Metalloporphyrins with special reference to Iron
porphyrins ( Haemoglobin and Myoglobin )
Porphyrins are one of the most important groups of
bioinorganic compounds in which a metal ion is
surrounded by the four nitrogens of porphin ring.
❑ Porphines are made of four pyrrole rings linked
together through methene bridges.
❑ Therefore, porphines have macrocylic pyrrole system
with conjugated double bonds as shown here:
❑ These porphines act as tetradentate ligands with four
nitrogen donor sites.
Two of these are tertiary nitrogen donor positions which can form
coordinate bonds by donating a pair of electrons each to the metal
ion.
❑ The other two are secondary nitrogen donor positions. each of
which lose a proton in forming a coordinate bond with a metal
ion.
❑ Thus, a porphin ring acts as a tetradentate dinegative ligand (or
dianion).
❑ Dipositive cations such as Mg2+ Fe2+ or Ni2+ are capable of
forming neutral complexes with porphine as shown here:
❑ Four pyrrole rings of porphin carrying substituents other than hydrogen
are called porphyrins. The complexes in which a metal ion is held in
the porphyrin ring system are called metalloporphyrins.
❑ Such complexes play a vital role in biological systems.
Bioinorganic Chemistry-Introduction,
Essential Elements,Functions of metal ions in biochemical process.Biochemistry Of Iron,Haemoglobin And Myoglobin,Biological Functions And Toxicity Of Some Elements
Quantum yield, experimental arrangement, reasons for high and low Quantum yield, problems, photochemical reactions, kinetics of photochemical decomposition of HI, photosensitized reaction, mechanism of photosensitization,
Non-heme oxygen carrier proteins, Hemocyanin, Copper containing metalloprotein, Active site of deoxyhemocyanin and oxyhemocyanin, Oxidative addition of dioxygen, peroxide bridging, antiferromagnetic, Hemerythrin, Active site structure of deoxyhemerythrin and oxyhemerythrin, Comparison between hemoglobin, hemerythrin and hemocyanin
Bioinorganic Chemistry-Introduction,
Essential Elements,Functions of metal ions in biochemical process.Biochemistry Of Iron,Haemoglobin And Myoglobin,Biological Functions And Toxicity Of Some Elements
Quantum yield, experimental arrangement, reasons for high and low Quantum yield, problems, photochemical reactions, kinetics of photochemical decomposition of HI, photosensitized reaction, mechanism of photosensitization,
Non-heme oxygen carrier proteins, Hemocyanin, Copper containing metalloprotein, Active site of deoxyhemocyanin and oxyhemocyanin, Oxidative addition of dioxygen, peroxide bridging, antiferromagnetic, Hemerythrin, Active site structure of deoxyhemerythrin and oxyhemerythrin, Comparison between hemoglobin, hemerythrin and hemocyanin
Introductory PPT on Metal Carbonyls having its' classification,structure and applications.This is a basic level PPT specially prepared for UG/PG Chemistry students.
Introductory PPT on Metal Carbonyls having its' classification,structure and applications.This is a basic level PPT specially prepared for UG/PG Chemistry students.
[Brief]Structure and functions of hemoglobin and myglobin (Bio-Inorganic chem...Anim60
This ppt is made from the bio-inorganic point of view for those who are having difficulty in finding the correct type and quality of information. This ppt has all the important points which one needs to know about this topic.
Role of co-ordination chemistry in myoglobin chemistry MyoglobinMaryumAkhter
in this presentation, one can see the structure, properties, function, binding capacity with Carbon dioxide and oxygen, co-ordination chemistry in myoglobin, difference and similarities with haemoglobin.
Structure & Biological role of Hemoglobin, myoglobin & Chrophyll . Biological...owaisyousf002
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Structure of HemoglobinHemoglobin is a chromo protein and is found.pdfannaimobiles
Structure of Hemoglobin
Hemoglobin is a chromo protein and is found in red blood cells, it’s a conjugated protein (heme
as prosthetic group + globin as the protein part apoprotein). Adults have 14.0 to 16.0 gm% of Hb
and 90 mg/kg of Hb will be produced and destroyed in the body on daily basis. Molecular weight
of Hb is 67,000 and 3.4 mg of iron present in each gram of Hb.
