The TRUE statements are 'proteins often have more than one transmembrane domain'; 'they are regions of a transmembrane protein that actually pass through the lipid bilayer' and 'they are usually shaped like alpha-helices'.
A transmembrane domain is a membrane-spanning region within a protein. The transmembrane domains are hydrophobic regions that can be inserted into the cell membrane.
The transmembrane domains are usually shaped like alpha-helices.
This secondary structure (alpha-helices) causes the amino acid R-groups to project radially, thereby these side chains can interact with each other.
Proteins need only a single transmembrane domain to be anchored to the membrane, but they often have more than one.
For example, Acyl-coenzyme A cholesterol acyltransferases 1 and 2 (ACAT1 and ACAT2) have multiple transmembrane domains.
The transmembrane domains are regions of a transmembrane protein that actually pass through the lipid bilayer.
These domains contain amino acids with hydrophobic R-groups that pass through the membrane and interact with the hydrophobic tails of the fatty acid chains present in the lipid bilayer.
The transmembrane domains anchor transmembrane proteins to the lipid bilayer.
The interactions between amino acids of the transmembrane domains and fatty acids in the lipid bilayer help to anchor transmembrane proteins and stabilize the cell membrane.
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Image result for Is work done when you carry a book across the room at a constant velocity
Work is not done when you carry an object forward. You may have learnt that carrying an object and moving horizontally at a constant velocity has no work done. The truth is, there is a slight amount of work done due to overcoming air resistance in the horizontal direction.
