Tema 3

Question 1

MEMBRANE CHARACTERISTICS

Answer 1

Selective permeability
permeable:non-polar molecules without charge (O2)
slightly permeable: small polar molecules without charge (water + urea)
impermeable: ions and large molecules with/without charge (glucose)

Question 2

Factors that a determine diffusion

Answer 2

Concentration difference
Membrane electrical potential (Nerst equation)
Pressure difference

Question 3

Transport systems - small molecules

Answer 3

PASIVE
simple diffusion
facilitated diffusion
*channel proteins or protein carriers

ACTIVE
primary transport
secondary transport

Question 4

simple diffusion

Answer 4

transport through the blips layer
in favour of the concentration gradient // without energy
–>Water, gases, fatty acids, steroids

PORES: for small, polar molecules

Question 5

facilitated diffusion

Answer 5

in favour of the gradient // no energy used

CARRIER PROTEINS: they are saturable and specific
*conformational change

Question 6

diagram of facilitated and simple diffusion

Answer 6

y : transport velocity
x: solute concentration

Question 7

active transport

Answer 7

when a cell membrane moves molecules against the concentration gradient using energy (ATP)

PRIMARY: Na+/K+ pump
SECONDARY or co-transport: uses energy from primary transport to move 2 solutes
–> symport (same direction as Na+), Na+ in and glucose in
–>antiport (opposite direction to Na+), Na+ in and Ca2+ out

Question 8

Na+/ K+ pump

Answer 8

For every molecules of ATP: 3 Na+ out, 2 K+ in
It maintains the concentration gradients of both ions

The carrier protein is formed by 2 alpha (contain binding domains) and 2 beta subunits

Question 9

Transport systems - large molecules

Answer 9

Endocytosis: incorporated into the cell
*The plasma membrane evaginates the cell interior
*Phagocytosis and pinocytosis

Exocytosis: excretion to exterior of the cell

Question 10

Endocytosis

Answer 10

Phagocytosis: cellular ingestion // incorporation of large molecules (leukocytes)

Pinocytosis: cellular drinking // incorporation of extracellular fluid or small solutes (LDL by endothelium)

Question 11

Exocytosis

Answer 11

1. fusion of the vesicle membrane that contains the macromolecules with the cytoplasmic membrane
2. diffusion of its content into the extracellular fluid

Very important in endocrine and nervous systems

Question 12

AQUAPORINES

Answer 12

Water is a polar molecule
It is neutral overall but the charge is not evenly distributes (O2 is -ve // H+ +ve)

The molecules move through them thanks to the electric field created by the atoms in the wall of the channel.
Strict orientation opposite to the water molecules stop protons maintaining an intense flux of water molecules.