The correct pair of terms that completes the sentence is Amino acid and polypeptides.
The correct option is B .
Nucleotides are the building blocks of nucleic acids (such as DNA and RNA), while amino acids are the building blocks of proteins. Just as nucleotides combine to form nucleic acids, amino acids combine to form polypeptides, which are the precursor molecules for proteins. Therefore, the pair "amino acid" and "polypeptides" correctly completes the sentence.
Nucleotides are small organic molecules composed of a nitrogenous base, a sugar molecule, and a phosphate group. They are the building blocks of nucleic acids, which include DNA and RNA. Nucleotides link together through phosphodiester bonds to form the long chains of nucleic acids. On the other hand, amino acids are organic compounds that consist of an amino group, a carboxyl group, and a side chain (R group). There are 20 different types of amino acids commonly found in proteins. Amino acids link together through peptide bonds to form polypeptides. Polypeptides are chains of amino acids that can vary in length and sequence.
Hence , B is the correct option
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The lipids within the fluid mosaic of the plasma membranes are held in place by:
a. covalent bonds.
b. hydrogen bonds.
c. ionic bonds.
d. hydrophobic interactions.
e. disulfide bridges.
The lipids within the fluid mosaic of the plasma membranes are held in place by d. hydrophobic interactions.
The plasma membrane is composed of a lipid bilayer, with the hydrophilic heads of the lipids facing the aqueous environment and the hydrophobic tails oriented toward the interior of the membrane.
The hydrophobic interactions between the lipid tails are the primary forces that hold the lipids together and maintain the integrity of the membrane structure. These interactions occur because the hydrophobic tails repel water and seek to minimize their exposure to it.
Hydrophobic interactions are non-covalent attractions between nonpolar molecules or regions of molecules. In the case of the plasma membrane, the hydrophobic tails of the lipids cluster together, forming a stable environment that excludes water. This arrangement provides a barrier to the passage of hydrophilic molecules, allowing the membrane to regulate the flow of substances into and out of the cell.
While other types of bonds, such as covalent, hydrogen, ionic, and disulfide bonds, are important for various biological processes, they are not primarily responsible for holding the lipids in place within the plasma membrane. Therefore, the correct answer is D.
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