The combination of iron with a porphyrin ring produces the heme.
Structure of Heme
Heme is derived from porphyrin and porphyrins are cyclic compounds and are formed when 4
pyrrole rings fuse and are linked by methenyl bridges and the four rings are named as I,II,III, IV
and Alpha, beta, gamma and delta are the bridges. To the side chain of Porphyrins, four pyrrole
rings are attached.
We can find one ferrous atom (Fe++) co-ordinated at the centre of the of protoporphyrin IX tetra
pyrrole ring.
Structure of Globin
We can find the tetramer of globin polypeptide chains and each Hb molecule will have 4 Heme
units and the subunits of hemoglobin are found to be arranged in a tetrahedral array. And this
arrangement will give tight spherical overall appearance (which allows the polar residues being
on the exposed surface and keeps the non-polar interactions internal).
A molecule of hemoglobin is known to transport up to four oxygen molecules and here iron ion
interacts with oxygen molecule to form oxyhemoglobin. Oxyhemoglobin blood is bright red and
interactions between the iron–oxygen are very weak and thus can easily be separated without
disturbing the heme unit/ the oxygen molecule (completely reversible binding).
Deoxyhemoglobin is the hemoglobin molecule without oxygen and dark red..
Primary structure of hemoglobin
141 AA residues will be present in linear sequence of alpha chain contains and non- (, and )
chains will be of 146 amino acids in length (here the beta chain will have valine and histidine as
their first residues and Tyr b145 and His b146 found at C-terminal residues). Only 10 residue
difference between the delta chain and the beta chain.
Secondary structure of hemoglobin
We can find nearly 75 percent of the amino acids in or chains in a helical arrangement and 8
helical areas will be found in the chains.
Tertiary structure of or chains
Sphere type o structure will result during the tertiary folding of each globin chain and this
folding brings the Polar or charged side chains directed towards the outer surface of the subunit
and non-polar structures directed inwards making Hb water soluble, Heme pocket will be created
and is open-toped cleft in the surface and this folding will bring Hb in correct orientation to
allow these bonds to form.
Quaternary structure of hemoglobin
Finally the Hb tetramer will be formed composed of two identical dimers ()1and ()2. These two
polypeptide chains are held together tightly (though hydrophobic and ionic interactions andy
hydrogen bonding). The two dimers can move with respect to each other.
T and R forms of Hb
T form (taut structure.
Haemoglobin is an essential component of blood. It contains iron and protein and its deficiency can cause anaemia and can even be fatalic. This ppt is all about important aspects of Haemoglobin , its history,its pH dependance inside the body, sickle cell disease etc.
A lesson plan is the instructor’s road map of what students need to learn and how it will be done effectively during the class time. Before you plan your lesson, you will first need to identify the learning objectives for the class meeting. Then, you can design appropriate learning activities and develop strategies to obtain feedback on student learning.
CHEM Study and CBA : Salient features, merits and demeritsADITYA ARYA
CHEM study.
Chem study originated in 1960 at United States J.A Campbell was the project Director.
Chem Study employs inductive approach in which practical work precedes theory. The
main objectives of the course are
1) To diminish the separation between Scientist and teachers in the understanding of
Science.
2) To stimulate and prepare those high school students who planned to continue the
study of Chemistry in College in preparation for a professional career.
The materials produced under this project consists of a text, laboratory manual ,
teachers guide, two self instruction programmes two series of achievement tests,
26 basic films and 27 teacher training films.
Chemical Bond Approach (CBA)
CBA course was originated in 1959. Lawrence Strong was the founder of this
project. In CBA theory precedes practical work, ie, it is deductive in approach.
Important texts are Chemical system and investigating Chemical system. The concept of
bonding forms the central theme in C.B.A. The whole course is planned in such a
manner that experiments suggest the ideas to be tested and ideas to be tested suggest the
experiments to be setup.
