Cells

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Type of cells

Prokaryote: Primitive cell type that does not possess a nucleus

Eukaryote: 'True Nucleus'. Type of cell found in multicellular organisms. 

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Cell Structure - Eukaryotes

Cell membrane: Provides cell shape, prevents contents from escaping and allows transport of molecules in and out of the cell. Made of a phospholipid bilayer (hydrophillic head and hydrophobic tail) and protein channels/transporters. 

Cytoskeleton: Provides support to the cell. Helps metabolic activities and anchors the organelles.

Microtubules - cables which the organelles are attached and may move. 

Intermediate fibres - tough, resists force to minimise cell damage.

Microfilaments- located near the cell membrane. Involved in cell division.

Cytoplasm: Fluid that fills the cell. Provides organelle support, nutrients and site for chemical reactions. 

Nucleus: Contains DNA in the form of chromosomes. Holds genetic material and manufactures ribosomes.

Ribosomes: Protein synthesis

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Cell Structure - Eukaryotes Continued

Rough Endoplasmic Reticulum: Manufacture and transport of proteins.

Smooth Endoplasmic Reticulum: Manufacture and transport of steriod substances.

Lysosomes and Vacuoles: Lysosomes contain digestive enzymes for disposal of waste products. The remains are packed into vacuoles and excretes by exocytosis.

Golgi body: Modification of cell products. Involved in lysosome production.

Mitochondria: Responsible for producing ATP for energy for metabolic activities.

Centrosomes: 2 centrosomes located near the nucleus for cell division.

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Water

  • 60 - 80% body made up of water
  • Factors: 
    • Age (youger has higher proportion)
    • Hydration status
    • Diet
    • Fluid intake
  • 66% Intracellular water: Water found within the cytoplasm
  • 33% Extracellular water: Free fluid found within plasma of blood, lymphatic system, Cerebal spinal fluid, joint fluid, interstital fluid (surrounding cells)
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Cell Transport

Maintanance of homeostasis, cells must control transport and movement 

Passive transport: 

  • Diffusion: Movement of solute molecules from a high concentration to low concentration through a semi permeable membrane.
    • Factors: 
      • Molecular size: Larger molecules do not pass through easily
      • Lipid solubility: Lipid molecules pass more easily as membrane is lipid.
      • Molecular charge : Charge reduce molecules ability to pass through membrane.
  • Faciliated diffusion: Molecules assisted tho pass through the membrane. No ATP used.
    • Carrier proteins
    • Protein Channels
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Active Transport

When a substance moves in and out of the cell in  the presence of ATP against the concentration gradient.

  • Exocytosis: Mass movement of molecules out of the cell 
  • Endocytosis: Mass movement of molecules into the cell
  • Phagocytosis: When the cell membrane surrounds and engulfs material. Digested by lysosomes. Occurs in phagocytes
  • Pinocytosis: Endocytosis of liquid
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Osmosis

Movement of water molecules down the water potential gradient. (No ATP required)

  • Tonicity: Defines relative concentration of 2 solutions separated by a semi permeable membrane.
  • Hypotonic : Less solute molecules outside the cell than inside. Water moves into the cell
  • Hypertonic: More solute molecules outside the cell than inside. Water moves out of the cell.
  • Isotonic: Solute molecules equal inside and outside the cell.
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Resting potential

  • Solute molecules become charged when dissolved in water 
  • Resting potential = -70mv 
  • Sodium potassium pump imbedded in the membrane 3Na+ leave 2K+ enter
  • requires ATP
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Mitosis

  • Occurs in all somatic cells
  • For tissue growth and repair
  • Binary Fission (identical daughter cells)

Interphase: DNA unravels

Prophase: DNA supercoils and replicates, Chromatids held together at centromere.

Metaphase: Chromosomes line up at equator, spindles attach to centromere.

Anaphase: Chromosomes are pulled apart to separate poles of the cell.

Telophase: Nuclear membrane reforms, pinches in center (cleavage furrow)

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Meiosis

  • Occures in gametes (sex cells)
  • 4 genetically UNidentical daughter cells
  • 1/2 chromosomes 

Interpase I: DNA unravels

Prophase I: Homologous pairs duplicate, crossing over and exchange genetic information

Metaphase I: Chromosomes line up at equator

Anaphase I: Chromosomes pulled to opposite poles

Telophase I: Cytoplasm divides

Metaphase II: Chromosomes line up at equator

Anaphase II: Chromatids pulled to opposite poles

Telophase II: Cytoplasm divides, nuclear membrane reforms

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Chromosomes in animals

Cat - 38 - 19 pairs

Dog - 78 - 39 pairs

Human - 46 - 23 pairs

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