Biology 2.1.5- Biological membranes

• What makes up the cell surface membrane? (5)

  Phospholipid, Cholesterol, Glycoprotein, Glycolipid, Channel protein
• What do phospholipids do?

  And describe the head and tail

  Controls fluidity and provides structural integrity

  Head is hydrophilic, Tail is hydrophobic
• What does cholesterol do?

  Controls membrane fluidity by restricting and letting go of phospholipids. High temperatures = more fluidity. More cholesterol = less fluid
• What are the 4 big roles of glycoproteins

  Cell-Cell recognition- Enables cells to recognise others as familiar. Stops immune system from attacking foreign cells

  Cell signalling- Acts as a receptor for hormone or neurosignal from other cell for communication

  Cell adhesion- Aids in cell adhesion (cells sticking together), vital for maintaining structural integrity of tissues

  Acts as an antigen- Acts as an antigen determining antigen specificity

  (glycolipids have similar functions)
• What are channel proteins, describe the inside and outside

  Intrinsic proteins that span the bilayer

  Inside is hydrophilic and outside is hydrophobic
• Define osmosis

  The net passive movement of water molecules from a region of higher water potential to a region of lower water potential

  Down a water potential gradient

  Across a partially permeable membrane
• What is water potenial?

  ψ- likelyhood that water molecules will move away from that region. Measured in KPa
• Define Diffusion

  Diffusion is the passive movement of molecules from a region of higher concentration to a region of lower concentration, down the concentration gradient
• Differences between simple and facilitated diffusion

  Simple- not always through a membrane and no component needed. performed by small molecules, lipid soluble and some polar like water

  Facilitated- always through a membrane and assisted by channel protein. performed by large molecules, polar molecules and charged molecules
• Factors that affect diffusion rate (5)

  Steepness of concentration gradient

  Diffusion distance

  Temperature

  Larger surface area

  (Some pressure)
• Define active transport

  What does it require?

  The movement of molecules from a region of lower concentration to a region of higher concentration, against the concentration gradient.

  Requires hydrolysis of ATP and carrier protein
• How does active transport work

  ATP is hydrolysed into ADP and Pi, which causes a conformational change in the shape of carrier protein

  
• Bulk transport: how does Endocytosis work

  The cytoskeleton changes the cell shape making pseudopodiums surround the molecule (e.g. bacteria). The membrane envaginates and the pseudopodiums merge. (requires hydrolysis of ATP)

  
• Bulk transport: how does exocytosis work (from the golgi)

  Golgi apparatus packages the molecule into vesicle(s). It is then transported via the cytoskeleton. The vesicle fuses with the cell surface membrane and the contents are secreted putside the cell. (requires hydrolysis of ATP)