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Quiz about How a Cell Communicates
Quiz about How a Cell Communicates

How a Cell Communicates Trivia Quiz


Cells are the simplest living units which define what we are. How a cell communicates is vital to its ability to carry out its function in living organisms. This quiz looks at the role of membrane proteins in cell communication.

A multiple-choice quiz by doublemm. Estimated time: 6 mins.
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Author
doublemm
Time
6 mins
Type
Multiple Choice
Quiz #
339,512
Updated
Dec 03 21
# Qns
10
Difficulty
Tough
Avg Score
5 / 10
Plays
1013
Awards
Top 20% Quiz
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Question 1 of 10
1. One of the simplest membrane proteins is the passive transporter, which binds a specific substrate and changes its conformation, allowing the substrate to be carried across the cell membrane. Which of the following is least likely to traverse the membrane via this method? Hint


Question 2 of 10
2. Active transporters are trans-membrane proteins which require extra energy to move substrate across the plasma membrane. This energy is provided either by ATP or the stored energy of a concentration gradient across the membrane. What are these two types of active transport commonly known as? Hint


Question 3 of 10
3. Enzyme-linked receptors are a second example of membrane proteins involved in cell communication, and often cause an intracellular cascade, eventually leading to enzyme activation. The cascade is often regulated by proteins which phosphorylate other molecules. What general term is used for these proteins? Hint


Question 4 of 10
4. The largest class of enzyme-linked receptors controls cell growth and cell survival. These receptors are characterised by two trans-membrane proteins brought together by a ligand to form a dimer. After which amino acid, commonly denoted by the one letter code Y, is this class of receptors named? Hint


Question 5 of 10
5. G-protein coupled receptors (GPCRs) are trans-membrane proteins and, as their name suggests, are coupled to a G-protein which is found within the cell. G-proteins, once activated, will generate diffusible, transient signals which will bring about a desired response. How are these signals commonly known? Hint


Question 6 of 10
6. Like enzyme-linked receptors, GPCRs often activate a cascade before the desired protein is activated. One such protein which is activated by the action of GPCRs is myosin light chain kinase (MLCK). Which activity does this system regulate? Hint


Question 7 of 10
7. The fastest acting type of trans-membrane receptor is the channels. Channels are characterised by a central pore, and a gate which opens according to a certain stimulus. Do ions move through channels actively (requires energy), or passively (does not require energy)?

Answer: (One word - Actively or Passively)
Question 8 of 10
8. Trans-membrane proteins play a vital role in the generation and propagation of nerve impulses, allowing the central nervous system to coordinate the actions of the rest of the body. Which of the following classes of trans-membrane protein is the most significant in the generation and propagation of nerve impulses? Hint


Question 9 of 10
9. As well as communicating with their surroundings, cells must also be able to communicate with neighbouring cells to which they are connected. Which of the following membrane proteins permits the exchange of ions and polar molecules between adjacent cells? Hint


Question 10 of 10
10. Neighbouring cells can be joined to one another by adherens junctions and desmosomes, which connect actin and intermediate filaments respectively. Which of the following is untrue of adherens junctions and desmosomes? Hint



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Quiz Answer Key and Fun Facts
1. One of the simplest membrane proteins is the passive transporter, which binds a specific substrate and changes its conformation, allowing the substrate to be carried across the cell membrane. Which of the following is least likely to traverse the membrane via this method?

Answer: Estrogen

Glucose, sodium ions and urea are all charged/display dipole-moments when in a water environment. Such molecules are unable to cross the hydrophobic phospholipid bilayer and so are more likely to be transported via integral (membrane-spanning) proteins. Estrogen, on the other hand, is lipid soluble and is able to diffuse through the phospolipid bilayer.
2. Active transporters are trans-membrane proteins which require extra energy to move substrate across the plasma membrane. This energy is provided either by ATP or the stored energy of a concentration gradient across the membrane. What are these two types of active transport commonly known as?

