Test 2 Unit 2

Question 1

How do the protein/lipid contents vary in different membranes of the cell?

Answer 1

It varies depending on the type of membrane. Plasma membrane and mithochondrial membrane don’t have the same content.

Because they are larger than lipid molecules, proteins move more slowly in the fluid environment of the membrane. Proteins are larger and therefore easily make up a bigger part of the membrane content.

Question 2

What are the 4 types of membrane proteins?

Answer 2

1. Transport (aquaporins): provides a channel/change its shape for the movement of a specific molecule
2. Enzymatic activity (respiratory and photosynthetic enzymes)
3. Signal transduction (insulin receptor): receptor proteins bind to specific chemicals and the receptor triggers changes on inside of membrane.
4. Attachment/recognition (tight junctions): attachment points for cytoskeleton elements.

Question 3

What is the difference between passive transport and active transport?

Answer 3

The need for ATP!
Passive: no need to expend chemical energy by diffusion down a concentration gradient.
Active: energy-dependent transport that moves molecules against a concentration gradient.

Question 4

What are the types of passive transport?

Answer 4

1. Simple diffusion
2. Facilitated diffusion
3. Osmosis (SD across membrane or FD through aquaporins)

Question 5

Describe simple diffusion.

Answer 5

Simple diffusion is the movement of molecules directly across a membrane WITHOUT the involvement of a transporter. Goes from high to low concentration. The rate depends on molecular SIZE and lipid SOLUBILITY.

Question 6

Describe facilitated diffusion.

Answer 6

It is the movement of molecules WITH the involvement of a transporter (transport protein)

Question 7

What are the types of channel proteins from facilitated diffusion?

Answer 7

• AQUAPORINS: diffusion of water only (does not allow the diffusion of ions)
• Gated channels: can open/close (Na+, K+, Ca2+, and Cl-)
• Leak channels: lets SOME ions move (tight)
• Voltage-gated ion channels : nerve conduction + muscle contraction

Question 8

What is the difference between dialysis and osmosis?

Answer 8

Dialysis is the movement of molecules in solute (e.g. glucose) and osmosis is the movement of the solvent (water) itself across a semi-permeable membrane.

Question 9

By what does osmosis occur?

Answer 9

• Passive diffusion
• and also by simple AND facilitated diffusion
• dictated by solute concentration (goes from LOW to HIGH solute conc.

Question 10

Explain hypotonic and hypertonic environmental conditions.

Answer 10

• Hypotoninc: env. has LOWER solute conc. than inside the cell = cell swells/turgid
• Hypertonic: env. has HIGHER solute conc. than inside the cell = cell shrinks/plasmolyzed

Question 11

Explain the relation between osmosis and cell walls (turgor pressure) in a hypotonic env.

Answer 11

In plants, the cell wall prevents the cells from bursting in a hypotonic solution because of its rigidity. Instead the cell pushes against the cell wall, resulting in what is called turgor pressure.

Question 12

How can water be drawn into aquaporins?

Answer 12

Aquaporins are made of non polar alpha helices to keep the protein embedded in the cell membrane and contains 2 + CHARGED POLAR A.A. that draw water into the channel. In fact, the partial negative charge on the oxygen is attracted to the + a.a.

Question 13

What do you say of plant cells in different osmotic pressure conditions?

Answer 13

• Hypertonic: plasmolyzed, microtubules still attached to cell wall, membrane turned inwards,small vacuole.
• Isotonic: flaccid, vacuole 90% of volume, no pressure on cell wall
• Hypotonic: turgid, over filled vacuole pushing against cell wall

Question 14

What do you say of animal cells in different osmotic pressure conditions?

Answer 14

• Hypertonic: crenated, surface is scalloped due to shrinkage
• Isotonic: biconcave disk
• Hypotonic: swollen, fully spheric

Question 15

What are the types of active transport?

Answer 15

1. Primary: the same protein that transports the molecules also hydrolyzes ATP to directly power the transport.
2. Secondary: the transport is indirectly driven by ATP.

Question 16

Describe the different primary active transports.

Answer 16

-Na+/K+ pump: pushes 3Na+ ions out of the cell and two K+ ions into the cell
-Ca2+ pump: pushes from the cytoplasm to the cell exterior, and from the cytoplasm into the ER lumen
-H+ pump: push from the cytoplasm to the cell exterior.
They create an electrochemical gradient because of the concentration and electrical charge difference

Question 17

Describe the different secondary active transports.

