unit 1 topic 1

• The four main structural components of the cell membrane are:

  1. Protein channels
  2. Cholesterol
  3. Phospholipids
  4. Glycoproteins
• Protein channels allow for rapid transport of substances such as ions and water molecules in and out of the cell.
• Cholesterol helps maintain fluidity despite changing conditions (e.g. temperature).
• Phospholipids contain a hydrophilic phosphate head, and hydrophobic lipid tail.
• Glycoproteins are proteins that have carbohydrate chains covalently bonded to the outside cell membrane of proteins.
• The fluid mosaic phospholipid bilayer describes the model of the cell membrane.
• “Fluid“ in the fluid mosaic phospholipid bilayer refers to the ability of phospholipids to move laterally (like a fluid) but not vertically.
• “Mosaic” in the fluid mosaic phospholipid bilayer refers to the mosaic-like scattering of peripheral proteins and visible integral proteins on the surface of the cell membrane.
• “Phospholipid” in the fluid mosaic phospholipid bilayer refers to the arrangement of phospholipids into a bilayer.
• “Bilayer” in the fluid mosaic phospholipid bilayer refers to the two layers of phospholipids present, with the tails facing inward forming a hydrophobic interior, and the phosphate heads on the outside, forming a hydrophilic exterior.
• The cell membrane helps maintain relatively stable internal conditions though active and passive transport.
• Transport of substances out of the cell is called exocytosis.
• In exocytosis, large, polar molecules move past the hydrophobic part of the cell membrane via active transport (active as the polar molecules are opposite polarity to the hydrophobic section of the membrane).
• Endocytosis is the movement of large, polar substances into the cell.
• There are three types of endocytosis:

  1. Phagocytosis
  2. Pinocytosis
  3. Receptor-mediated endocytosis
• In phagocytosis, large, solid particles (e.g. bacteria) enter the cell as the membrane pinches off around it into a transport vesicle.
• Phagocytosis eliminates bacteria and maintains tissue homeostasis by breaking down the substance after being brought into the cell.
• In pinocytosis, extracellular fluids and fluids containing solutes (e.g. sugar, proteins) enters the cell as the cell membrane pinches off into a transport vesicle contains the fluid.
• In receptor-mediated endocytosis, large molecules (e.g. macromolecules) enter the cell as the receptors (proteins) on the surface of the membrane detect the molecule and pinches off into a protein coated pit.
• The surface area to volume ratio (SA:V) measures the difference in volume compared to surface area.
• More efficient cells have a larger SA:V as more surface area allows more area for diffusion to occur while only needing to provide for a small volume.
• Prokaryotic cells:

  • Lack membrane-bound organelles
  • Lack a true nucleus
  • Have circular DNA
  • Reproduce through binary fission
  • Are relatively smaller and simpler
• Eukaryotic cells:

  • Have membrane-bound organelles
  • Have a true nucleus
  • Have linear DNA
  • Reproduce through mitosis or meiosis
  • Are relatively larger and more sophisticated
• Internal membranes/organelles control biochemical processes though compartmentalisation.
• An organelle’s internal surface area is increased through the folding and stacking of membranes.
• Compartmentalisation creates specialised environments for specific functions, allowing for a large number of activities to occur simultaneously in a limited space under different conditions.
• Membrane-bound areas allow enzymes to be concentrated and recycled, reducing the number of enzymes required for a reaction.
• Membrane-bound structures can concentrate reactants and store products.
• There is also compartmentalisation within each organelle:

  • Cellular respiration in mitochondrion
  • Photosynthesis in chloroplast
• Function of lysosomes:

  • Break down compounds brought into the cell
  • Uses digestive enzymes in an acidic environment
  • Encloses strong enzymes in a membrane to prevent damage to the cell
  • Prevents damage to surrounding cells by programming cell death (progression of apoptosis)
• Mitochondria structure:

  • Outer mitochondrial membrane
  • Contains proteins and enzymes involved in the transport of substances in and out of the organelle
  • Inner mitochondrial membrane
  • Contains cristae (folds of membrane organised in layers)
  • Studded with enzymes needed for the electron transfer chain
  • Reduces space between matrix and inner membrane
  • Matrix
  • Contains enzymes for Kreb’s Cycle
• Mitochondria is the site for cellular respiration.
• Cellular respiration stages and sites:

  Cytoplasm: Glycolysis

  Matrix: Kreb’s Cycle

  Inner mitochondria membrane: Electron Transfer Chain
• Biochemical pathways are a series of enzyme-regulated steps.
• Biochemical pathways are reversible under certain conditions, and once a product is produced it becomes the reactant for the next step (to encourage forward reaction).
• Enzyme structure:

  • Active site of enzyme is complementary to substrate to allow for binding
  • Specific shape
  • Globular shape (spherical)
• Enzyme role:

  • Catalyse a chemical reaction
  • Speed up chemical reaction by binding to substrate and lowering activation energy
• Enzyme properties:

  • Types of proteins consisting of amino acids
  • Specific in function
  • Not altered during catalysis
  • Are not a reactant or product in the chemical reaction
  • Remain chemically unchanged after a reaction and can be reused
  • Speeds up chemical reaction
  • Catalyse by lowering activation energy
  • Temperature specific
• Types of enzymes:

  • Intracellular
  • Used within the cell where it is produced
  • Speed up and control metabolic reactions
  • E.g. enzymes in cellular respiration and photosynthesis
  • Extracellular
  • Produced by cells
  • Used outside cell that produces them
  • E.g. digestive enzymes in small intestine produced by cells
• There are two stages of photosynthesis:

  • Light dependent
  • Light independent