What do cells use electrochemical gradients for? (4 points)
- Transport
- ATP Production (mitochondria, bacteria, chloroplasts)
- Cell Signalling (action potential)
- Other functions (e.g. opening and closing stroma)
What type of transport diffusion is the slowest out of simple, channel mediated, and transporter mediated?
- Transporter mediated is slowest
- simple diffusion and channel mediated are faster because molecules can just go right through without a conformational change
What is the example of passive transport that brings glucose in the cell?
GLUT Trasnporters
Difference between GLUT1 and GLUT2?
-GLUT 1 is expressed mainly in red blood cells and other tissues
-GLUT 2 is expressed in the liver and gut epithelium
Mutations in these GLUT transporters can lead to disease (neuro diseases that associated with epilepsy)
3 different forms of energy that powers conformational change? (Active transport)
- coupled transport (help of another solute)
- ATP-driven pump (uses ATP hydrolysis)
- light-driven pump
What type of transport can coupled transport be?
-antiporters or uniporters 9secondary active transport)
antiporters–> transports two molecules across the membrane in DIFFERENT directions
symporters–> transports two molecules across the membrane in the SAME direction
What is an example of coupled transport?
Na+ - glucose cotransporter (type of symporter)
What are the 3 classes of ATP driven pumps?
- P Type
- ABC
- V Type
What drives the conformational change of P-type pumps
- During the pumping stage, P-type pumps are phosphorylated by ATP which drives the conformational change to move solutes against its concentration gradient
- specifically, the conformational change is by the amino acids shift in position, which is shifted by the phosphorylation and dephosphorylation of asparic acid
Some of the roles of P-Type pumps inside the cell?
- Maintain calcium levels in the cytoplasm/cytosol - keep them low
- Some of them pump calcium in the ER and the plasma membrane
- Create Na+/K+ gradients (eg in plants and fungi)
- Transport of important trace metal ions such as iron, magnesium, cobalt, copper, manganese, and zinc copper
- Many are drug targets for drug development
- They are responsible for primary transport
Typical P-Pump Structure?
10 transmembrane α helices connected to three
cytosolic domains
What are the 3 cytosolic domains of a P-Type Pump?
- Nucleotide binding domain: uses atp to move solute across the membrane
- Phosphorylated aspartic acid: this domain is phosphorylated. The phosphate is from ATP
- Activator domain:
What is the structure of the ABC Transporter and what do they transport?
- ABC transporters contain two highly conserved ATPase, domains or ATP-binding cassettes on the cytoplasmic side and two hydrophobic domains
- Transport of sterols, lipids, sugars, vitamins, nucleotides, peptides, amino acids, etc
difference between bacteria ABC pump and eukaryotic ABC pump
Some ABC transporters export solutes and take in solutes. In eukaryotes, the transporter mainly only exports solutes out of the cell
What are 3 types of membrane transport flip flops
- Flippase (P-Type ATPase)
- flips phospholipid from outer to inner membrane layer - Floppase (ABC flippase)
- flops phospholipids from inner to outer membrane layer or out of membrane - Scramblases
- move in both directions (do not require ATP)
What are the types of channels associated with PASSIVE transport?
- Water Channels (aquaporins)
- Ion channels (Voltage, ligand and mechanically)
What channel proteins are selective?
While some channel proteins can be non-selective, the majority of them are selective. Selective channel proteins include aquaporins, and most ion channels (sodium, potassium, calcium, chloride)
What is the structure of water channels?
One half of the channel (left side) is hydrophobic and the other side that are the carbonyl bonds
What are the 3 properties of ion channels?
- Selectivity
- Gating–> They can open and close in confirmation
- desensitization/inactivation–> Many gated channels can be stimulated to open for a certain amount of time and it just closes up again
What is the selectivity filter on Ion channels?
Selectivity filter is the point in which the channel becomes very narrow, only allowing only 1 and sometimes a specific ion through
- This controls which ions can pass through the channel
How does an Ion channel open and close?
- This happens through the movement of inner helices
What is associated with the voltage-gated ion channels?
- neurons, membrane potential
What is membrane potential?
-The membrane potential is created by the Na+/K+ pump (10%) and the activity of K+ leak channels (90%)
What is resting membrane potential?
-cells are at rest; there are equal charges on both sides of the membrane which means voltage or membrane potential is 0
