Metabolic Pathways

My exam for Chemistry is finally over and this is the final part of my pathetic study, The rest of the info I had to learn is locked away in books, so until next time…

Metabolic Pathways


Is catabolic reactions: break down large and complex molecules to provide energy and smaller molecules. Anabolic reactions use ATP to build large molecules.


  • Stage 1. Digestion breaks the large molecules down smaller so that they can enter the blood stream.
  • Stage 2. Molecules are broken down from complex to 2 and 3 carbon compounds.
  • Stage 3. Compounds.
  • Stage 2. Molecules are broken down from complex to 2 and 3 carbon compounds.
  • Stage 3. Compounds are oxidized in the citric acid cycle to provide energy.


Energy is stored in cells in adenosine triphosphate (ATP)

The hydrolysis of ATP to ADP releases energy and the hydrolysis of ADP to AMP also releases energy.

ATP and Muscle Contraction:

  • Filaments of actin and myosin aer found in muscle fibers.
  • When nerve impulses increase Ca2+, the filaments move closer together to contract muscle.
  • They hydrolysis of ATP provides the energy to contract the muscle.
  • As Ca2+ and ATP decrease the filaments relax.


In cells, oxidation of compounds makes 2H as 2H+ and 2e- that reduce coenzymes.

Nicotinamide adenine dinucleotide (NAD+)  is involved in reactions that make a carbon oxygen double bond. NAD+ contains: Nicotinamide, ribose and ADP. When nicotinamide group accepts H+ and 2e- , NAD+ turns to NADH.

Flavin Adenine Dinucleotide is involved in reactiosn that produces carbon-carbon double bonds. C=C. FAD has ADP and riboflavin. FAD changes to FADH2 when  flavin takes on 2H+ and 2e-.

CoA (Co-Enzyme A) activates acyl groups, which the 2 carbon acetyl group for transfer and the fatty acids for oxidation.


Digestion of Carbohydrates:

Step 1 :Digestion

  • Digestion starts in the mouth, saliva= amylase hydrolyzes alpha glycosidic bonds in polysaccharides = breaks down molecules smaller = smaller polysaccharides, glucose and maltose.
  • Pancreatic amylase hydrolyzes dextrins (polysaccharides) to maltose and glucose in the Small intestine.
  • Maltose, glucose and sucrose are hydrolyzed to monosaccharides : maltase, lactase and sucrose enzymes.
  • Then they enter the blood stream to be taken to the cells.

Step 2 :Glycolysis

  • Glycolysis (metabolic pathway) turns glucose (from step 1 in digestion) to pryuvate
  • Don’t need oxygen and it happens in cytosol.
  • Glycolysis is stimulated by insulin.

Step 3 : Energy Investment

  • Energy from ATP is used to add phosphate groups (Pi using 2 kinase enzymes)and glucose  to glucose 6pi(step 1)   and fructose  6p  (step 3) fructose 1, 6-bisphosphate.

Step 4:

  • Fructose 1, 6 Bisphosphate is changed (converted) to 2, 3 carbon molecules

Step 6: Glycolysis – Energy Production

  • NADH is produced.
  • The hydrolysis of phosphates in the triose phosphates generate four ATP molecules using ADP in reaction 7 and 10.

Glycolysis :

  • Generates 2 ATP and 2 NADH.
  • The energy from the 2 ATP is used to add phosphate groups to glucose and fructose-6-phophate
  • From a Direct transfer of phosphate groups to four ADP, energy is generated and four ATP are formed
    Glucose + 2ADP+2Phosphate +2NADH = 2Pyruvate +ATP+2NADH+ 4H+

Regulation of Glycolysis :

Reaction: 1

Hexolinase is inhibited by high levels of glucose-6-phosphate = which stops the phosphorylation of glycose

Reaction 3

Phosphofructokinase, allosteric enzyme, is turned on by high levels if ADP and Amp, it is stopped by high levels of ATP and ac

Reaction 10

Pyruvate Kinase, allosteric enzyme, high levels of  ATP or acetyl Co Enzyme A inhibits the enzyme


  • Glycolysis produces pyruvate, it is oxidatively decarboxyliclated to produce acetyl Co Enzyme A and CO2 when Oxygen is present(aerobic) in the cell.


  • When there is no oxygen available, Anaerobic, pyruvate is turned to lactate to replenish NAD+ to be able to continue glycolysis
  • In strenuous excerise, oxygen in the muscle is depleted = lactate accumulates in muscles = muscles become sore and tired = Rest is needed to restore oxygen and reform pyruvate in the liver.
  • Lactate is also formed due to reduced oxygen.


  • Stores glucose by changing it to glycogen
  • Oppereates due to the high levels of glucose -6-phosphate that happens in the first reaction of glycolosis
  • Occus in fed states, insulin activates the process.
  • Glucose is not turned to glycogen when energy stores are full, the additional glucose is turned to body fat.


  • The breakdown of glycogen to glucose, the opposite of gylcogenesis
  • Occurs between meals, excersise and starvation = it is activated by glucagon (low blood glucose)
  • Bonds glucose to phosphate to form glucose-1-phosphate



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