Celulas Plasma Membrane

Cells

Plasma Membrane

Made of more than one macromolecule, mostly lipids; many proteins embedded; phospholipid with many proteins embedded in it; glycerol, choline, and phosphate group and two fatty acids molecules (nonpolar); phospholipids = amphipathic; significance of the proteins = facilitate the exchange of material in and out of cell – molecules the cell needs or exporting molecules or ions out = allows the cell to survive. For most cells in our body, they are in close proximity to each other; plasma membrane – not only for exchange, but also for connectivity between adjacent cells; tissue = multiple cells strung together! Cell must associate with neighboring cells; membrane allows for this; each cell is well anchored to the cell next to it, thanks to the plasma membrane; How are cells able to communicate with their environment and connect to their surrounding cells? We thank the plasma membrane for this! It functions in exchange and anchorage! Cells are very close together in certain parts of the body; in other parts of the body, they are slightly separated; cells are always exchanging material in water; water = major part of our body; everything is dissolving and traveling in water; inside the cell, the watery environment is called the cytosol = the ICF (intracellular fluid); the ECF (extracellular fluid) is called interstitial fluid, the fluid that surround the cell; we also have fluid specifically found in the blood (the plasma component of the blood cell)

Where is the majority of water found in humans? The highest amount is found inside the cell (intracellularly is the highest amount of water); average is 42L of water total in our body 66% of these 42L are found in our cells collectively; 5-6L in blood; the rest is in interstitial fluid

Cells

Cells must have the energy-rich molecules constantly moving in and out of the cell; glucose, sugar, fatty acids, glycerol, nucleotides = important molecules that need to constantly move in and out of the cell. Pathway of molecules in body: Blood > interstitial fluid > into cell (intracellular). Oxygen is major ingredient for ATP synthesis. CO2 = waste = highly toxic. Blood to interstitial fluid to intracellular fluid. Concentration of waste products should always be low..pH should be regulated; 7.4 for most cells. Concentration of water, salt, and other electrolytes; temp must be maintain; regulation of environment is vital; the cytosol concentration is constantly changing; interstitial fluids also dynamic; blood also dynamic to ensure a healthy cell. Take-home message: homeostasis is always occurring!

Neurons – cells of brain. Epithelial cells – cells of skin – small, spherical. Muscle cells – cylindrical.

Cells look differently for different functions – all have similar components and a successful plasma membrane that has the right PROTEINS – having certain proteins on the membrane is vital for the functionality of a cell. So each type of cell has a different amount of different proteins in its membrane.

Portions of the Cell Membrane and Cell Junctions

Membrane of the cell. Keeps cell’s integrity. Selectively permeable. Plasma membrane ensures that the inside of the cell is independent from the outside. The room is a cell, the temp is different in here than outside, the walls are the boundaries of this room, allowing us to have a separate environment. Lipids in form of phospholipids and proteins integrated (integral or peripheral); these proteins have many functions; within the plasma membrane, selective permeability; some can pass through lipid portion, others to the protein portion; plasma membrane ensures communication between outside and inside of cell; also, allows for connectivity between adjacent cells. Junctions  connections between neighboring cells

Desmosomes are intercellular junctions that tether intermediate filaments to the plasma membrane via adhesion. They are proteins found on the membrane that support the neighboring membrane of two neighboring cells. They bind muscle cells to one another. Specifically, desmosomes are anchorage proteins, they strengthen the connection between neighboring cells by wrapping the membranes around the two cells. Significance: anchorage is essential; in places in our body where there is a lot of activity, like pulling and pushing (contraction of muscles, for example); also in skin (boundary for entry of pathogens in our body); desmosomes are found in body for strengthening to pull and push, allowing the cells to act in unity)

Tight junctions = similar proteins, similar mechanisms; tightens, or anchors the two membranes together; significance: for different purposes, structurally serving the same thing but they are mainly for transport, to minimize movement of substances in between cells; we don’t want to have movement, or leakage in between cells (places of lots of activity, like digestive organs in small intestine, lots of nutrients passing through, renal system where we have lots of waste products passing through; these substances in the digestive system or renal system must pass THROUGH the cell not in between the cells; through the cell is vital because it’s a good way to regulate; cell is in charge; it allows substances to move in and out at the discretion of the cell as opposed to leakage, where we have no control; we call this leakage movement “paracellular pathways”; **function of tight junctions: to prevent paracellular pathways; we want a transcellular pathway – the movement of large molecules THROUGH the cell from one side to another; the idea from transport regulation is to ensure that the molecules enter the cell than leave the cell

Gap junctions = junctions connective between neighboring cells but for different purposes; for exchange of material between neighboring cells; to ensure synchrony; way different than plasmodesmata; this is not within the environment, its between one cell and another cell; in the brain – electrical communications, the heart (contracts in synchrony); exchange of material like certain ions like calcium, chemical messengers between neighboring cells; very large sophisticated protein that half is in one cell and the other half in another cell; both haves have to be in accordance for it to open; each half junction is a connexon; two connexons make a gap junction; it’s a quaternary structure made of 6 subunits; each subunit is called connexin; 6 connexins make 1 connexon; *function of gap junctions is to facilitate exchange between neighboring cells

Driving force, concentration, diffusion + transport across membrane.

Surrounding fluid = interstitial fluid, the fluids that bathe the cells; whenever we talk

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