How a Cell Communicates Trivia Quiz

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.