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These are amazing mechanisms!

This is really great, i cant believe you’re not making more videos. So clear and to the point.

Extremely simple and satisfying explanation for clearing the concept. Thank you very much, Ma'am!

well explained and simple diagrams thank you so much

Thank you for the video! Note: the pancreas does not sit underneath the liver :-)

Fantastic explanation!!! Thank you so much! Could you tell the size of a glut receptor in nanometers?

thankyouu so much

This was great, thank you :)

Thanks so much

Great video. Thanks a lot.

Thank you! This really helped!

Thanks a lot for your help! Otherwise, I can never understand phagosome

very well explained. Thank you very much for such a clean video

Best explanation! I love it :) Thank you so much :)

Good vid, thx @mp stein

Great work, Thank you

well explained and great diagrams for visualisation. Thank you!

Thanks. I always wanted to know the mechanism behind the directed movements of molecules in the cell because they seem to have a mind of their own in that they are able to find that needle in the haystack. One question: Do the molecules that direct and escort have escorts themselves? And do those in turn have escorts? Also, what is the name of this field in cell biology so I can study it more?

Thank you

🤙🤙🤙

thank you =] very helpful

you didn't define ploidy

Such good explanation!

Thank you for this explanation of where the gene is in a DNA sequence. Not only did you show that in this efficient and clear video, but you showed what the gene expressed.

Glut 5, the name, DOES NOT make sense. Sometimes scientists just don't get it right and unfortunately, it gets stuck in people's thinking! So, we are stuck with a transporter called a GLUT that doesn't transport glucose!

Glut 5 doesn't make sense?? Why?? Smdh.

Junctions: Cell-cell - how cells interact with one another Junctions - proteins that the cells make and allow cells to interact with one another Human body - tissues and organs; made of cells; nerve cells interact with one another; muscle cells work together; blood is considered a tissue; although they are individual, they all have to interact with one another in a community EM images: bottom right shows cells that are coated with something and sitting on BL basal lamina; cells have molecules on them that are secreted by exocytosis; upper left image is a fibroblast that is sitting in connective tissue; surrounded by ECM molecules (collagen); cells interact with one another as well as extracellular molecules EM images - left is a Scanning EM image which shows 3D structures; right is TEM, transmission cuts through (I said this incorrectly on the video); white space in TEM is not electron dense (sugars outside cells) Epithelial Tissues - polarized cells; squares with cilia (microvilli); sit and interact with one another; basolateral sides interacts with one another; transcytosis- transport across (through) the cell; between the cells is called paracellular transport; transport from one side to another is important in polarized cells Cartoon - two different extracellular spaces; basolateral and apical spaces outside of cells; transcytosis can occur through early endosomes; late endosomes is where apical/basolateral transport processes meet; junction that makes the two side different is the tight junction Tissues of the gut - cells that are on the lumen are the cells that need to absorb nutrients (apical sides); nutrients taken through cells and transported to blood vessels found in connective tissues; connect epithelial cells with smooth muscle cells which allow for the expansion and contraction of these tissues; then more connective tissue; finally, another layer of connective tissue which is really a lot of ECM and not tons of cells Glucose transport across epithelial cells; glucose taken into cytosol; high concentration in the cytosol; glucose transporters take glucose into