AH Bio 1.3

what is the structure of the plasma membrane usually described using?

the fluid mosaic model

what gives a membrane fluidity and flexibility?

phospholipid bilayer

What forms a mosaic within the membrane?

proteins

what parts of the phospholipid molecules make up the central region of the bilayer?

hydrophobic

what is the hydrophilic surface of the membranes attracted to?

the watery cytosol of cells

what does the phospholipid bilayer act as a barrier for?

ions and most uncharged polar molecules

what molecules can pass through the bilayer by simple diffusion?

oxygen and carbon dioxide

what allows integral proteins to be held permanently within the bilayer because of strong hydrophobic interactions with it?

regions of hydrophobic R groups on amino acids

where are embedded proteins found?

completely embedded in the membrane and exposed at both ends

what is facilitated diffusion?

the passive transport of substances across the membrane though specific transmembrane proteins that have channels within their structure

What are peripheral membrane proteins?

proteins that bind temporarily to the surface of membranes mainly by ionic and hydrogen bonding

what do many peripheral proteins interact with?

the surfaces of integral membrane proteins

what do transmembrane proteins do?

control ion concentrations and gradients

by what mechanism do channel proteins promote the passage of specific substances?

facilitated diffusion

what are channel proteins?

multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane

how do transporter proteins transfer solute across a membrane?

they bind to the substance then undergo a conformational change

what are pumps that mediate active transport coupled with?

an energy source

what do ATPase proteins do?

hydrolyse ATP to provide the energy for the conformational change required to move substances across the membrane

what feature of some channel proteins prevents or allow diffusion?

they are gated

what can ligand-gated channels be controlled by?

binding of signal molecules

what can voltage-gated channels be controlled by?

changes in ion concentration

for a solute carrying a net charge, what combines to form the electrochemical (ion) gradient that determines the direction of the transport of the solute?

the concentration gradient and the electrical potential difference

when is a membrane potential created?

when there is an electrical potential difference between two sides of a membrane

what do ion pumps use energy from ATP for?

to establish and maintain ion gradients

what number of sodium and potassium ions enter/leave the cell?

2 potassium in, 3 sodium out

How does the sodium potassium pump work?

The pump has a high affinity for sodium ions inside the cell, so sodium ions bind to the pump, then phosphorylation of the pump by ATPase is stimulated. The pump the changes conformation affecting the affinity of the pump which means the sodium ions are released outside the cell. The release of the sodium ions then leaves 2 active binding sites available for the potassium to bind from outside the cell. When the potassium ions bind to these sites, the phosphate group is released from the pump and it is dephosphorylated. This changes the conformation of the pump and lead to the potassium ions being released inside the cell.

in the small intestine, what does the sodium-potassium pump drive the active transport of?

glucose

in intestinal epithelial cells, where is there always a low concentration of sodium?

inside the cell

what do sodium ions enter the intestinal cells though?

a glycose symport channel