Final answer:
Acetyl coA for cholesterol synthesis mainly originates from glycolysis and is used in the lipogenesis process to create cholesterol and other lipids. This process is regulated by the enzyme HMG-CoA reductase, which is influenced by cholesterol levels and hormonal signals.
Step-by-step explanation:
The acetyl coA used in cholesterol synthesis predominantly comes from the metabolic pathway known as glycolysis, during which glucose is broken down to produce energy. When glucose levels are high, the excess acetyl coA can undergo lipogenesis to generate fatty acids, triglycerides, cholesterol, steroids, and bile salts. Particularly in the liver, acetyl coA can be channeled towards the creation of cholesterol; it is first converted into hydroxymethylglutaryl coA (HMG CoA), which serves as a precursor for cholesterol.
This process is subject to complex regulation, with the enzyme HMG-CoA reductase playing a central role. Its activity is modulated through feedback inhibition by cholesterol itself as well as hormonal signals, such as those from glucagon and epinephrine, which affect the enzyme's phosphorylation state.
Cholesterol synthesis takes place in the cytoplasm and in the endoplasmic reticulum (ER). The first step in the pathway catalyzed by 3-hydroxy-3-methylglutaryl (HMG) -CoA Synthase (HMGCS) occurs in the cytosol while the subsequent steps occur in the ER.
Cholesterol synthesis is an expensive process for cell in terms of energy. These pathways take place in the cytoplasm. Liver and intestines are major contributors of endogenous production.