Biology - Life Processes at the Cellular Level

Enzymes
1. What effects enzyme activity?
  1. Temperature
    1. Increases activity until exceed optimum temperature, then enzyme is denatured and activity stops.
  2. pH
    1. Increase activity until exceed optimum pH, then enzyme activity starts to drop off. Bell curve.
  3. Solvents
  4. Surface Area
  5. Concentration of enzyme and substrate
    1. Increase activity. If too high concentration enzyme, then no enzyme activity as substrate used up. If too high concentration substrate, the rate of reaction plateaus as enzymes are saturated.
  6. Salts
  7. Coenzymes and Cofactors
    1. Coenzymes go in active site and help substrate fit in better. Cofactors help enzyme function correctly
  8. Poisons
    1. They alter enzyme shape, denaturing it so it can react with substrate, or they'll block active sites
2. What are they?
  1. Globular Proteins. Functional Proteins. Made up of amino acids. Natural catalysts. Can be catabolic (break molecules) or anabolic (build molecules). Lower activation energy for reaction.
3. Two models: Lock and Key model and Induced Fit model
4. Enzymes are specific to a certain substrate. If enzyme shape changed, it will be useless as substrate won't fit. It becomes denatured.
Cell Structure
1. Animal Cell
  1. Mitochondria
    1. Aerobic Respiration. Creates ATP needed for muscles, protein, and active transport. Powerhouse of Cell. Has own DNA
    2. Aerobic Respiration
      1. Glucose + Oxygen —> ATP + CO₂ + H₂O
        C₆H₁₂O₆ + O₂ —> 6H₂O + 6CO₂ + 38ATP
      2. Controlled by enzymes
      3. Steps:
        Glycolysis
        In Cytoplasm
        No Oxygen
        Breaks down 6 Carbons in Glucose into Pyruvic acid (3 Carbons x2)
        2 ATP made
        Kreb Cycle
        Pyruvic acid goes into liquid matrix
        Oxygen unused by needed to proceed
        Pyruvic acid broken down for H⁺ ions
        CO₂ produced
        Electron Transport Chain
        On cristae of Mitochondria
        Oxygen used
        Lots of ATP produced
        H⁺ ions combine with electrons and Oxygen to form Water
        Drives electron pumps across cristae membrane to produce ATP from ADP, by adding an extra phosphate
      4. Difference between anaerobic and aerobic
        Anaerobic: 1 glucose -> 2 ATP in glycolysis. Creates Lactic acid. Only goes through Glycolysis
        Aerobic: Same as anaerobic but also 32 ATP made in Electron Transport Chain
    3. Oval/rod shaped
    4. Cristae increase surface area with folds, so rate of reaction increases
    5. Cells that need lots of energy have lots of mitochondria
  2. Cytoplasm
    1. Fluid in cell, organelles float freely. Medium of transport.
  3. Ribosomes
    1. Creates proteins from RNA. Free floating or connected to Endoplasmic Reticulum.
  4. Nucleus
    1. Holds DNA. Regulate Cell Activity
      1. DNA
        Structure
        Bases: Cytosine, Guanine, Adenine, Thymine
        The hydrogen bonds that these bases have ensure that only Adenine can pair with Thymine and Cytosine can only pair with Guanine. Base Pairing Rule
        Direction of strand can be distinguished as if top phosphate is attached to the 5th side of sugar and the other is attached to 3rd side of sugar, direction is 5' to 3'.
        Replication
        Helicase unzips DNA and DNA polymerase adds new nucleotides to each half strand according to base pairing rule to create two daughter strands
        Semi-conservative as new strands are made up of half of the old strand
  5. Endoplasmic Reticulum
    1. Network of plumbing. Rough Endoplasmic Reticulum (with ribosomes)
  6. Plasma Membrane
    1. Separates cell innards from outside. Regulates what goes in and out
      1. Plasma Membrane Structure
        Fluid Mosaic Model : Components can move and are randomly scattered.
        Cholesterol keeps things moving easily and maintains fluidity of membrane (think grease).
        Selectively Permeable
        Lipids, soluble solutes and small molecules can pass through with ease
        Phospholipids made up of a nonpolar, hydrophobic tail and a polar, hydrophillic head.
        Intrinsic proteins span length of membrane. Extrinsic don't.
        Allows movement in and out of cell
        Protection to organelles as it's a boundary
        Maintain shape of cell
        Allows cell recognition with carbohydrates
  7. Vacuole
    1. Holds stuff.
  8. Lysosome
    1. Digest old organelles and old parts of organelles with enzymes.
  9. Nucleolus
    1. Transcribe DNA to RNA and assembles it. Ribosomes also made.
  10. Golgi Body
    1. Modifies proteins made in Endoplasmic Reticulum and packages them for transport out of cell
  11. Vesicle
    1. Transport for molecules out of cell
2. Plant Cell
  1. Chloroplast
    1. Absorb light (photosynthesis). Flat for lots of surface area to get more sun.
