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Sodium-potassium pump:

• The sodium-potassium pump is a transmembrane protein that actively transports sodium (Na+) out of the cell and potassium (K+) into the cell, maintaining essential ion gradients.

• The pump operates through a cycle of binding and conformational changes. It binds three sodium ions from inside the cell, which triggers ATP hydrolysis and changes the pump’s shape to release sodium outside the cell. It then binds two potassium ions from outside, returning to its original shape and releasing potassium inside the cell.

• This pump is an example of active transport, meaning it requires energy (in the form of ATP) to move ions against their concentration gradients. This is essential for maintaining the proper concentration of these ions in and out of the cell.

• The pump exchanges three sodium ions for two potassium ions. This 3:2 ratio is crucial for maintaining the electrochemical gradient, resulting in a net loss of one positive charge from the cell, contributing to a negative resting membrane potential.

• By maintaining higher concentrations of potassium inside the cell and sodium outside, the pump is vital for establishing the resting membrane potential, typically around -70 mV in neurons and muscle cells. This electrical gradient is crucial for cell excitability.

• The sodium-potassium pump helps regulate cell volume by controlling the concentrations of sodium and potassium, influencing osmotic balance and preventing excessive cell swelling or shrinkage.

• In neurons and muscle cells, the pump is essential for resetting the membrane potential after an action potential. It helps restore ion concentrations, allowing cells to repolarize and become ready for subsequent excitations.

• The pump is critical in various physiological processes, including nerve impulse transmission, muscle contraction, and maintaining overall cellular homeostasis.

• Dysregulation or inhibition of the sodium-potassium pump can lead to serious health issues, including hypertension, heart failure, and neurological disorders, highlighting its importance in both health and disease.

How does it happen:

1.Binding of Sodium Ions:

Three sodium ions (Na+) from the inside of the cell bind to the pump.

2.ATP Hydrolysis:

The binding of sodium triggers the hydrolysis of ATP into ADP and inorganic phosphate (Pi), releasing energy.

3.Conformational Change:

ATP hydrolysis causes the pump to change shape, opening towards the outside of the cell and releasing the three sodium ions into the extracellular space.

4.Binding of Potassium Ions:

The pump then exposes binding sites for potassium ions (K+) and two potassium ions from outside the cell bind to the pump.

5.Release of Phosphate Group:

The binding of potassium triggers the release of the inorganic phosphate (Pi), which was attached to the pump during ATP hydrolysis.

6.Return to Original Conformation:

The release of the phosphate group causes the pump to return to its original shape, now facing inward.

7.Release of Potassium Ions:

The pump releases the two potassium ions into the cytoplasm of the cell.

8.Cycle Repeats:

The pump is now ready to begin another cycle, continuously transporting sodium out and potassium in.

This step-by-step process allows the sodium-potassium pump to maintain the essential ion gradients necessary for various cellular functions.

Questions:

1- What type of protein is involved in active transport

a) channel protein

b) carrier protein

c) gated channel protein

2- The sodium-potassium pump is an example of _________ transport

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What is Phagocytosis? :

Phagocytosis is a cellular process for ingesting and eliminating particles that are larger than 0.5 µm in diameter, including microorganisms, foreign substances and apoptotic cells. Phagocytosis is found in many types of cells and it is, in consequence, an essential process for tissue homeostasis.

Phagocytosis is a basic process for nutrition in unicellular organisms, and it is also found in almost all cell types of multicellular organisms

Only specialized groups of cells called professional phagocytes accomplish phagocytosis with high efficiency.

Phagocytes, also known as phagocytic cells, circulate through the body, looking for and destroying foreign substances that may harm it. These specialized cells are part of your immune system’s defense mechanism, which protects you from infections, diseases, and other harmful invaders.

Phagocytosis is a process wherein a cell binds to the item it wants to engulf on the cell surface and draws the item inward while engulfing around it. The process of phagocytosis often happens when the cell is trying to destroy something, like a virus or an infected cell, and is often used by immune system cells.

Phagocytosis differs from other methods of endocytosis because it is very specific and depends on the cell being able to bind to the item it wants to engulf by way of cell surface receptors. Phagocytosis won’t happen unless the cell is in physical contact with the particle it wants to engulf.

How does it happen:

1. The virus and the cell must first come into contact with each other. This contact can happen randomly, such as when an immune cell accidentally encounters a virus in the bloodstream. Alternatively, cells can actively move toward the virus through a process called chemotaxis, which is their directed movement in response to chemical signals. Many immune cells are guided by cytokines—small proteins involved in cell signaling. These cytokines signal the cells to move to specific areas in the body where a virus or other pathogens are present, especially during localized infections like a bacterial skin wound.

2. The virus binds to the cell surface receptors on the macrophage. Remember that different cell types express different receptors. Some receptors are general, meaning that they can identify a self-produced molecule versus a potential threat (and that’s about it), and others are very specific, like toll-like receptors or antibodies. The macrophage will not initiate phagocytosis without successful binding of the cell surface receptors.

3. The macrophage starts to surround the virus and engulf it into the cell. Instead of moving the large item across the plasma membrane, which might damage the membrane permanently, phagocytosis uses extensions of the cytoplasm (pseudopods) to surround the particle and enclose it in a membrane. For our virus example, the macrophage and virus are bound at the cell surface. The pseudopods protrude outward on either side of the virus until both sides meets and the virus is enclosed. Remember, cells are reasonably flexible and fluid.

4. The surrounded virus becomes completely enclosed in a bubble-like structure, called a “phagosome”, within the cytoplasm. The lips of the pocket, formed as a result of the extensions of the pseudopodsIn extend towards each other in order to close the gap. This action creates a phagosome, where the plasma membrane has moved around the particle, encasing it safely inside the cell.