Characters of Apiaceae:
Stem fistular, leaves alternate, much dissected mostly decompound, sheathing leaf base; inflorescence umbel or compound umbel occasionally simple; flowers epigynous, pentamerous, regular rarely zygomorphic, hermaphrodite; calyx superior, pentafid or 0; corolla five, polypetalous, often inflexed; stamens 5; carpels 2; syncarpous, bicarpellary with 2 pendulous ovules; honey-disc surrounding the stigmas – stylopodium is present; fruit cremocarp; seeds endospermic and oily.
A. Vegetative characters:
Habit:
Plants are mostly herbs which may be annual, biennial or perennial, the herbs may be large (Bupleurum, Heracleum, Agelica) rarely shrubs with aromatic odour due to the presence of oil ducts. Pseudocarum climbs by means of its petioles which are very sensitive to contact.
Family Leguminosae (Fabaceae) is generally characterized by typical legume fruit and the ability to symbiotically fix nitrogen. Among the three subfamilies, Papilionoideae is the largest and possesses the lion’s share of economically important legumes including pulses and forages. Although monophyletic origin is generally considered, traces of polyphyly and paraphyly are evidenced in the subfamilies Mimosoideae and Caesalpinioideae by molecular phylogenetic studies. Development of robust cytogenetic stocks (aneuploids, polyploids, chromosomal aberrations, somaclonal variants, transformants, etc.) and novel functional genomic tools (mutants, molecular markers, DNA libraries, barcode sequences, etc.) have paved the way to legume classical and molecular breeding for high-yield, nutritional quality, biotic and abiotic stress tolerance, and enhancement of its bioactive natural antioxidants.
Integration of peace in different subjectsADITYA ARYA
PEACE EDUCATION
☼ It is necessary that children are taught pedagogy of peace that
includes recognition and rejection of violence, understanding
of differences through dialogue, critical awareness of
injustice, social justice and imaginative understanding of
peace.
☼ The prime responsibility of a teacher is to help students to
become good human beings, motivated to fulfil their true
potential for their own benefit as well as for the betterment
of the society as a whole.
3
PEACE EDUCATION
☼ Peace education is a psychological, social, political, ethical and
spiritual state with its expressions in intrapersonal,
interpersonal, intergroup, international and global areas of
human life.
☼ Developing capabilities for peace through broad based education
involves behavioural, cognitive, spiritual and attitudinal
components.
☼ Discourses of empathy and reconciliation in curriculum and
pedagogy are critical components of reformation of peace
education goals.
A business plan is a written document that describes in detail how a business—usually a startup—defines its objectives and how it is to go about achieving its goals. A business plan lays out a written roadmap for the firm from marketing, financial, and operational standpoints.
Business plans are important documents used to attract investment before a company has established a proven track record. They are also a good way for companies to keep themselves on target going forward.
Although they're especially useful for new businesses, every company should have a business plan. Ideally, the plan is reviewed and updated periodically to see if goals have been met or have changed and evolved. Sometimes, a new business plan is created for an established business that has decided to move in a new direction.
Healthy discipline among school children ( Gender Issues & Peace Education )ADITYA ARYA
Healthy discipline among
school children {Gender Issues & Peace Education}
❖ The Latin origin of the word discipline is ‘to teach’.
❖ Disciplining the student child means teaching them responsible behavior and selfcontrol.
❖ With appropriate and consistent discipline, then students will learn about
consequences and taking responsibility for their own actions.
❖ At its best, discipline rewards the student for appropriate behavior and discourages
inappropriate behavior, using fair and positive means, it is known as healthy discipline.
The biosynthesis of the main auxin in plants (indole-3-acetic acid [IAA]) has been elucidated recently and is thought to involve the sequential conversion of Trp to indole-3-pyruvic acid to IAA. However, the pathway leading to a less well studied auxin, phenylacetic acid (PAA), remains unclear. Here, we present evidence from metabolism experiments that PAA is synthesized from the amino acid Phe, via phenylpyruvate. In pea (Pisum sativum), the reverse reaction, phenylpyruvate to Phe, is also demonstrated. However, despite similarities between the pathways leading to IAA and PAA, evidence from mutants in pea and maize (Zea mays) indicate that IAA biosynthetic enzymes are not the main enzymes for PAA biosynthesis. Instead, we identified a putative aromatic aminotransferase (PsArAT) from pea that may function in the PAA synthesis pathway.
