MEMBRANE PROTEINS - Types and Functions
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- Опубліковано 6 вер 2019
- Membrane proteins are those proteins that are either a part of or interact with biological membranes. They make up around a third of human proteins and give difference kinds of membranes their unique properties. They help with both facilitated diffusion and active transport, connect cells together, participate in signal transduction, and act as markers for cell identification. Proteins carry out most of the specific functions of membranes, so the amount/types of proteins vary between different membranes. Membranes can be up to 75% protein by mass!
Membrane proteins can be integral/intrinsic or peripheral/extrinsic. Integral membrane proteins are a permanent part of the membrane, while peripheral proteins are only transiently associated with either the membrane or integral proteins, with hydrophobic, electrostatic, or other non-covalent interactions.
There are several different kinds of integral proteins. Integral monotopic proteins are attached to only one of the two leaflets of phospholipids making up the membrane and don’t span across. There are also transmembrane proteins and lipid-anchored proteins. Transmembrane proteins are those that span the lipid bilayer, and can be bitopic, spanning across the membrane once, or polytopic, spanning across it more than once. Lipid-anchored proteins are those which are covalently attached to lipids embedded in the lipid bilayer. For example, GPI, or glycosylphosphatidylinositol, is a glycolipid that gets attached to a protein’s C-terminus during post-translational modification. It acts as an anchor for proteins to the outer leaflet of the plasma membrane. Both integral and peripheral proteins can be post-translationally modified (e.g. fatty acids, diacylglycerol, prenyl chains, or GPI).
Recall that cellular membranes are made up of a phospholipid bilayer, which consists of two leaflets of phospholipids. These phospholipids have polar heads which are hydrophilic, or water-loving, and non-polar fatty acyl tails that are hydrophobic, or water-hating. Polar substances like to interact with other polar substances and non-polar substances hang out with other non-polar substances. This really attests to the power of hydrogen bonding. Water molecules want to interact so badly that anything non-polar getting in the way of their hydrogen bonding results in decreased entropy. The result is what’s called the hydrophobic effect. Hence, phospholipids in water will spontaneously form lipid bilayers - minimizes contact between polar and nonpolar molecules, maximizes hydrogen bonding, and maximizes entropy.
This is also why transmembrane proteins are amphipathic - which means that they have regions which are hydrophilic and regions that are hydrophobic. The hydrophilic regions are exposed to water on either side of the membrane, while the hydrophobic bits are happily interacting with the hydrophobic tails of lipid molecules in the interior of the bilayer. As a result, transmembrane proteins are stuck permanently into the cell membrane and are very hard to isolate. To get them out, you need to add a detergent, which is amphipathic and will disrupt the lipid bilayer.
There are two basic types of transmembrane proteins: α-helical proteins, and β-barrel proteins. Note that while helix bundle proteins are found in all types of biological membranes, beta-barrel proteins are only found in the outer membranes of gram-negative bacteria, mitochondria, and chloroplasts - evidence for the endosymbiotic theory.
Transmembrane protein structure can be predicted using a hydropathy plot - hydrophobicity index on Y axis, amino acid number on X axis. The amino acids making up a protein are localized according to polarity within its final structure in such a way that the polar amino acids face the outside aqueous solutions and the nonpolar amino acids are adjacent to the lipid bilayer.
Transmembrane proteins can be classified by topology - based on the position of N- and C-termini, as well as start-transfer and stop-transfer sequences. Type I is a single transmembrane pass with the N-terminus on the extracellular side of the membrane. Type 2 is also a single transmembrane pass but the N-terminus is on the cytosolic side of the membrane.
Often, transmembrane proteins function as gateways, allowing specific substances to pass across the membrane. They can undergo conformational changes as they do this. They might participate in facilitated or active transport. Facilitated transport is spontaneous passive transport of substa nces via transmembrane proteins. Active transport requires energy and may be necessary, for instance, if a substance is being carried across the membrane against its chemical or electrical gradient.
In animal cells, most transmembrane proteins are glycosylated. These sugar residues are always present on the noncytosolic leaflet of the membrane. As a result, the cell surface is covered in carbohydrates, which form what’s called the “cell coat”.
Ok but can we all applaud the fact that the voicer was able to say Glycosylphosphatidylinositol?
😂😂
😂😂😂😂
Lol😂😂
Tomorrow I've got my cell Biology exam. Got a fresh start by watching this video. Thank you so much for covering up a whole lot of topic in one single video.
Yea... I still don’t understand 😩
this is exactly what I 've been looking for ..
thank you so much
Thanks for the video!Would be awesome if you could make more videos to do with neuroscience e.g. about the parasympathetic and sympathetic nervous system.
Perfectttt!!! It really helped me a lot. I understood things that i was confused for weeks studying this content. Thank you ty ty!
Amazing video, very informative and understandable!!!!!
Thank you! Great video, i was a bit confused regards to the transmembrane protein structure until now :)
Thank you, this is very useful!
Thanks for the video! Great diagrams.
Broooo you even made me fall in love with my study’s 😍😍😍😍
I'm so glad!! :-D
thats sus
@@Sliccc25 very
Would be good to cover peripheral proteins a bit more
Really good video !!
Thank you!!!
Very good
Thank you
This video helped so much! Thank you!
I don't know the type (II membrane protein) Can you give me a link to a Wikipedia article about this type?
Please i need information on type I, II, III, IV, V, VI Protein.
What are leaflets plz explain
how did you make the animation? appreciate it if you share your knowledge.
Procreate on Ipad and then Adobe AfterEffects
This seems better as a review than as instruction. Too much material goes flying by too fast to learn.
Actin: A cytoskeletal protein crucial for cellular structure and movement.
Myosin: Motor protein involved in cell motility and contractility.
Tubulin: Forms microtubules, aiding in intracellular transport and cell division.
Vinculin: Connects actin filaments to integrins, contributing to cell adhesion.
G-actin and F-actin: Monomeric and polymeric forms of actin, respectively.
Fibronectin: An extracellular matrix protein interacting with cell surface receptors.
Calmodulin: Involved in calcium-dependent signaling pathways.
Profilin: Regulates actin polymerization
and dynamics.
Talin: Binds to integrins, linking them to the actin cytoskeleton.
Cofilin: Modulates actin dynamics by promoting depolymerization.
Can anyone tell me if these are peripheral proteins even if it can be perpheral proteins and transmembrane both....ai provided this..I wanna check it's accuracy
👍💯
Please, give me importance of membrane proteins because the video is mixed up with different things.
I'm here for bio 112 cell bio
nice
perfect speed, some people forget about the pause button!
The content delivered is good but you're too fast please
Can't analyse the data properly.
Thanks
If I wanted someone to read the book to me I would have just continued doing it myself. Can I get a teacher please? Pleaseeeee
thank you, i wish you were bit slower but thanks anyway
I have a question plzz answer this question
Wow
Lipids is 40 percent in cell but protein is 60 percenta when we see in cell wo looks more lipids in quaranty than proteins why ?
plz lz muje is ka answer dedo plzzz plzzz i req u yeh question hain name and explain the model in which protein molecule fluid nplzz answer this quetestion
Fluid mosaic model
❤
I think u mixed up type 1 and 2 trans membrane proteins
Am I the only 9th grader studying this?
Glycoconjugates & Proteins in
membrane system, Protein Localization
Give a new video in this topic
list of definitions and a word salad
Ye kia hy
The art style makes me uncomfortable.
I think art style is the best for learning and understanding
@@deepika8900 The more messed up the more you remember. When I was taking a medical terminology class they played these super messed up videos to us. Still remember them to this day.