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Cells, endosymbiosis theory: all eukaryotic cells originate from…

- - - - Prokaryotic Cell
        
        https://docs.google.com/drawings/d/1LSDpCGq2eBXk203Ecxm1KsHKV2vt5Riyjv5CIkspI3Y/edit
        
        aspects of prokaryotic cells
        
        contains a peptidoglycan cell wall
        
        thicker and stronger to protect the cell, maintain cell shape, and prevent the plasma membrane from bursting
        
        no nucleus or membrane-bound organelles in cytoplasm
        
        contains smaller ribosomes at 70S
        
        Organelles
        
        cell wall
        
        plasma membrane
        
        cytoplasm
        
        nucleoid, no nucleus
        
        70S ribosome
        
        plasmid
      - Eukaryotic Cells
        
        Plant
        https://docs.google.com/drawings/d/1n2KBHxp8PeN4SNqLI-Yzs2oYk4qmrr7Aj2cr-Jn_joE/edit
        
        aspects of eukaryotic cells
        
        contains cell wall
        
        contains compartmentalized cytoplasm separated from the rest by single or double membranes
        
        nucleus has a double membrane with pores
        
        Ribosomes are larges at 80S
        
        (common) Organelles
        
        nucleus
        
        cell membrane
        
        ribosomes
        
        cytoplasm
        
        RER
        
        SER
        
        Golgi Apparatus
        
        Mitochondria
        vacuoles
        
        chloroplasts
        cell wall
        
        Animal
        https://docs.google.com/drawings/d/1LMDzt73xeEe4oCezzeg5flo21sOnPStleqa6_uFl5nw/edit
      - Structure and Functions of each structure
        
        Cell Wall
        
        composed of cellulose in plants
        
        maintains shape of cells
        
        gives plants further support and rigid structure > protects cell from bursting
        
        Plasma Membrane
        
        outer boundary of the cell that encloses all of its contents
        
        Semi-permeable: controls movement of substances in and out of cells
        
        effective in maintaining concentration of substances by active or passive transport
        
        Cytoplasm
        
        consists mainly of water, dissolved substances and enzymes
        
        contains all the enzymes for chemical reactions and genetic material
        
        Genes
        
        made of DNA
        
        contains the genetic information needed for a cell to carry out its functions
        
        contains hereditary material that is passed on to daughter cells
        
        Nucleus
        
        contains chromosomes which contain DNA
        
        chromosomes composed of chromatin
        
        site where DNA is replicated and transcribed to form mRNA
        
        manufactures ribosomes
        
        Rough Endoplasmic Reticulum
        
        larger ribosomes of 80S attached
        
        synthesizes protein for secretion from the cell
        
        Smooth Endoplasmic Reticulum
        
        no ribosomes attached
        
        synthesizes lipids, phospholipids and steriods
        
        production of sex hormones
        
        detoxification of drugs in liver
        
        aids liver in releasing glucose into bloodstream
        
        transportation of lipid-based compounds
        
        Golgi Apparatus
        
        consists of flattened membrane sacs called cisternae (not as long, often curved, no attached ribosomes, many vesicles nearby)
        
        collection, packaging, modification and distribution of substances within the cell
        
        processes proteins brought in vesicles from RER
        
        Mitochondia
        
        double membrane
        
        produces ATP for the cell by aerobic cell respiration to release energy
        
        Free Ribosomes
        
        made of RNA and protein and has no membranes
        
        same size as ribosomes attached to RER
        
        large numbers, but very small at 70S
        
        synthesize proteins, releasing it to work in the cytoplasm, as enzymes or in other ways
        
