Some Questions about Hemoglobin

Some questions about Hemoglobin:


Question P-02


The affinity of Hemoglobin for Oxygen increases when:


a)     a molecule of Oxygen binds to one of the Hem groups

b)     protons concentration increases

c)      the concentration of 2,3-BPG increases

d)     an acidosis is established

e)     the concentration of Carbon Dioxide increases


Question P-03


This substance, transported by Hemoglobin, promotes the relaxation of vascular walls, producing an important and potent vasodilator effect.

a)     2,3, BPG

b)     Carbon monoxide

c)      Carbon Dioxide

d)     Nitric Oxide

e)     Oxygen


Question P-04


Hemoglobin F is formed by:


a)     1 Hem group, two alpha peptide chains and two beta peptide chains

b)     1 Hem group, two alpha peptide chains and two gamma peptide chains

c)      2 Hem groups, two alpha peptide chains and two beta peptide chains

d)     2 Hem groups, two alpha peptide chains and two gamma peptide chains

e)     4 Hem groups, two alpha peptide chains and two beta peptide chains

f)       4 Hem groups, two alpha peptide chains and two gamma peptide chains


Question P-05


An important difference between Methemoglobin and hemoglobin is that:


a)     Methemoglobin has four  alpha chains

b)     Methemoglobin has four beta chains.

c)      Methemoglobin has two alpha chains and two gamma chains

d)     Methemoglobin has iron in Ferric state instead of Ferrous state

e)     Methemoglobin has cupper instead of iron.



Basic Questions about Enzymes.



Choose the best answer:



Enzyme Question E-02



Inactive precursors of some enzymes that are activated through hydrolysis reactions are called:


a)     allosteric enzymes

b)     apoenzymes

c)      holloenzymes

d)     prosthetic groups

e)     zymogens




Enzyme Question E-03


L-amino acid dehydrogenase is an enzyme that can catalyze the oxidation of different L-amino acids. It can not catalyze the oxidation of D-amino acids or other L-compounds. Based on these characteristics we can say that this enzyme shows:


a)     absolute specificity over substrate

b)     allosteric regulation

c)      relative specificity over substrate

d)     specificity of action

e)     specific inhibition




Enzyme Question E-04


These enzymes have different structure but the same catalytic function. Frequently they are oligomers made from different polypeptide chains. These enzymes are called:


a)     allosteric enzymes

b)     isozymes

c)      lyases

d)     proenzymes

e)     zymogens





Enzyme Question E-05



The model that explain that the active site is flexible and the catalytic group(s) of the enzyme is (are) brought into proper alignment by the substrate is called


a)     Concerted model

b)     Induced fit model

c)      Lock and key model

d)     Michaellis Menten model

e)     Sequential model




Krebs Cycle Extended Matching Question

Krebs Cycle Extended Matching Questions.


(Another format you can expect to see in your Multiple Choice medical exams)





a) Aconitase

b) Alpha-ketoglutarate dehydrogenase

c) Citrate synthase

d) Fumarase

e) Isocitrate dehydrogenase

f) Malate dehydrogenase

g) Succinate dehydrogenase

h) Succinil Co A synthase


Lead in:


For each enzyme feature, select the most likely Krebs Cycle enzyme:






This enzyme catalyzes the SLP reaction of the Krebs Cycle in which GDP is phosphorylated to GTP.






This is the enzyme of the Krebs cycle that is most similar to pyruvate dehydrogenase.





(B-08 )

The deficit of enzymes of the TCA cycle is rare, indicating the importance of this pathway for survival. Several cases, however, are on record in which there is a severe deficiency of the enzyme that catalyzes the interconversion between fumarate and malate.  The patient is characterized by severe neurological impairment, encephalomyopathy, and dystonia developing soon after birth. Urine contains abnormal amounts of fumarate and other metabolites of Krebs Cycle. Which of the above enzymes would be deficient?





Did Porphyria help American Revolution?


King George III has been known as “the king that lost America”…


Did King George madness was a consequence of a type of Porphyria?




Scientific papers, books, movies, defend the theory that King George suffered from a certain type of porphyria..



 The Madness of King George (Trailer)




The Biochemistry at the Movies Page has been updated.




Visit the Biochemistry at the Movies Page and learn about the theories that have described King George as a patient suffering from Intermittent Porphyria.



Answer to Carbohydrate Question (C-04)


Original Question C-04 







Answer: (d)


Heparin is a heteropolysaccharide (a polysaccharide formed by different kinds of monosaccharides).


