cell.Two copiesof originOriginOriginReplication continues. One copy of the origin is now at each end of the cell.Replication finishes.The plasma membrane grows inward, andnew cell wall is deposited.Two daughtercells result.
54The Evolution of Mitosis Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fissionCertain protists exhibit types of cell division that seem intermediate between binary fission and mitosis
55LE 12-12 Bacterial chromosome Prokaryotes Chromosomes Microtubules Intact nuclearenvelopeDinoflagellates (Type of plankton)KinetochoremicrotubulesIntact nuclearenvelopeDiatoms (Type of Algae)KinetochoremicrotubulesCentrosomeFragments ofnuclear envelopeMost eukaryotes
56The Cell Cycle Control System The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clockThe clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received
57G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint LE 12-14G1 checkpointControlsystemSG1G2MM checkpointG2 checkpoint
58For many cells, the G1 checkpoint seems to be the most important one If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divideIf the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase
59LE 12-15G0G1 checkpointG1G1If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.
60An example of external signals is density-dependent inhibition, in which crowded cells stop dividing Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum (connective tissue) in order to divide
61Cells anchor to dish surface and divide (anchorage dependence). LE 12-18aCells anchor to dish surface anddivide (anchorage dependence).When cells have formed a completesingle layer, they stop dividing(density-dependent inhibition).If some cells are scraped away, theremaining cells divide to fill the gap andthen stop (density-dependent inhibition).25 µmNormal mammalian cells
62Cancer cells do not exhibit anchorage dependence LE 12-18bCancer cells do not exhibitanchorage dependenceor density-dependent inhibition.25 µmCancer cells
63Loss of Cell Cycle Controls in Cancer Cells Cancer cells do not respond normally to the body’s control mechanismsCancer cells form tumors, masses of abnormal cells within otherwise normal tissueIf abnormal cells remain at the original site, the lump is called a benign tumorMalignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors
64LE 12-19 Lymph vessel Tumor Blood vessel Glandular tissue Metastatic Cancer cellA tumor grows from asingle cancer cell.Cancer cells invadeneighboring tissue.Cancer cells spreadthrough lymph andblood vessels toother parts of thebody.A small percentageof cancer cells maysurvive and establisha new tumor in anotherpart of the body.