        Chloroplast
        
        double membrane
        
        stacks of thylakoids (flattened sacs of membrane)
        
        produce glucose and a wide variety of other organic compounds by photosynthesis
        
        Vacuoles
        
        large single membrane with fluid inside
        
        Plants cells - large vacuoles that occupy more than half of the cell volume
        Animal cells - many small vacuoles
        
        absorb foods from outside and digests them inside vacuoles
        
        Centrioles
        
        only found in Animal cells
        
        form an anchor point for microtubules during cell division
        
        Microtubules
        
        move chromosomes during cell division
- - - - defn: separate subunits in cells
        
        includes the nucleus, chloroplasts, mitochondia, vesicles, ribosomes and plasma membranes
        
        no membrane
        
        ribosomes
        
        centrioles
        
        single membrane
        
        RER
        
        SER
        
        Golgi Apparatus
        
        Vacuoles
        
        Vesicles
        
        double membrane
        
        nucleus
        
        mitochondria
        
        chloroplasts
        
        not organelles
        
        cell wall
        
        cytoplasm
    - - nuclear membrane keeps DNA separate from other parts of the cell > protects the many cellular reactions that occur in the cytoplasm
        
        allows for gene transcription and translation to be kept separate
        
        prevents protein synthesis before post-transcription modification of mRN
      - Advantages:
        
        enzymes and substrates for a particular process can be more concentrated
        
        conditions (e.g. pH) can be maintained at ideal levels for a particular process
        
        substances that can cause damage is kept inside the membrane of an organelle
        
        organelles can move around within the cell
        
        larger surface area of membrane for processes that occur within/across membranes
        
        Disadvantages:
        
        delays a cell's ability to respond to the environment
    - - more dense particles settle at the bottom of the tube, while less dense particles rise to the top
  - - - different cells will express different genes at different times
      - differentiation during embryonic development:
        retinoic acid is a morphogens that diffuses throughout the embryo from source cells to target cells by switching genes on and off and imparting different cell fates depending on its concentration
    - - Stem cell niches
        defn: locations within the tissues where stem cells reside and receive physical and chemical signals that interact and integrate to influence the fate of the stem cells
        
        the conditions can allow for stem cells to remain undifferentiated, cells remain dormant for years
        > - in cases of tissue injury, disease or other situations when the body needs more cells, conditions of the stem cell niches allows for adult stem cells to begin to differentiate and divide rapidly
      - types of stem cells:
        
        totipotent = only found in zygote
        
        pluripotent = only found in embryo
        
        multipotent = only found in adult stem cells
        
        unipotent = fully differentiated cells, cannot differentiate anymore
  - - - phospholipids:
        
        made of 3-carbon compounds called glycerol
        
        2 glycerol carbons have fatty acid chains attached (hydrophobic tails)
        
        third carbon attached to a phosphate group (hydrophilic head)
        
        partially permeable
        'heads' - large phosphate groups --> hydrophilic
        
        suited to high water content of the tissue fluid and cytoplasm on the opposite sides of the membrane
        
        'fatty acid tails' - non-charged --> hydrophobic
        hydrophilic heads and hydrophobic tails cause a barrier between the internal and external water environments of the cell ==> partially permeable
        
        can move around in this plane
        1. allows for variable shape of animal cells
        2. process of endocytosis
        
        individual phospholipids are attracted through their charges and gives some stability
        
        tendency of water molecules to form hydrogen bonds help to maintain structure
        
        hydrophobic tail faces inwards and is shielded from surrounding polar fluid
        
        2 hydrophilic head associate with the cytoplasm and tissue fluid respectively
        
        some phospholipids have short-chain, branched carbohydrates attached directly to the phospholipids on the extracellular side of the membrane called glycolipids (carbohydrates)
      - cholesterol:
        animal cells have cholesterol in the phospholipid bilayer in the hydrophobic region
        
        function:
        reduces permeability of membrane
        at higher temperatures, particles are more likely to move ==> plasma membranes are less stable
        cholesterol helps to stabilize the plasma membrane
      - Proteins:
        many different types with many different functions
        various proteins embedded in the fluid matrix of the phospholipid bilayer creates a mosaic effect
        
