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Biology 1201A

1 Midterm Review The Cell Early Microscope  Developed by Anthony Van Leeuwenhoek  Took off in 1600’s in Dutch Republic when people started building microscopes Robert Hooke  First person to coin the word ―cell‖ to describe tiniest components of living system (plants)  Initially studied cork  Set up microscopes too Electron Microscope (1950’s)  Enabled organelles, viruses, proteins etc. to be viewed  Resolution limit is 0.2 microns  Magnification limit of 1000x (at higher magnification image blurs) Transmission Electron Microscope (TEM) Cross-Section  Very large in size  Electrons flow and thus they can be seen as pictures Scanning Electron Microscope (SEM) Surface  Stereo or dissecting microscope  Surface of cell seen; not internal components Cell Fractionation  Take cells apart to study their components; need to isolate cells to study them  Centrifuge is used to fractionate cells and separate their major organelles  Cannot figure out the interactions of things with just a microscope 1. Take cells apart and isolate them 2. Put them into a homogenizer (like a blender) 3. Spin at low speed see the largest components like nucleus 4. Spin at high speed see ribosomes The Cell  Simplest collection of matter which has all the properties of life  Lowest hierarchical level which is alive  Basic unit of life  Perform all necessary functions to live and reproduce Virus  Occur in every organism; highly specific to host  Some cause illness others cause no disease or outward sign of their presence  Can reproduce only when enter a cell (thus cause harm) 1 2 Prokaryotic Cells: (before – nucleus)  No nucleus; all genetic information is in the nucleoid  Plasma membrane needs to be around the cell or it would not differentiate from surroundings  Standard visible components: plasma membrane, ribosomes, nucleoid, cytoplasm  May have: cell wall, pili, flagella, mesosomes, photosynthetic membranes  Four kingdoms: Protista, fungi, animalia, planta Eukaryotic Cells (true – nucleus)  Have a nucleus; surrounded with nuclear membrane that contains DNA  Standard visible components: plasma membrane, cytoplasm, nucleus, ribosomes, organelles, endomembrane systems, cytoskeletons  May have: cell wall, cell matrix, some organelles, flagella Nucleus (may be more than one)  Most of the genes in a eukaryotic cell are here; some are in the mitochondria and chloroplast  Averages 5 microns in diameter  Separated from the cytoplasm by a double membrane; where they fuse a pore allows large macromolecules and particles to pas through  The nuclear side of the envelope is lined by the nuclear lamina; filaments that maintain shape  Used so mRNA can get in and out  Specialized structures for control with each pore Inside of Nucleus  DNA and associated proteins are organized into fibrous material (chromatin)  When cell prepares to divide, the chromatin fibers coil up as separate structures (chromosomes)  Traits are passed on by genes of chromosomes not by the actual chromosome  Nucleolus: Region of densely stained fibers and granules adjoining chromatin  Ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits  Messenger RNA (mRNA) directs protein synthesis Cytoplasm  Material between the plasma/cell membrane and the nuclear envelope  Variable viscosity  Ribosome and protein factories located in cytoplasm Ribosomes  Contain rRNA and protein  Composed of two subunits that combine to carry out protein synthesis  Cell types that synthesize large quantities of protein (pancreas) has lots of ribosomes  Types of ribosomes (can still switch between roles): 2 3 i) Free Ribosomes: Suspended in the cytosol and synthesize proteins that function within cytosol ii) Free Ribosomes: Attached to the outside of the endoplasmic reticulum Endomembrane System  Many internal membranes in a eukaryotic cell  Membranes are in direct contact or connected via transfer of vesicles or sacs of membrane  Includes: nuclear envelope, endoplasmic reticulum, Golgi Apparatus, lysosomes, vacuoles, plasma membrane  Plays a key role in synthesis and digestion of macromolecules in the cell i) Smooth Endoplasmic Reticulum:  Lacks ribosomes  Rich with many enzymes  Plays a role in many metabolic processes (synthesizes lipids)  Catalyzes key step in mobilization of glucose from stored glycogen in liver  Enzymes from it help detoxify drugs and alcohol ii) Rough Endoplasmic Reticulum  Bound ribosomes are attached to the outside, including the outside of the nuclear envelope  Abundant in cells that secrete proteins  Membrane factory; membrane bound proteins are synthesized directly into membrane  Parts can be transferred as transport vesicles to other components of the endomembrane system Golgi Apparatus  Transports vesicles from the ER  Centre of manufacturing, warehousing, sorting and shipping  Extensive in cells responsible for secretion (ie. Liver)  After proteins are transcribed, they are not necessarily correct so the Golgi Apparatus corrects this  Cisternae: Flattened membranous sacs o Separates internal space from cytosol o ―Cis‖ side: receives material by fusing with vesicles o ―Trans‖ side: buds off vesicles that travel to other sides o When moving from one side to the other, the products from the ER are modified to reach the final state Lysosomes  Membrane-bounded sac of hydrolytic enzymes that digest macromolecules  Produced as result of initial synthesis in the rough ER 3 4  Lysosomal enzymes can break down proteins, fats, polysaccharides, and nucleic acids which work best at a pH 5  Rupturing one or a few lysosomes has little impact on a cell  Autodigestion: massive leakage can destroy a cell  Can fuse with food vacuoles, formed when a food item is brought into the cell by phagocytosis  Autophagy: Recycling; lysosomes can fuse with another organelle or part of the cytosol ie. Cancer cells: egg -> tadpole -> frog Vacuoles (larger version of a vesicle)  Membrane bound sacs with varied functions: o Food vacuoles: from phagocytosis; fuse with lysosomes o Contractile vacuoles: found in freshwater protists, pump excess water out of cell and regulate water (ie. Fills with water and contracts to get rid of it) o Central vacuoles: found in many mature plants Plant Central Vacuole (largest part in plant cell)  Membrane surrounding the central vacuole (tonoplast) is selective in its transport of solutes into the central vacuole  Functions: o Storing proteins or inorganic ions o Depositing metabolic byproducts o Storing pigments o Storing defensive compounds against herbivores Mitochondria and Chloroplast – Main Energy Transformers of a Cell  The organelles that convert energy to forms that cells can use for work  Both are mobile and able to move around the cell along tracks in cytoskeleton  Mitochondria: are at the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen o Act and look like bacteria as they have their own DNA o When dividing they do not follow instructions but rather sense environment o Comes from mother’s cells  Chloroplasts: found in plants and eukaryotic algae; at the site of photosynthesis o Liquid part inside is stroma o Proteins and pigments present for photosynthesis o Dynamic structures: their shape is plastic and they can reproduce themselves by pinching in two Microtubules  Hollow tubes composed of the protein tubulin (25nm diameter) 4 5  Cell shape, cell mobility, chromosome movement, organelle movement, guide motor proteins to their destination Microfilaments  Two intertwined actin strands (7nm diameter)  Cell shape, muscle contraction, cytoplasmic streaming, cell motility, cell division Peroxisomes  Found in plant and animal cells  Single membrane bound compartment  Enzymes that transfer hydrogen from various substrates to oxygen o Produces hydrogen peroxide which is then converted to water Cytoskeleton  Network of fibers, extending throughout the cytoplasm; act as dome to stabilize a balance between opposing forces  Mechanical support and maintains shape of the cell  Organizes structures and activities of the cell Cilia  Large numbers on the cell surface (2-20 microns long)  Smaller than flagella (10-200 microns long) so there are more of them on cell surface  Similar to flagella in ultrastructure o Nine doublets of microtubules arranged around a pair in the center (9+2 pattern) o Anchored by a basal body (centriole) Flagella  Wavelike movement: force is generated parallel to the flagellum’s axis Dynein  Motor protein that drives the bending of the arms of cilia and flagella  ATP supplies energy  Dynein arms grab, move and release outer microtubules Intermediate Filaments  Thick cables  Different proteins (keratin family)  Anchorage of nucleus and organelles Centrosomes and Centrioles  Centrosomes are located near nucleus (barrel shaped made up of microtubules)  Within the centrosomes are centrioles  Each centrosome has a pair of centrioles containing 9 sets of triplet microtubules arranged in a ring in (animal cell only) 5 6 Plant Cell Wall  Much thicker than plasma membrane  Very strong  Composed of fibers of cellulose, embedded in other polysaccharides and pecin (which acts like a glue to hold the structure together) Plasmodesmata  Required for intercellular activity as plant cells are protected by an impermeable cell wall  Microscopic channels of plants that facilitate transport and communications between individual cells Intercellular Junctions  Anchoring Junctions o Form button-like spots or belts that run entirely around cells o Welds adjacent cells together o Desmosomes: intermediate filaments that anchor the junction in the underlying cytoplasm  Tight Junctions o Tight connections between membranes of adjacent cells; controls ions in some cases o Seals spaces between cells in cell layer o Not joined continually; intercellular space o Formed by direct fusion of proteins on the outer surfaces of the two plasma membranes of adjacent cells  Gap Junctions o Open direct channels that allow ions and small molecules to pass directly from one cell to another o Protein cylinders embedded in the plasma membrane (controls flow of ions) o Allow the cells of the organ to operate as a coordinated unit Cell Cycle and Mitosis Cell Division  Needed for growth, repair, development  Transmit a complete copy of genetic information (DNA)  