POLLINATION LESSON PLAN (PC: BIOLOGICAL SCIENCES)ADITYA ARYA
Lesson plans are the best way to deliver an effective and engaging lesson. Lesson plans also help keep you on track to ensure that your learners hit their goals and targets, in line with your course curriculum.
Pollination, transfer of pollen grains from the stamens, the flower parts that produce them, to the ovule-bearing organs or to the ovules (seed precursors) themselves. In plants such as conifers and cycads, in which the ovules are exposed, the pollen is simply caught in a drop of fluid secreted by the ovule. In flowering plants, however, the ovules are contained within a hollow organ called the pistil, and the pollen is deposited on the pistil’s receptive surface, the stigma. There the pollen germinates and gives rise to a pollen tube, which grows down through the pistil toward one of the ovules in its base. In an act of double fertilization, one of the two sperm cells within the pollen tube fuses with the egg cell of the ovule, making possible the development of an embryo, and the other cell combines with the two subsidiary sexual nuclei of the ovule, which initiates formation of a reserve food tissue, the endosperm. The growing ovule then transforms itself into a seed.
PROJECT WORK: TOOLS AND TECHNIQUES FOR ASSESSMENTADITYA ARYA
PROJECT WORK: TOOLS AND TECHNIQUES FOR ASSESSMENT
Project-based assessments are an alternative to tests that allow students to engage with their learning in more concrete ways. Instead of merely studying theory, a hands-on project asks students to apply what they've learned to an in-depth exploration of a topic. You can use projects as part of the ongoing learning process or as a capstone assessment in place of a traditional final exam.
Project-based assessment is often a component of project-based learning (PBL), in which the entire focus of a course or unit is to teach via student engagement in problem-solving and exploration. Like PBL, project-based assessment is student-centered and requires reflection on both the process and the content to be meaningful.
CARBOHYDRATE METABOLISM : GLYCOLYSIS
Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. Glycolysis consists of an energy-requiring phase followed by an energy-releasing phase.
What is glycolysis?
Glycolysis is a series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates. Glycolysis is an ancient metabolic pathway, meaning that it evolved long ago, and it is found in the great majority of organisms alive today^{2,3}
2,3
start superscript, 2, comma, 3, end superscript.
In organisms that perform cellular respiration, glycolysis is the first stage of this process. However, glycolysis doesn’t require oxygen, and many anaerobic organisms—organisms that do not use oxygen—also have this pathway.
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
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Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
How to Split Bills in the Odoo 17 POS ModuleCeline George
Bills have a main role in point of sale procedure. It will help to track sales, handling payments and giving receipts to customers. Bill splitting also has an important role in POS. For example, If some friends come together for dinner and if they want to divide the bill then it is possible by POS bill splitting. This slide will show how to split bills in odoo 17 POS.
The Art Pastor's Guide to Sabbath | Steve ThomasonSteve Thomason
What is the purpose of the Sabbath Law in the Torah. It is interesting to compare how the context of the law shifts from Exodus to Deuteronomy. Who gets to rest, and why?
