Plasma membrane components (B1.1.7,B1.1.12)+ membranes topic

• What are glycoproteins?


  Glycoproteins are polypeptides (proteins) with carbohydrates covalently attactched. Usually, the carbohydrate is an oligosaccharide (a short chain of monosaccharides linked via glycosylic bonds). Glycoproteins are embedded in the plasma membrane, facing outwards, aiding in cell-to-cell recognition via receptors (RBCs and phagocytes)
• What is a specific example of a glycoprotein?

  A specific example of a glycoprotein is hemagglutinin, which is found on the surface of the influenza virus. Its function is to allow the virus to bind to host cells by recognizing and attaching to sialic acid residues on the surface of the host's cell membranes. This interaction is crucial for the virus to infect the host cell, as it facilitates entry into the cell for viral replication.
• What is cell-to-cell recognition?

  Cell-to-cell recognition is facilitated by glycoproteins, and helps with organisation of tissues and identification of foreign cells to be identified and destroyed.
• What are ABO glycoproteins?

  RBCs contain glycoproteins on their membranes that affect blood transfusions, but do not have any other known function. Any three possible types of oligosaccharide can be present on the glycoprotein, O, A and B. Two may be present at the same, time, but never all three. The A, B, and O blood types are determined by glycoproteins and glycolipids on the surface of red blood cells, specifically the carbohydrate chains attached to the H antigen (carbohydrate chain, triggering an immune response).
• What is the form of an A glycoprotein?


  Extra N-acetyl galactosamine on the H antigen
• What is the form of a B glycoprotein?

  Extra galactose on the H antigen
• What is the form of an O glycoprotein?

  H antigen is unaltered.
• How does the A glycoprotein react during blood transfusions?


  A Glycoprotein: Individuals with blood type A produce anti-B antibodies. They can receive blood from A and O donors but will react to B or AB blood.
• How does the B glycoprotein react during blood transfusions?


  B Glycoprotein: Individuals with blood type B produce anti-A antibodies. They can receive blood from B and O donors but will react to A or AB blood.
• How does the O glycoprotein react during blood transfusions?


  O Glycoprotein: Type O individuals produce both anti-A and anti-B antibodies. They can only receive blood from O donors but are universal donors as their red blood cells lack A and B antigens.
• What happens if incompatible blood is transfused?

  If incompatible blood is transfused, the recipient's immune system recognizes the foreign glycoproteins as antigens, triggering an immune response. This triggers agglutination, which is when antibodies bind to foreign glycoproteins, causing red blood cells to clump together.
• What is a phospholipid?

  Phospholipids are amphipathic, with their phosphate heads being hydrophilic and their two hydrocarbon chains being hydrophobic.

  O ← Phosphate-Glycerol Head (hydrophilic)

  / \

  Two Fatty Acid Tails (hydrophobic)
• How are bilayers formed in water?

  Phospholipids form bilayers in water, because the phosphate-glycerol heads face outward toward the aqueous environment, due to their attraction to water molecules, and the fatty acid tails face one another because they are more attracted to one another than they are to the water (they are hydrophobic). This arrangement minimizes the energy required for the system by maximizing interactions between hydrophilic heads and water while isolating the hydrophobic tails in the interior. The bilayer creates a stable barrier that is essential for cell membranes, separating the interior and exterior of cells and allowing selective permeability.
• What do glycoproteins and glycolipids do?

  They form a carbohydrate-rich layer on the outside of the membrane, known as the glycocalyx. The glycocalyx of adjacent cells can fuse, binding the cells together and preventing tissue from falling apart.
• What is the form of an integral protein?

  • Transmembrane
  • On the outside, contain hydrophobic amino acids (to remain embedded in the membrane)
  • Usually span the bilayer, but not always
  • Can be a single helix, or multiple
• What is the function of an integral protein?

  • Enzymatic activity
  • Receptors
  • Transport
  • Recognition (glycoproteins)
  • Adhesion
  • Anchorage
• What are the types of integral protein receptors?

  • Chemoreceptors contain binding sites for chemical signals, triggering cellular response- Olfactory detect smell
  • Hormone receptors are binding sites for every specific hormone, activating a secondary messenger within the cell to trigger a response- Insulin receptors
  • Sensory receptors respond to non-chemical stimuli, triggering an ion channel to open and close, activating a message to be sent to the CNS- Thermoreceptors for heat, Electromagnetic for light, mechanoreceptors for touch/sound, baroreceptors for blood pressure
• What are the types of transport proteins?

  • Channels are specialised with a pore of certian diameter and hydrophilic properties facilitation transport of a specific ion or molecule. If they are gated they can open and close- Calcium for muscle contraction
  • Pumps used in active transport, via a conformational change through hydrolysis of ATP- proton pump
• What is a globular/pump protein?

  They use energy (ATP from aerobic cell respiration) to carry out active transport. They only move particles across the membrane in one direction, against the concentration gradient. The molecule or ion enters the globular protein and binds in its central chamber. Then the hydrolysis process of ATP releases energy that changes the shape of the globular protein, (conformational change- from one state (stable) to the other (less stable) – the reverse change does not require energy) meaning the molecule or ion is able to pass through the membrane
• What does and anchorage protein/integrin do?


  ECM is present in most eukaryotic cells, and the integral proteins (integrins in this case) anchor the membrane to it
• What is a peripheral protein?

  Involved with transportation of materials to various locations within the cell, signalling, moving molecules through the bilayer and maintaining cell shape.

  • Do not fully span the membrane-are on the surface
  • Either bound to the bilayer or to an integral protein
• What are the fatty acid tails?

  They are also hydrocarbon chains/lipid tails. As they are lipids, they are hydrophobic, meaning that they protect the cell by having low permeability to hydrophilic particles, such as ions. There are two, and if they are unsaturated, they are kinked resulting in a more fluid and permeable membrane
• Functions of the phospholipid bilayer

  Form continuous sheet-like barriers in water

  They may be used for borders between a cell and its environment or to divide the cell into compartments.

  It allows cells to have different internal conditions to their environment, either side of it to have an aqueous solution, and its core has low permeability to large and hydrophilic particles. Hydrophilic molecules may penetrate the phospholipid heads but then are more attracted to the aqueous solution than the hydrophobic tails so they move back out of the membrane.
• Glycolipid



  Consists of a lipid tail and a carbohydrate tail. They maintain the stability of the plasma membrane and aids cellular recognition. They appear on the outside of a cell.