Active Transport across Plasma Membrane Flashcards
What active transport do ?
exhibit specificaty, transport maximum and saturation
Energy source of active transport
- hydrolysis of ATP (primary)
- derived from concentration gradient of another substance (secondary)
What can the energy do in active transport ?
-alter affinity of binding site
- alter rates at which binding sites of solute is shifted from one side to another
What happen in primary active transport ?
- ATPase enzyme catalyzes breakdown of ATP into ADP (hydrolysis) and inorganic phosphate (phosphorylation)
- transporters directly linked to primary metabolic reaction
- phosphorylation changes shape and affinity of transpoter’s solute binding site
Sequence of molecules
phosphorylated transporter > high affinity to solute > solute binds to binding site > conformational change > phosphate group removed > low affinity of binding site > solute release > transporter changes back to original
Sodium-potassium pump
transport 3 Na+ out of cell and 2 K+ into cell in each ATP used (one cycle)
Calcium pump
- calcium is important second messenger
- helps to maintain low level of calcium in cytosol by transport Ca2+
- in plasma membrane : cytosol > ECF
- in organelle membrane : cytosol > organelles
Secondary active transport
- indirectly use energy derived from hydrolysis of ATP (in primary)
- have 2 binding sites : for actively transported solute and ion that will be moving down concentration gradient
Cotransport
transportation in same direction
Countertransport
transportation in opposite direction
Examples of sodium - dependent secondary active transport systems
Na+ - glucose cotransporter
Na+ - amino acids cotransporter
Na+ - Ca2+ countertransporter
Na+ - H+ countertransporter
Macromolecules
too big to be transported across membrane via membrane channels or transporters
Vesicular transport
- energy supplied by ATP
- consist of endocytosis and exocytosis
Endocytosis
transport of molecules into cell in vesicle formed by plasma membrane
Receptor-mediated endocytosis
- highly selective process in regions called clathrin-coated pit (molecule + membrane receptor)
Process of receptor-mediated endocytosis
- molecules with coated protein (clathrin) form basketlike structure & form veclsicles
- clathrin molecules recycle back
- vesicle + endosome undergo sorting process
- receptor & membrane recycle back
- transported molecule + lysosome undergo degradation
- some vesicle release content to ECF
Pinocytosis
no receptor protein involved, the cell takes in fluid that contains solute particles and nutrients
Process of pinocytosis
- endocytic vesicle pinches off from plasma membrane
- vesicle + lysosome digest the engulfes solutes
Exocytosis
intracellular vesicles move to cell membrane, fuse with it, then releasr the content to ECF
Important of exocytosis
- provides replacement materials for plasma membrane
- route to export large lipophotic molecules synthesized by cells
Gradients across plasma membrane
- many body solutes are in chemical disequilibrium
- our body is electrically neutral with excess of -ve ions in ICF
Resting membrane potential
uneven distribution of ions causes cells to be in electrical disequilibrium
Electrochemical gradient
combination of chemical and electrical gradients