      1. Photosynthesis
        6CO₂ + 6H₂O with light —> C₆H₁₂O₆ + 6O₂
        Carbon Dioxide + Water + Light —> Glucose + Oxygen
        Light Dependant Stage
        In Grana
        Requires Light
        H₂O split into O₂ and H⁺ ions. ATP synthesised
        Light Independant Stage (Calvin Cycle)
        In Stroma of Chloroplast
        CO₂ bonds with H⁺ ions (carbon fixation)
        ATP used
        Glucose produced
        Depends on enzymes so if enzyme activity inhibited, so will photosynthesis.
    2. Thylakoids
      1. Chlorophyll and Lumen
    3. Stroma is liquid in chloroplast. Some reactions happen here.
  2. Cell Wall
    1. Cell shape. Made of cellulose
  3. Palisade Cells
    1. Hold Chloroplasts. Near top of the cell for maximum exposure to sunlight
Transport
1. Active
  1. Up concentration gradient from low concentration to high. Need ATP.
  2. Uses some types carrier proteins to pump substances across membrane
    1. Phosphate from ATP attaches to protein = change protein shape to pump molecule/ion into cell
  3. Examples: Uptake glucose + amino acids in small intestines. Absorption of mineral ions by plant roots. Excrete H⁺ and urea from kidney. Exchange sodium and potassium ions in neurons and muscles.
  4. Cells that do this have lots of Mitochondria
  5. Cytosis (Bulk transport)
    1. Endocytosis
      1. Molecules into cell
      2. Phagocytosis
        Taking in lots of solid materials e.g. white blood cells with viruses
      3. Pinocytosis
        Takes in liquid into cell
      4. Receptor-mediated endocytosis
        Molecules bind to receptors on cell membrane. When molecules on receptors, membrane folds inward to form protein coated pit.
    2. Exocytosis
      1. Molecules out of cell
      2. Excrete waste and other substances
      3. Vesicles formed in Golgi fuse with cell membrane and release contents out of cell
    3. Involve changes to membrane shape
2. Passive
  1. Facilitated Transport
    1. Channel Proteins allow big molecules/ions through membrane. Some cells need more water and so have specialised water channels called Aquaporins
  2. No energy
  3. Down concentration gradient from high to low concentration
  4. Diffusion
    1. Particles dissipate over area until equilibrium/same concentration of particles
  5. Osmosis
    1. Diffusion but only with water
    2. Exclusively with semi-permeable membranes
    3. Tonicity
      1. Hypertonic
        A solution is hypertonic if it has more solutes or less water than other side of membrane
        Plant cell is considered plasmolysed and animal cell is crenated if solution outside cell is in this state
        Water will rush out of cell and into hypertonic solution
      2. Isotonic
        A solution is isotonic if it has the same concentration of solutes and water as other side of membrane
      3. Hypotonic
        A solution is hypotonic if it has less solutes or more water than the other side of membrane
        Plant cell is considered turgid and animal cell has lysed (bursted), if solution outside cell is in this state
        Water will rush into cell and out of hypotonic solution
Cell division
1. Mitosis
  1. PMAT: Prophase, Metaphase, Anaphase and Telophase
    1. Prophase: DNA condenses into chromosomes
      1. Metaphase: Chromosomes align to equator.
        Anaphase: Chromosomes torn in half by spindle network to poles of cell.
        Cytokinesis: Cytoplasm divided between two daughter cells.
        Telophase: Nuclear envelope redevelops and chromosomes unwind.
  2. Interphase: Cell is carrying out normal functions. Cells usually in this stage.
    1. G1: Protein synthesis and respiration
    2. S: DNA replication
    3. G2: Cell gets bigger, gathers resources, repairs any damage to DNA
  3. Nuclear division, one strand of each chromosome into each daughter nucleus. Each identical to parent.
  4. For growth, repair, and to replace cells
2. Meiosis
  1. Meiosis similar to Mitosis, but make 4 daughter cells with half the number of chromosomes.
  2. DNA wound into chromosomes in Interphase
    1. Chromosomes replicate in S phase.
      1. Homologous Chromosomes line up at equator randomly (Independant Assortment).
        Crossing over between homologous chromosomes (exchanging of alleles) occurs in Prophase.
        The chromosomes with two chromatids are separated into two daughter cell (Cytokinesis).
        Then the chromosomes line up at equator again and are pulled apart
        4 daughter cells are created with half of the starting number of chromosomes.
        Increase variation
        Increase variation
  3. Creates sex cells (gametes)

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Biology - Life Processes at the Cellular Level

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