Question

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Fill in the blanks in the table so as to match the membrande described with the organism having such an membrane: (A) a bacterium living in a compost heap (at a temperature of 50 °C), (B) a (cold blooded) fish living in arctic waters, (C) an oak tree growing in a temperate forest during the spring. and (D) a pathogenic yeast infecting a (warm blooded) mammal (8 points) Fatty Acid Fatty Acid sacrel or lipod equivalent function 70% 90% 50% 40% 30% B) cold blooded fi (2) Look at the sequence of the human GABA-receptor (03 subtype) -a ligand gated CI channel as found at and identify the following (providing both the one letter code and residue # for any particular residue meeting the indicated criterion, 2 points. each) (A) A residue predicted to bind (or have attached to it) a polysaccharide (B) A postively charged (at physiological pH) residue (e.g. one that can favorably interact with CI ions) within a transmembrane helix (C) A tryptophan or tyrosine at the C-terminal end of a transmembrane helix (D) A residue in an extra-cellular part of the receptor (hint: what happens to cysteine residues co-located in space, even if apart in sequence, in an oxidizing environment?)

Answer 1

(1) (A) Bacterium living in 50^oC, known as thermophiles should have membrane that has high saturated fatty acids. In table, row 4 has 60% saturated fatty acids, hence the organism corresponding to that lipid content is Thermophiles.

(B) Cold blooded fish has more cholesterol to provide fluidity to the membrane at the lower temperature.

(C) Indian oak tree has stigmasterol in the cell membrane.

(D) Candida is an yeast that has ergosterol in the cell membrane.

%fatty acid unsaturated 70 90 50 40 Membrane sterol or lipid Stigmasterol Cholesterol Ergosterol %Fatty Acid saturation Organism Indian oak tree Cold blooded fish Candida Thermophile 10 50 60