Lecture 03

• What is the importance of lipids in biological membranes?

  They form the barrier component of membranes
• What is the role of proteins in biological membranes?

  They perform all cell membrane functions
• How do carbohydrates function in biological membranes?

  They bind to lipids and proteins for communication
• What is the most abundant substance in organisms?

  Water
• What type of molecule is water?

  It is a polarised molecule
• What is the charge of lipids?

  They have no net charge
• What do lipids form in cell membranes?

  A barrier separating cytosol and extracellular medium
• What is the nature of lipids in terms of polarity?

  They are non-polarised molecules
• What is one function of biological membranes?

  Protect the cell
• How do membranes control the movement of molecules?

  By regulating permeability
• What is the fluid mosaic model of membrane structure?

  It describes the arrangement of lipids and proteins
• What are the basic building blocks of membranes?

  Phospholipids
• What role does cholesterol play in membranes?

  It maintains membrane fluidity

  
• What do carbohydrates bind to in membranes?

  They bind to lipids and proteins
• What is the structure of the phospholipid bilayer?

  Hydrophilic head and hydrophobic tail

  
• What are amphipathic molecules?

  Chemical compounds that are polar and non-polar
• Name one class of lipids.

  Phosphoglycerides
• What is a characteristic of sterols?

  They are smaller than other membrane lipids
• Where are sterols commonly found?

  In eukaryotic cells
• What does membrane fluidity refer to?

  The viscosity of the lipid bilayer
• What factors affect membrane fluidity?

  Saturated/unsaturated fatty acids, temperature, cholesterol
• How do saturated fatty acids differ from unsaturated fatty acids?

  Saturated have no double bonds; unsaturated have double bonds

  
• What happens to membrane fluidity at low temperatures?

  Fluidity decreases due to low energy
• What effect does cholesterol have at cold temperatures?

  It keeps phospholipids apart, increasing fluidity
• What happens to membrane fluidity at warm temperatures?

  Fluidity decreases as cholesterol binds lipids tighter
• What is the role of lipid rafts?

  They organise plasma membranes into domains

  
• How do lipid rafts contribute to immune response?

  They concentrate immune receptors and enhance sensitivity
• What are the types of membrane proteins?

  Peripheral, integral, transport, glycoproteins
• What do integral transmembrane proteins do?

  They anchor proteins for cell attachment
• What is the function of enzyme proteins in membranes?

  They catalyse reactions and decrease activation energy
• What do carrier proteins do?

  They move ions and proteins with specific binding sites
• Which amino acid is likely present in the transmembrane domain?

  A hydrophobic amino acid like valine
• Why does RNA find it difficult to diffuse through a phospholipid bilayer?

  Because it is a large complex charged molecule
• What happens to a marine algal cell in freshwater?

  It absorbs water and increases in volume
• Which organism has the highest percentage of unsaturated fatty acids?

  Antarctic fish
• What makes an animal cell membrane more fluid at room temperature?

  More cis-unsaturated and polyunsaturated fatty acids