Presentation on theme: "Cells and Cell Division"— Presentation transcript:
1Cells and Cell Division Chapter 2Cells and Cell Division
22.1 The Chemistry of CellsALL Cells are constructed from four classes of large molecules called macromolecules.Carbohydrates include small sugars and large polymers of sugarsLipids consist of fats and oils, phospholipids, and steroids.Proteins are polymers of amino acids and carry out a multitude of functions and activitiesNucleic acids are polymers of nucleotides. They store and transfer genetic information in the cell.Go through each description.In this course we will focus on how nucleic acids and how they code for proteins.
32.1 Cell Structure Reflects Function The cell is the basic unit of structure and function in all organisms, including humansAlthough cells of different tissues (nerve cell vs. muscle cell) differ in their size, shape, function, and life cycle, at the structural level they are all similar.All cells have a plasma membrane, cytoplasm, organelles, and a membrane bound nucleus.The function of a cell is under genetic control and many genetic disorders are caused by changes in cell function.
4Inside the Eukaryotic Cell You may think of a cell as a bag of jelly, a single cell is rather structurally dense—full of organelles.
5The Plasma MembraneA double-layered plasma membrane separates the cell from the external environment. The membrane controls the movement of molecules into and out of the cell.The tan area represents the cytoplasm or inside of the cell. The grey represents the extracellular space—usually filled with fluid.Some proteins in the membrane form channels and these control the flow of substances or molecules into and out of the cell.
6OrganellesNucleusMembrane-bound organelle in eukaryotic cells that contains the chromosomesThe nucleus is bounded by a double membrane called the nuclear envelope. When you look at a cell, the nucleus is the most prominent structure.Wittman, Bokoch, Waterman-Storer, CIL: 9537
7Elements within the Nucleus NucleolusDense region within the nucleus where ribosomes are synthesizednucleolusThe nucleolus (arrow) is a prominent structure in the nucleus and is the site of ribosome synthesis. (b) The nuclear envelope is studded with pores, which allow exchange of materials between the nucleus and the cytoplasm. (c) When the cell is not dividing, the chromosomes are uncoiled and dispersed throughout the nucleus as clumps of chromatin, clustered just inside the nuclear envelopechromatinNuclearpores
8Organelles Endoplasmic reticulum (ER) Ribosomes System of cytoplasmic membranes arranged into sheets and channelsSynthesizes and transports gene productsRibosomesCytoplasmic particles that aid in the production of proteins
9Organelles Golgi complex Lysosomes Membranous organelles composed of a series of flattened sacsSort, modify and package proteins synthesized by the ERLysosomesMembrane-bound organelles that contain digestive enzymes
10OrganellesProteins travel to the Golgi complex and then out of the cell (secreted proteins) or to the lysosomes (digestive proteins)Pathways of proteins from ER and right is the EM of Golgi complex.secreted proteins
11Vesicle fusing with plasma membrane Milk proteinbeing secrectedfrom a cell inthe mammarygland of a rat.Marilyn G Farquhar, CIL: 9537
12Organelles Mitochondria (singular: mitochondrion) Membrane-bound organelles in the cytoplasm of all eukaryotic cellsSites of energy production (where ATP is made)
13Keep In MindA problem with any one of the organelles just described can cause a genetic disease.
14Back to the Nucleus… Chromosomes Genes Threadlike structures in the nucleus that carry genetic information46 chromosomes (diploid number, 2n) are present in most human cellsGenesFundamental units of heredity present on chromosomesChromosomes are the main component of the nucleus…
15Structures of the Chromosome Sister chromatidsTwo chromatids joined by a common centromereEach sister chromatid carries identical genetic information
16Structures of the Chromosome CentromereRegion of a chromosome to which microtubule fibers attach during cell divisionCentromere location gives a chromosome its characteristic shape as we will discuss in Chapter 6
17Human Chromosomes Sex chromosomes Autosomes Human X and Y chromosomes are involved in sex determinationAutosomesChromosomes other than the sex chromosomesHuman chromosomes 1 through 22 are autosomes
182.3 The Cell Cycle Cell cycle The sequence of events that takes place between cell divisionsThe proper order of these events is under genetic control
19The cell cycleBeginning with G1 or Gap 1, this is a growth phase where all of the cell components except the chromosomes are duplicated.S is when the chromosomes are duplicated—or DNA is synthesized.G2 or Gap 2 is a period when the cell is preparing to divide.
20Three Phases of the Cell Cycle 1. InterphaseG1, S, and G2 phases2. MitosisProcess where the duplicated chromosomes are segregated into two daughter cells.3. CytokinesisProcess by which the cytoplasm is divided between the two daughter cells.
21Interphase has Three Stages G1 PhaseGrowth takes place after division - the cell doubles in size and replenishes organelles and ribosomes and prepares for chromosome replication.S PhaseDNA synthesis stage. Each chromosome is copiedG2 PhasePeriod of preparation for cell division
22Mitosis Occurs in Four Stages Prophase PrometaphaseChromosomes Nuclear envelope breaks downcondense. chromosomes attach to microtubules andbegin to align at the metaphase plate.
23Mitosis Occurs in Four Stages Metaphase Anaphase TelophaseChromosomes align at Chromosomes Chromosomes continuethe cell equator, known separate to move apart and toas the metaphase plate decondense.
242.4 Mitosis is Essential for Growth and Cell Replacement Human cells are genetically programmed to divide about 50 times (known as Hayflick limit)This limit allows growth to adulthood, and repairs such as wound healingAlterations in the limits to cell division can lead to genetic disorders (such as premature aging) or to cancer
25Keep In MindCancer is a disease of the cell cycle—cells lose their ability to stop growing, in a sense, they have found the “fountain of youth”
26Spotlight on…Cell Division and Spinal Cord Injuries Many highly differentiated cells, such as those of the nervous system do not divide (They are in the G0 phase.)As a result injuries to nervous tissue such as spinal cord do not heal though cell replacementNew approaches using embryonic tissue suggests that is may be possible to reconnect damages nerve tissue.Newly described growth factors also show potential for stimulating the growth and division of cells of the nervous system.
272.4 Cell Division by Meiosis: The Basis of Sex Meiosis: A form of cell division that produces four haploid cells containing only one copy (paternal or maternal) of each chromosomeMeiosis IMeiosis II
28Homologous Chromosomes Have identical gene lociYou receive one from mother and one from fatherChromosomes that physically pair during meiosisDiploid (2n)23 chromosomes from mom, 23 from dad (46 total)Haploid (n)Each chromosome is represented once, in an unpaired conditionThe result of meiosis
29Meiosis I prophase I metaphase I anaphase I telophase I homologous chromosome homologues cytokinesischromosomes pairs align separatefind each other (sister chromatidsstay together)
30Meiosis IIinterkinesis prophase II metaphase II anaphase II telophase IINo DNA chromosomes chromosomes sister 4 haploidreplication attach to align at the chromatids cellsmicrotubules metaphase plate separate
312.5 Formation of GametesMeiosis results in two kinds of haploid, sexual gametesMales produce spermatids by the process of spermatogenesisFemales produce oocytes by the process of oogenesisMeiosis maintains a constant chromosome number from generation to generation
32Meiosis Produces New Combinations of Genes in Two Ways 1. Crossing over: The exchange of chromosome segments of non-sister chromatids of a between homologous pair during prophase I2. Independent or random assortment of maternal and paternal chromosomes in metaphase I.Chromosome pairs line up at random