The passage describes proteins in living organisms.
Complete the passage by writing a suitable word in each blank space.
Proteins contain the elements carbon, hydrogen, oxygen and (1) ‾\underline{\quad\quad\quad\quad\quad}. They are polymers composed of monomer units called (2) ‾\underline{\quad\quad\quad\quad\quad} joined together by condensation reactions. The covalent bonds linking these monomer units are called (3) ‾\underline{\quad\quad\quad\quad\quad} bonds.
The biochemical test for proteins is known as the (4) ‾\underline{\quad\quad\quad\quad\quad} test. In this test, sodium hydroxide and dilute copper(II) sulfate are added to the sample. If proteins are present, a positive result is shown by a colour change from blue to (5) ‾\underline{\quad\quad\quad\quad\quad}.
Proteins have highly specific three-dimensional shapes. The primary structure is the specific sequence of amino acids. The secondary structure, such as an alpha-helix or beta-pleated sheet, is stabilised by (6) ‾\underline{\quad\quad\quad\quad\quad} bonds. The tertiary structure is further folded and held in place by several types of bonds, including strong covalent (7) ‾\underline{\quad\quad\quad\quad\quad} bridges.
In terms of function, globular proteins often act as (8) ‾\underline{\quad\quad\quad\quad\quad} to catalyse metabolic reactions. Fibrous proteins, such as (9) ‾\underline{\quad\quad\quad\quad\quad}, have structural roles and are typically insoluble in water. In cell membranes, proteins can act as (10) ‾\underline{\quad\quad\quad\quad\quad} proteins to facilitate the active transport of substances across the phospholipid bilayer.
