Bio- Life Science Khan Based (Part 10) Membrane transport, Passive, Active, Bulk-Facilitated, Na-K Pump, Uniporters, Symporters, Antiporters

Uniporter

A carrier protein that transports a single molecule across the plasma membrane.

Concentration gradient

A region along which the density of a chemical substance increases or decreases. *a concentration gradient itself is a form of stored (potential) energy, and this energy is used up as the concentrations equalize. Each individual substance in a solution or space has its own concentration gradient, independent of the concentration gradients of other materials, and will diffuse according to that gradient. Other factors being equal, a stronger concentration gradient (larger concentration difference between regions) results in faster diffusion.

Pinocytosis "cell drinking"

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes. Pinocytosis occurs in many cell types and takes place continuously, with the cell sampling and re-sampling the surrounding fluid to get whatever nutrients and other molecules happen to be present. Pinocytosed material is held in small vesicles, much smaller than the large food vacuole produced by phagocytosis.

In order for a voltage channel to pump against a concentration gradient channel, it requires:

ATP energy

secondary active transport

Form of active transport which does not use ATP as an energy source -> the transport is coupled to ion diffusion down a concentration gradient established by primary active transport.

A transmembrane protein complex has an affinity for Na ions, it draws 3 into the pump- what are the steps that occur in a Na-K Pump?

It will be phospholated by an ATP, adenosine triphosphate. -This changes the constitution of the protein and it opens up to the outside while closing up to the inside. -Protein loses its affinity for Na -Protein gains affinity for K; >The K ions (2of them) will bind to the outside of the protein receptacle, the protein becomes DEphospholated, and returns to the state it was in initially (regaining its affinity for Na) *The net charge outside of the cell becomes slightly more positive

Passive Transport (Diffusion)

Moving molecules in the direction (not against) its concentration gradient. substances move from an area of high concentration to an area of low concentration, until the concentration becomes equal throughout a space only small, uncharged substances like carbon dioxide and oxygen can easily diffuse across the cell membrane

sodium-potassium pump

Primary Active Transport A special transport protein in the plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients.

Proton ATPase

Primary Active Transport A special transport protein in the plasma membrane of plants, fungi, protos cells that transports sodium out of the cell and potassium into the cell against their concentration gradients.

potassium ion channels

Protein lined channels in the cell membrane that prevent sodium from passing into the cell. Once the voltage hits

Passive transport

Requires NO energy, Movement of molecules from high to low concentration, Moves with the concentration gradient

symporter; Sodium-Glucose transport

Secondary Active Transport A carrier protein that transports two molecules across the plasma membrane in the SAME DIRECTION, from HIGH TO LOW gradients. *For example, the Na+-glucose cotransporter in intestinal cells is a symporter. *Sodium-Glucose: if the electrochemical conditions are more attractive to the sodium ions on the other side of the membrane, then the symporter may take both- transporting the glucose against its gradient channel (which requires energy)-> it achieves this secondary transport by taking advantage of the potential energy of the sodium molecule.

cotransporter

Secondary Active Transport AKA: Exchange Transport Protein that transports 2 types of molecules in different directions through a membrane. Ex: Ca ions & Na ions

The Na-K Pump process results in the electrochemistry outside of the cell being more positive; this partially due to the fact that although both Na and K ions are positive, 3 Na are pumped out while 2 K ions are returned. What is the second reason for the change in the electric potential difference?

The difference of electric potential, with the inside of the cell being more more negative while the outside is more positive and there being more K ions inside the cell than out; while their are more Na ions outside the cell than inside > The K ions will passively diffuse OUT of the cell, as they go along in the SAME direction as their gradient channel, but go AGAINST their charge. > The differences will not balance out; this natural state is called: resting membrane potential

electrochemical gradient

The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).

