Ferritin Overview and Properties

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Questions and Answers

What is the primary function of cytochrome c oxidase?

Oxidizing Fe(III) to Fe(II)

Reducing dioxygen (O2) to water (correct)

Transferring electrons to cytochrome b

Facilitating electron transfer between cytosines

Which oxidation states of iron are involved in the function of cytochrome c?

Fe(II) and Fe(III) (correct)

Fe(III) and Fe(I)

Fe(I) and Fe(IV)

Fe(0) and Fe(V)

What occupies the 5th and 6th coordination sites of the iron in cytochrome c?

Valine and Tryptophan

Histidine and Methionine sulfur (correct)

Cysteine and Histidine

Methionine and Arginine

How many amino acids can cytochrome c have in its polypeptide chain?

103 to 112 Signup and view all the answers

What type of redox change does cytochrome c undergo?

Reversible redox change between Fe(II) and Fe(III) Signup and view all the answers

Cytochromes are classified based on:

The type of heme and its binding mode Signup and view all the answers

What structural feature of porphyrin contributes to its rigidity?

Delocalization of pi electrons in the pyrrole ring Signup and view all the answers

What type of spectroscopy might be used to investigate cytochrome c oxidase?

Extended X-ray absorption fine structure (EXAFS) Signup and view all the answers

What is the primary role of enzymes in biological systems?

They decrease the activation energy necessary for reactions. Signup and view all the answers

Which statement accurately describes Carboxypeptidase A (CPA-1)?

It contains a single Zn(II) ion as a cofactor. Signup and view all the answers

What characteristic allows chlorophyll to participate effectively in capturing light energy?

Its ability to undergo dimerization in certain solvents. Signup and view all the answers

Which wavelengths of light are absorbed by the two reaction centers P680 and P700?

680 nm and 700 nm Signup and view all the answers

What is produced during the redox reactions initiated by P680 and P700?

G3P (glyceraldehyde triphosphate) Signup and view all the answers

How do carotenoids contribute to the function of chlorophyll during photosynthesis?

They undergo photoexcitation and transfer energy to chlorophyll. Signup and view all the answers

What is the molecular weight of Carboxypeptidase A (CPA-1)?

34600 Da Signup and view all the answers

Which feature differentiates the reaction centers P680 and P700?

The kind of accessory chemicals they utilize. Signup and view all the answers

What is the main function of cytochrome c in the reaction with dioxygen?

To reduce dioxygen to water Signup and view all the answers

How many electrons does each cytochrome c molecule carry?

One Signup and view all the answers

What happens to the protons during the dioxygen reduction process?

They are pumped into the intramembrane space Signup and view all the answers

What is the net product of the electron transfer reaction involving cytochrome c and dioxygen?

All of the above Signup and view all the answers

How many protons are required for the complete reduction reaction involving cytochrome c?

Four protons Signup and view all the answers

What triggers the electron transfer process involving cytochrome c?

Oxidation of chlorophyll Signup and view all the answers

What is the product formed alongside protons when cytochrome c donates electrons in the reduction of dioxygen?

Water Signup and view all the answers

What structural feature of cytochrome c allows it to carry electrons?

Porphyrin ring Signup and view all the answers

Study Notes

Ferritin

Ferritin is a blood protein that stores iron.
A ferritin test measures iron stores in the body.
Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion.
This protein is found in almost all living organisms (archaea, bacteria, algae, plants, and animals).
In humans, ferritin acts as a buffer against iron deficiency and iron overload.
Ferritin is a globular protein consisting of 24 protein subunits forming a nanocage.
It facilitates multiple metal-protein interactions, maintaining iron in a soluble, non-toxic form.
Ferritin without iron is called apoferritin.

Additional Properties of Ferritin

Ferritin is approximately 12 nm in diameter
The iron core is approximately 8 nm in diameter
The protein shell of ferritin is about 12nm in diameter.
The composition of the iron core is about 8(FeOOH). FeO. H2PO4

Red-brown color observation

Ferritin displays a red-brown color
The molecule structure is aspherical shaped and contains a hollow sphere.

Magnetic Behavior & Protein Composition

Ferritin protein core has a high-spin state of Fe3+ and exhibits anti-ferromagnetic coupling with S = 5/2
Protein consists of 24 subunits with a molecular weight of 480 kDa
8 hydrophilic channels and 6 hydrophobic channels for controlled access to the core
The Fe core density is 2.5 times that of apoferritin
Iron enters via hydrophilic channels and exits via hydrophobic channels
Average channel diameter measures ~ 0.4 nm (as determined by X-ray)
Molecules larger than 0.4 nm can still penetrate the interior due to conformational flexibility

Protein Channels

4-fold channels lined with leucine residues which are hydrophobic
3-fold channels lined with glutamate and aspartate residues which are hydrophilic

Iron Release Mechanism

Iron is released by dissolving the iron lattice structure
Dihydroxy fumarate is used as a reducing agent
Iron reacts with water forming a "water cage" around Fe2+, resulting in a hydrated Fe2+ ion
Fe2+ is released from ferritin through 3-fold protein channels due to polarity reasons

Transferrin

A protein that transports iron in blood plasma
Molecule weight of ~ 80 kDa
Contains two high-affinity iron (III) binding sites
This glycoprotein binds iron tightly yet reversibly
High affinity for Fe(III) (association constant ~10^20 at pH 7.4)
Produced in the liver

Hemoglobin

A protein responsible for oxygen transport
Approximate tetramer of myoglobin
Molecular weight ~ 64,500 g/mol
Contains four heme groups bound to four protein chains
Quaternary globins with four subunits; 2α– chains and 2β– chains
Peptide chains bound through hydrogen bonds, salt bridges, and hydrophobic interactions

Heme

Organic planar protoporphyrin consisting of four pyrrole rings, four methyl groups, two vinyl groups, and two propionate side chains.
Inorganic Fe2+ is bonded to four pyrroles and has additional coordination sites on each side of the heme plane

Hemerythrin

An oxygen carrier that does not contain heme but contains two iron atoms
Single chain protein of 115 amino acid residues
Fe atoms (2Fe2+) bound to 2-carboxylates (Aspartic or Glutamic) with 5-imidazole N from histidines
In blood in the octomeric form and as monomers, dimers, trimers, or tetramers in tissues

Ferredoxin

Non-heme Fe-S protein
Mediates electron transfer in metabolic reactions
Two types of iron-sulfur clusters: [2Fe-2S] and [4Fe-4S]

Chlorophyll

Green pigments in thylakoid membranes (found in chloroplasts)
Involved in photosynthesis
Two types: Chl-a and Chl-b
Contain a magnesium (Mg2+) center
Phytyl group for membrane binding

Cytochromes

Redox-protein containing heme with a central iron atom
Involved in electron transport of chains and redox catalysis
Classified based on heme type and binding mode (a, b, c, d)
Functional groups affect the cytochrome redox potential

Other Natural Oxygen Carriers

Respiratory metalloproteins in lower animals (Hemerythrin & Hemocyanins) differ from hemoglobin

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Description

This quiz focuses on ferritin, a key blood protein that stores and releases iron in the body. It explores its structure, properties, and biological significance, along with unique observations related to its appearance. Gain a deeper understanding of this essential protein and its role in maintaining iron balance.