Question

1. The bacterium Micrococcus luteus lives on mammalian skin where it feeds on amino acids and lactic acid found in sweat. Answer the following questions about carbohydrate metabolism[1] in M. luteus.

1. M. luteus lacks any hexokinase orthologs (e.g. any enzyme catalyzing the reaction glucose + ATP ⇌ glucose-6-phosphate + ADP) as well as any phosphohexose isomerase homologs (e.g. any enzyme catalyzing the reaction glucose-6-phosphate ⇌ fructose-6-phosphate), but they express all other enzymes involved in glycolysis. Are M. luteus bacteria capable of catabolizing glucose via glycolysis? (1 point)

2. M. luteus expresses glycogen phosphorylase as well as phosphoglucomutase; i.e. these bacteria can convert glycogen to glucose-6-phosphate. Assuming M. luteus bacteria can transport glycogen into their cytoplasm, can M. luteus catabolize glycogen (e.g. via glycolysis) and, if so, how many ATP molecules can M. luteus produce (via glycolysis) for each 6 carbons of glycogen? (3 points)

3. Given your answer to the previous question, how many ATP molecules can an M. luteus bacterium produce (via glycolysis) from one 30,000 carbon molecule of glycogen? (2 points)

Which pathway enables M. luteus to produce sugars (e.g. for oligosaccharide biosynthesis) from glucogenic amino acids: glycolysis, gluconeogenesis, the Calvin cycle or the pentose phosphate reactions?

in response to comment: ok..so take time then

Answer 1

A 1. No, in absence of any hexokinase orthologs as well as phosphohexose isomerase orthologs M. luteus bacteria is not capable of catabolizing glucose via glycolysis. Hexokinase is the first enzyme and also a rate limiting enzyme catalyzing the irreversible conversion of glucose to glucose 6-phosphate in glycolysis pathway. So in absence of hexokinase orthologs glucose cannot be catabolised in the cells via glycolysis. Absence of Phosphohexose isomerase will lead to accumulation of dihydroxyacetone phosphate which will shift the final product of glycolysis from ethanol to glycerol. Since the first step of glycolysis cannot happen to lack of hexokinase other steps of glycolysis cannot take place.

A 2. Glycogen is found in the cytoplasm of cell. In glycogenolysis process glycogen is broken down glucose 1-phosphate and glycogen chain which is short of one glucose molecule with the help of enzyme glycogen phosphorylase. With the help of enzyme phosphoglucomutase glucose 1-phosphate is converted into glucose 6-phosphate. Glucose 6-phosphate can either be converted into glucose or it can enter the glycolysis pathway and metabolised into pyruvate. Glucose is a 6 carbon containing carbohydrate and via glycolysis it produces 2 ATP molecules. Since glycogen is step wise broken down into 6 carbon containing compound glucose 1-phosphate and which is converted to glucose 6-phosphate, for each 6 carbons of glycogen 2 ATP molecules will be produced via glycolysis.

A 3. From 1 molecule of glucose, a 6 carbon containing compound which is formed from glycogen via glycogenolysis 2 ATP molecules are produced by glycolysis pathway. So 30,000 carbon molecules will make up 5000 glucose molecules. Therefore M. luteus bacteria will produce 10,000 ATP molecules (5000 x 2= 10,000) via glycolysis of 30,000 carbon molecules of glycogen.

A 4. Gluconeogenesis pathway enables M. luteus to produce sugars from glucogenic amino acids. The glucogenic amino acids are alanine, arginine, aspargine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, methionine, proline, serine and valine. These amino acids are converted to alpha keto acids and then to glucose.