直达转运

流通加工转运

直通转运

投机转运

The less unsaturated the fatty acid tails of the phospholipid, the more fluid the membrane.

The more unsaturated the fatty acid tails of the phospholipid, the more fluid the membrane

The higher the temperature, the less fluid the membrane

The lower the temperature, the more fluid the membrane.

When newly synthesized, these proteins are embedded in the ER. Only the soluble regulatory domain fragment of an SREBP functions as a transcription activator. When cholesterol and oxysterol levels are high, SREBPs are held in the ER in a complex with another protein called SREBP cleavage-activating protein (SCAP), which in turn is anchored in the ER membrane by its interaction with a third membrane protein, Insig (insulin-induced gene protein).

SCAP and Insig act as sterol sensors. When sterol levels are high, the Insig-SCAP-SREBP complex is retained in the ER membrane. When the level of sterols in the cell declines, the SCAP-SREBP complex is escorted by secretory proteins to the Golgi complex.

There, two proteolytic cleavages of SREBP release a regulatory fragment, which enters the nucleus and activates transcription of its target genes, including those for HMG-CoA reductase, the LDL receptor protein, and other proteins needed for lipid synthesis.

When sterol levels increase sufficiently, the proteolytic release of SREBP amino-terminal domains is again blocked, and proteasome degradation of the existing active domains results in rapid shutdown of the gene targets.

They include phosphatidylcholine, phosphatidylethanolamine and cholesterol, among others.

They are amphipathic

They have two fatty acids attached to a glycerol molecule, and a polar head group attached via a phosphate

They can have both saturated and unsaturated fatty acids

右肺结核

右肺肺炎

右肺恶性肿瘤

右肺脓肿

右肺组织部分不张

正确

错误