Question

Name at least 4 metabolically significant membrane bound cellular compartments and the metabolic pathways that take place within each compartment.

Based on your knowledge of membrane characteristics, would you expect the metabolic substrates and cofactors glucose, pyruvate, ATP, NADH, and FAD to transit across membrane? Explain your reasoning, including specific references to chemical characteristics of these molecules. Be sure to consider whether transit would be controlled or uncontrolled.

Answer 1

Metabolically significant membrane bound cellular compartments are:

1. Mitochondria:

• It is surrounded by a double membrane system and these two membranes are seperated by intermembrane space.
• Function: It is responsible for the useful energy which is derived from the breakdown of carbohydrates and fatty acids. This energy is then converted to ATP by the process of oxidative phosphorylation.

• Pyruvate and fatty acids are imported from the cytosol and converted to acetyl CoA in the mitochondrial matrix. Acetyl CoA is then oxidized to CO2 via the citric acid cycle, the central pathway of oxidative metabolism.

• In this entire process,the oxidation of acetyl CoA to CO2 is coupled to the reduction of NAD+ and FAD to NADH and FADH2, respectively.

• Thus, mitochondria transit metabolic substrates and cofactors glucose , pyruvate , ATP, NADH and FAD across the membranes to follow up the oxidative metabolism in cells.

2. Chloroplasts:

• Chloroplasts are present in plants and are quite similar to mitochondria . It is also helpful in generation of ATP but more importantly it is responsible for the photosynthetic conversion of CO2 to carbohydrates.
• Also chloroplasts synthesize amino acids, fatty acids, and the lipid components of their own membranes. Reduction of nitrite to ammonia also accurs in cholroplast.
• Chloroplast consist of three membranes. The two membranes form a type of envelope while the third one, thylakoid membrane, is internal one dividing the chloroplast into three compartments.
• The outer membranes allow the metabolic substrates and cofactors like that of mitochondria bu the inner membrane is impermeable to such ions and species. But protiens can be easily imported into the chloroplast as they are not positively charged.

3. Peroxisomes:

• Peroxisomes are small organelles closed within membranes that contain enzymes involved in a variety of metabolic reactions.
• Peroxisomes can be defined as organelles that carry out oxidation reactions which results in the generation of hydrogen peroxide but as hydrogen peroxide is harmful to the cell, peroxisomes also contain the enzyme catalase, which can decomposes hydrogen peroxide either by converting it to water or by using it to oxidize another organic compound.
• such oxidation reaction helps in the break down of substrates like uric acid, fatty acid or amino acids. Break down of amino acids is one of the major source of metabolic energy.
• They are very crucial in plants as they are also involved in photorespiration and are also helpful in conversion of stored fatty acid into carbohydrates thus providing energy and raw materials for the growth of plants.
• All the above functions involve the trasfer of ATP, glucose , pyrvate and other metabolic substrates, thus it can easily transit them across membranes.