I. Signaling cascades (4 pts)
1. Which of the following is an example of a signaling cascade?
A. Binding of lactose to the lac repressor
B. Binding of the lac repressor to the lac operon
C. The series of proteolytic digests that occur during clotting
D. The Collins Toggle Switch
2. Why is it important that signaling cascades have negative feedback loops?
II. Metabolism (4 pts)
1. What is a benefit of a negative feedback allosteric regulator?
A. It prevents starting materials from being unnecessarily consumed.
B. It regulated metabolism without requiring new protein synthesis.
C. It can be rapidly reversed as conditions change.
D. All of the above.
2. How is a metabolic cycle, like the citric cycle, distinct from a metabolic pathway, like glycolysis?
III. Transcription (4 pts)
1. Transcription factors, repressors, and activators are examples of proteins that _________.
A. randomly activate RNA polymerases.
B. bind specific DNA sequences.
C. bind specific rRNA sequences.
D. are found in the lysosome.
2. The trp operon is attenuated by a stem-loop structure that can form near RNA polymerase. The RNA sequencing encoding the stem loop is:
5â-AUACCCAGCCCGCCUAAUGAGCGGGCUU-3â
The stem loop is composed of 7 nucleotides which perfectly base pair. Indicate the two halves of the stem loop on the sequence above.
IV. DNA replication/repair/genome editing (4 pts)
1. What is a consequence of the need for RNA primers during DNA replication?
A. Linear chromosomes gradually shorten each cell division.
B. Transcription factors often trigger DNA replication.
C. RNA primers are not actually needed for DNA replication.
D. Lagging strands can be avoided.
2. CRISPR-mediated genome editing has gene-specific components: an sgRNA, and a double-stranded repair template. Describe the role of the sgRNA in directing genome editing.
V. Genetic circuits (4 pts)
1. Which statement best describes the mechanism of the toggle switch?
A. Inducers must be continuously applied to maintain one of two states.
B. Competing repressors keep the cell in one of two transcriptional states.
C. An activator and a repressor keep the cell in one of two states.
D. A pair of repressors cause the cell to oscillate between two states without input.
2. How is bistability achieved by the Collins toggle switch?
