Questions to ask when studying cellular respiration:


1. where is glycolysis occurring?

2. what are the 10 enzyme involved?

3. what are the reactants and products formed?

4. is there any gain of loss at the end of glycolysis?

5. what does this process require in order to continue?

6. is there any cofactors necessary for the catalyzed reactions to continue?


1. what is the reactant and product involved?

2. what is the enzyme involved?

3. is there any cofactors needed for this process to continue?

4. at the end of this reaction what happens to the products formed (Acetyl-CoA)?

5. where in the cell does this process occur?


1. how many ATP, NADH and FADH2 is generated?

2. is ATP used in this process?

3. what product of respiration is formed at this stage through the metabolism of Acety-CoA?

hint- Glucose + Oxygen —-> Carbon Dioxide + Water + Energy

C6H12O6 + 6O2 —-> 6CO2 + 6H2O + Energy

4. where in the cell does this process occur?


1. what do you understand by the chemiosmosis theory?

2. where in the cell is the ETC located?

3. what is the product of respiration formed at this stage?

4. how is ATP generated by this process?

5. what do you understand by the terms ATP synthase, Complexes 1, 2, 3 and 4?

6. how do protons and electrons flow across and along the organelle’s membrane?









It is made up of four complexes which is found on the inner membrane of the mitochondria. The goal of this chain is to break down NADH and FADH2 and pump H+ into the outer compartment of the mitochondria. In this reaction the Electron Transport Chain creates a gradient which is used to produce ATP similar to chloroplast. Electrons move down an energy gradient until they meet the ultimate electron acceptor-> oxygen gas (O2).

  • Electron Transport Phosphorylation typically produces 32 ATP’s.
  • ATP is generated as H+ moves down its concentration gradient through a special enzyme called ATP syntase.




One of this week’s topic is the TCA cycle. It occurs after glycolysis, where 2 molecules of pyruvate is generated. This pyruvate is converted to acetyl – CoA via a linked reaction between glycolysis and the Kreb’s cycle. Five cofactors are involved in this conversion which are: CoA-SH, NAD+, TPP, lipoate and FAD. In this process NAD+ is used and NADH is generated. The following diagram shows the various steps in this cycle.



The Krebs cycle, also called the citric acid cycle, is a fundamental metabolic pathway involving 8 enzymes essential for energy production through aerobic respiration. This pathway is also an important source of biosynthetic building blocks used in gluconeogenesis, amino acid biosynthesis, and fatty acid biosynthesis. The Krebs cycle takes place in mitochondria where it oxidizes acetyl-CoA, releasing carbon dioxide and extracting energy primarily as the reduced high-energy electron carriers NADH and FADH2. NADH and FADH2 transfer chemical energy from metabolic intermediates to the electron transport chain to create a different form of energy, a gradient of protons across the inner mitochondrial membrane. The energy of the proton gradient in turn drives synthesis of the high-energy phosphate bonds in ATP. An acetyl-CoA molecule (2 carbons) enters the cycle when citrate synthase condenses it with oxaloacetate (4 carbons) to create citrate (6 carbons). One source of the acetyl-CoA that enters the Krebs cycle is the conversion of pyruvate from glycolysis to acetyl-CoA by pyruvate dehydrogenase. Acetyl-CoA is a key metabolic junction, derived not only from glycolysis but also from the oxidation of fatty acids. As the cycle proceeds, the Krebs cycle intermediates are oxidized, transferring their energy to create reduced NADH and FADH2. The oxidation of the metabolic intermediates of the pathway also releases two carbon dioxide molecules for each acetyl-CoA that enters the cycle, leaving the net carbons the same with each turn of the cycle. This carbon dioxide, along with more released by pyruvate dehydrogenase, is the source of CO2 released into the atmosphere when you breathe. The Krebs cycle is regulated to efficiently meet the needs of the cell and the organisms. The irreversible synthesis of acetyl-CoA from pyruvate by pyruvate dehydrogenase is one important regulatory step and is inhibited by high concentrations of ATP that indicate abundant energy. Citrate synthase, alpha-ketoglutarate dehydrogenase and isocitrate dehydrogenase are all key regulatory steps in the cycle and are each inhibited by abundant energy in the cell, indicated through high concentrations of ATP or NADH. The activity of the Krebs cycle is closely linked to the availability of oxygen although none of the steps in the pathway directly use oxygen. Oxygen is required for the electron transport chain to function which recycles NADH back to NAD+ and FADH2 back to FADH, providing NAD+ and ADH required by enzymes in the Krebs cycle. If the oxygen supply to a muscle cell or a yeast cell is low NAD+ and FADH levels fall and the Krebs cycle cannot proceed forward so the cell must resort to fermentation to continue making ATP. Some Krebs cycle enzymes require non-protein cofactors for activity such as thiamine, vitamin B1. Insufficient quantities of this vitamin in the diet leads to decreased activity of pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase and a decrease in the ability of the Krebs cycle to meet metabolic demands causing the disease beriberi.





