Arrange the sequence of events for the conversion of succinyl-coa to succinate and atp (or gtp) in the correct order: the phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide. inorganic phosphate reacts at the thioester of succinyl-coa to yield a mixed phosphoanhydride. a histidine residue from the protein is phosphorylated by succinyl phosphate.

Inorganic phosphate reacts at the thioester of succinyl-CoA to yield a mixed phosphoanhydride.

A histidine residue from the protein is phosphorylated by succinyl phosphate.

The phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide.

Explanation:

The conversion of succinyl-CoA to succinate and ATP (or GTP) starts with the help of enzyme known as succinyl-CoA synthetase which has two sub units named as alpha and beta. Alpha subunit comprises phosphorylated histidine residue and binding site for CoA while beta sub unit is responsible for providing specificity for either GTP/ATP.

In the very first step, the phosphorylated histidine residue of this enzyme reacts to replace CoA of succinyl-CoA which is already bound to the enzyme to yield enzyme-bound succinyl phosphate.  

In the next step, this succinyl phosphate donates its phosphate group to the histidine residue of the enzyme thereby producing high energy phosphohistidyl enzyme  and succinate.

In the last step, the phosphate group from  the histidine residue of the enzyme is transferred to the terminal phosphate of GDP or ADP which leads to the formation of either of the two nucleotides, GTP or ATP .

Here, it may be noted that in animals there exist two isozymes of succinyl-CoA synthetase, one of them is specific to ATP while another one is specific to GTP.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation: