PLASMA MEMBRANE AND ORGANELLES

• The cell membrane is composed of phospholipids, cholesterol, proteins, and carbohydrates.
• Functions of Cell

  • Manufacture cellular materials.
  • Remove waste products
  • Generate energy
• What is the plasma membrane?

  The outer boundary of a cell that controls the movement of substances in and out of the cell. They provide special conditions within the cell and allow things to move across called the semi-permeable membrane.
• The plasma membrane has a phospholipid bilayer containing hydrophilic heads and hydrophobic tails.
• Hydrophilic Heads face outside the cell and inside and the hydrophobic parts where the tails touch each other. They are embedded and stuck to proteins.
• The plasma membrane is constantly moving , so the consistency must be right by saturation.
• What is saturation?

  it makes the phospholipid more fluid and happens in the tails.

  low temperature - less fluid

  high temperature - fluid
• Cholesterol helps keep the membrane stable at different temperatures, it also stops the membrane from becoming too permeable. It's not very soluble but can dissolve into the lipids.
• Plasma membrane proteins determine the function of the cell.
• Functions of membrane proteins:

  • Signal transduction
  • cell recognition
  • intercellular joining
  • linking cytoskeleton and extracellular matrix
  • membrane transport
• Signal transduction relays messages from the envrionment into the cells. This can result to die, divide and grow. `
• Cell recognition recognises cells as they move around the body which is important for the immune system.

  They have sugars used for a label to recognise the cell.

  They have a membrane which will have a shape to match the sugar ann the two will become a protein.
• Intercellular joining are adhesions that hold cells together. They allow cells to stick together so they don't fall apart.
• Linking cytoskeleton and extracellular matrix allows the cell to be anchored down by linking the cytoskeleton with the ECM. The cytoskeleton gives structure to the cell while the ECM provides support.
• Membrane transport is a way to get from one side of the membrane to another. it allows small molecules to move across the membrane.
• Cells are able to get substances in and out depending on:

  • what the molecules are and made of
  • size
  • how much it is moving
• For small molecules in small volumes and large molecules use bulk transport
• Passive transport is the easiest way to move down the concentration gradient, moving from high concentration to low concentration, requiring no energy, by simple diffusion.
• If the molecule is lipid soluble small molecules and the membrane is permeable, it can go across the phospholipids into the cell without energy.
• If the molecule is charged, the plasma membrane will not let it get through, so they use membrane proteins called facilitated diffusion.
• Facilitated diffusion is where the carrier protein has more outside, so the concentration gradient moves for free. the carrier undergoes a shape change and guide the molecules through.
• Active transport requires ATP Energy to push against the concentration gradient. Active transport is the movement of molecules from an area of low concentration to an area of high concentration.
• Co-transport is indirect transport where the transport protein is a carrier protein that binds to the substrate and transports it.
• Osmoregulation is moving water in and out the cell.

  the water will move across if there are membrane proteins in the membrane called aquaporins.
• Aquaporins is a water channel. We go down the concentration gradient.
• When we have a high water concentration = low solute

  When we have a low water concentration = high solute
• Organelles have different functions:

  1. They provide special conditions for specific processes
  2. And keep incompatible processes apart
  3. They allow specific substances to be concentrated and form concentration gradients
  4. They package substances for transport or export.
• Key organelles:

  • Endoplasmic reticulum
  • Mitochondria
  • Golgi apparatus
  • Nucleus

  in the plant:

  • Central Vacuole
  • Chloroplast

  in animals:

  - Lysosome