Bio 202 Exam 2 - Chps 4, 5, & 6

What is the effect of submerging cells in a hypertonic solution

• water will move out the cell, causing it to shrink

• There’s more solute outside the cell

What is the effect of submerging cells in a hypotonic solution

• water will move into the cell, causing it to swell and burst

• less solute outside

What are the properties of the sodium potassium pump(how many ions move and in what direction when hydrolyzing an ATP)

1. primary active transport that requires ATP.

2. For each ATP used, 3 Na⁺ ions are pumped out of the cell and 2 K⁺ ions are pumped into the cell

3. both moving against their concentration gradients.( Na goes from low inside to high outside) (K goes from low outside to high inside)

4. more + charge leaves so the inside is more negative

How do large molecules enter and exit cells

Endocytosis(enter the cell):

• The membrane engulfs large molecules and forms vesicles to bring them into the cell. (Phagocytosis)

• phagocytosis, uses extensions of the membrane to engulf large molecules

Exocytosis(exit the cell):

• Vesicle membrane fuse with the plasma membrane and release their contents outside the cell.

How does oxygen and carbon dioxide move across the plasma membrane. 

• by simple diffusion through the lipid bilayer

• from high to low concentration

• passive process(no energy required)

• they are small and lipid soluble

What are integral proteins.

• Integral proteins are membrane proteins that span the entire phospholipid bilayer, containing hydrophobic and hydrophilic regions./ proteins imbedded in the plasma membrane

• penetrate or completely cross the phospholipid bilayer.

• They can function in transport, signaling, or cell junctions.

• Some integral proteins function as ion channels that allow substances to move by facilitated diffusion.

How does glucose move across the plasma membrane. 

• by facilitated diffusion through carrier proteins

• from high to low concentration(down the concentration gradient)

• passive process(does not require energy)

What transport proteins work by passive mechanism.

No energy needed → moves high to low

• Ion channels(leak channels)

• Mediated transport; specifically “facilitated diffusion”(carrier proteins), secondary active transport

What transport proteins work by active mechanism. 

Uses energy(needs energy) → moves low to high.

• Pumps (primary active transport) Ex. Na⁺/K⁺ pump falls under antiport transporters

• Na+ glucose cotransporter, secondary active transport and falls under symport transporters.

What factors affect the rate of diffusion (Fick’s law).

• Permeability(higher P, faster diffusion)

• Surface area(more surface area, more movement/diffusion)(more membrane, more diffusion)

• Distance(longer the distance, the slower the diffusion)

• Concentration gradient(the bigger the concentration gradient the faster the rate of diffusion)

• Molecular weight(lighter substances diffuse faster)

What are the properties of osmosis. Is it active or passive.

• Osmosis is the movement of water across a selectively permeable membrane by special proteins called aquaforin

• low solute to high solute concentration

• passive process (does not require energy)

• membrane is permeable to water

• occurs until equilibrium is reached.

What are the properties of facilitated diffusion. Is it active or passive. 

the process by which molecules pass across the plasma membrane through channel proteins(ion channels)or carrier proteins.

• Moves from high → low concentration

• Uses specific membrane proteins(carrier proteins)

• Can become saturated

• Passive process

• constant change in the shape of the protein

What are symports.

• transporter proteins that move two solutes in the same direction across the membrane

• often using the Na⁺ gradient.

The types of receptors that function as enzymes. 

1. Receptor tyrosine kinase ( activated by insulin)

• Insulin binds to the receptor

• The receptor becomes activated

• Then it triggers reactions inside the cell

• Leads to changes in the cell

• Found in muscle and adipose tissue

2. Acetylcholine esterase receptor(activated by acetylcholine)

• Acetylcholine binds to the receptor

• The receptor becomes activated

• Then it causes reactions at the membrane of skeletal muscle

• Leads to a cellular response

• found on membrane of skeletal muscles

What is the difference between hydrophobic messengers and hydrophilic messengers

• Hydrophobic messengers can cross the plasma membrane and bind to intracellular receptors(cytosol or nucleus). Ex. testosterone, estrogen

• Hydrophilic messengers cannot cross the membrane and bind to extracellular receptors on the cell surface. Causes internal change via signaling pathways. Ex. Insulin, Epinephrine

Know all the steps of the G-protein coupled receptor (in-order)

1. Messenger binds to receptor and activates it

2. Receptor activates a G-protein

3. The inactive G-protein is bound to GDP

4. GDP unbinds and GTP binds to the alpha subunit

5. The alpha subunit translocates

6. The alpha subunit activates adenylyl cyclase (AC)

7. AC converts ATP to cAMP

8. cAMP activates protein kinase A (PKA)

9. PKA phosphorylates other proteins

10. Cellular response occurs

Know the different parts of the action potential and values of resting potential, peak potential, threshold…

• Action potential includes:

  • Depolarization→ membrane becomes less negative(more positive)

  • Repolarization→ returns toward resting potential

  • Hyperpolarization→ membrane becomes more negative than resting potential

• Membrane potential values:

  • Resting potential: −70 mV

  • Threshold: −50 to −55 mV

  • Peak potential: +30 mV

The different part of the neuron and the function of each part. 

• Soma (cell body): contains abundant protein synthesis organelles and processes signals

• Dendrites: receptive sites for electrical signals (receive signals)

• Axon hillock: beginning of the axon. action potential begins here

• Axon: conducts signals away from the soma

• Axon terminals: release neurotransmitters (chemical signals)

• Myelin: covers the axon and speeds up the spreading of the action potential

The role of the sodium ions in the action potential. 

• Sodium ions enter the cell when voltage-gated sodium channels open at threshold, causing the membrane to become more positive (depolarization).

• This is responsible for the rising phase of the action potential, and continues until the channels inactivate at peak potential.

The role of the potassium ions in the action potential.

• Voltage-gated potassium channels are triggered at threshold but open slowly, around peak potential.

• When they open, K⁺ leaves the cell, causing the membrane to become more negative (repolarization).

• Because these channels close slowly, more K⁺ continues to leave, causing hyperpolarization.

• When the channels close, the membrane returns to the resting potential.

• VGKC are resonsible for the falling phase of action potential

The properties of the potassium leak channels. 

• Always open

• passive

• More permeability for K⁺ than Na⁺

• allows K+ to leave cell(diffusion)

What membrane proteins does the resting membrane potential depends on. 

• Na⁺/K⁺ pump: most important because it prevents equalibrium

• K⁺ leak channels

• Na⁺ leak channels

*leak channels both passive

What are the properties of the voltage gated sodium channels. 

• Specific to sodium

• Open at threshold (−55 mV)

• 3 states:

  • Closed (resting)(−70 mV)

  • Open at threshold (−55 → +30 mV)

  • Inactivated (+30 → −70 mV)

• Very fast

What is summation.

the process of adding together graded potentials at the axon hillock. It involves multiple signals combining to determine if threshold is reached.

• Can be temporal summation (rapid signals from the same neuron)

• Can be spatial summation (signals from multiple neurons)

What is saltatory conductance

• the process by which the action potential jumps from one node of Ranvier to the next along a myelinated axon.

• The depolarization at one node triggers the next, allowing the signal to travel faster.

• faster transmission

Stages that occur in the axon

resting potential → graded potential → action potential → propagation of action potential (how it travels down the axon), → neurotransmitters release