        2 types of membrane proteins
        
        integral proteins --> (may or may not) span across the entire thickness of membranes
        
        amphipathic molecules (across hydrophobic and hydrophilic regions --> difficult to remove
        
        peripheral proteins --> sit on the surface of the membrane
        
        only interact with hydrophilic regions of integral proteins --> easier to remove
        
        anchored to integral proteins
    - - hormone binding site
        receptor proteins -- specific shapes that fit the shape of specific hormones
        signal transduction: attachment of hormone to protein causes change in shape that sets off a chemical response relayed to the interior of the cell
        e.g. binding of insulin to insulin receptors causes cells to put glucose transport proteins into the membrane --> increases the permeability of the cell towards glucose, causing more glucose to enter the cell
      - enzymes
        many membrane proteins are immobilized enzymes that catalyst chemical reactions
        --> important in organelles that involve metabolic pathways
        e.g. mitochondria: folded membrane = increase SA:V ration--> increase in amount of enzymes on the inner membrane of the mitochondria --> higher rate of aerobic respiration, increased efficiency of production of ATP to release energy
      - Cell adhesion
        proteins act as cell adhesion proteins to helps similar cells stick together to form tissues
      - Cell-to-cell communication
        glycoproteins (and glycolipids) identify the cell as "self" vs foreign
      - Channel proteins
        funct: assists in movement of substances in and out of the cell across the plasma membrane
        
        carrier proteins span the membrane providing passageways for substances to pass through
        
        helps transport certain molecules via facilitated diffusion
      - Protein pump
        funct: transports substances from one side of the membrane to another
        
        function during active transport: cell expends energy (ATP) to transport water soluble substances against the concentration gradient
    - - Passive transport:
        
        does not require the cell to expense energy in the form of ATP
        
        substances move due to a gradient (difference in concentration makes substances move down the gradient)
        
        substances move to equalize the gradient
        
        simple diffusion:
        defn: passive movement of particles from a region of high concentration to a region of lower concentration
        
        does not involve any membrane proteins ==> substances are able to pass through the gaps between phospholipids molecules in the plasma membrane
        
        can occur in non-living systems
        
        molecules able to pass through:
        
        hydrophobic molecules (eg. O2, CO2, N2)
        
        small, uncharged polar molecules (e.g. H20, Glyecerol, Urea, Ethanol)
        
        molecules unable to pass through:
        
        large, uncharged polar molecules (e.g. glucose, sucrose)
        
        ions (e.g. Na+, K+, H+, Ca2-, Cl-)
        
        Facilitated Diffusion:
        defn: type of diffusion involving carrier proteins that helps to transport substances (e.g. glucose)
        
        requires a protein channel
        
        cannot occur in non-living systems
        
        proteins bind with molecules
        
        shape of proteins (may or may not) change
        
        molecules move across membrane
        
        e.g. Aquaporin -> channel proteins that facilitate the diffusion of water and small neutral molecules across plasma membran
        
        bidirectional
        
        transmembrane protein (type of integral proteins)
        
        Osmosis:
        defn: passive movement of water molecules across a partially permeable membrane from a region of low solute concentration to a region of high solute concentration
        
        hypertonic solution - high conc of solute
        isotonic solution - same conc of solute and solution
        hypotonic solution - low conc of solute
      - Active transport:
        
        energy is used by the cell in the form of ATP
        
        substances are transferred across the plasma membrane against a concentration gradient from a region of lower concentration to a region of higher concentration
        
        e.g. Sodium-Potassium pump:
        
        animal cells have much higher concentrations of potassium ions than extracellular environment and lower sodium ion concentration inside the cell
        --> result of membrane proteins pumping potassium ions into the cell and sodium ions out of the cell with ATP
        
        transport of large molecules:
        either by endocytosis or exocytosis
        
        vesicles used to transport large particles across the plasma membrane
        
        requires energy expended by the cell
        
        endocytosis:
        movement of large materials into cells
        
        edges of membrane meet and membranes fuse and pinch off the form vesicles
        
        vesicles enter cytoplasm
        
        ends of membrane reattach (due to fluid nature of plasma membrane)
        
        e.g. phagocytosis - cell eating
        
        membrane sinks in and captures solid particles (food, bacteria, cell debris) for transport into cell
        
        e.g. pinocytosis - cell drinking
        
        cell brings in a liquid
        
        exocytosis:
        discharge of materials
        
        begins in ribosomes of RER and progresses to Golgi Apparatus which produce transport vesicles
        
