Chapter 4 Multiple choice questions

. How is Channelrhodopsin typically used in synthetic biology?

It can be added to any ion channel to render it light-sensitive.

Its inclusion in neuronal membranes causes the neurons to fire continuously.

It acts as a light-sensitive Ca²⁺ pore in membranes, activation of which can cause neurons to fire.

It reports neuronal activity using light.

. What is a RASSL?

Any activator of the Ras oncogene

A receptor activated only by a synthetic ligand

A receptor antagonized by a semi-synthetic ligand

A receptor activating synthesis of a synthetic ligand

. How do negative feedback loops work?

The loop tells the cell that something has not yet happened.

The output of a controlled process rises as its regulating signal goes more negative.

The output of a controlled process is compared with a set-point to yield a difference signal that controls the process.

An unpleasant stimulus (e.g. a mild electric shock) is used to deter an animal from a behaviour.

. Which one of the following correctly describes a graph of input and output in a system showing hysteresis?

The output value relates linearly to the input value.

The input-output relationship follows the same line throughout, whether the input is rising or falling.

The input-output relationship has two paths between minimum and maximum, the one associated with rising input being to the right of the one associated with falling input.

The input-output relationship has two paths between minimum and maximum, the one associated with rising input being to the left of the one associated with falling input.

. What is the use of an IRES sequence?

It allows one transcript to encode two separate proteins.

It allows ribosomes to enter the nucleus to interact with the mRNA.

It causes ribosomes to interact with the endoplasmic reticulum for synthesis of secreted proteins.

It ensures proteins made from an mRNA carrying it remain in the cell and are not secreted.

. Which of the following is the best description of a genetic motif in the context of synthetic biology?

A DNA gene sequence that is present in more than one module

A short, non-coding sequence added as a 'trade mark' by the constructing lab

A functional arrangement of elements present in more than one module

A genetic system that makes cells move

. Which of the following best describes patterning by phase separation?

Separation of cells in different phases of the cell cycle into different locations

Separation of cells with different adhesive properties into different locations

Separation of different phases of pattern formation into successive stages of development

Separation of patterning activity of a synthetic system into distinct phases of activity

. Which of the following best describes a system 'trapped in a local minimum'?

A colony of cells is trapped in a space too small for it to escape.

A system is too small to be able to generate the energy resources to allow it to grow, trapping it to remaining its minimum size.

A system is in a state of minimum possible free energy and cannot reach any other state without extra energy being provided.

A system has more free energy than the lowest possible energy state, but moving from its current state to the lowest one could be achieved only via higher energy intermediate states.

. Which of the following best defines a chimaeric protein?

A protein made from a gene that includes protein-coding sequences derived from more than one natural protein

A protein made by covalent linkage of two different types of precursor protein

A multimeric protein complex consisting of subunits of different types

A protein made when two cells of different types fuse together

. Which one of the following statements about positive and negative feedback is correct?

Negative feedback can be used to make a latch.

Positive feedback confirms that a cell is behaving correctly.

Only negative feedback can be used to clamp the output of a system in a particular state.

Both positive and negative feedback can clamp the output of a system in a particular state, positive feedback clamping it to a maximum and negative feedback to a value between the minimum possible and maximum possible.

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