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Chapter 15: Problem 88

What is the key structural difference between fibrous and globular proteins? How is it related, in general, to the proteins' amino acid composition?

Short Answer

Expert verified
Fibrous proteins are elongated and provide structural support, while globular proteins are compact and functional. This difference stems from their amino acid composition and how they fold.

Step by step solution

01

Understand Fibrous Proteins

Fibrous proteins are elongated, rope-like structures that provide structural support and strength. They are typically found in connective tissues, tendons, and keratin in hair and nails.
02

Understand Globular Proteins

Globular proteins are compact, spherical proteins that are soluble in water. They function in catalysis (as enzymes), transport (like hemoglobin), and regulation (such as hormones).
03

Compare Structural Differences

The key structural difference is that fibrous proteins have long, linear chains that align parallel to each other, whereas globular proteins have chains that fold into a compact, spherical shape.
04

Connect to Amino Acid Composition

Fibrous proteins often contain repetitive amino acid sequences that allow for the formation of extended structures, while globular proteins have a diverse range of amino acid sequences that enable the protein to fold into a specific three-dimensional shape.
05

Summarize the Relationship

In summary, the structurally elongated nature of fibrous proteins versus the compact structure of globular proteins is directly related to their amino acid sequences and the interactions among those amino acids.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fibrous Proteins
Fibrous proteins have an elongated, thread-like structure, giving them a rope-like appearance. These proteins primarily provide structural support and strength within various biological materials.
Examples of fibrous proteins include:
  • Collagen: found in connective tissues
  • Keratin: present in hair, nails, and the outer layer of skin
  • Elastin: which helps tissues to resume their shape after stretching or contracting

Fibrous proteins are generally insoluble in water and more resistant to changes in temperature and pH. This sturdiness makes them ideal for their structural roles.
Globular Proteins
Globular proteins are compact and spherical in shape. Unlike fibrous proteins, they are usually water-soluble due to their hydrophilic outer surfaces.
Globular proteins perform various functions in the body, such as:
  • Enzymes: catalyze biochemical reactions
  • Transport proteins: like hemoglobin, which transports oxygen in the blood
  • Regulatory proteins: such as hormones that control various physiological processes

Because of their solubility and mobility, globular proteins play critical roles in metabolism and regulation of cellular processes.
Amino Acid Composition
The amino acid composition of a protein influences its overall structure and function.
In fibrous proteins, the amino acids are often repetitive, creating long, linear chains that align parallel to each other. This alignment allows for the formation of sturdy, extended structures.
In globular proteins, the amino acid sequences are more varied. These sequences enable the protein chains to fold into specific three-dimensional shapes necessary for their diverse functions.
Hence, the arrangement and variety of amino acids are key to the functional capabilities and physical form of the proteins.
Protein Structure
The structure of proteins is essential to their function and can be divided into four levels:
  • Primary structure: the linear sequence of amino acids in the polypeptide chain
  • Secondary structure: regular, repeating structures formed by hydrogen bonds, such as alpha-helices and beta-pleated sheets
  • Tertiary structure: the overall three-dimensional shape of a single protein molecule, formed by interactions between the side chains of amino acids
  • Quaternary structure: the arrangement of multiple protein molecules or polypeptide chains in a multi-subunit complex

These structures dictate how proteins interact with other molecules and carry out their respective functions.
Protein Function
Proteins are vital for numerous biological functions and their roles can be broadly categorized into:
  • Structural: providing support in cells and tissues (e.g., collagen, keratin)
  • Enzymatic: speeding up chemical reactions (e.g., digestive enzymes)
  • Transport: moving molecules across cell membranes and throughout the body (e.g., hemoglobin)
  • Regulatory: controlling processes like gene expression and cellular signaling (e.g., hormones, transcription factors)
  • Defense: protecting the organism from pathogens (e.g., antibodies)

The specific structure of a protein enables it to perform its unique function effectively. Changes in structure, often due to mutations or environmental factors, can disrupt protein function and lead to diseases.

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Most popular questions from this chapter

Draw the organic product formed when the following compounds undergo a substitution reaction: (a) acetic acid and 1-hexanol; (b) propanoic acid and dimethylamine; (c) ethanoic acid and diethylamine.

Other nonmetals form compounds that are structurally analogous to those of carbon, but these inorganic compounds are usually more reactive. Predict any missing products and write balanced equations for each reaction: (a) the decomposition and chlorination of diborane to boron trichloride; (b) the combustion of pentaborane \(\left(\mathrm{B}_{5}\mathrm{H}_{9}\right)\) in \(\mathrm{O}_{2} ;\) (c) the hydrolysis of trisilane \(\left(\mathrm{Si}_{3} \mathrm{H}_{8}\right)\) to silica \(\left(\mathrm{SiO}_{2}\right)\) and \(\mathrm{H}_{2} ;\) (d) the complete halogenation of disilane with \(\mathrm{Cl}_{2} ;\) (e) the thermal decomposition of \(\mathrm{H}_{2} \mathrm{~S}_{5}\) to hydrogen sulfide and sulfur molecules; (f) the hydrolysis of \(\mathrm{PCl}_{5}\).

Polyethylene terephthalate (PET) is used to make synthetic fibers, such as Dacron; thin films, such as Mylar; and bottles for carbonated beverages. PET is produced from ethylene glycol and either of two monomers, depending on whether the reaction proceeds by dehydration-condensation or by displacement. Write equations for the two syntheses. (Hint: The displacement is reversed by adding methanol to PET at high \(T\) and \(P .\) )

The polypeptide chain in proteins does not exhibit free rotation because of the partial double-bond character of the peptide bond. Explain this fact with resonance structures.

Which compounds exhibit geometric isomerism? Draw and name the two isomers in each case: (a) propene (b) 3 -hexene (c) 1,1 -dichloroethene (d) 1,2 -dichloroethene
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