Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 18: Problem 33

What is a polypeptide? How does it differ from a protein?

Short Answer

Expert verified
A polypeptide is a linear chain of amino acids linked together by peptide bonds, formed during the protein translation process. In contrast, a protein is a large, complex biomolecule made up of one or more polypeptide chains that have folded into a specific 3D structure and perform various functions in the body. The main differences between polypeptides and proteins are their structure, size, functionality, and complexity, with proteins being more complex and functionally diverse than polypeptides.

Step by step solution

01

Definition of a Polypeptide

A polypeptide is a linear chain of amino acids linked together by peptide bonds. It is the product of the protein translation process that occurs inside the ribosomes. Polypeptides have a specific sequence of amino acids, which is determined by the sequence of nucleotides in the mRNA (messenger RNA) that is being translated.
02

Definition of a Protein

A protein is a large, complex biomolecule made up of one or more polypeptide chains that have a specific 3D structure. Proteins perform a variety of functions in the body, such as structural support, catalysis of chemical reactions, transport of molecules, signaling, and immune defense. The function of a protein is largely determined by its 3D structure, which results from the specific folding and interactions of the amino acids within the polypeptide chains.
03

Differences Between Polypeptides and Proteins

There are several key differences between polypeptides and proteins: 1. Structure: A polypeptide is a linear chain of amino acids, while a protein is composed of one or more polypeptide chains that have folded into a specific 3D structure. 2. Size: Polypeptides can range in size from a few amino acids to hundreds of them, while proteins generally consist of larger polypeptide chains and often have multiple chains interacting with each other. 3. Functionality: Polypeptides may not be fully functional on their own, whereas proteins have specific functions in the body, such as catalysis, transport, or signaling. 4. Complexity: Proteins are more complex than polypeptides, as they consist of folded polypeptide chains, sometimes with additional prosthetic groups or modifications, and can participate in a wide range of biological activities. In summary, a polypeptide is a linear chain of amino acids, while a protein is a complex, functional biomolecule consisting of one or more folded polypeptide chains. The main differences between them lie in their structure, size, functionality, and complexity.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

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

Polypeptide Definition
A polypeptide is essentially a string of amino acids bound together by peptide bonds. It's the outcome of the protein translation process that decodes the genetic instructions carried by mRNA inside the cellular factories known as ribosomes. Each polypeptide has a unique amino acid sequence, dictated by the nucleotide sequence of the mRNA it translates, serving as the blueprints for constructing these biochemical chains.

Think of polypeptides as the initial draft or the raw material that will eventually fold and twist into a functional protein, much like a chain of paperclips can be bent and shaped into a sculpture.
Protein Structure
Proteins are the architects of biology, crafting the complex molecular structures that sustain life. Their structure can be described at four levels: primary, corresponding to the linear amino acid sequence; secondary, which includes alpha-helices and beta-pleated sheets; tertiary, the overall three-dimensional shape of a single polypeptide chain; and quaternary, how multiple polypeptides fit together.

Their design is not random but intricately organized to allow proteins to carry out a symphony of cellular tasks with precision. This biological origami is essential because a protein's function is intimately tied to its structure.
Amino Acids Sequence

The Alphabet of Life

Just as letters form words, amino acids are the building blocks that align to craft polypeptides. The sequence is vital: each position held by a specific amino acid impacts the polypeptide's properties and its eventual function as a protein. These sequences are not just strings of beads; they are encoded life instructions, detailing the recipes for proteins that will conduct a myriad of biological functions.
Protein Functions
Proteins are the doers in the cell; they're involved in practically every process within an organism. From acting as catalysts (enzymes) that speed up chemical reactions, to offering structural support (like collagen in your skin), transporting vital molecules (like hemoglobin), sending and receiving signals (like insulin), to defending the body against invaders (antibodies), proteins are indisputably versatile.

They're not just specialty tools; they're the multitools of molecular biology, with an elaborate toolkit suited for an endless array of functional outcomes.
Peptide Bonds
The peptide bond is the thread that sews amino acids into the tapestry of polypeptides. They are the chemical links formed between the carboxyl group of one amino acid and the amine group of another. This bond is a type of covalent bond, it's as if the amino acids are shaking hands, joining forces to create a longer and stronger entity. Each bond is a commitment, ensuring that the amino acid sequence is maintained, setting the stage for the protein's eventual role in the cellular drama.
Protein Translation

The Cellular Production Line

Imagine the cell as a high-tech factory where protein translation is a key production process. It's here that ribosomes read the mRNA, a molecular messenger carrying genetic instructions, and translate this genetic script into polypeptides. Translation is a meticulous and rapid process, involving various helpers like tRNA and enzymes, to ensure that the language of nucleic acids is accurately converted into the language of proteins.
mRNA in Protein Synthesis
mRNA serves as the intermediary between the genetic library (DNA) and the cellular machinery. It delivers the genetic code from the nucleus to the ribosome, where protein synthesis comes to life. This translation from nucleotide sequence to amino acid sequence is directed by mRNA, dictating which building blocks are assembled to form the polypeptide. It's the template, ensuring that each protein is constructed according to the master plan encoded within the organism's DNA.
3D Structure of Proteins
The 3D structure of proteins is less like static statues and more like dynamic machines changing shape to perform tasks. They can be globular, like enzymes that are geared to speed up reactions, or fibrous, providing scaffolding for cells. The final shape a protein takes is crucial — it determines how it interacts with other molecules. This three-dimensional form is determined during the process of protein folding, where the polypeptide chain crumples into a specific shape guided by its amino acid sequence and helped by molecular chaperones.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Nylon fabric owes much of its strength to the formation of hydrogen bonds between the polymer chains. Suppose functional groups \(\bar{A}\) and \(\mathrm{B}\) bond covalently with each other. Draw two different monomers that can form a polymer in which the interchain attractive forces are stronger than those in nylon. (Hint: Each of your monomers can contain all A, all B, or any number of A combined with any number of B.)

In an amino acid, a carbon atom bound directly to the carbonyl carbon of the acid function is called the alpha carbon \((\alpha\) -carbon \() .\) Draw glycine, point out the \(\alpha\) -carbon, and then explain why all 20 amino acids used to build human proteins are called \(\alpha\) -amino acids. Then draw the simplest \(\beta\) -amino acid.

In the olden days (the \(1970 \mathrm{~s})\), the sequence of amino acids in a protein was determined by running a series of chemical reactions known as the Edman degradation. This technique worked only on short peptide chains, however, and large proteins had to be broken down into small parts in order to be sequenced. One way to chop large proteins into small chains was with enzymes known as proteases. The protease trypsin breaks the amide bond on the \(\mathrm{CO}_{2} \mathrm{H}\) side of arginine and lysine, and the protease chymotrypsin breaks the amide bond on the \(\mathrm{CO}_{2} \mathrm{H}\) side of tyrosine, phenylalanine, and tryptophan. An octapeptide treated with trypsin breaks down to the peptides Ala-Gly-Trp-Gly-Lys and Thr-Val-Lys, and the same octapeptide treated with chymotrypsin breaks down to the peptides Gly-Lys and Thr-Val-Lys-Ala-Gly-Trp. What is the sequence of the octapeptide?

What two peptides are possible from the combination of alanine and glycine? Draw both of them.

What is a polymer? How does it differ from a monomer?
See all solutions

Recommended explanations on Chemistry Textbooks

Kinetics

Read Explanation

Chemical Reactions

Read Explanation

Chemistry Branches

Read Explanation

Organic Chemistry

Read Explanation

Physical Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free