Question

Which statement about generation of reactive oxygen species below is NOT correct? Select one: a. Hydroxyl radical is formed from hydrogen peroxide O b. Hydroxyl radical can react with lipides O c. Hydroxyl radical can react with DNA and proteins O d. Hydroxyl radical react with hydrogen peroxide O e. Hydroxyl radical react with glutathione Check Estimate how many molecules of ATP is produced from complete oxidation of 1 molecule of tyrosine Answer: Check

Answer 1

Questions 1st) Ans is C Hydroxyl radicals damage DNA by reacting with the individual strands of the DNA molecule, causing single-strand breaks in the nucleic acid. This is due to its strong oxidative effect on the phosphate sections of the molecule.

A hydroxyl radical reacts with fatty acids by oxidatively removing a hydrogen atom from a methylene group on the polyunsaturated fatty acid, which leaves an unpaired electron on the carbon atom. The carbon atom then rearranges itself to a conjugated diene which reacts with 'normal' oxygen to form another peroxy radical, this propagating the oxidative effect. The fatty acids themselves are reduced in this reaction to reactive aldehydes and hydrocarbons.

Hydroxyl radicals bind with proteins to form protein aggregates, especially dimers, and also affects the direct protein factory in a cell upsetting the balance of aminao acids, bad for tryptophan, good for tyrosine. Hydroxyl radicals also tend to increase cellular proteolysis to up to 50 times faster than normal, under an unknown process.

Answer 2 )

number of molecules of ATPand GTP consumed in the synthesis of a 200-residue protein, starting from amino acids? Assume that the hydrolysis of PPi is equivalent to the hydrolysis of ATP for this calculation.

Two hundred molecules of ATP are converted into AMP + 400 Pi to activate the 200 amino acids, which is equivalent to 400 molecules of ATP. One molecule of GTP is required for initiation, and 398 molecules of GTP are needed to form 199 peptide bonds.

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