Prokaryotes adapt to hot temperatures by increasing the length of their hydrophobic tails and decreasing the amount of double bonds in their phospholipid bilayer.
(a) true
(b) false

True

Explanation:

Microorganisms that are capable of growing at temperatures between 45 and 110 degrees Celsius belong to the Bacteria and Archaea domains (the two groups in which prokaryotic organisms are currently classified, whose cells do not have a nucleus defined by a membrane). Aquifex and Thermotoga are the only hyperthermophilic bacterial genera; The Archaea domain is composed of two branches: Crenarchaeota and Euryarchaeota. These microorganisms can thrive at high temperatures thanks to their enzymes and heat-stable cellular proteins, which differ in few amino acids from mesophilic enzymes (from organisms that live at usual temperatures between 20 and 40 degrees Celsius). These small amino acid changes at key points allow the protein to fold differently, providing stability or heat resistance. The cytoplasmic membrane of thermophilic bacteria is rich in saturated fatty acids, which form heat-stable hydrophobic bonds with each other; In the case of the Archaea, the membrane does not contain fatty acids. Instead it has long chain hydrocarbons (glycerol diesters and tetraethers). Another factor involved in the thermostability of bacteria is the presence of special proteins with two different enzymatic activities: the opening and closing of the deoxyribonucleic acid (DNA) helix, preventing its denaturation.

The cytoplasmic membrane of cells is normally in the liquid-crystalline phase, but other phases have been found, such as gel and transition phases, which depend on factors such as temperature, fatty acid composition, pH and presence of divalent cations.

To preserve membrane fluidity, many microorganisms modify the composition of lipids. Psychophilic microorganisms (living at low temperatures), maintain the fluidity of their membrane including short chain lipids with unsaturated acyl groups (C14-C16), which have a low boiling point. Thermophilic microorganisms introduce long chain lipids with saturated acyl groups (C18-C24).

Adaptation of homeoviscosity: The term "adaptation to homeoviscosity" refers to the ability of bacteria to maintain their membrane in the liquid-crystalline phase, through the variation of lipid composition when they are subject to environmental or temperature changes. Heat adaptation of the lipid layer may involve an increase in the length of the acylated chain, saturation or cyclisation of fatty acids

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