Рũßłїѕђёď åŗțїćłё #1

Kahn et al. 2010. “Identification and Importance of Brown Adipose Tissue in Adult Humans.” Accessed March 28, 2013. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2859951/

Identification and Importance of Brown Adipose Tissue in Adult Humans:

         Adipose tissue in humans is composed of brown and white fat. Brown adipose tissue affects the entire body where it modifies weight gain, alters insulin sensitivity and works with the uncoupling protein 1 (UCP1). On the other hand white adipose tissue stores energy and is the site for release of hormones and cytokines for body metabolism and resistance.

            In this article the authors conduct research using 18F-fluorodeoxyglucose (18F-FDG) and PET-CT scans to determine the presence of deposits of brown adipose tissue.  From 2003 – 2006 data was collected on patients that were studied.  Various statistical tests were used to analyze the information which includes a Mann-Whitney U test and a Student’s t-test. Factors were analyzed closely including sex, age, body-mass index (BMI), smoking history and medication history. This was performed using logistic regression to determine if there was a relationship between humans and the various factors.

            Brown adipose tissue was found in areas of the body such as the neck, muscles of the face, thoracic and abdomen. Evidence was obtained which showed that adipose tissue decrease rapidly in increased outdoor temperatures. It was detected to be a higher concentration of 7.5% in women than in men 3.1%. Results obtained indicated that the patients younger than 50 years, those the least obese, those with the lowest glucose levels, who is not using beta-blockers and who had never smoked showed that they were the most frequently detected for brown adipose tissue using the univariate analysis. It was detected to be less frequently in patients above 64 years. BMI was not a factor which predicted the presence of the brown adipose tissue in the multivariate analysis.

            In conclusion men contained more deposits of white adipose tissue than women while women below the age of 50 contained browner adipose tissue than men.



Did you all know that VIAGRA is a drug that was developed in 1998 as a pharmaceutical product used to treat high blood pressure but it was later observed that in young medical students it causes an adverse event called an erection which was a shock to the scientists. ‘Viagra is the first orally administered phosphodiesterase (PDE) inhibitor and was approved by the Food and Drug Administration in 1998 as the first truly effective oral medication for the treatment of erectile dysfunction.’

How does this inhibitor work? The smooth muscle in the human penis is called the corpus cavernosum which contains compounds called PDE receptors. The type-5 receptor is responsible for creating the erection. Nitric oxide is released from nerves within the corpus cavernosum during sexual stimulation which activates an enzyme called guanylate cyclasa. This enzyme helps elevate the level of cyclic guanosine monophosphate (cGMP) which in turn acts to relax the cavernosum tissue and an erection occurs. By inhibiting the breakdown of the cGMP the ingredients in Viagra induce and enhance the relaxation of the corporeal smooth muscle. Thus Viagra prevents the breakdown of a compound that produces an erection thereby prolonging it and even stimulating its occurrence in men who would not have a strong erection otherwise. When taken orally Viagra is rapidly absorbed and maximum concentrations are seen within one hour after taking the pill while the speed which a drug is broken down by the body is about three to five hours.





(Note this post is not encouraging any one to use this inhibitor)



Fermentation is an anaerobic process in which energy is released from glucose in the absence of oxygen. It occurs in yeast cells, erythrocytes, bacteria and in the muscle cells of animals.




