unit one - cells and membranes

• Cell theory


  All living organisms are made of cells, the cell is the smallest fundamental unit of life, cells come from pre-existing cells
• Requirements for a cell to be self-replicating

  • DNA
  • Proteins
  • Mechanisms to transform energy
  • Mechanisms to read instructions (DNA)
  • Ability to pass instructions to new replicates
  • A container to keep everything inside
• Eukaryotes


  Highly diverse and microbial
• Eukaryotes


  Can be multicellular or unicellular but are usually unicellular
• Organism


  Individual creature (animal, plant, or single-celled)
• Chloroplasts and mitochondria


  • Have bacteria-like characteristics: double membranes, circular DNA, grow and multiply by binary fission, have own ribosomes, synthesize proteins, etc.
• Location of RNA in eukaryotes

  • Nucleus (where it's processed)
  • Cytoplasm
  • Mitochondrial matrix
  • Plastid stroma (chloroplasts)
• Location of carbohydrates in eukaryotes

  • Cytoplasm
  • Plastids
  • Cell wall
• Location of carbohydrates in bacteria

  • Cytoplasm
  • Plastids
  • Cell wall
• Location of proteins in bacteria

  • Cytoplasm
  • Bound to DNA
  • Inner and outer cell membranes
  • Maybe cell wall
• Organic molecule


  Contains one or more C-H bond
• Macromolecules


  Polymers that are made up of repeated units (monomers) held together by covalent bonds
• Macromolecular Assembly


  Macromolecules assemble into functional structures (e.g. proteins to folded proteins)
• Macromolecules


  • Exhibit polarity: have two chemically distinct ends
• Lipids


  • Do not have the same polarity as other macromolecules: have one head group attached to three monomer tails
• Phospholipids in water


  Form a bilayer that makes up the liposome, vesicle, etc.
• Cell membrane


  A bilayer made up of phospholipids through macromolecular assembly
• Bilayer formation


  Spontaneous in water (the universal solvent that makes up around 70% of cell mass) due to the hydrophobic effect: non-polar molecules are buried away from water to increase system stability driven mostly by increasing the entropy of water
• Water molecules not directly interacting with the membrane have freedom to move therefore greater entropy
• The decrease in entropy of lipids (through them becoming aggregated and ordered) is offset by the increase of entropy in water (molecules become less ordered)
• Hydrophilic


  Contain polar bonds and are charged molecules so interact with water since it's also charged
• Hydrophobic


  Contain non-polar bonds and are not charged molecules so have weak or little interactions with water
• Amphipathic


  Have both hydrophobic and hydrophilic regions (e.g. phospholipids)
• Intramolecular interactions


  Covalent, ionic, hydrophobic (polymerization)
• Intermolecular interactions


  Non-covalent (macromolecular assembly)
• Entropy


  Measure of randomness of a system
• Enthalpy


  Measure of heat released or absorbed by system
• Lipid bilayer


  • Semi-permeable and selective to help maintain homeostasis: active maintenance of a constant environment
• Small, non-polar molecules


  Can easily permeate the lipid bilayer without assistance
• Diffusion


  When molecules move through the lipid bilayer ALONG the concentration gradient so they do not stop moving at equilibrium (small uncharged polar molecules and small non-polar molecules)
• Energetically favourable for molecules to diffuse from regions of high to low concentration to result in increased entropy
• Integral Membrane Proteins


  • Include transmembrane proteins that cross through the entire bilayer
• Peripheral Membrane Proteins


  • Associated with bilayer on either side so does not span the entire bilayer
• Ways materials can move across the membrane

  • Passive transport
  • Active transport
• Passive transport


  Transport along a concentration gradient that does not require input of energy
• Types of passive transport

  • Simple Diffusion
  • Facilitated Diffusion
• Simple Diffusion


  Diffuses through the bilayer alone
• Facilitated Diffusion


  Uses a protein transporter
• Channel Proteins


  • Channels can be open or gated (open or close due to a signal), can help molecules diffuse through into the membrane, usually selective for a specific type of molecule that has to interact with the protein channel to be transported, provides a hydrophilic passway (aqueous pore), transport through a channel usually occurs at a faster rate than carrier proteins
• Carrier Proteins


  • Gated, carry more specific molecules than channels, open and closed formations, protein undergoes a shape change (conformational change) to open and close the protein