What structural level is represented by the coiling of the protein chain backbone into an alpha helix?
primary structure
quaternary structure
secondary structure
tertiary structure
The Correct Answer is C
A. Primary structure: The primary structure refers to the linear sequence of amino acids in a polypeptide chain. It does not include any folding or coiling of the chain.
B. Quaternary structure: Quaternary structure arises when multiple polypeptide chains or subunits associate to form a functional protein complex. It is not related to the coiling of a single chain.
C. Secondary structure: Secondary structure is characterized by local folding patterns of the polypeptide backbone, including alpha helices and beta sheets, stabilized by hydrogen bonds between backbone atoms. The alpha helix is a classic example of this level of structure.
D. Tertiary structure: Tertiary structure refers to the overall three-dimensional folding of a single polypeptide chain, determined by interactions between side chains, not the regular coiling of the backbone.
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Related Questions
Correct Answer is B
Explanation
A. Vitamin D: Vitamin D is fat-soluble and is absorbed along with dietary fats. It is stored in the liver and adipose tissue and plays a key role in calcium and phosphorus regulation.
B. Vitamin C: Vitamin C is water-soluble, not fat-soluble. It dissolves in water, is not stored extensively in the body, and must be obtained regularly through the diet. Its main functions include collagen synthesis and antioxidant protection.
C. Vitamin E: Vitamin E is a fat-soluble antioxidant that protects cell membranes from oxidative damage. It is stored in adipose tissue and the liver for long-term use.
D. Vitamin A: Vitamin A is fat-soluble and essential for vision, immune function, and epithelial tissue health. It is stored in the liver and released as needed.
E. Vitamin K: Vitamin K is fat-soluble and plays a critical role in blood clotting and bone metabolism. It is absorbed with dietary fats and stored in the liver.
Correct Answer is C
Explanation
A. Osmosis: Osmosis specifically refers to the movement of water across a selectively permeable membrane, not gases like oxygen or carbon dioxide.
B. Secondary active transport: Secondary active transport uses energy indirectly from an ion gradient to move molecules against their concentration gradient. Oxygen and carbon dioxide move passively.
C. Simple diffusion: Oxygen and carbon dioxide are small, nonpolar molecules that can freely cross the lipid bilayer of the plasma membrane. They move down their concentration gradients without the need for energy or transport proteins.
D. Channel-mediated facilitated diffusion: This process requires specific protein channels to transport polar or charged molecules. Since oxygen and carbon dioxide are nonpolar, they do not require channels to diffuse across the membrane.
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