W1/L2 - Principle of cell function Flashcards
Ionic chemicals, such as Na+ and phosphate PO43- are:
- Lipophilic
- Have low solubility in water
- Can readily move across membranes by passive diffusion
- Are hydrophobic
- Prefer to be dissolved in aqueous solutions rather than lipid environments.
Answer 5.
Anything with a charge wont be able to go through by passive diffusion
Comparing unsaturated and saturated hydrocarbon molecules, which of the followng is INCORRECT?
- Unsaturated hydrocarbons have double or triple bonds
- Saturated hydrocarbons have a more rigid shape than unsaturated hydrocrabons
- A double bond results in a kink in a hydrocarbon
- Both types of hydrocarbons are lipophilic
- Both types are hydrophobic
Answer is 2.
Saturated hydrocarbons have a very maleable structure.
Which statement about animal cell membranes is CORRECT?
- Unsaturated phospholipids cause increased viscosity of the membrane
- Saturated phospholipids result in reduced membrane fluidity
- At body temperatude, cholesterol increased the fluidity of membranes
- Unsaturated phospholipids are less kinked than saturated lipids
- Because of its ordered structure, cholesterol always decreases the fluidity of the membrane
Answer is B
Unsaturated makes is more fluid as they are not densely packed together
Facilitated diffusion: Passive transport aided by proteins
- In facilitated diffusion, transport proteins speed up the passive movement of molecules across the plasma membrane
- 2 types of transport proteins for facilitated diffusion:
A. A channel protein (tube like proteins)
B. A carrier (transporter) protein (Pacman like protein)
Transport proteins
- Transport proteins include:
- Aquaporins and Ion channels that open or close in response to a stimulus (gated channels)
- Carriers (or transporters) that bind to molecules and change shape to shuttle them across membrane – e.g. glucose transporters; amino acid transporters
- Chanel and transporters are proteins that allow passage of hydrophilic substances across the membrane
- Facilitated diffusion occurs along the solute concentration gradient and does NOT require energy
Passive diffusion vs Active
Passive = Down a concentration gradient (No energy required)
Active = Against a concentration gradient (Uses energy as ATP)
- Only transporter (or carrier) proteins can mediate active transport of hydrophilic substances across the membrane; NOT channels
- Transport solutes against concentration gradient
- Requires work – from energy of ATP
- e.g. Na+/K+‐ATPase = sodium‐potassium pump
What are the types of pumps
- An electrogenic pump is a transporter that generates voltage across a membrane
- The sodium‐potassium pump is the major electrogenic pump of animal cells – see Nervous Systems Module
- The main electrogenic pump of plants, fungi, and bacteria is a proton pump
Cotransport: Coupled Transport by a Membrane Protein
- Cotransport occurs when active transport of a solute indirectly drives transport of another solute
- Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
- Animal cells: Na+/K+‐ATPase working together with, for example, the Na+‐glucose cotransporter to drive glucose uptake against its concentration gradient
Which of the following is NOT true about membrane phospholipids
- They are the main component of all cell membranes
- They are amphipathic
- they are mobile
- They mediate movement of ions across membranes
- They can be saturated or non-saturated
Answer is D
Proteins mediate the movement of ions, NOT phospholipids
Which of these molecules will move most quickly across a lipid bilayer membrane by simple diffusion?
- K+
- CO2
- Fructose
- HCO3-
- H2O
Answer is CO2
Non polar, small molecule. Faster than H2O
Which of these statement is correct?
Both facilitated diffusion and active transport:
- use protein to mediate transport across cell membrane
- Can be mediated by ion channels
- can generate electrical potentials across cells
- require the solute to dissolve in the phospholipid bilayer
- require energy from ATP
Answer is 1.
Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Endo solution goes inside membrane vesicle
- Phagocytosis (Engulfing particles)
- Pinocytosis (Cells drinking)
- Receptor-mediated endocytosis (Not to worry about for this course)
Exo expells solution out from membrane vesicle
- the mechanism of neurotransmitter release from neurons