cytosol; different transporters on the basolateral membrane that allow glucose to go from high concentration in cells to lower concentration in the body; green are pumps (against gradient); red are channels Selective permeability barriers - certain molecules can go through; molecules wanted or needed can be moved across, through and into cells TABLE 19-1 Three types of junctions: Occluding - means to STOP going from one place to another Tight junctions Septate junctions Anchoring Junctions - anchors hold things down; cell-cell and cell-ECM Communicating junctions Gap junctions Chemical synapses Plasmodesmata Occluding - BLOCK; no transport Tight junctions - keep macromolecules from going paracellular; also keep the apical region (proteins and lipids) on the apical side and basolateral proteins and lipids on the basolateral side; EM image of microvilli - see many, many tight junctions (meaning the interactions of the proteins that make up the tight junctions TJ - proteins; claudins, occludins and zona occludens TM proteins are the claudins and occludins (4 passes each with the N and C terminus in the cytosol); claudins interact with claudins and occludins interact with occludins outside the two cells; multiple interactions to prohibit things going through; claudins and occludins have protein domains that are on the intracellular side of the cell that interacts with the peripheral membrane protein ZO ZO- zona occludins; this protein interacts with actin on the inside of the cell; all of the interactions across the cell links to actins across the cell; this links one cell to the next Septate junctions are the “tight” junctions that are found in invertebrates; noticeable difference because the spacing is very regulated ANCHORING JUNCTIONS Four types - two link to actin and two link to Intermdiate Filaments Two different types Cell-Cell - one links to actin, one to IF Cell-ECM (molecules that are outside the cells)- one links to actin, one to IF Each has a transmembrane protein that links with a peripheral membrane protein that links to the cytoskeletal filament (TM-PM-CYTOSK) Adherens - stick together (cell-cell); Desmosomes - cell-cell Proteins are Cadherins (TM protein) PM proteins Adherens, actin; desmosomes - IF Adherens Junction Cadherins - (TM) multiple domains that interact extracellularly with other cadherins Catenins (PM protein) Actin - binds to cantenins The adherins junctions are below the tight junctions and links a lot of actin across the cell called the adhesion belt; keeping cells in place Desmosomes - linked to Intermediate Filaments; these are very structurally sound; not polar; lots of subunits that are linked together in bundles of 8 protofilaments TM proteins - desmoglein, desmocollin (considered cadherins) - paddles PM proteins - desmoplakin, plakoglobin (considered catenins) - pink proteins Links to Intermediate Filaments - like keratin Anchoring Junctions - Cell-ECM Focal Adhesions and Desmosomes Anchoring of cells goes awry in cancer cells - metastases Hemi-Desmosomes - links to IF Focal Adhesion - links to actin Integrins - TM proteins; always linked together alpha and beta with lots of combination; interact with ECM proteins outside the cell (collagen, elastin, fibronectin) Peripheral membrane proteins (lots of different names) Links to Actin Communicating Junctions Gap junctions - allow small molecules to be shared across cells; think of these as portholes to connect one ship to the next; made of proteins called connexins; each connexin is a four pass TM protein and you need 6 of those to make up a gap junction; allows things <5000 daltons to pass; monosaccharides, nucleotides and amino acids to pass along with ions; electrical coupling in the heart is based on the sharing of ions across gap junctions; regulated by pH and calcium Plasmodesmata - communicating junctions in plants; channels between the plant cells that allows smooth ER crosses between cells; both aqueous and molecules made in ER pass through

