Answer:
Proteins and lipids exist as separate but loosely attached molecules that can move around
Explanation:
Cell membranes are mainly composed of lipids, proteins, and also carbohydrates. Phospholipids are the most abundant type of lipid and the main constituent of the cell membranes. Membrane proteins are divided into two types according to their interactions with the cell membrane: 1-integral (intrinsic) and peripheral (extrinsic) proteins. These peripheral proteins are loosely attached by ionic bonds or calcium bridges with the phosphate heads of the phospholipids; whereas integral membrane proteins contain side chains that interact with fatty acyl groups of the phospholipids. Cell membrane fluidity indicates how easily lipids (e.g., phospholipids and cholesterol) and proteins (e.g., intrinsic proteins) diffuse laterally in the cell membrane. This fluidity is affected by the amount of cholesterol, temperature, and the ratio of unsaturated to saturated fatty acids. Saturated fatty acids have no double bonds in the hydrocarbon chain, whereas unsaturated fatty acids have at least one double bond (these double bonds increase fluidity). Moreover, higher temperatures increase membrane fluidity, whereas cholesterol molecules function to regulate membrane fluidity: at high temperatures cholesterol molecules stabilize the membrane, whereas at low temperatures intercalate between phospholipids, thereby preventing them from clustering together.
Answer: zap70, ITAM.
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.
The ITAM motifs (immunoreceptor tyrosine-based activation motif) are sequences of four amino acids present in the intracellular tails of certain proteins that serve as receptors within the immune system. Thus, <u>some receptors such as the TCR have ITAM sequences that, when activated, trigger an intracellular reaction based on consecutive phosphorylations</u>. Kinases are recruited for this purpose.
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>.
The correct answer is
Stasis
Population becomes isolated
After rapid change in isolated population
Reintroduction
You would find layers in a sedimentary rock, because it has different types of other rock combined in it.
