Lecture : Membrane Transport; Active Transport

Active Transport moves which way

Moving uphill against the concentration gradient

Active transport: energy cost

Requires ATP

What direction does active transport go in

From low concentration to High Concentration

Active transport uses

Specialized membrane proteins (pump)

Primary (Direct) active transport

Directly burns ATP to pump molecules

Secondary (Indirect) active transport

Hitches a ride - using energy from an existing gradient

Bulk transport

Moving large groups or big molecules (Endo/Exocytosis)

Molecular Transport (small scale) : primary

Directly burns ATP to move ions (Na+/K+pump)

Molecular transport (small scale) : secondary

Uses an existing electrochemical gradient (built by primary transport) to pull a second molecule along

Bulk transport (Large Scale)

Moves entire cells, fluid droplets or large proteins

Bulk transport (large scale) requires

Wrapping cargo in membrane vesicles (envelopes)

Transporter for active transport

Specific carrier proteins or pumps that facilitate movement

Uniporter

Moves one molecule at a time

Symporter

Moves two different molecules in the same direction

Antiporter

Moves two different molecules in opposite/different directions

Unidirectional Flow

These are one-way streets for each substance

Cellular Balance

This precise control keeps the internal environment stable

ATP hydrolysis

Provides energy for the movement of molecules and ions across a concentration gradient

Inside the cell

Endocytosis

Out of the cells

Exocytosis

The gradient

[Na+] inside, [Na+] outside =0.08:1

[K+] inside:

[K+] outside= 35:1

Na-K pump transports ___ Na+ outside and brings ____ K+ inside cell

3 Na+ and 2 K+

Direct transport

Primar transport because it burns ATP directly to power pump

Cell’s battery

Result in creating electrochemical gradient

Chemical Gradient

The difference in the amount of a substance

Electrical Gradient

The difference in charge (positive vs negative)

Mostly negative due to trapped proteins

The cell’s interior

Use ATP indirectly

Co-transport

Borrows the “downhill” energy of one molecule to pull another molecule “uphill”

The energy swap

Relies on a primary pump (like the sodium-potassium pump) to set up the gradient first

The power source

Substance 1:

Moves down its concentration gradient (releasing energy)

Substance 2:

Moving up its concentration a gradient (harnessing that energy)

The power source (Na+ ions)

Moves high to low concentration

The “hitchhiker” (glucose)

Moves from low to high concentration

Sodium gradient

The cell successfully pulls in fuel (sugar)

Sodium potassium pump

Is primary active transport — Spends (ATP) directly

Sodium-Glucose

Is secondary active transport (cotransport)

Moving things uphill

Requires ATP

The cell ——- pumping to keep its balance

Never stops

How does the sodium- potassium pump make the interior of cell negatively charged

By expelling more cations that are taken in

Cell ____ to build a gradient (primary), then ______ harvests that gradient to stay alive (secondary)

Spends energy and harvest

Endocytosis

The process of active transportation of molecules into the cells by the action of engulfing it along with membrane

Exocytosis

The process is responsible for the release of molecules or particles from the cells

Endocytosis (phagocytosis)

Cell-eating

Phagocytosis

Engulfment of large particles or even entire cells (like bacteria) into the cell through the formation of a large vesicle called a phagosome

What size do phagocytosis ingest cells or particles

0.5um

Pinocytosis

Cell drinking

Pinocytosis is

The intake of small dissolved molecules or fluids from the extracellular environment into the cell through the formation of smaller vesicles

It allows absorption and transport of many different molecules

Non specific : Pinocytosis

Endocytosis (receptor-mediated Endocytosis is high or low selective ?

High selective

Binding of specific extracellular molecules to receptor proteins on the cell membrane

Receptor-mediated Endocytosis

Binding triggers the formation of a vesicle that carries the targeted molecules into the cell

Endocytosis

Where does Endocytosis occur

In special regions fo membrane called clathrin-coated pits

Ligand binding

Ligand bind to specific receptors on the cell surface

Lateral movement

The receptor - ligand complexes move laterally in the membrane, reaching a region called a coated pit

Coated pit formation

Coated pits are are of the membrane with a special coat made of protein

Membrane invagination

Starting to engulf the receptor-ligand complexes

Vesicle formation

The invaginated membrane pinches off from the cell surfance, creating a vesicle

Forces molecules out of the cells

What is Exocytosis

Exocytosis

Reverse of Endocytosis

Exocytosis

Process of moving materials from within a cel to exterior of the cell

Exocytosis requires what

Requires energy (active transport)

Golgi apparatus ( exocytotic )

Majorly for exocytotic vesicle containing protein products

Endosomes (exocytotic)

Majorly for exocytotic vesicle containing proteins, lipids, microbes

Constitutive Exocytosis

Involves the regular secretion of molecules

Regulated Exocytosis

Relies on the presence of extracellular signals

Lysosome-mediated Exocytosis

Lysosomes carry their digested material to the cell membrane for fusing

Vesicle trafficking

Vesicles transported to cell membrane

Tethering

Vesicle becomes linked to and pulled into constant with membrane

Docking

Attachment of vesicles w/cell membrane. Phospholipid bilayers of vesicle and cell membrane merging

Priming

Only occurs in regulated Exocytosis, not in constitutive Exocytosis. Modifications in cell membrane molecules.

Fusion

Vesicle memebrane fully fuses with the cell membrane. ATP energy required. “Fusion pore” expels content inside the vesicle and vesicle become part of membrane.

Exocytosis

In pancreas, small clusters of cell (islets) produce the hormones insulin and glucagon

The double gradient

Electrical charge also determines where and ion want to go