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The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
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Metalloporphyrins with special reference to Iron porphyrins ( Haemoglobin and Myoglobin )
1. NAME: ADITYA ARYA
B.SC.B.ED. (CBZ) 6TH SEMESTER
CHEMISTRY
Topic:
Metalloporphyrins with special reference to Iron
porphyrins ( Haemoglobin and Myoglobin )
2. CONTENTS :
1. What is Bioinorganic Chemistry
2. Metalloporphyrins
3. Structure of Metalloporphyrins
4. Iron Porphyrins (Haemoglobin & Myoglobin)
5. Functions of Haemoglobin & Myoglobin
6. Structure of Myoglobin
7. Structure of Haemoglobin
8. Role of Haemoglobin & Myoglobin
9. Coordination Chemistry of Iron Porphyrins
10. Functions & Cooperativity of Hb & Mb
11. CO2 Transport & Bohr’s effect
3. What is Bioinorganic Chemistry ?
Fast developing branch
because of the importance
of inorganic substances in
biological systems
Branch of chemistry
which correlates
inorganic materials with
biological processes
These ions are present in
specific parts of the
biomolecule, and are
responsible for initiating or
inhibiting reactions in
biological systems.
This has helped to
synthesise new inorganic
compounds which resemble
those found in biological
systems naturally
This branch highlights
the role of metal ions
in biology
4. ❑ Porphyrins are one of the most important groups of
bioinorganic compounds in which a metal ion is
surrounded by the four nitrogens of porphin ring.
❑ Porphines are made of four pyrrole rings linked
together through methene bridges.
❑ Therefore, porphines have macrocylic pyrrole system
with conjugated double bonds as shown here:
❑ These porphines act as tetradentate ligands with four
nitrogen donor sites. Porphin ligand
5. ❑ Two of these are tertiary nitrogen donor positions which can form
coordinate bonds by donating a pair of electrons each to the metal
ion.
❑ The other two are secondary nitrogen donor positions. each of
which lose a proton in forming a coordinate bond with a metal
ion.
❑ Thus, a porphin ring acts as a tetradentate dinegative ligand (or
dianion).
❑ Dipositive cations such as Mg2+ Fe2+ or Ni2+ are capable of
forming neutral complexes with porphine as shown here:
❑ Four pyrrole rings of porphin carrying substituents other than hydrogen
are called porphyrins. The complexes in which a metal ion is held in
the porphyrin ring system are called metalloporphyrins.
❑ Such complexes play a vital role in biological systems.
Metalcomplexwithporphin
ligand
6. ❖ With delocolisation of
electrons in the
pyrrole rings we
obtain stable
porphyrin system.
❖ The best value of the
size of the central hole
has been estimated to
be of radius 0.2 nm.
❖ The size of the central
hole in the centre of
the porphyrin ring is
ideal for
accommodating metals
of first transition series
or lighter alkaline
earth metals.
❖ The metal ion of
appropriate size are
surrounded by four
nitrogens of porphine
ring in a square planar
geometry and the axial
sites are available for
other ligands.
❖ However, if the size of
the metals ion is
smaller than required
(or ideal) size, the ring
becomes ruffled to
allow closer approach
of the nitrogen atoms
to the metal.
❖ On the other hand, if
the size of the metal
ion is lager than the
size of the hole, the
metal ion cannot fit
into the hole and stays
out of the Plane of four
nitrogen atoms.
❖ In such a case the
metal sites above the
ring which becomes
domed and acquires
square pyramidal
configuration.
7. The structures of two important metalloporphyrins heme and chlorophyll are being considered here:
❖ Chlorophyll is magnesium complex of porphyrin which plays
important role in photosynthesis. In this metalloporphyrin, in
addition to substituents, a double bond in one of the pyrrole ring is
reduced to form a magnesium dihydro porphyrin complex as shown
here:
❖ A cyclopentane ring is also fixed to a pyrrole ring.
❖ Heme contains iron
{II}which is present in
hemoglobin and myoglobin.
Iron protoporphyrin in heme
Structure of chlorophylla & b
8. All organisms require oxygen in order to survive. It is formed during
photosynthesis involving biologically important redox reactions.
Different proteins have different tendencies to bind and transfer
oxygen.
These proteins are known as oxygen carriers.
The most important two oxygen carrier proteins are haemoglobin (Hb)
and myoglobin (Mb).
These are iron porphyrin complexes which are oxygen transfer and
oxygen storage agents in the blood and muscle tissues respectively.
Myoglobin is a small intracellular protein present in vertebrate muscles
while hemoglobin is a large intracellular protein responsible for the red
color of the red blood cells. :
9. ➢ Haemoglobin picks up oxygen in the lungs and
delivers it to the rest of the body.