In fact, Heparin is a family of molecules that are usually composed by the repetition of a sulfated amino sugar and an acid sugar. The most abundant pair of monosaccharides whose repetition forms heparin is this one                                               



The physiological function of heparin is subject of discussion:  it is related to the inflammation process and not to coagulation in physiological conditions.


Heparin inhibits the coagulation process by inhibiting, indirectly, the action of Thrombin.


Normally, during the coagulation process, Thrombin (factor II), a proteolytic enzyme, (as many coagulation factors), catalyzes the conversion of fibrinogen to fibrin, activates factors V, VIII and XI and also promotes platelet activation.


Antithrombin is an antiprotease protein with an important role in the regulation of normal coagulation. It inhibits mainly the proteases of the intrinsic pathway of coagulation, but also affects other factors or the extrinsic and the complement pathways.


Heparin increases the inhibitory action of antithrombin in thousands of times. Heparin can act through two mechanisms:


1.- An allosteric mechanism, in which Heparin provokes conformational changes in antithrombin that increases its ability to inhibit some of the coagulation factors,


 2.- By forming ternary complexes Heparin-antithrombin-Thrombin.


Since it is necessary that the heparin molecule be big enough to bind properly to antithrombin and thrombin for forming the ternary complex (Heparin molecule should have more than 18 monosaccharides for allowing the simultaneous binding), small molecules of Heparin have no effect on Thrombin but maintain anticoagulant activity affecting other factors, mainly factor X. Because of this fact and that natural Heparin molecules are very heterogeneous, Low Molecular Weight Heparins (LMWHs), that show better pharmacokinetics properties, have been developed in order to achieve a better medical regulation of the anticoagulant therapy.


The medical uses and indications of Heparins and LMWH are discussed in detail in this article of the American Heart Association.


AHA Scientific Statement


Guide to Anticoagulant Therapy: Heparin: a Statement for Healthcare Profession




1000 Views…let’s have a Biochemical party!




Certainly a lot of people do not think that having 1000 views in a blog is enough for having a party…but look at it this way:



1.- This blog has a little more than a month of existence


2.- I do not write about Obama, Hillary or Mc Cain,


3.-I do not write about Britney Spears or American Idol


4.- I do not write about Sports


5.- I write about BIOCHEMISTRY, people!!!



 So I think I can have a little celebration because of these 1000 views…


Let’s have some Biochemical Music!!!


Hemoglobin is moving around





The Ribosome




Protein synthesis dance




No Air/Aerobic vs anaerobic




The OSU Band presents the Krebs Cycle



And for finishing, the already famous…


Bio-Rad PCR song


Thanks to the visitors! I hope that……


You’ll be back!


Hormones: Answer to H-01


Original Question



The answer is  (a)


The mechanism of the “second messenger” is used by hormones that can not cross the plasma membrane, like peptides hormones and hormones derived from amino acids (T3 is an exception, since it has a hydrophobic lateral chain). Since these hormones can not cross the plasma membrane, they interact with a receptor located in the membrane, like this transmembrane protein:







The interaction between the receptor (a membrane protein that frequently has seven intramembrane domains) and the hormone provokes the activation of one of the G-Proteins, a family of amphipatic proteins associated to the inner surface of the plasma membrane.


In this graphic, the receptor is represented as a transmembrane protein in blue, and the G-Protein is represented in pink color:








The interaction between the hormone and the receptor provokes changes in conformation of the G-Protein associated to the receptor, facilitating the release of GDP and the binding of GTP in the alpha subunit of the G-Protein.  The alpha subunit-GTP complex dissociates from the Beta-Gamma subunits, and it can produce activation of membrane associated enzymes like Adenyl Cyclase, Phospholipase C or other enzymes, depending on the specific Hormone-Receptor-G Protein system.


If the GTP-alpha subunit complex released in the Hormone-Receptor-G Protein System activates Adenyl Cyclase, then this enzyme catalyses the transformation of ATP to cAMP; if the system activates Phospholipase C, then it produces the hydrolysis of phosphatidyl inositol diphosphate, releasing Inositol triphosphate (IP3) and diacylglycerol, that act as second messengers.


Molecules as different as cAMP, IP3, diacylglicerol,  Ca++ and Nitric Oxide can function as second messengers.


More information about this topic can be found in the following links:


Kimball, J.K. :Second Messengers


King, M.W. : The Medical Biochemistry Page