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Hatshy [7]
3 years ago
5

PLEASE HELP ASAP IM TIMED!! 100 PTS WILL GIVE BRAINLIEST TO WHOEVER ANSWERS FIRST AND CORRECTLY

Biology
1 answer:
Vesna [10]3 years ago
4 0

Answer: More than 99 percent of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. At least a handful of times in the last 500 million years, 75 to more than 90 percent of all species on Earth have disappeared in a geological blink of an eye in catastrophes we call mass extinctions.

Though mass extinctions are deadly events, they open up the planet for new forms of life to emerge. The most studied mass extinction, which marked the boundary between the Cretaceous and Paleogene periods about 66 million years ago, killed off the nonavian dinosaurs and made room for mammals and birds to rapidly diversify

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Metabolic pathways can be controlled through the availability of enzymes and modulation of their catalytic activities. Enzyme av
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Answer: a) substrate and cofactors b) covalent modification

Explanation:

Metabolic pathways involve all the chemical processes takes place in the enviornment or in an organisms.The metabolic pathways are controlled through the catalytic activities of enzymes.

The availability of enzyme is regulated  by substrate and cofactors present in enzyme and enzyme activity is commonly regulated via covalent modification.

Enzymes are highly selective in nature and bind to a specific substarte only. The active site in enzyme binds with the substrate to form enzyme substrate complex. Coactors assist the enzyme activity, without cofactor enzyme can not perform its activity.

Hence enzyme availibility is regulated by  substrate and cofactors regulates.

Covalent modifications regulates activity of enzyme as it involves addition and removal of chemical group to synthesis required protein. It can change the chemical properties of the site by targeting one or multiple amino acid.

Thus the correct answer is a) substrate and cofactors b) covalent modification

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