Biochemistry of Proteins and Iron Storage

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Questions and Answers

Which type of protein is primarily responsible for oxygen storage in muscle tissue?

Ferritin

Myoglobin (correct)

Hemoglobin

Casein

What is the primary function of ferritin in the cell?

To facilitate enzymatic reactions

To transport oxygen in the bloodstream

To provide immunological protection

To save iron for hemoglobin biosynthesis (correct)

What distinguishes a monomeric protein from a multimeric protein?

Monomeric proteins consist of a single polypeptide chain (correct)

Multimeric proteins are more stable than monomeric proteins

Monomeric proteins cannot contain any amino acids

Multimeric proteins have a fixed number of subunits

What indicates that hemoglobin is an oligomeric protein?

It contains four subunits, two of which are identical Signup and view all the answers

Which protein serves as a nutrient protein and provides immunological protection for infants?

Casein Signup and view all the answers

How many amino acids are consistently used to compose all proteins, regardless of the organism?

20 Signup and view all the answers

What is the largest known protein in vertebrate muscle?

Titin Signup and view all the answers

What is true of amino acid compositions in proteins?

Some amino acids can be absent from certain proteins Signup and view all the answers

What defines the properties of amino acids?

The side chains of the amino acids Signup and view all the answers

Which group of chemical reactions is associated with carboxylic acid groups in amino acids?

Formation of esters, amides, and acid anhydrides Signup and view all the answers

What is the average molecular weight of an amino acid residue in a protein after peptide bond formation?

110 Da Signup and view all the answers

What is the main reason for the variation in side chains of amino acids?

Their charge and reactivity Signup and view all the answers

How is the common name 'Asparagine' derived?

From asparagus Signup and view all the answers

Which of the following is a correct three-letter abbreviation format for amino acids?

First letter capitalized, last two lowercase Signup and view all the answers

What happens during the formation of a peptide bond between amino acids?

A water molecule is produced Signup and view all the answers

Which amino acid was first isolated from cheese?

Tyrosine Signup and view all the answers

What is a defining characteristic of fibrous proteins?

They tend to have simple, regular, linear structures. Signup and view all the answers

Which substance is primarily responsible for the hardness of keratin?

Disulfide bridges Signup and view all the answers

What distinguishes alpha-keratin from beta-keratin?

Alpha-keratin exhibits a coiled coil structure. Signup and view all the answers

What is the secondary structure of alpha-keratin primarily composed of?

Hydrophobic amino acid residues Signup and view all the answers

How are collagen molecules described in terms of shape and structure?

Long, thin, and rigid Signup and view all the answers

What type of protein classification does keratin fall under?

Fibrous proteins Signup and view all the answers

Which of the following best describes the function of the disulfide bonds in keratin?

They form cross-links and enhance strength. Signup and view all the answers

What is the result of having more disulfide bonds in keratin?

Increased hardness of nails and bones. Signup and view all the answers

What is the shape adopted by a single protein chain in an alpha (α) helix?

Coiled spring shape Signup and view all the answers

What maintains the coil configuration of the alpha (α) helix?

Intramolecular hydrogen bonds Signup and view all the answers

How many amino acid residues are included in one turn of an alpha (α) helix?

3.6 Signup and view all the answers

What is the effect of proline on the alpha (α) helix structure?

Disrupts the helix Signup and view all the answers

In a beta (β) pleated sheet, how are the protein chain segments linked?

Hydrogen bonds Signup and view all the answers

What pattern does the beta (β) pleated sheet structure exhibit due to hydrogen bonding?

Zigzag pattern Signup and view all the answers

Where are the amino acid R groups positioned in relation to the beta (β) pleated sheet?

Above and below the plane of the sheet Signup and view all the answers

How do hydrogen bonds in a beta (β) pleated sheet relate to the polypeptide backbone?

They are orthogonal to the backbone Signup and view all the answers

What characterizes a zwitterion?

Net charge is zero with both positive and negative groups. Signup and view all the answers

At which pH does the zwitterionic form of an amino acid predominate?

At neutral pH. Signup and view all the answers

What happens to the predominant form of an amino acid as pH changes?

It may change between cationic, zwitterionic, and anionic forms. Signup and view all the answers

What is the form of an amino acid at its isoelectric point (pI)?

Zwitterionic form with net charge zero. Signup and view all the answers

Which of the following statements about amino acids is false?

The nonionic form occurs significantly at any pH. Signup and view all the answers

What is the predominant form of an amino acid when the pH is greater than the pI?

Anionic fully deprotonated form. Signup and view all the answers

Which of the following describes the behavior of zwitterions?

They can act as either proton donors or acceptors. Signup and view all the answers

Which point corresponds to the cationic fully protonated form of an amino acid?

Point a. Signup and view all the answers

Study Notes

Protein Overview

Ferritin functions as an iron-storage protein, essential for hemoglobin synthesis.
Myoglobin is an oxygen-storage protein, found in muscle tissue.
Regulatory proteins are located on cell membrane surfaces, acting as receptor sites and controlling enzyme activity.
Nutrient proteins are crucial during early development, providing immunological protection, with milk (casein) and egg white (ovalbumin) being prime examples.

Protein Structure

A protein is defined as a polypeptide consisting of at least 40 amino acids.
Protein size varies significantly; small proteins have 40-100 residues, common proteins contain 400-500, and titin is the largest known protein at 26,926 amino acids.
Proteins can be monomeric (single polypeptide) or multimeric (multiple polypeptides), with oligomeric proteins containing at least two identical subunits.
Hemoglobin, a heterotetramer, comprises two α and two β subunits, forming a diprotomer structure.

Amino Acid Composition

Protein amino acid compositions are highly variable, with different frequencies and proportions of amino acids.
All proteins are formed from the same 20 amino acids, each coded by DNA during protein synthesis.
The average molecular weight of amino acids in proteins is approximately 128 Da, while the molecular weight of each amino acid residue is about 110 Da after peptide bond formation.

Amino Acid Nomenclature

Amino acids have common names often derived from their sources, e.g., asparagine from asparagus and glutamate from wheat gluten.
A three-letter abbreviation system is used for naming amino acids, starting with a capitalized first letter followed by two lowercase letters.

Acid-Base Properties of Amino Acids

Amino acids exist predominantly as zwitterions, possessing both positive and negative charges, balancing to a net charge of zero.
The physiological form of amino acids shifts with pH, impacting their acid-base behavior.
The isoelectric point (pI) of an amino acid is the pH at which the zwitterionic form predominates.

Secondary Protein Structures

Alpha (α) helices are coiled structures maintained by hydrogen bonds between C=O and N-H groups, extending outward with side chains.
Proline acts as a helix breaker due to its unique structure, disrupting α-helices.
Beta (β) pleated sheets consist of aligned protein chain segments held together by hydrogen bonds, resulting in a zigzag folding pattern with side chains alternating above and below the plane.

Protein Classification and Functions

Fibrous proteins, such as keratin and collagen, lack tertiary structures and are water-insoluble, providing structural functions.
Keratin exists as alpha-keratin (alpha-helical) in mammals and beta-keratin (twisted beta sheet) in birds and reptiles, with strength derived from disulfide bonds.
Collagen is known for its rigidity and structural role in connective tissues.

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Description

Explore the roles of ferritin and myoglobin in iron storage and oxygen transport. Understand the function of regulatory and nutrient proteins in enzymatic regulation and early development. This quiz is essential for students studying biochemistry and molecular biology.