The alpha helix and beta sheet are very different secondary structures but share
ID: 81101 • Letter: T
Question
The alpha helix and beta sheet are very different secondary structures but share some common features. Which of the following is NOT true of both alpha helices and beta sheets? a. They are both stabilized by H-bonding between donors and acceptors in the backbone. b. Many different sequences can be found in either structure. c. The side chains project out from the axis. d. They are both stabilized by H-bonding between donors and acceptors in the R groups. Which amino acid best fits the characteristics described below (each is only used once)? a. Proline b. Arginine c. Threonine d. Valine Most likely to be found within a trans-membrane alpha helix. (A, B, C, D) Most likely to make contact with the DNA backbone. (A, B, C, D) Least likely to be found in an alpha helix (A, B, C, D) Most likely to be found on an exposed surface of a cytosolic enzyme (A, B, C, D) The core histones are proteins with lysine tails that are originally _____charged, and the charge can be chemically neutralized by_____ a. Negatively; Acetylation b. Positively: Acetylation c. Negatively: Methylation d. Positively. Methylation e. None of the above Under which condition is the lac operon highly expressed? a. When no sugar is present b. When only glucose is present c. When only lactose is present d. When both glucose and lactose are present e. When glucose and arabinose are presentExplanation / Answer
1. d. They are both stabilized by H-bonding between donors and acceptors in the R-groups.
It does not occur in the R-groups but occurs in the backbone.
2. a. Valine
3. c. Threonine
4. a. Proline
5. b.Arginine
6. b. Positively; Acetylation
Histone acetylation and deacetylation are the processes by which the lysine residues within the N-terminal tail protruding from the histone core of the nucleosome are acetylated and deacetylated as part of gene regulation.
7. c. when only lactose is present
The lac operon is involved in lactose metabolism. It's expressed only when lactose is present and glucose is absent.
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