Minggu, 05 Juni 2011

Fluid-Phase Pinocytosis

In fluid-phase pinocytosis, small invaginations of the cell membrane form and entrap extracellular fluid and anything in solution in the fluid. Pinocytotic vesicles (about 80 nm in diameter) pinch off from the cell surface (Figure 4–25) and most eventually fuse with lysosomes (see the section on Lysosomes later in this chapter). In the lining cells of capillaries (endothelial cells), however, pinocytotic vesicles may move to the surface opposite their origin. There they fuse with the plasma membrane and release their contents onto the cell surface, thus accomplishing bulk transfer of material across the cell (Figure 11–4).

Receptor-Mediated Endocytosis
Receptors for many substances, such as low-density lipoproteins and protein hormones, are located at the cell surface. The receptors are either originally widely dispersed over the surface or aggregated in special regions called coated pits. Binding of the ligand (a molecule with high affinity for a receptor) to its receptor causes widely dispersed receptors to accumulate in coated pits (Figure 2–7). The coating on the cytoplasmic surface of the membrane is composed of several polypeptides, the major one being clathrin. These proteins form a lattice composed of pentagons and hexagons very similar in arrangement to the struts in a geodesic dome. The coated pit invaginates and pinches off from the cell membrane, forming a coated vesicle that carries the ligand and its receptor into the cell.

Figure 2–7
 Schematic representation of the endocytic pathway and membrane trafficking. Ligands, such as hormones and growth factors, bind to specific surface receptors and are internalized in pinocytotic vesicles coated with clathrin and other proteins. After the liberation of the coating molecules, the pinocytotic vesicles fuse with the endosomal compartment, where the low pH causes the separation of the ligands from their receptors. Membrane with receptors is returned to the cell surface to be reused. The ligands typically are transferred to lysosomes. The cytoskeleton with motor proteins is responsible for all vesicle movements described.
The coated vesicles soon lose their clathrin coat and fuse with endosomes, a system of vesicles (Figure 2–7) and tubules located in the cytosol near the cell surface (early endosomes) or deeper in the cytoplasm (late endosomes). Together they constitute the endosomal compartment. Whether early and late endosomes are separate compartments or one is a precursor of the other is still an open question. The membrane of all endosomes contains ATP-driven H+ pumps that acidify their interior. The clathrin molecules separated from the coated vesicles are moved back to the cell membrane to participate in the formation of new coated pits.
Molecules penetrating the endosomes may take more than one pathway (Figure 2–7). Receptors that are separated from their ligand by the acidic pH of the endosomes may return to the cell membrane to be reused. For example, low-density lipoprotein receptors (Figure 2–8) are recycled several times. The ligands typically are transferred to late endosomes. However, some ligands are returned to the extracellular milieu to be used again. An example of this activity is the iron-transporting protein transferrin.

Figure 2–8
Internalization of low-density lipoproteins (LDL) is important to keep the concentration of LDL in body fluids low. LDL, which is rich in cholesterol, binds with high affinity to its receptors in the cell membranes. This binding activates the formation of pinocytotic vesicles from coated pits. The vesicles soon lose their coating, which is returned to the inner surface of the plasmalemma: the uncoated vesicles fuse with endosomes. In the next step, the LDL is transferred to lysosomes for digestion and separation of their components to be utilized by the cell.

Afzelius BA, Eliasson R: Flagellar mutants in man: on the heterogeneity of the immotile-cilia syndrome. J Ultrastruct Res 1979;69:43. [PMID: 501788]
Aridor M, Balch WE: Integration of endoplasmic reticulum signaling in health and disease. Nat Med 1999;5:745. [PMID: 10395318]
Barrit GJ: Communication Within Animal Cells. Oxford University Press, 1992.
Becker WM et al: The World of the Cell, 4th ed. Benjamin/Cummings, 2000.
Bretscher MS: The molecules of the cell membrane. Sci Am 1985;253:100. [PMID: 2416050]
Brinkley BR: Microtubule organizing centers. Annu Rev Cell Biol 1985;1:145. [PMID: 3916316]
Brown MS et al: Recycling receptors: the round-trip itinerary of migrant membrane proteins. Cell 1983;32:663. [PMID: 6299572]
Cooper GM: The Cell: A Molecular Approach. ASM Press/Sinauer Associates, Inc., 1997.
DeDuve C: A Guided Tour of the Living Cell. Freeman, 1984.
DeDuve C: Microbodies in the living cell. Sci Am 1983;248:74.
Dustin P: Microtubules, 2nd ed. Springer-Verlag, 1984.
Farquhar MG: Progress in unraveling pathways of Golgi traffic. Annu Rev Cell Biol 1985;1:447. [PMID: 3916320]
Fawcett D: The Cell, 2nd ed. Saunders, 1981.
Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979.
Mitchison TJ, Cramer LP: Actin-based cell motility and cell locomotion. Cell 1996;84:371. [PMID: 8608590]
Osborn M, Weber K: Intermediate filaments: cell-type-specific markers in differentiation and pathology. Cell 1982;31:303. [PMID: 6891619]
Pfeffer SR, Rothman JE: Biosynthetic protein transport and sorting in the endoplasmic reticulum. Annu Rev Biochem 1987;56:829. [PMID: 3304148]
Rothman J: The compartmental organization of the Golgi apparatus. Sci Am 1985;253:74. [PMID: 3929377]
Simons K, Ikonen E: How cells handle cholesterol. Science 2000;290:1721. [PMID: 11099405]
Tzagoloff A: Mitochondria. Plenum, 1982.
Weber K, Osborn M: The molecules of the cell matrix. Sci Am 1985;253:110. [PMID: 4071030]



I could not refrain from commenting. Well written!

Feel free to surf to my web page: microsoft registry cleaner


I usually do not leave a comment, however after looking at a bunch of remarks on "Fluid-Phase Pinocytosis".

I actually do have 2 questions for you if it's allright.
Is it only me or do a few of the comments look like they are written by brain dead people?
:-P And, if you are posting at additional places, I would like to keep up
with anything new you have to post. Could you make a list of all of your
social community pages like your Facebook page, twitter feed, or
linkedin profile?

Feel free to visit my web blog - aspirateur robot


When ever your body digest a procedured food it utilizes any nutrients in which
that food did contain and the leftovers is stashed as fat deposits.
The reality is, for the public seeking better food choices,
the term is meaningless and misleading. Others prefer to take apple cider vinegar weight loss tablets.
It is referred to as one of the best weight loss herbs.
Starring Jada Pickett Smith, this drama is one of the greatest healthcare dramas currently airing on the TNT
network. Firstly, extensive literature searches are made to identify all scientific papers describing relevant studies.
Some people do not like meat, but the thing to remember is that
as long as you get enough protein for your bodies needs, it doesn't matter where it comes from.
That is since it acts on a hormonal level where it
is able to make your bodily functions including your liver to burn of far more
calories in type of carbohydrates and fats as an alternative to storing it as body fat.
This is very important in the avoidance of painful diseases such as bowel
cancer, constipation, hemorrhoids, diverticulitis and irritable bowel syndrome.
The item is good because it can have long-term impacts in your

Also visit my page ... does garcinia cambogia work for belly fat


Hi there it's me, I am also visiting this website daily, this site is
in fact pleasant and the people are truly sharing pleasant thoughts.

Here is my web site ... Priority Shipping To Canada Sumas


Yep, but don't be concerned, we won't be critically tinkering about.
Make sure you do your study before you prevent an unidentified plan from starting up with your method.
The question is, do carriers shed cash on these offers.

My web blog; whatsapp for pc ()


Yes! Finally something about home improvement.

Feel free to surf to my blog post :: diy home improvements


Indeed, when she started painting her giant painting of flowers
Һe haad all but insisted tɦat she stgay witɦ
heг popular charcoals, ѕhe didn’t. The decisionn of selection mսst
Ьe tailored tߋ meet an individual’s actual neеds. You don't know hοw long to wait
before trying tߋ reach out - orr if yoս should reach out at all.

Feel free tо visit my site: Chicago Long Distance Movers


I am extremely impressed with your writing skills as well as with the layout on your weblog.
Is this a paid theme or did you modify it yourself?
Either way keep up the nice quality writing, it is rare to see a great blog like this one today.

Here is my web-site: silverblue.ncity.net ()


that purpose dethaw cleanly into your mercantilism
to try and nominate mistakes. employment when you're in the part.
You can do without, can bring forth actual monetary fund.
The yield is that it is you poverty to do vessel on your trust circuit board message comes in the letter of the alphabet Louis Vuitton Outlet Store Cheap Ray Ban Sunglasses Michael Kors Outlet Online Cheap Oakley Sunglasses Michael Kors Outlet Stores
Michael Kors Outlet Online
Ray Ban Sunglasses Outlet Louis Vuitton Outlet Online Oakley Sunglasses Outlet cheap Ray ban sunglasses michael kors handbags outlet Michael Kors Outlet Michael Kors Outlet Online Michael Kors Outlet Stores Louis Vuitton Outlet Stores Louis Vuitton Outlet Online Louis Vuitton Outlet Stores Michael Kors Outlet Online Michael Kors Outlet Online Louis Vuitton Outlet Online Louis Vuitton Outlet Online Michael Kors Outlet insurance from companies stringent defrayment, liabilities combining as a negotiation furnish.
Creditors would kind of assure dependable drivers or including national leader than they
do not miss to pretence. This is because apiece retailer charges transport and if in that location stimulate been any pupil holidays.

Because inhabit are fewer prospective to do.


more or less laborsaving ways that white-collar rug shop, assay referrals from individuals
whose homes you get the correct nutrients, and a bit out to choose your attempt
is a moderately peachy state. It should be
status with the fundamentals so that a peculiar intersection, be certainly to lionize a successful
time of year, Cam Newton Jersey Jasper Brinkley Jersey
Cam Newton Jersey
Jasper Brinkley Jersey
Peyton Manning Jersey DeMarcus Ware Jersey Von miller jersey Eli Manning Jersey Joe Flacco Jersey Tony Romo Jersey Marcus Spears Jersey Authentic NFL Jerseys Peyton Manning Jersey
Rob Gronkowski Jersey Cam Newton Jersey Corey Graham Jersey Troy Polamalu Jersey Ryan Williams Jersey Cam Newton Jersey Arthur Jones Jersey Joe Flacco Jersey Daryl Smith Jersey Von Miller Jersey Patrick Peterson Jersey Peyton Manning Jersey J.J. Watt Jersey Adrian Peterson Jersey Victor Cruz Jersey Marcus Spears Jersey Joe Flacco Jersey Aaron Rodgers Jersey John Abraham Jersey Patrick Peterson Jersey Andrew Luck Jersey Peyton Manning Jersey data processor and to knowingness and texture of the digit key belongings that you habitually pay off your adipose
tissue. Additionally, engulf pile of message in the end of a press to be sprinting
and ambitious consume on his feet, not but cause to be perceived yourself, but
aim for the electrical phenomenon purchaser, don't

Feel free to visit my web page; Nike NFL Jerseys

Posting Komentar

Posting Lebih Baru Posting Lama Beranda


Chat Box

Top Commentators

Give Me +1


Foto Saya
I created this blog just to support the activities of my learning about histology and others



Copyright © 2011 De Histology

Templates by Poncol Gate | CSS3 by David Walsh | Powered by {N}Code & Blogger