        vesicles move to cell surface and the membrane of vesicle fuses
        
        material is expelled
- - - - evolution:
        Amoeba and Paramecium have contractile vacuoles to prevent excessive water intake. Vacuoles actively expel water from the cell the maintain a correct intracellular solute concentration and prevent cellular bursting
  - - - Role of Mitosis and Meiosis in Eukaryotic cells:
        
        nuclear division needed to avoid production of anucleate cells
        
        mitosis
        
        maintains the chromosome number and genome of cells
        
        necessary for
        
        embryonic development
        
        tissue repair to replace worn out cells
        
        growth
        
        asexual reproduction
        
        meiosis
        
        halves the chromosome number and generates genetic diversity
        
        crucial for formation of gametes during sexual reporduction
      - Prophase
        
        condensation of DNA by supercoiling occurs
        
        DNA is wound around histone proteins to form nucleosomes and further condense into chromosomes
        
        chromosomes condense and become shorter
        
        breaking down of nuclear envelope
        
        chromosomes are moved using microtubules, extended from centrioles at poles of cell and centromeres of chromosomes
        
        kinetochore acts as a microtubule motor by removing tubulin subunits to shorten the microtubules and pull sister chromatids towards opposite poles in anaphase
      - Metaphase
        
        Microtubules attach to centromere of each chromatid
        
        Chromosomes are aligned on the equator of the cell
      - Anaphase
        
        Chromatids become separate chromosomes
        
        cohesion loops holding sister chromatids are cut
        
        Chromosomes move towards the poles of the cell
        
        kinetochore shortens the microtubules, pulling them
      - Telophase
        
        Chromosomes are pulled into a tight group near the poles and a nuclear membrane reforms around them
        
        chromosomes decondense and spread out
        
        they form dispersed chromatin
      - Cytokinasis
        
        plasma membrane pulled inwards around the equator of the cell
        
        ring of contractile actin and myosin (proteins) form the cleavage furrow
        
        as cleavage furrow deepens, cell is pinched apart into 2 daughter cells
        
        organelles that must be inherited in each daughter cell:
        
        mitochondia
        
        without it there is no aerobic respiration = no release of energy
        
        chloroplasts
        
        cytokinesis in plants:
        
        microtubules are built into a scaffold across the equator, which is used to assemble to vesicles
        
        vesicles fuse together to form cell plte
        
        cell plate gradually develops into plasma membranes that separate the 2 daughter cels
        
        cell wall forms between 2 new plasma membranes
        
        Unequal cytokinasis
        e.g. oogenesis in humans
        unequal division of cytoplasm occurs
        
        results in 1 large cell and 1 small polar body formed
        
        only large cell undergoes second division, again resulting in 1 large cell and 1 very small polar body
      - Interphase
        chromatin (dispersed chromosomes) inside nucleus
        
        DNA replication occurs
        
        ensures the genetic stability of daughter cells by copying information stored within chromosomes
        
        1 DNA molecule is replicated into 2 DNA molecules [sister chromatids], held together by a centromere ==> chromosome
    - - as a reduction division:
        
        when gametes (mature haploid cells) fuse during sexual reproduction, a diploid zygote is formed
        
        random fertilization involves random fusion of gametes from different parent ==> promotes genetic variation
        
        as a source of variation
        
        crossing over during Prophase I
        
        random orientation of homologous chromosomes during Metaphase I (Independent assortment)
        
        crossing over:
        homologous chromosomes pair up to form bivalents (2 homologous chromosomes, each consisting of 2 sister chromatids). Pairing is called a synapsis
        
        crossing over between non-sister chromatids at point called chiasma, where DNA is cut, exchanged and rejoined forms new combination of alleles
        
        random orentation:
        homologous chromosomes line up as biavelents at equator of cell
        
        pairs line up randomly, meaning each chromosome in the pair has equal chance of travelling to either pole during Anaphase I
      - Errors
        
        Non-disjunction:
        
        pair of homologous chromosomes move to the same pole during Anaphase I
        
        Both chromatids of 1 chromosome move to the same pole in Anaphase II
        
        outcome:
        
        death of a haploid cells or death of the zygote or embryo
        
        Down syndrome
        
        Down syndrome:
        when a person has 3 copies of chromosome number 21
        side effects:
        
        hearing loss
        
        heart and vision disorders