Membrane Protein and Membrane Structure 3

Question 1

What is active transport ?

Answer 1

active transport is the movement of molecules across a membrane from a region of their lower concentration to a region of their higher concentration—against the concentration gradient.

Active transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses ATP, and secondary active transport that uses an electrochemical gradient.

An example of active transport in human physiology is the uptake of glucose in the intestines.

Question 2

How is active transport mediated by transporters ?

Answer 2

Pumping activity is directional because it is tightly coupled to a source of metabolic energy such as ion gradient and atp hydrolysis

Question 3

What are the three types of active transport ?

Answer 3

Different forms of energy may be harnessed for active transport of solutes

Couple Carrier /atp driven pumps and light or redox driven pumps

Couple Carrier : Harness the energy stored in concentration gradients to couple the uphill transport of one solute across membrane to the downhill transport of another .

Atp Driven Pumps : Couple uphill transport to the hydrolysis of ATP .

Light or redox driven pumps known as bacteria or archaea mitochondria and chloroplasts couple uphill transports to an input of energy from light .

Question 4

Why do active transport require assistant from carrier proteins not channel ?

Answer 4

Because channel proteins are not used in active transport because substances can only move through them in concentration gradient

Where as passive transport is area from high to low concentration

Question 5

What is Uniport ?

Answer 5

Is an integral membrane proteins that transports a single type of substrate species chargered or uncharged across a cell membrane .

Question 6

What is Symport?

Answer 6

Is an intergral membrane proteins that is involved in the transport of many different types of molecules across a cell membrane .

Ions move down the electrochemical gradient allowing other molecules to move against concentration gradient

co

Question 7

What is antiporter ?

Answer 7

Exchanger or counter transport

Involved in 2 active transport of two or more different molecules /ions across phospholipids in opposite directions .

Question 8

What does the Tight coupling between the transfer of two solutes allow ?

Answer 8

Harvest energy stored in the electrochemical gradient of one solute which is inorganic ion to transport the other

Question 9

What energy can be released during the movement of inorganic ion ?

Answer 9

Free energy can be realised during the movement of an inorganic ion down an electrochemical gradient is used as a driving force to pump other solutes uphill against their electrochemical gradient

This strategy can work either direction some couples transporters ,function as symporters as antiporters

Question 10

What is the Co transported ion ?

Answer 10

Na + is because its electrochemical gradient provides a large driving force for the active transport of a second molecule

Question 11

How does the NA+ ion do ?

Answer 11

Enters the cell it is during the coupled transport is pumped out by an ATP driven NA+ K= PUMP IN The plasma membrane by maintaining the NA+ gradient indirectly drives the coupled transport .

Question 12

What is Secondary active transport ?

Answer 12

across a biological membrane in which a transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient.

Ion driven coupled transported mediate the secondary active transport

Question 13

What is primary active transport ?

Answer 13

In primary active transport, the energy is derived directly from the breakdown of ATP

ATP driven pumps mediate primary because free energy of ATP hydrolysis is used to directly drive the transport of a solute against the concentration gradient

Question 14

What do intestinal and kidneys epithelial cells contain ?

Answer 14

Variety of symptoms driven by Na+ gradient across plasma membrane

Na+ driven symporters is specific for improving a small group of related sugars or amino acids into the cells .Na+ tends to move into the cell down the elecrochecial gradient .

Question 15

Why are amino acids and sugars dragged into the cell ?

Answer 15

Greater the electrochemical gradient the sugar or amino is in a since of dragged into the cell with it .

Question 16

What is used to drive Na+ /K+ against electrochemical gradients ?

Answer 16

ATP

Question 17

The Na+/K+ ATP-asecombines these principles

Answer 17

K+ leaks back more (through K+ channels) and less is brought in à one driving force for membrane potential (10% direct contribution)

Question 18

The Na+ gradient across the plasma membrane of animal cellsis harnessed to drive other processes

Answer 18

Pumping Ca2+ out of the cell, and across the membrane of the endoplasmic reticulum (Ca2+/Na+ antiporter) n

Cytosolic acid/base balance (acids produced by metabolism) q Na+/H+ antiporter q Na+-driven Cl- [outward] / HCO3- [inward] exchanger n

Osmotic regulation q Export of Na+ > K+ import counteracts osmotic pressure n Nerve conductance (see later) n

In bacteria, a proton (H+) gradient serves a similar function

Question 19

Osmotic balance must be regulated

Answer 19

Animals: Net outward pumping of Na+ reduces internal osmotic pressure

Plants, fungi, bacteria: Turgor pressure from rigid cell wall counterbalances osmotic pressure

Protozoa: Contractile vacuoles expel excess water

Question 20

Na+/K+ ATPase

Answer 20

: Actively pumps ions against electrochemical gradient
At rest, ion channels are largely closed.
The voltage generated in neurons at rest is about -70 mV to -80 mV (i.e., negative inside)

Question 21

Summary

Answer 21

All channels allow solute to cross the membranes passively (along their concentration gradient, from more concentrated to less concentrated). •

If the solute carries a net charge both the concentration gradient and the electrical potential difference across the membrane (the membrane potential) influence its transport.

• The concentration gradient and the membrane potential combine to form the electrochemical potential.

Question 22

Summary

Answer 22

Almost all plasma membranes have an electrical potential with the inside of the cells negatively charged.

This means that:

• Entry (influx) of cations is favored to entry of anions -

Exit (efflux) of anions is favored to exit of cations.

• In order to transport a ion against the electrochemical gradient energy is spent (Active Transport).

Question 23

phospholipid membranes create a permeability barrier

Answer 23

Order of permeability: q Small nonpolar or hydrophobic molecules, such as benzene, pass freely q Small polar (but neutral) molecules, such as water, less so q Larger polar (but neutral) molecules even less so q Ions have very low permeabilities n

This enables cells to maintain distinct intra- vs. extra-cellular composition of many molecules q In eukaryotes, sub-cellular compartments with membrane boundaries also maintain distinct molecular composition n

However, this creates a problem, because cells must: q Acquire nutrients q Excrete waste products The transport systems found at the plasma membrane are important for cell homeostasis (including pH, osmolarity, nutrient supply) and electrical signalling (nerve conductance)