➢ Myoglobin accepts oxygen from the
haemoglobin in the muscles and stores it until
needed for energetic processes.
➢ Deoxygenated hemoglobin uses some of its
amino groups to fix up CO2 and then transports
CO2 back to the lungs
10. ❖ Myoglobin consists of one polypeptide chain (globin) with
one heme group . The peptide chain consists of 150-160
amino acid residues folded about the single heme group.
❖ The heterocyclic ring system of heme is porphyrin
derivative containing four pyrrole groups joined, by
methene bridges.
❖ The Fe (II) atom present at the centre of the heme is
bonded by four porphyrin nitrogen atoms and one
nitrogen atom from imidazole side chain of histidine
residue which is a part il of long protein chain of amino
acid residues.
❖ This polypeptide chain plays an important role in
biological fixation of O2.
The structure of myoglobin containing
heme group and polypeptide chain
11. ❑ Haemoglobin is a large protein with a molecular weight of
about 60000. It consists of four sub units each of which
contains one heme group associated with protein globin.
❑ Therefore, there are four heme groups bonded to four protein
chains.
❑ One heme group with its protein chain is called sub unit.
❑ The four sub units are similar but not identical, two sub units
form alpha (α) chains of 141 amino acids and two form β
chains of 146 amino acids. It may be noted that amino acid
sequences of neither α nor β sub units of haemoglobin match
the sequences in myoglobin.
12. ❖ Both Hb and Mb have five coordinated Fe (II) atom.
❖ It is bonded by four nitrogen atoms from pyrrole rings
and fifth from protein chain.
❖ The sixth position is occupied by weakly bonded water,
Mb and fib in such molecules are usually called as de-
oxymyoglobin (deoxy-Mb) and de-oxyhaemoglobin
(deoxy-Hb).
❖ However when the sixth position which is trans to
histidine is occupied by molecular oxygen then these
molecules are called oxymyoglobin (oxy-Mb) and
oxyhaemoglobin (oxy-Hb).
13. Role of haemoglobin (Hb) and myoglobin (Mb):
➢ Haemoglobin and myoglobin play very important role in transporting
oxygen from lungs to tissues and CO2 (as HCO3
- ) from tissues to the
lungs.
➢ Oxygen is inhaled into the lungs at very high pressure when it binds Hb
in the blood forming HbO2.
➢ The oxygen Is then transported to tissues where the partial pressure of O2
is low.
➢ The O2 then gets dissociated from Hb and diffuses to the tissues where
myoglobin picks it up and stores it until it is needed. Mb has greater
affinity for O2, than Hb.
➢ This increases the rate of diffusion of O2 from the capillaries to the tissues
by increasing its solubility. The Hb and CO2 (as HCO3
- ) are returned to
the lungs from where CO2, is exhaled.
15. Coordination Chemistry of Iron Porphyrins:
✓ The heme group consists of Fe2+ ions enclosed in a porphyrin ligand. Fe2+
ion has six coordination sites.
✓ The porphyrin ligand takes up only four of the six sites, leaving two free
binding sites on opposite sides of the metal ion.
✓ If a free heme is present in aqueous solution, the two vacant sites may be
occupied by water molecules.
✓ A naked heme group binds to oxygen molecule in an irreversible manner
when Fe2+ is oxidised to Fe3+.
✓ This oxidation of iron destroys its oxygen binding capacity.
✓ The following reaction takes place:
16. ✓ Porphyrin Fe is protected due to the presence of
hydrophobic protein chain around the Fe (II) and blocks
the approach of larger molecules to the neighbourhood
of Fe (II) and hence prevent oxidation of Fe (II) in
haemoglobin to Fe (III).
✓ The hydrophobic groups also prevent the solvation of
ions.
✓ Fe (II) of myoglobin and hemoglobin can be oxidised
under certain controlled conditions to Fe (III) forming
metmyoglobin of Mb and methemoglobin of Hb.
