SH2 and SH3 domains are Src homology domains that interact with insulin receptor tyrosine kinase substrates. They are especially important in the Ras-activated MAP kinase cascade. SH2 domains, because of their deep positive arginine pockets, tightly bind phosphotyrosine residues but not phosphoserine and phosphothreonine residues.

The most common point of transfer of an ATP phosphate group is to the hydroxyl of tyrosine, serine, and threonine. Tyrosine and serine/threonine-specific kinases, in particular, help regulate signal transduction. As for the other amino acids, another kinase that sometimes appears is a histidine kinase, mostly in prokaryotes. Sulfur, nitrogen, and carboxyl groups are not typical targets for phosphorylation within proteins for signaling purposes.

Insulin, platelet-derived growth factor and, epidermal growth factor all use receptors that have intrinsic tyrosine activity. The hormones bind to the receptor which activates the tyrosine kinase. This in turn induces receptor transautophosphorylation and activation of -domain downstream molecules. Epinephrine is a hormone that when bound, activates a G protein-coupled receptor and leads to activation of adenyl cyclase.

Integrins have two subunits, alpha and beta. They do indeed bind the cell's cytoskeleton to its matrix, and can indicate to the cell the nature of that matrix. Integrins attach to a cell's actin and intermediate filaments. Blood platelets contain integrins, which bind proteins, like fibrinogen, in the matrix. This permits blood clotting, and the absence of certain integrins can cause a pathology in which people's blood does not clot well.

Transport proteins (such as the GLUT1 transporter) are asymmetric. They have two conformational states that accept the ligand from the extracellular environment and release it inside the cell after transport.

The sodium-potassium ATPase and the calcium-hydrogen ATPase (active transporters) are both correct and form high energy aspartyl phosphate intermediates inside the cell.

Many of the distractors have partially correct statements. In full, the sodium-potassium ATPase pump is an active exchanger, meaning it is a transporter that uses ATP to move two different ions across the membrane. In this case, the transporter hydrolyzes ATP to move 3 sodium ions out of the cell and 2 potassium ions into the cell. This means that with every transport the cell looses a negatively charged cation, making the cytosol a little more negatively charged. 

The sodium-potassium pump often moves the molecules against their concentration gradients. 

Toll-like receptors are special molecules that recognize specific portions of pathogens called PAMPs (pathogen associated molecular patterns). The toll-like receptors on the immune cells recognize PAMPs on the pathogen. One of the most common PAMPs recognized by toll-like receptors is peptidoglycan on the cell walls of the bacteria.

Toll-like receptors found on immune cells recognize pathogens and recruit other immune cells to clear the pathogen. These toll-like receptors are found in both innate immune system (macrophages and neutrophils) and in adaptive immune system (lymphocytes). Recall that acute inflammation is mediated by neutrophils and macrophages whereas chronic inflammation is mediated by lymphocytes; therefore, toll-like receptors can activate both acute and chronic inflammation. Complements are part of the innate immune system and serve as markers (opsonins) for pathogen recognition. Complements bind to an infected cell or to an antibody-antigen complex and signal immune cells to eliminate the pathogen. They do not utilize toll-like receptors.

Upon activation, toll-like receptors activate a transcription factor called nuclear factor kappa-light-chain-enhancer of activated B cells (NF-KB). This transcription factor ultimately activates genes in the genome that are involved in immune response. Upon activation of NF-KB, genes undergo transcription and produce mRNA which can eventually be converted to proteins that facilitate the immune response; therefore, activation of toll-like receptors (TLR's) activates transcription.