Receptor-mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in *enables a cell to acquire bulk quantities of specific substances *receptor proteins (transmembrane proteins) cluster in regions of the plasma membrane known as coated pits on the cell surface, where they are used to capture a specific target molecule *allows cells to take up large amounts of molecules that are relatively rare (present in low concentrations) in the extracellular fluid. However, flu viruses, diphtheria, and cholera toxin all use receptor-mediated endocytosis pathways to gain entry into cells

What would happen if the receptor protein for that molecule were missing or defective?

The target molecule would no longer be pulled out of the blood, so it might start building up to abnormally high levels. In people who have familial hypercholesterolemia, the LDL receptors don't work right or may be missing entirely. People with this condition can have life-threateningly high levels of cholesterol in their blood because their cells cannot remove LDL particles from the bloodstream.

Phosphorylation

The transfer of a phosphate group, usually from ATP, to a molecule. Nearly all cellular work depends on ATP energizing other molecules by phosphorylation.

Clathrin-coated vesicles

coat protein

Exocytosis

form of bulk transport in which materials are transported from the inside to the outside of the cell in membrane-bound vesicles that fuse with the plasma membrane. -waste, leftover export -Some of these vesicles come from the Golgi apparatus and contain proteins made specifically by the cell for release outside, such as signaling molecules. *"kiss-and-run" model, fusing just enough to release their contents ("kissing" the membrane) before pinching off again and returning to the cell interior

Endocytosis

general term for the various types of active transport that move particles into a cell by enclosing them in a vesicle made out of plasma membrane.

electric gradient

is simply a difference in electrical charge between adjoining regions

bulk transport mechanisms (cell membrane)

large particles (or large quantities of smaller particles) are moved across the cell membrane These mechanisms involve enclosing the substances to be transported in their own small globes of membrane, which can then bud from or fuse with the membrane to move the substance across. *bulk transport is an energy-requiring (and, in fact, energy-intensive) process For instance, a macrophage engulfs its pathogen dinner by extending membrane "arms" around it and enclosing it in a sphere of membrane called a food vacuole (where it is later digested)

facilitated diffusion (passive transport)

movement of molecules across a membrane via transport proteins without energy from ATP hydrolysis. many polar or charged substances (like chloride) need help from membrane proteins. Membrane proteins can be either channel proteins or carrier proteins. Substances transported through facilitated diffusion still move with the concentration gradient, but the transport proteins protect them from the hydrophobic region as they pass through

Even when equilibrium is reached, particles do not stop moving across the cell membrane.

nearly equal numbers of particles cross the membrane in both directions. This means that there is no net change in the concentration of the substances.

Protein Channels: Some channel proteins are open all the time, but others are "gated," meaning that the channel can open or close in response to a particular signal (like an electrical signal or the binding of a molecule). The opening and closing of these channels, and the resulting shifts in ion levels inside the cell, play an important role in What are some examples of cells with "gated channels"?

nerve cells- electrical transmission along membranes muscle cells- muscle contraction Cells involved in the transmission of electrical signals, such as nerve and muscle cells, have gated ion channels for sodium, potassium, and calcium ions in their membranes.

voltage gated channels

open or close in response to changes in membrane potential -ex neuron voltage gated channel

different modes of bulk transport: (4)

phagocytosis, pinocytosis, receptor-mediated endocytosis, and exocytosis

antiporters and symporters

secondary active transport

diffusion

the process by which molecules move from an area of higher concentration to an area of lower concentration

antiporter

transporter that carries two ions or small molecules in DIFFERENT DIRECTIONS across the plasma membrane

chemical gradient

uneven distribution of molecules

resting membrane potential

An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. -Important for channeling signals, co-transport glucose, etc -In most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell. -3 Na ions pumped for every 2 K ions

Phagocytosis

An endocytosis process in which extensions of cytoplasm surround and engulf large particles and take them into the cell Single-celled eukaryotes called amoebas also use phagocytosis to hunt and consume their prey.

Active transport

Energy-requiring (usually ATP) process that moves material across a cell membrane against a concentration difference Active transport uses carrier proteins, not channel proteins.