✓ These Fe (III) proteins are responsible for brown colour
of old meat and dried blood.
The structure of myoglobin containing
heme group and polypeptide chain
17. ❑ Deoxymyoglobin abbreviated as (Deoxy-Mb) is a five coordinate high spin Fe
(II) complex with four of the coordination positions occupied by the
porphyrin N atoms.
❑ The fifth position is occupied by an N atom of an imidazole ligand of a
histidine residue which joins the heme to the protein.
❑ In the absence of O2, the ligand field is weak so that such five coordinate heme
complex: of Fe( II) are always high spin having the configuration t2g
4 eg
2.
❑ Therefore these five coordinated complexes are paramagnetic.
❑ In this high spin state, Fe 2+ has substantially larger radius than in the spin Fe
(II) state having the configuration t2g
6 because of repulsive effect of one
electron occupying the dx2-y2 orbital directed towards the four N atoms of the
porphyrin ring.
❑ The estimated Fe-N distance is larger than the size of the central hole in the
porphyrin ring.
❑ Theefore, Fe lies above the plane of the four nitrogen atoms by about 70 pm to
give a square pyramidal arrangement as shown:
Square pyramidal structure
with Fe lying about 70 pm
above the plane of the ring
18. ➢ When oxygen bonds to the sixth position the iron becomes
coplanar.
➢ In such a situation oxygen gets coordinated to Fe (II).
➢ The ligand field becomes strong resulting in spin pairing giving a
low spin t2g
6 complex.
➢ The resulting complex is diamagnetic and Fe — N bond distance is
approximately same as porphyrin hole.
➢ Therefore, the iron becomes coplanar.
➢ The release of strain energy of the square pyramidal complex
compensates the loss of spin pairing energy in going from 5-
coordinated deoxy Hb or Mb to six-coordinated oxy-Hb or oxy Mb.
➢ Therefore, the coordination of O2, will result in dropping of Fe in
the plane of the heme group.
Oxy hemoglobin low spin
octahedral complex. Fe lies in
the plane of porphyrin ring.
19. The net result of this interaction in haemoglobin is to increase the affinity of 02 of the
second heme site and so on. In other words, as one iron binds an oxygen molecule, the
molecular shape changes to make the binding of additional oxygen molecules easier.
This phenomenon is called cooperativity.
The shrinkage in size of Fe" and dropping into the plane of porphyrin ligands.
20. Cooperativity
enables Hb to bind
and release 02
more effectively.
❖ But when the hemoglobin reaches the cells where the pressure
of O2 is low, O2 begins to dissociate from the complex.
❖ The myoglobin picks up all the O2.
❖ Since myoglobin has only one heme group, it does not have
any cooperative binding, so it does not lose its affinity for O2 .
❖ This shows the Mb has a higher affinity for O2 than Hb at low
partial pressure of O2 in the muscle.
❖ The main function of haemoglobin is to bind O2 at high partial pressure of O2 in the
lungs and then carry it through blood t the tissues where myoglobin picks up O2 from
Hb.
❖ In the lungs where the pressure O2 is high and much O2 is bound, the affinity of heme for
O2 becomes very high.
❖ It efficiently loads up with as much O2 as possible.
21. ❑ The graph shows that Hb and Mb have almost similar
binding affinity for O2 at high O2 pressure but Hb is
much poor O2 binder at lower pressures of O2 in muscles.
❑ As a result, Hb passes its O2 onto Mb as required.
Moreover, the need for O2 is greatest in tissues which
have already consumed oxygen and simultaneously
produced CO2.
❑ The CO2, lowers the pH ( 2H20 + CO2 ⇌ HCO3
- + H30+ )
and the increased acidity favours the release of O2 from
oxyhaemoglobin to Mb.
❑ The oxygen affinity of haemoglobin varies with the pH of the medium. This pH sensitivity effect is called Bohr
effect.
❑ In other words the variation of oxygen affinity with the pH of the medium is called Bohr effect. It can be
explained in terms of the effect of pH on the interaction between the heme group and the ionizable groups of
the protein.