Name: protein building blocks and folding
Uploaded: 2023-04-30T10:34:00.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-1

What are Proteins?

Une protéine est une chaîne d’acides aminés, des composés qui contiennent des groupes amines et carboxyles, ainsi que différentes chaînes latérales désignées R, attachées à un noyau de carbone.
Les acides aminés sont liés par des liaisons peptidiques covalentes, et la série répétitive d’atomes le long du noyau est appelée squelette polypeptidique.
La séquence commence à l’extrémité N, avec un groupe d’aminés libre, NH3<span style="color : rgb(0, 0, 0) ; font-family : Arial ; font-size : 13px ; font-style : normal ; font-variant-ligatures : normal ; font-variant-caps : normal ; font-weight : 400 ; letter-spacing : normal ; orphans : 2 ; text-align : left ; text-indent : 0px ; text-transform : none ; white-space : pre-wrap ; widows : 2 ; word-spacing : 0px ; -webkit-text-stroke-width : 0px ; background-color : rgb(255, 255, 255) ; text-decoration-thickness : initial; style-de-décoration-de-texte : initial ; text-decoration-color : initial ; display : inline !important ; flottant : aucun ; >+, et se termine par l’extrémité C, un groupe carboxyle libre, COO<span style="color : rgb(0, 0, 0) ; font-family : Arial ; font-size : 13px ; font-style : normal ; font-variant-ligatures : normal ; font-variant-caps : normal ; font-weight : 400 ; letter-spacing : normal ; orphans : 2 ; text-align : left ; text-indent : 0px ; text-transform : none ; white-space : pre-wrap ; widows : 2 ; word-spacing : 0px ; -webkit-text-stroke-width : 0px ; background-color : rgb(255, 255, 255) ; text-decoration-thickness : initial ; style-de-décoration-de-texte : initial ; text-decoration-color : initial ; display : inline !important ; flottant : aucun ; >-.
Chaque protéine est unique, en fonction du nombre d’acides aminés et de leurs chaînes latérales.
Il y a 20 chaînes latérales différentes, qui se répartissent en quatre groupes. Les acides aminés acides, comme les acides aspartique et glutamique, ont des chaînes latérales avec un groupe carboxyle. Pour cette raison, ils agissent comme des acides au pH physiologique.
Les acides aminés basiques ont un groupe amino dans leur chaîne latérale et agissent comme des bases.
Plusieurs acides aminés sont polaires mais non chargés. Ils ont tendance à être hydrophiles et constituent la partie externe d’une protéine repliée, où ils sont libres d’interagir avec l’environnement aqueux.
Enfin, un grand groupe d’acides aminés contient des chaînes latérales non polaires. Ils peuvent être simples, comme dans la glycine, ou complexes, comme la proline et le tryptophane.

que sont les protéines ?

Les protéines sont des polymères d'acides aminés liés entre eux par des liaisons peptidiques. Les protéines et les polypeptides sont utilisés de manière interchangeable pour désigner de longues chaînes d'acides aminés. Cependant, les polypeptides ont un poids moléculaire inférieur à 10 000 daltons, tandis que les protéines ont un poids moléculaire plus élevé. Les polypeptides contenant moins de 20 acides aminés sont appelés oligopeptides ou simplement peptides. Les interactions entre les chaînes latérales d’acides aminés constitutives des protéines les aident à se replier en une structure tridimensionnelle stable appelée structure native. La structure native d’une protéine est sa forme fonctionnellement active.

Les Résidus D’acides Aminés sont les Eléments Constitutifs des Protéines

Un acide aminé est une molécule qui contient un groupe carboxyle (–COOH), un groupe amino (–NH2), une chaîne latérale, appelée groupe R, et un atome d'hydrogène attaché au même atome de carbone ou au carbone α. Les propriétés chimiques du groupe R déterminent la structure finale de la protéine lorsqu'elles interagissent entre elles et avec les molécules d'eau polaires. Par exemple, l’acide aminé le plus simple, la glycine, possède un seul atome d’hydrogène comme groupe R. D'autres acides aminés portent des groupes R plus complexes, tels qu'ils peuvent attirer ou repousser l'eau (hydrophile ou hydrophobe), porter une charge négative (acide) ou positive (basique) et former des liaisons hydrogène (polaires).

L'identité de chaque acide aminé est également déterminée par son groupe R spécifique. Le code génétique eucaryote ne spécifie que 20 acides aminés utilisés dans la synthèse protéique de tous les acides aminés connus. Chacun de ces 20 acides aminés est représenté de manière unique par des abréviations utilisant un code à trois lettres (par exemple, Gly, Val, Pro) ou à une lettre (par exemple, G, V, P).

La synthèse des protéines est une réaction de déshydratation.