5. The phagosome fuses with a lysosome, becoming a “phagolysosome”. Lysosomes are also bubble-like structures, similar to phagosomes, which process wastes inside the cell. “Lysis” means “to break down”, making it easy to remember the function of a lysosome. Without fusing with a lysosome, the phagosome wouldn’t be able to do anything with the contents inside.

6. Phagolysosome lowers the pH to break down its contents. A lysosome or phagolysosome is able to break down the stuff inside of itself by drastically lowering the pH of its internal environment. Lowering the pH makes the environment inside the phagolysosome very acidic. This is an effective way of killing or neutralizing whatever is inside the phagolysosome so it cannot infect them cell.

7. Once the contents have been neutralized, the phagolysosome forms a residual body that contains the waste products from the phagolysosome.The residual body is eventually discharged from the cell.

- Questions:

1- What is a phagocyte?
a) The pouch in which a consumed cell or cellular debris has been contained
b) The cell that engulfs another cell or debris by phagocytosis
c) Any immune cell
d) A macrophage

2- Macrophages are the dominating cells to take action in the early stage of infections.
a) True
b) False

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What is it:

process by which the cell takes in the fluids along with dissolved small molecules

Pinocytosis is a form of endocytosis in which cells ingest extracellular fluid and the solutes dissolved in it, often referred to as “cell drinking.

It allows cells to take in nutrients, small molecules, and other substances from their environment, contributing to nutrient acquisition and cellular homeostasis.

Pinocytosis is a non-specific process that indiscriminately engulfs whatever is present in the extracellular fluid, rather than targeting specific substances.

This mechanism is crucial for cells, especially those lacking specific transporters, to absorb essential nutrients, ions, and other small molecules necessary for cellular functions.

Many cell types, including intestinal epithelial cells, kidney tubular cells, and immune cells like macrophages, utilize pinocytosis to acquire nutrients and engage in immune functions.

Pinocytosis differs from phagocytosis, which is the uptake of larger particles or cells. Pinocytosis specifically focuses on the uptake of fluids and small solutes.

In immune cells, pinocytosis helps capture antigens from pathogens, aiding in the immune response by allowing the processing and presentation of these antigens.

Process:

1.Cell Membrane Invagination:

The cell membrane begins to fold inward, creating small pockets that will capture extracellular fluid and dissolved substances.

2.Formation of Pockets:

These invaginated pockets deepen as they move further into the cytoplasm, containing extracellular fluid along with various solutes.

3.Vesicle Budding:

The pockets continue to deepen until they pinch off from the membrane, forming vesicles filled with the ingested fluid and solutes.

4.Vesicle Movement:

The newly formed vesicles move into the cytoplasm, where they can interact with other organelles.

5.Fusion with Lysosomes:

The vesicles often fuse with lysosomes, which contain digestive enzymes that break down the contents of the vesicle.

6.Release of Nutrients:

The digested substances are then released into the cytoplasm, making nutrients available for the cell to use.

7.Cycle Repeats:

The cell can continuously perform pinocytosis to take in more extracellular fluid and nutrients as needed.

Questions:

1- Pinocytosis is an example of:

a) active transport

b) endocytosis

c) exocytosis

2-What is pinocytosis primarily known for?

a) The engulfment of large particles or cells.

b) The selective uptake of specific molecules using receptors.

c) The non-specific uptake of extracellular fluid and small solutes.

d) The release of waste materials from the cell.

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What is it:

Exocytosis is a cellular mechanism in which substances are expelled from the cell through the fusion of vesicles with the plasma membrane.

It allows cells to secrete hormones, neurotransmitters, enzymes, and other important substances into the extracellular space, playing a crucial role in communication and signaling between cells.

Common substances released through exocytosis include neurotransmitters (such as dopamine), hormones (like insulin), and digestive enzymes.

Exocytosis is vital for various physiological processes, including neurotransmission, where it enables the release of signaling molecules that transmit information between nerve cells.

The process helps maintain homeostasis by regulating the composition of the extracellular environment, allowing the export of excess substances and waste materials.

Many cell types utilize exocytosis, including endocrine cells that secrete hormones, neurons that release neurotransmitters, and glandular cells that produce and secrete various substances.

Exocytosis is the opposite of endocytosis, where materials are brought into the cell. While endocytosis involves the uptake of substances, exocytosis is focused on the export of materials.

How does it happen:

1.Vesicle Formation:

Secretory vesicles containing substances to be released are formed in the cell, typically originating from the Golgi apparatus.

2.Vesicle Transport:

The formed vesicles are transported to the cell membrane with the help of the cytoskeleton, which guides them along microtubules.

3.Vesicle Docking:

The vesicles move to specific sites on the plasma membrane, where they prepare to fuse with it. This involves the interaction of proteins on the vesicle with proteins on the membrane.

4.Membrane Fusion:

The vesicle membrane and the plasma membrane fuse, forming a continuous lipid bilayer. This fusion is facilitated by proteins known as SNAREs.

5.Release of Contents:

Once the vesicle and plasma membranes are fused, the contents of the vesicle are released into the extracellular space.

6.Vesicle Membrane Integration:

The vesicle membrane becomes part of the plasma membrane, increasing the surface area of the cell membrane and contributing to membrane dynamics.

7.Cycle Repeats:

The cell is now prepared to perform exocytosis again, continuously regulating the secretion of substances as needed.

Questions:

1- What is the primary function of exocytosis in cells?

a) To engulf large particles or cells.

b) To transport substances into the cell.

c) To expel substances from the cell into the extracellular space.

d) To maintain the resting membrane potential.

2- Which of the following substances is commonly released from cells via exocytosis?

a) Oxygen

b) Carbon dioxide

c) Hormones

d) Glucose