IB Bio SL Flashcards, Membranes and Neurons

Outline the function of cholesterol in cell membranes

• Reduces fluidity of membrane

• Reduces permeability of membrane to some molecules

List functions of proteins found in cell membrane

• Facilitated diffusion by channel proteins

• Active transport by protein pumps

• Cell recognition by glycoproteins

• Receptors for hormones

• Cell adhesion

Outline simple diffusion

• Passive movement of molecules along a concentration gradient

• Passive transport

Outline facilitated diffusion

• Passive transport

• Passive movement of molecules along a concentration gradient through a protein channel

Outline osmosis

• Passage of water through a membrane from lower solute concentration to a higher solute concentration

• Usually uses a protein channel

• Passive transport

Outline passive transport

• Does not require ATP

• Molecules move from high concentrations to low concentrations (concentration gradient)

Outline the process of the Sodium-Potassium pump

• Active transport

• Pump binds to the three intracellular Na ions

• ATP molecule attaches to the protein

• ATP phosphorylated, loses one phosphate molecule, resulting in ADP

• Phosphorylation causes the pump to change its shape, causing Na ions to exit cell

• Two extracellular K ions bind to pump

• Phosphate group released from pump

• Causes protein to retain its original shape, releasing K+ into the cell

Outline endocytosis

• Allows large molecules to enter cell that cannot fit through membrane proteins

• Portion of the plasma protein is pinched off to enclose macromolecules, creating a vesicle around it

• Temporarily changes shape of membrane

• Ends of the cell membrane resume the correct shape, vesicle is taken into the cell

• Active transport

Outline exocytosis

• Active transport

• Protein produced by the ribosome of the ER

• Protein exits ER and enters the Golgi apparatus on the cis side

• Protein is modified and packaged in a vesicle, then exits the trans side of the Golgi

• Vesicle with protein fuses with the cell membrane and the contents are secreted from the cell

Outline hypertonicity in osmosis

• When the solution has a high concentration of solutes relative to the cell

• Water flows out of the cell to reach equilibrium of solutes

• May cause the cell to shrivel up

Outline hypotonicity in osmosis

• When the solution has a low concentration of solutes relative to the cell

• Water flows into the cell to reach equilibrium of solutes

• May cause the cell to inflate and burst

Outline isotonicity in osmosis

• When the solution has an equal concentration of solute relative to the cell

• No water flow

• Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis to create an isotonic situation once transferred into the body

Label parts of a neuron

1. Nucleus

2. Dendrites

3. Myelin sheath, made of lipid Schwan cells

4. axon

5. action potential

6. axon terminal button

7. synaptic terminals

8. nodes of Ranvier

9. cell body

Explain the action of neonicotinoid pesticides in insects

• Has similar structure to a neurotransmitter such as acetylcholine

• Binds to postsynaptic receptors that normally accept acetylcholine in postsynaptic membrane

• When pesticide binds to receptor proteins, action potential isn’t propagated nor is itbroken down by acetylcholinesterase

• Receptor is blocked and overstimulated, leading to paralysis and furthermore death

Outline neurones

• Designed to transport electrical impulses

• Can be long or short

• Electrical impulses are received in the dendrites, then transmitted through the axon and ends at the synaptic terminal buttons

• Synaptic terminal buttons release the neurotransmitter to continue the electrical impulse to the next neuron

• A group of neurons is called a nerve

Outline the function the myelin sheath

• Increases the rate at which an action potential passes down an axon

• Schwann cells, lipids and squishy

• Surrounds axons

• Active potential goes around them

• Acts as an insulator and prevents charge leakage through the membrane

• Wrapped around axon multiple times

Outline resting potential

• State where the neuron is not sending an imuplse

• Polarized

• Na+ out, K+ in, through sodium-potassium pump

• Transports 3 Na+ out for every 2 K+ in

• Cytoplasm has permanent negativity, results in net positive charge outside the axon membrane

• -70mV

Describe how an action potential is propagated down the axon

• Nerve impulses are action potentials propagated along axons of neurons

• Resting potential is -70mV, Sodium-potassium pumps maintain resting potential, more Na+ outside, more K+ inside

• Action potential stimulates wave of depolarization along the axon

• When neuron is stimulated, if the threshold potential is reached, Na+ channels open, Na+ diffuses in, depolarizing as inside becomes more positively charged

• Depolarized area then initiates the next area of the axon to open Na+ channels, causing action potential to move down axon, self-propagating part, self-propagates to the axon end

• K+ moves out of the cell, repolarizing and goes back to resting potential

• No such thing as a strong or weak impulse, only minimum impulse required to stimulate

Outline Saltatory Conduction

• Phenomenon where an action potential of myelinated axons skips from one node of Ranvier to the next

  • Action potential doesn’t have to undergo ion movements in area under the myelin sheath

• This jumping from one node to the next causes the impulse to travel faster because it allows areas of the membrane to be skipped

  • More efficient

  • Requires less ATP

• Only places where resting potentials need to be re-established is at the nodes of Ranvier

What is an example of a neurotransmitter?

Acetylcholine

Outline synaptic transmission

• Action potential (AP) has travelled to the axon terminal buttons filled with vesicles full of neurotransmitters (NT)

• AP activates voltage-gated Ca+ channels to take in Ca+, making the vesicles fuse with the cell membrane

• NT released into the synapse cleft

• Dendrites in postsynaptic neuron (second neuron) receive neurotransmitter through a receptor protein

• Binding causes an ion channel to open and Na+ diffuses in

• Initiates action potential, moves down the postsynaptic neuron

• Neurotransmitter is broken down by an enzyme and released from the receptor protein, diffusing back to be reassembled in the receptor protein buttons (reuptake)

• Ion channel closes to Na+

Define synapse

Area where two or more neurons adjoin and one neuron communicates with another through chemicals

Define amphipathic

Having both hydrophobic and hydrophilic parts, can be seen in the membrane bilayer

Outline the significance of the surface area to volume ratio in the limitation of cell size

• Surface area of the cell affects the rate of material exchange

• When the cell increases in size, so does its chemical activity

• When the cell grows, more substances need to be taken in and waste products excreted

• When the cell gets bigger, its surface area to volume ratio gets smaller

• Substances will not be able to enter the cell fast enough