In yeast cells glucose is metabolized through cellular respiration as in other cells. However, when oxygen is lacking glucose is still metabolized to pyruvic acid (pyruvate) via glycolysis. The pyruvate is first converted to acetaldehyde by the enzyme pyruvate decarboxylase and then to ethyl alcohol by the enzymic process of alcohol dehydrogenase. There is no net gain or loss just regeneration of NAD+. This process is essential because it removes electrons and hydrogen ions from NADH during glycolysis. The effect is to free the NAD so it can participate in future reactions of glycolysis.
Yeast is used in bread and alcohol production. Alcohol fermentation is the process that yields beer, wine, and other spirits. The carbon dioxide given off during fermentation supplements the carbon dioxide given off during the Krebs cycle and causes bread to rise.

yeastbuds       bread     images (2)



When muscles contract too frequently (as in strenuous exercise) they rapidly use up their oxygen supply. As a result, the electron transport system and Krebs cycle slows down as well as ATP production. However, muscle cells have the ability to produce a small amount of ATP through glycolysis in the absence of oxygen. The muscle cells convert glucose to pyruvate. Then the enzyme lactate dehydrogenase in the muscle cells converts the pyruvic acid to lactic acid. This reaction regenerates NAD+. Eventually the lactic acid buildup causes intense fatigue and the muscle cell stops contracting.
randy-orton-246        300px-Illu_muscle_structure





Growing Up With Galactosemia

The video is about a young boy named Everet who was diagnosed with galactosemia at birth. He has grown up and is still able to survive with the help of his family and changing his lifestyle to accommodate this rare genetic disorder. He is unable to eat any dairy products such as milk, butter and cheese. He avoids foods high in galactose such as beans.
I have learnt more about this disease since it is the first time I ever heard about this disease and its effects.


It is a rare genetic metabolic disorder that affects an individual’s ability to metabolize the sugar galactose properly. There are three forms of this disease Galactose-1-phosphate uridyl transferase deficiency, Galactokinase deficiency or Galactose-6-phosphate epimerase deficiency.

Infants with galactosemia can develop symptoms in the first few days of life if they eat formula or breast milk that contains lactose. The symptoms may be due to a serious blood infection with the bacteria E. coli.

  • convulsions
  • irritability
  • poor feeding habits where the baby refuses to eat formula containing milk
  • poor weight gain
  • yellow skin and whites of the eyes (jaundice)
  • vomiting

gal 1

gal 3


The above photo indicates that the absence of the GALT enzyme leads to health problems as indicated above.







1. Which stage in the metabolic pathway is ATP generated as  a NET gain for the call?

a. glucose to glucose 6-phosphate

b. fructose 6-phosphate to fructose 1,6-bisphosphate

c. fructose 1,6-bisphosphate to glyceraldhyde 3-phosphate

d. 1,3-bisphosphoglycerate to 3-phosphoglycerate

e. phosphoenolpyruvate to pyruvate

2. Phosphorylation of glucose and its conversion to glyceraldhyde 3-phosphate refers to:?

a. energy generation phase

b. pay off phase

c. energy conservation phase

d. preparatory phase

e. energy splitting phase

3. Which of the following enzymes does not have a delta G that is close to zero (0) where it is not in equilibrium?

a. hexokinase

b. aldolase

c. enolase

d. pyruvate kinase

e. phosphoglycerate kinase

4. What is the  name of the enzyme that catlyses the only oxidation reaction in glycolysis?

a. phosphoglycerate kinase

b. glyceraldehyde 3-phosphate dehydrogenase

c. triose phosphate immerase

d. aldolase

e. phosphoglycerate mutase

5. Converting one molecule of glucose to two molecules of pyruvate yields a total of ____ ATP?

a. 1

b. 2


d. 4

e. 5

6. Glucolysis occurs in the __________ ?

a. mitochondria

b. nucleus

c. cytoplasm

d. cytosol

e. golgi apparatus

7. Which of the follwing enzyme is the most regulated in glycolysis and controls the second priming effect ?

a.  aldose

b. hexokinase

c. phosphohexose isomerase

d. phosphofructokinase

e. pyruvate kinase

8. Why is glucose 6-phosphate more important than glucose molecules itself?

a. no transporters for the form

b. only glucose is transported across

c. phosphorous is attached to ATP

d. becomes unstable and promotes the reaction

e. all of the above


More quizzes are available in the page entitled ‘βï¤čħḝмḯşŗŷ ξxåღ ტմεșțΐǿŋŝ’. Do enjoy! 🙂

By biochemist01 Posted in Quiz