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Delicious77 [7]
3 years ago
7

A biological membrane is selectively permeable in that it can, to some extent,control which substances pass through it. Based on

t he information provided in Book 5, describe the general structure of a biological membrane making particular reference to the significance of the hydrophobic and hydrophilic properties of the major biological molecule component of membranes.Explain how this membranes tructure results in the essential property of semi-permeability. Your answer should include a brief, simple explanation of the term diffusion in the context of cell membranes.
Could anyone give me an idea how to answer this question?
Thank you!
Biology
1 answer:
Vanyuwa [196]3 years ago
5 0

Cell membranes are composed of what we call a "phospholipid bilayer" composed of phospholipids. Phospholipids have a hydrophillic (‘water loving’) head and a hydrophobic (‘water fearing’) tail. Water can get close to the hydrophillic head while it cannot pass through the hydrophobic tail, thus protecting the cell from foreign substances it does not need. Because of this dual property, the membrane can choose what substances may enter through it and this is what constitutes its semi-permeability.

One of the ways substances can enter through the membrane is through passive transport or diffusion, the movement of substances from higher concentration to lower concentration. This process does not require energy. Substances like oxygen and water easily diffuse through channel proteins when the concentration outside the cell is higher than the inside. 

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Following antigenic stimulation, phosphorylation of _________ relieves inhibition of the transcription factor
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Explanation:

An antigen is any substance that is capable of stimulating an immune response by activating lymphocytes, which are the body’s infection-fighting white blood cells. Examples of antigens could be proteins that are part of bacteria or viruses or components of serum and red blood cells from other individuals, all of them are foreign antigens originated outside the body. However, there can also be autoantigens (which are self-antigens), originated within the body. In normal conditions, the body is able to distinguish self from nonself. <u>And the antigens that represent a danger induces an immune response by stimulating the lymphocytes to produce antibody or to attack the antigen directly</u>. This is called an antigenic stimulation of the immune system.

ZAP-70 (Zeta-chain-associated protein kinase 70) is a protein that is part of the T cell receptor, thereby it plays a critical role in T-cell signaling. When the TCR (receptor of T cells) is activated by the presentation of the specific antigen through the MHC, a protein called Lck acts to phosphorylate the intracellular CD3 chains and the ζ chains of the TCR complex, allowing the binding of the cytoplasmic tyrosine kinase, ZAP-70. Lck then phosphorylates and activates ZAP-70, which in turn phosphorylates another molecule in the signaling cascade called LAT (short for Linker of Activated T cells), a transmembrane protein that serves as an anchor site for several other proteins. The tyrosine phosphorylation cascade initiated by the Lck culminates in the intracellular mobilization of calcium ion (Ca2+) <u>and the activation of important signaling cascades within the lymphocytes.</u> These include the Ras-MEK-ERK pathway, which is based on activating certain transcription factors such as NFAT, NFκB and AP-1. These transcription factors regulate the production of of certain gene products, most notably cytokines such as interleukin-2 that promote the long-term proliferation and differentiation of activated lymphocytes.

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So, ZAP-70 is a protein tyrosine kinase with a role in T-cell receptor signal transduction. During T-cell activation, ZAP-70 binds to ITAM and becomes tyrosine phosphorylated. The binding of ZAP-70 to the phosphorylated ITAM is able to activate its kinase activity, <u>and relieves the inhibition of the transcription factor which regulates genes that are involved in the immune reaction</u>.

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2 years ago
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