active transport. quite often substances need to move against their concentration gradient. active...
TRANSCRIPT
• Quite often substances need to move against their concentration gradient.
• Active Transport allows this to happen.
• I.e. Glucose and amino acids are pumped out from urine back inside the blood.
• I.e. Gill cells in fish pump out sodium ions into sea water
• I.e. Maintaining the pH level with in the cell by pumping protons (H+) out.
• (40 % of your cell’s energy is used for active transport.)
We will look at 3 types:
• Sodium – Potassium Pump
• Purpose:
• Transports– Sodium ions (Na+) out of the cell– Potassium ions (K+) into the cell
How does it work?
• With the energy from 1 ATP molecule, – 3Na+ ions are able to move out and
– 2 K+ ions are able to move in.
• To get the energy stored from ATP, the pump must ‘hydrolize’ (or break a part)– ATP ADP + Pi
– (Adenosine Triphosphate – Adenosine (Dipohsphate) + 1 phosphate)
The Process:
• 3 Na+ ions bind to the Na+ binding site on cytosolic side of the pump
• 2 K+ ions bind to the K+ binding site on the extracellular side of the pump
• This Triggers the Na+/K+ pump to hydrolyze 1 ATP molecule (ATP ADP + Pi)
• The pump then changes shape allowing 3 Na+ ions to move out and 2 K+ ions to move in
The end result from this main pump
• helps other protein pumps in the membrane transfer ions and molecules against their concentration gradient by creating an artificial concentration gradient.
• To achieve this, – Na+ ions must continually be diffusing inside
the cell and – K+ ions continually be diffusing out.
Two pumps that depend on this are….
• 1. Na+/glucose pump
• I.e. Found in the • lining of small
intestine• Kidney tubules
• Here, glucose needs to move against a large concentration gradient
• Na+ ions and glucose bind to their specific binding sites of this carrier protein
• Shape of protein changes
• Na+ and Glucose move easily through
• 2. K+/H+ Pump
• I.e. Found in Stomach lining
• These protein pumps move H+ out of the cell against its concentration gradient to maintain a normal pH level in the cell.
Endocytosis
• The process where the cell membrane folds around and traps substances from the extracellular fluid to form a vesicle.
• There are 3 types:
1. Phagocytosis (Cell ‘eating’)(p. 36)
• Seen in the macrophages of our immune system
• Eats up bacteria• The cell envelops
bacteria and other large particles and then internalizes them.
2. Pinocytosis (‘drinking’)
• The cell takes up small droplets of extracellular fluid and any material dissolved in it.
• Molecules in the extracellular fluid have proteins on their surface that ‘fit’ with a receptor on the cell membrane. (binding protein)
• The specific receptor on the cell surface recognizes the molecule by its binding protein or protein ‘tag’(I.e. ‘like a code’) and binds tightly to it.
• This triggers endocytosis• Results in a vesicle carrying the macromolecule
• I.e. LDL • Cholesterol is not water soluble, thus,• Must be carried by a particle called LDL• LDL
– Droplets covered with a single layer of phospholipids
– Has a protein ‘tag’
• The protein ‘tag’ binds to the cell surface receptor
• Triggers endocytosis• Once internalized, the vesicles empty its
contents• The Membrane with receptors (from the
vesicle) returns to the surface • Turns inside out so receptors face outside
once again.• Process is repeated
HIV
• Is a virus with a binding protein that mimics a specific binding protein required for a receptor on the cell surface
• It tricks the cell to believe it is a macromolecule needed for the cell
• Once inside, the virus uses the cell’s ‘machinery’ to replicate
• Problem?
• The binding protein on the virus is constantly changing to fit different receptors on various cell surfaces therefore, the cell does not recognize HIV as a virus.