Transmit materials necessary for cells to survive and use genetic information Chromosomes  Long thread like structures  Highly condensed during mitosis  Contains DNA and protein; most of the organism’s genetic information Chromatin  Many proteins are bound to the DNA: protect, packaging, duplication, transcription, regulation, modification 6 7  DNA + bound protein = chromatin  Contains only about 50% of DNA Eukaryotic Chromosome Structure  Strands of linear DNA  46 coiled up strands; average length of 4cm (3 meters of DNA) Binary Fission  Occurs in prokaryotic cells (DNA is in cytoplasm)  Bacteria divide this way  Prokaryotic chromosomes are in a circular loop  The cell elongates and a new plasma membrane is added between chromosomes, pushing them toward opposite ends of the cell  Plasma membrane grows inward at the middle of the cell  Parent cell is divide into two identical daughter cells Basics of Mitotic Cell Division  Happens in a eukaryotic cell (DNA is in the nucleus)  Division of somatic cells (non-reproductive cells)  Single cell divides into two identical daughter cells (cellular reproduction)  Fungi, protists, plants and animals divide this way  Eukaryotic chromosomes contain almost all the genetic information Non-Division Phase of Cell Cycle  DNA molecule is extended in uncondensed form (chromatin)  Call can only use DNA to produce molecules when in extended form Division Phase of Cell Cycle  DNA molecules condense to form chromosomes prior to division (helps transportation)  Each chromosome is a single molecule of DNA Ploidy  The number of pairs or chromosomes in cells o Haploid: One copy of each chromosome (n) o Diploid: Two copies (pair) of each chromosome (2n) o Triploid: Three copies of each chromosome (3n) o Polyploid: More than two complete sets (common in plants) Eukaryotic Cell Cycle  Two major phases: o Interphase (3 stages where DNA is uncondensed [chromatin]) o Mitotic Cell Division (5 stages where DNA is condensed [chromosomes]) Interphase (first part of Mitotic cell Divison) 7 8 Interphase  Cell grows and replicates its DNA  It begins as soon as the daughter cell from a previous division cycle enters an initial period of cytoplasmic growth  Genetic material is called chromatin o G1 Phase (First Gap):  Absence of DNA synthesis  Period of cell growth before the DNA replicates  Size increases  Organelles may replicate Normal Growth and Development  Whether the cell divides rapidly or slowly depends on this stage o S Phase (DNA Synthesis):  Stage is initiated by DNA replication  Period when DNA replicates and chromosomal proteins are duplicated  Synthesis of protein and other cellular molecules is then continued  Ploidy does not change o G2 Phase (Second Gap):  Absence of DNA synthesis  Period after DNA replicates  Cell continues to synthesize the RNA’s and proteins  Cell continues to grow and prepares for division o G0 Phase:  Stage of division arrest  In humans, the cells of the nervous system (plus nerve, liver, muscle cells) normally enter G0 once they are fully mature Mitotic Cell Divison: 1. Prophase  Chromatin fibers become tightly coiled chromosomes (condense)  Nucleus is smaller and eventually disappears; reflects a shutdown of all types of RNA synthesis  Mitotic spindle in the cytoplasm begins to form  Centrosomes move away from each other  Spindle poles are formed in this stage 2. Prometaphase  Nuclear envelope breaks down  Bundles of spindle microtubules grow from centrosomes at the opposing spindle poles toward the center of the cell 8 9  Microtubules connect to chromosomes  Kinetochores have formed  Some microtubules connect with those from the opposite pole 3. Metaphase  Centrosomes now at opposite poles  Centrosome at metaphase plate  Single reaches its final form  Centromeres of the chromosomes are on the metaphase plate (aka spindle midpoint- middle)  Chromosomes complete their condensation in this stage and assume their characteristic shape determined by centromere/chromatid arms  Kinetochores of each chromatid connected to the microtubules from different pole  The karyotype of a given species is formed here 4. Anaphase  Begins when paired centromeres separate  Chromosomes (1/2 of each sister chromatid pair) move to opposite spindle poles  Kinetochores are the first sections to move toward opposite poles  Poles of cell move further apart at the same time  At this stage, chromosome separation is complete 5. Telophase  Daughter nuclei form at the two poles  Nuclear envelope reforms  Chromatin fibers become less condensed  Nucleus reforms  Mitosis is complete and cell has two nuclei  Cytokinesis is underway Mitotic Spindle  Arises from two microtubule organizing centers (centrosomes)  Microtubules spontaneously arise from tubulin dimmers  Microtubules arising from MO centers have opposite polarity; they meet at equatorial plane  Chromatids attach to microtubules via kinetochores (protein complexes) of opposite polarity  They pull chromatids apart after centromere breaks down (beginning of anaphase) Cytokinesis  Process of splitting daughter cells apart  Division of the nucleus
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