Lipids, Membranes and Transport Flashcards
What is a triglyceride made up of?
- 3 fatty acids combined with 1 molecule of glycerol.
- Joined with ester bonds.
What are the two types of fatty acids?
Saturated - contain no double bonds between carbon atoms
Unsaturated - one or more double bonds between carbon atoms.
How is a triglyceride formed?
- It is a condensation reaction producing 3 molecules of water.
- Ester bonds are formed between the -OH group of the glycerol and the -COOH group of the fatty acid.
Why are triglycerides not classed as polymers?
- They are not made from repeating monomers.
- They are made from 1 glycerol and 3 fatty acids.
What are the biological roles of triglycerides?
- Storage of energy.
- Insulation - electrical and heat.
- Protection.
What is the structure and properties of triglycerides?
- High ratio of energy storing carbon-hydrogen bonds to carbon atoms —> so excellent source of energy.
- Low mass to energy ratio —> so lots of energy can be stored in a small volume.
- Large, non-polar molecules, insoluble in water —> so do not affect the water potential in cells.
What is the test for lipids?
- Add ethanol to the sample.
- Shake thoroughly to dissolve any lipid.
- Then add water to the sample and shake gently.
- A milky white emulsion indicates the presence of a lipid.
What is the structure of a phospholipid?
- One phosphate group, one glycerol molecule and two fatty acids.
- Hydrophilic (attracts water) head (glycerol and phosphate).
- Hydrophobic (repels water) tails (fatty acids).
What are the functions of plasma membranes?
- To control the transport of substances into and out of the cell or organelles.
- To act as a receptor site.
- To compartmentalise, separate off the cell from the environment and forming organelles.
How are phospholipids arranged in the membrane!
- Form a bilayer.
- Hydrophobic tails point away from water as they repel water.
- Hydrophilic head points to water as they attract water.
How are proteins arranged in the membrane?
- Protein molecules float around in the bilayer, forming a fluid mosaic structure.
- Extrinsic proteins are only in one layer of the membrane, whereas intrinsic proteins are across the whole membrane.
- They have hydrophilic channels in the middle to allow transport of some substances more easily.
What are the functions of membrane proteins?
Intrinsic proteins:
- Transport through channel and carrier proteins.
Extrinsic proteins:
- Enzymes.
- Receptors.
- Antigens.
How are glycoproteins arranged in the membrane?
- Short, branching carbohydrate chains are attached to proteins in the membrane.
- The glycoproteins act as receptors for hormones and neurotransmitters or antigens.
How are glycolipids arranged in the membrane?
- Made up of a carbohydrate covalently bonded to a lipid.
- Act as recognition sites, help to maintain the stability of the membrane and help cells attach to one another, so forming tissues.
How is cholesterol arranged in the membrane?
- Restricts the movement of other molecules making up the membrane and increases strength and stability of membranes by making them less flexible.
- Helps to prevent the loss of water and dissolved ions from the cell.
Why is the fluid mosaic model described as that?
- Fluid refers to the fact that all the different molecules can move around.
- Mosaic because there are different types of molecules: the proteins and carbohydrates ‘float around’ within the phospholipid bilayer.
What are the factors that affect rate of diffusion?
- Surface area over which diffusion occurs.
- The thickness of the exchange surface.
- The concentration gradient.
- The size of the diffusing molecule.
- Temperature.
- Water solubility/polarity.
What is Fick’s law?
Rate of diffusion is directly proportional to surface area X difference in concentration divided by thickness of exchange surface.
What is the process of simple diffusion?
- The movement of substances from a region of higher concentration to a region of lower concentration.
- The difference is called a concentration gradient.
- Diffusion is the movement of molecules down a concentration gradient.
- Small, non-polar molecules through the bilayer.
What is the process of facilitated diffusion?
- The movement of substances from a region of higher concentration to a region of lower concentration.
- Uses a channel of carrier protein.
- Large, charged, polar molecules.
What is the process of osmosis?
- The movement of water across a partially permeable membrane down a water potential gradient.
How does adding solutes affect water potential?
- Reduces the water potential of a solution by reducing the number of water molecules.
What is the process of active transport?
- The movement of substances against their concentration gradient.
- Uses a carrier protein and ATP.
- Large, charged, polar molecules.