Extracellular Matrix Materials that are made by cells and sent outside of cells through the process of exocytosis; what cells sit on and interact with outside of the materials that are bound to cells (either peripheral membrane proteins or transmembrane proteins); some are proteins, some are proteoglycans, glycoproteins; lots of sugars and proteins involved in these ECM molecules Cell-cell and cell-ECM contacts are important for how cells interact (important with junctions) Images - fibroblast; cells found in connective tissue and fibroblasts make a lot of ECM; no space in images - white space is filled with sugars (which do not show up on EM); also see fibrous proteins - collagen; TEM, transmission EM; cells are cut through - see longitudinal fibers and also dots which are the bundles of collagen cut on end; fibrobast sitting in ECM; bottom image - SEM, scanning EM; cells sitting on basal lamina; see fibrous tissues and see connections between cells; cells are not floating freely; held in place by interacting with proteins and sugars in ECM Sugars (polysaccharides) and fibrous proteins - how do they function to hold molecules and cells in place Proteoglycans - proteins with sugars Glycosaminoglycans - tons of sugars Fibrous proteins Collagen Elastin Fibronectin Laminins - NOTE: different than lamins (which are the Intermediate Filaments of the nucleus) GAGS - sugars • Sugars with amino groups attached - N-C-C’s but the important part are the charged groups attached - sulfates (SO3-) and carboxyl (COO-); attached to sugars; makes GAGs most negatively charged molecule in animals; MOST ANIONIC; repeating structures • Negative charges attract positives - in particular sodium (Na+); if sodiums are attracted, water follows to dilute the concentration of sodiums (g/v = concentration); water follows sodium; water creates tugor pressure (also found in plants); the xylem and phloem move water and nutrients; the pressure due to swelling when water is around; joints of body - lots of GAGS; attracting sodium and water; prevents forces of nature acting negatively on you; prevents bone-on-bone; as you age, you lose GAGS, don’t make enough; COMPRESSIVE forces - due to gravity; Torsion, twisting, bending torsion are other forces; tension -pulling apart; take supplements; chondroitin sulfate and glucosamine (others are dermatin and several other sulfates which have negative charges); hyaluron - another GAG… question when taking supplements is how do they get absorbed into your body • Function in protection • Can immobilize secreted molecules - creates a reservoir of these molecules and allows for the formation of a gradient when molecule are secreted • Protects proteins from proteolytic degradation - outside the cell • Block activity until “something” happens to activate Inflammatory Response Video - fish embryo; make a wound in the fin (see through); causes recruitment of immune cells from veins (NOT ARTERIES); get a gradient of signal - molecules that are secreted by cells near the would that are calling the immune cells to the site of infection or inflammation (lymphocyte homing) Fibrous proteins of the ECM: Collagen creates places for cells to sit within; • Particular structure - GXY - glycine, any amino acid, any amino acid repeating structure; 3 alpha helices (individual collagen strands - that link together to make quaternary structures); small glycines help the strings link togheter • Modified amino acids - proline (P) and lysine (K); hydroxyl groups added to each of these - called hydroxyproline and hydroxylysine • Amino acids - lots of GXX; occasionally GPK • Proline is an imino group; third carbons have the hydroxyl groups • Can crosslink the individual chains in collagen - intrachain (within an individual triple helix structure); or interchain (across one triple helix to another triple helix chain); these are covalent linkages • Proteins are incredibly strong - people get collagen injections • Resist tensile forces - pulling apart • Deficiencies in Vitamin C - found in sailors out at sea for long periods of time - due to lack of modified amino acids; get a disease called scurvy; Vitamin C is a cofactor to make these modified amino acids; tensile forces keep teeth in their gums - British navel forces sent seamen out with limes - called them Limey’s; scurvy causes problems with teeth, skin, eyes Elastin - looking at aorta; comes out of heart; aorta is squeezed and expanded; structures have to be elastic; when it doesn’t, can get ruptures; • Elastin found on extracellular side of organs; such as heart, arteries, stomach, bladder; there are limits to the elasticity • Elastin has modified amino acids hydroxyproline and hydroxlysine; not the same structure as collagen; very different; here just single chains - thus all intermolecular linkages • Fibrillin - a molecule that wraps around elastin and limits its elasticity; defects in this result in elastin that can break; Marfan’s syndrome - ruptured aorta; Flo Hymen; Olympian - from UCLA; tall thin African American population; tall skinny; arms very long; changes in structure Fibronectin - third fibrous structure of ECM • Structure is two proteins covalently linked through a disulfide bridge (cysteines) • Lots of domains within a protein; • Self-association - bind to itself • Collagen binding domain - ECM binding to ECM • Cell-binding domain - RGD sequence (amino acids); sequence of amino acids that binds to cells; fibronectin can bind to junctions (focal adhesions and hemidesmosomes) because of the integrins found in these junctions; cells are bound to lots of stuff - not floating around; RGD binds to integrins • Heparin-binding domain (heparin-sulfate - GAG) • RGD sequences - found in fibrinogen (is a preprotein); gets cleaved into fibrin molecules; RGD sequences are found in fibrins that help in blood clotting; snake venoms block binding of RGD in fibrins to integrins - this prevents blood clotting; this is good for a snake to get venom everywhere; NOTE: fibrinogen has nothing to do with ECM - just another protein that has an RGD • RGD binding integins; lots of them bind to fibronectin; fibronectin binds to all sorts of ECM and creates structure in which cells sit down

How did you get your audio so crisp?

When referencing electronegativity, you say how oxygen, fluorine, and nitrogen do not share equally. Wouldn't that make them polar covalent bonds?

Thanks so much for the video :)

Helped a lot, thanks!

Void

you done the pretty good job :) well done - keep going

Thank you!!! Great help!!