Answer: Primary and secondary

The energy provided by ATP originates in the hydrolysis of the high energy phosphoanhydride bond adjoining the terminal phosphate group to the rest of the molecule.
If a concentration gradient is present across the membrane, it can be utilised to move substrate against a concentration gradient. This is done by allowing the molecules which generate the concentration gradient to move either in the same direction of the substrate (symport) or in the opposite direction to the substrate (antiport).
Energy obtained via the movement of molecules due to a concentration gradient is known as secondary active transport, as the gradient was originally set up by energy provided by ATP. Energy obtained via ATP is therefore termed primary.
3. Enzyme-linked receptors are a second example of membrane proteins involved in cell communication, and often cause an intracellular cascade, eventually leading to enzyme activation. The cascade is often regulated by proteins which phosphorylate other molecules. What general term is used for these proteins?

Answer: Kinases

Activation of an enzyme-linked receptor via ligand binding activates kinase activity (usually this activity is intrinsic, i.e. within the receptor). Phosphorylation of other regulatory proteins, themselves often kinases, leads to a cascade, eventually activating the target enzyme.
4. The largest class of enzyme-linked receptors controls cell growth and cell survival. These receptors are characterised by two trans-membrane proteins brought together by a ligand to form a dimer. After which amino acid, commonly denoted by the one letter code Y, is this class of receptors named?

Answer: Tyrosine

With the full title of "receptor tyrosine kinases", this is the largest class of enzyme-linked receptors. The proteins are rich in tyrosine residues, which posses an alcohol (-OH) group and so can be phosphorylated. Serine and threonine (the other two non-essential amino acids with an -OH in their R chain) also have families of receptor kinases.
5. G-protein coupled receptors (GPCRs) are trans-membrane proteins and, as their name suggests, are coupled to a G-protein which is found within the cell. G-proteins, once activated, will generate diffusible, transient signals which will bring about a desired response. How are these signals commonly known?

Answer: Second messengers

GPCRs are typified by seven trans-membrane domains and sites which can bind ligands (on the outside of the cell) and G-proteins (on the inside of the cell). G-proteins are so named as they bind guanosine triphosphate (GTP), an alternative energy source to ATP.
6. Like enzyme-linked receptors, GPCRs often activate a cascade before the desired protein is activated. One such protein which is activated by the action of GPCRs is myosin light chain kinase (MLCK). Which activity does this system regulate?

Answer: Smooth muscle contraction

In this system, the GPCR activates the G-protein, which activates phospholipase C, leading to the splitting of PIP2 into IP3 and DAG. These second messengers increase the intracellular calcium ion concentration, activating myosin light chain kinase, leading to smooth muscle contraction.
7. The fastest acting type of trans-membrane receptor is the channels. Channels are characterised by a central pore, and a gate which opens according to a certain stimulus. Do ions move through channels actively (requires energy), or passively (does not require energy)?

Answer: Passively

The passive movement of ions through channels is part of the reason for their efficiency.
Channels can be either:
1) Ligand-gated - opened by the binding of two or more molecules. Receptors are characterised by possessing 5 subunits.
2) Voltage-gated - opened by a change in potential difference. These are typified as having 4 subunits.
Each channel also has an inactivation mechanism, preventing excessive ion flow.
8. Trans-membrane proteins play a vital role in the generation and propagation of nerve impulses, allowing the central nervous system to coordinate the actions of the rest of the body. Which of the following classes of trans-membrane protein is the most significant in the generation and propagation of nerve impulses?

Answer: Ion channels

As mentioned previously, ion channels are the most rapidly acting trans-membrane proteins, which is what is needed for propagating nerve impulses. Both ligand-gated and voltage-gated channels are important in firing an action potential, though voltage-gated channels play a greater role in propagating the impulse.
9. As well as communicating with their surroundings, cells must also be able to communicate with neighbouring cells to which they are connected. Which of the following membrane proteins permits the exchange of ions and polar molecules between adjacent cells?

Answer: Gap junctions

Gap junctions may be called connexins in vertebrates or innexins in invertebrates.
These are also found in the nervous system, forming what are known as electrical synapses (as opposed to chemical synapses). Electrical synapses are much faster than chemical synapses.
10. Neighbouring cells can be joined to one another by adherens junctions and desmosomes, which connect actin and intermediate filaments respectively. Which of the following is untrue of adherens junctions and desmosomes?

Answer: Both allow epithelial sheets to contract

Adherens junctions connect actin fibres which, in the presence of myosin, can bring about contraction. Intermediate filaments, however, only provide a supportive structural role (e.g. keratin in the skin).
Several adjoining adherens junctions form an adhesion "belt" capable of contraction, which is vital for neurulation during embryonic development.
Source: Author doublemm

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