Answer 17

The

• symport: cotransport, same direction as the driving ion
• antiport: exchange diffusion, opposite direction

Question 18

Describe an electrochemical gradient.

Answer 18

Because of difference in charge as well as from the unequal distribution of ions. It stores energy that is used for other transport mechanisms. A gradient across the membrane that is involved with the movement of ions associated with nerve impulse transmission

Question 19

Why is endo/exocytosis useful?

Answer 19

To import/export larger molecules.

Question 20

Do endocytosis and exocytosis require energy?

Answer 20

Yes. both.

Question 21

Descrive and explain endocytosis.

Answer 21

IMPORTS.

1. Bulk-phase: cell drinking. No binding by surface receptors
2. Receptor-mediated: the molecules to be taken in are bound to the outer cell surface by receptor proteins (integral proteins)

Question 22

Descrive and explain exocytosis.

Answer 22

EXPORTS.
Secretory vesicles move through the cytoplasm and contact the plasma membrane. The vesicle membrane fuses with the plasma membrane, releasing the vesicle’s contents to the cell exterior.

Question 23

True or False? Exocytosis is used by neurons during the synapse process.

Answer 23

True.

Question 24

What is phosphorylation?

Answer 24

A signalling mechanisms where the signal is relayed inside the cell by protein kinases, enzymes that transfer a phosphate group from ATP to one or more sites on particular proteins one after the other like a cascade.

Question 25

What does phosphorylation do?

Answer 25

It implifies the signal and the response (inflammation, proliferation, differentiation, survival,…)

Question 26

What are the main parts of the neuron?

Answer 26

• the dendrites: receive a signal and transmit it to…
• spike initiaion zone: generate action potential
• axons: conduct signals from SIZ to another neuron
• axon hillock and axon terminals

Question 27

What 5 channels are involved in the process of a nerve impulse?

Answer 27

1. K+ leak
2. Na+ leak
3. Na+/K+ pump
4. Voltage-gated K+
5. Voltage-gated Na+

Question 28

What initiates a nerve impulse?

Answer 28

When the resting membrane potential of -70mV is changed because an ACTION POTENTIAL is initiated in the SIZ

Question 29

When does the Na+ gated channels open?

Answer 29

When the local voltage shifts from -70 mV to -50 mV. This is called the threshold potential. When the treshold potential is reached = depolarization

Question 30

When does the K+ gated channels open?

Answer 30

When voltage reaches a peak after depolarization = repolarization. K+ ions will reset the resting membrane potential to -70 mV.

Question 31

Why does the K+ gated channel does not close right after repolarization?

Answer 31

When the voltage reaches -70 mV again, the K+ gated channels remain open a little longer (hyperpolarization), preventing other nerve impulse from being fired right away.

Question 32

Explain the synapse process.

Answer 32

• When the action potential reaches the axon terminal, the synapse process enables the signal to transfer from a presynaptic neuron to a postsynaptic neuron.
• Upon reaching the axon terminal, depolarization triggers the opening of Ca2+ gated channels.
• The inward flow of Ca2+ ions forces the exocytosis of neurotransmitter vesicles.
• The neurotransmitters are expelled into the synaptic cleft and are detected on the postsynaptic neuron.

Question 33

Why do humans produce hyperosmotic urine?

Answer 33

It is a waterconserving adaptation.

Question 34

What 3 features interact to conserve nutrients and water, balance salts, and concentrate wastes for excretion from the body?

Answer 34

1. The structural arrangement of the loop of Henle
2. Differences in the permeability of successive regions of nephron
3. Gradient in the concentration of ions and molecules in kidney

Question 35

What are the 6 steps of formation of urine?

Answer 35

1. Bowman’s capsule filters evthing
2. Proximal convoluted tubule reabsorbs ions, water and nutrients
3. Descending loop of Henle aquaporins allow water to pass into the interstitial fluid
4. Acending loop of Henle secrets Na+ and Cl- into the interstitial fluid
5. Distal convoluted tubule secretes/absorbs ions to maintain blood pH
6. Collecting duct controls final conc. of urine.

Question 36

What are the 2 types of transport proteins?

Answer 36

2 main types of transport protein:
1. Channels = hydrophilic pathways for water and ions (Na+ and K+)
2. Carriers = bind a SPECIFIC solute like sugar and a.a
1*. AQUAPORINS: diffusion of water only.

*it is a type of channel that does not allow the diffusion of ions.