Glycolysis

Glycolysis is the metabolic process that serves as the foundation for both aerobic and anaerobic cellular respiration. In glycolysis, glucose is converted into pyruvate.

Step 1

The first step in glycolysis is the conversion of D-glucose into glucose-6-phosphate. The enzyme that catalyzes this reaction is hexokinase.

Step 2

The second reaction of glycolysis is the rearrangement of glucose 6-phosphate (G6P) into fructose 6-phosphate (F6P) by glucose phosphate isomerase.

 Step 3

Phosphofructokinase, with magnesium as a cofactor, changes fructose 6-phosphate into fructose 1,6-bisphosphate.

Step 4

Aldolase splits the hexose ring of glucose 1,6-bisphosphate into two triose sugars, dihydroxyacetone phosphate, a ketone, and glyceraldehyde 3-phosphate, an aldehyde.

Step 5

Triosephosphate isomerase converts dihydroxyacetone phosphate (DHAP) into glyceraldehyde 3-phosphate (GADP)

Step 6

Glyceraldehyde phosphate dehydrogenase (GAPDH) dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-bisphosphoglycerate.

Step 7

Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP for form ATP and 3-phosphoglycerate.

Step 8

Phosphoglycerate mutase changes 3-phosphoglycerate into 2-phosphoglycerate.

Step 9

Enolase with magnesium as a cofactor changes 2-phosphoglycerate into phosphoenolpyruvate

Step 10

Pyruvate kinase with magnesium as a cofactor changes phosphoenolpyruvate into pyruvate.

END

Oxidative decarboxylation isn't part of glycolysis, but it is the route most organisms take to enter the citric acid cycle. Pyruvate dehydrogenase converts pyruvate into acetyl coA.

Lipids

 

Lipids are class of naturally-occurring organic compounds that you may know by their common names: fats and oils. Here's a look at the function, structure, and physical properties of lipids.

What Is a Lipid?

A lipid is a fat-soluble molecule. To put it another way, lipids are insoluble in water but soluble in at least one organic solvent. The other major classes of organic compounds (nucleic acids, proteins, and carbohydrates) are much more soluble in water than in an organic solvent. Lipids do not share a common molecule structure.

Examples of Common Lipids

There are many different types of lipids. Examples of common lipids include butter, vegetable oil, cholesterol and other steroids, waxes, phospholipids, and fat-soluble vitamins. The common characteristic of all of these compounds is that they are essentially insoluble in water yet soluble in one or more organic solvents.

What Are the Functions of Lipids?

Lipids are used by organisms for energy storage, as a signalling molecule (e.g., steroid hormones), and as a structural component of cell membranes.

Lipid Structure

Although there is no single common structure for lipids, the most commonly occurring class of lipids are triglycerides, which are fats and oils. Trigylcerides have a glycerol backbone bonded to three fatty acids. If the three fatty acids are identical then the triglyceride is termed a simple triglyceride. Otherwise, the triglyceride is called a mixed triglyceride.The second most abundant class of lipids are the phospholipids, which are found in animal and plant cell membranes. Phospholipids also contain glycerol and fatty acids, plus the contain phosphoric acid and a low-molecular-weight alcohol. Common phospholipids include lecithins and cephalins.

Enzymology-intro

Enzymes are proteins that participate in cellular metabolic processes with the ability to enhance the rate of reaction between biomolecules. Some enzymes can even reverse a reaction from the direction it would normally take, by reducing the activation energy (Ea) to the extent that the reaction favours the reverse direction. Simlarly, enzymes can catalyze reactions that might not otherwise occur, by lowering the Ea to a more "affordable" level for the cell.
Enzymes can be isolated using various protein purification methods. The purity of an enzyme preparation is measured by determining it's specific activity
Enzyme Composition Enzymes can have molecular weights ranging from about 10,000 to over 1 million. A small number of enzymes are not proteins, but consist of small catalytic RNA molecules. Often, enzymes are multiprotein complexes made up of a number of individual protein subunits.
Many enzymes catalyze reactions without help, but some require an additional non-protein component called a co-factor. Co-factors may be inorganic ions such as Fe²⁺, Mg²⁺, Mn²⁺, or Zn²⁺, or consist of organic or metalloorganic molecules knowns as co-enzymes.
Enzyme ClassificationsEnzymes are classified according to the reactions they catalyze. The six classes are:

1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases

Examples:

1. Alcohol dehydrogenase: an oxidoreductase converting alcohols to aldehydes/ ketones.
2. Aminotransferases: transferases catalyzing the amino acid degradation by removing amino groups.
3. Glucose-6-phosphatase: a hydrolase that removes the phosphate group from glucose-6-phosphate, leaving glucose and H₃PO₄.
4. Pyruvate decarboxylase: a lyase that removes CO₂ from pyruvate.
5. Ribulose phosphate epimerase: an isomerase that catalyzes the interconversion of ribulose-5-phosphate and xylulose-5-phosphate.
6. Hexokinase: a ligase that catalyzes the interconversion of glucose and ATP with glucose-6-phosphate and ADP.