Au cours de la synthèse polypeptidique, des liaisons peptidiques covalentes se forment entre le groupe amino (groupe –NH2) d'un acide aminé et le groupe carboxyle (–COOH) de l'acide aminé adjacent en éliminant l'eau. La synthèse des protéines est une réaction de déshydratation. La liaison covalente résultante est une liaison peptidique. Le polypeptide nouvellement formé est constitué d’un groupe amino libre à une extrémité, appelé extrémité N-terminale, et d’un groupe carboxyle libre à l’autre extrémité, appelé extrémité C-terminale. La séquence d'acides aminés est toujours lue de l'extrémité N à l'extrémité C.

Le pH du milieu environnant détermine la fonction chimique des acides aminés.

Les acides aminés ont à la fois un groupe basique et un groupe acide. Ils peuvent donc agir comme une base (récepteur d’ions hydrogène) ou comme un acide (donneur d’ions hydrogène). Cependant, leur propriété chimique dépend du pH du milieu environnant. À faible pH (p. ex. pH 2), les groupes carboxyle et amino sont protonés (–NH3, –COOH), de sorte que l'acide aminé agit comme une base. À un pH alcalin (par exemple, pH 13), les groupes carboxyle et amino sont déprotonés (–NH2, –COO-) et l'acide aminé agira comme un acide. À un pH neutre (c'est-à-dire dans la plupart des environnements physiologiques, ~pH 7,4), le groupe amino est protoné (–NH3+) et le groupe carboxyle est déprotoné (–COO-), donnant naissance à un zwitterion, une molécule avec à la fois un charge positive et négative. Cette propriété chimique des acides aminés à pH physiologique leur permet de former des liaisons hydrogène avec le milieu aqueux environnant et contribue ainsi à des structures protéiques plus complexes.

Les protéines présentent une énorme diversité dans leur structure, leur composition et donc leur fonction. Ils aident à fournir un soutien structurel à la cellule (par exemple, sous forme de collagène), aident au mouvement cellulaire (par exemple, sous forme de protéines d'actine et de myosine dans les muscles), aident à catalyser les réactions biologiques (sous forme d'enzymes), transportent des molécules à travers la membrane cellulaire (sous forme de canaux) et défend les vertébrés contre les envahisseurs (sous forme d'anticorps).

Que sont les protéines ?

Les protéines sont des polymères d’acides aminés liés entre eux par des liaisons peptidiques. Les protéines et les polypeptides sont utilisés de manière interchangeable pour désigner de longues chaînes d’acides aminés ...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Protein Structure

Structure des protéines

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

protein building blocks and folding

Proteins are built from amino acids linked by peptide bonds. Long chains of amino acids are often called polypeptides, and the terms proteins and polypeptides are sometimes used the same way. In this context, polypeptides with a molecular weight below 10,000 daltons are called polypeptides, while proteins have a higher molecular weight. Very short chains with fewer than 20 amino acids are called peptides or oligopeptides.

Amino acids are the basic units of proteins. Each amino acid has a carboxyl group, an amino group, a hydrogen atom, and a side chain called the R-group attached to the same carbon, called the alpha-carbon. The R-group helps determine the amino acid’s identity and its chemical behavior. Some R-groups are hydrophilic or hydrophobic, some are acidic or basic, and some are polar and can form hydrogen bonds. Glycine is the simplest amino acid because its R-group is just a hydrogen atom. The eukaryotic genetic code uses 20 amino acids for protein synthesis, and each one has a three-letter code and a one-letter code.

Protein synthesis is a dehydration reaction. During polypeptide formation, the amino group of one amino acid reacts with the carboxyl group of the next amino acid. This reaction removes water and forms a covalent peptide bond. The growing chain has a free amino end called the N-terminus and a free carboxyl end called the C-terminus. Amino acid sequences are read from the N-terminus to the C-terminus.

The pH of the surrounding medium changes how amino acids behave chemically. At low pH, both the amino and carboxyl groups are protonated, so the amino acid acts as a base. At alkaline pH, both groups are deprotonated, and the amino acid acts as an acid. At about pH 7.4, which is close to most physiological conditions, amino acids exist as zwitterions. A zwitterion has both a positive and a negative charge. This helps amino acids form hydrogen bonds with water and supports more complex protein structures.

Proteins fold because the side chains of their amino acids interact with one another and with water. These interactions help create a stable three-dimensional native structure, which is the active form of the protein. Protein shape is closely tied to function. Proteins can provide structural support, as collagen does, help cells move, as actin and myosin do in muscles, speed up reactions as enzymes, move molecules across cell membranes as channels, and defend vertebrates against invaders as antibodies.

Protein Building Blocks and Folding

what are proteins?

Proteins are built from amino acids linked by peptide bonds. Long chains of amino acids are often called polypeptides, and the terms proteins and polypeptides are sometimes used the same way. In this context, polypeptides with a molecular weight below 10,000 daltons are called polypeptides, while proteins have a higher molecular weight. Very short chains with fewer than 20 amino acids are called peptides or oligopeptides. Amino acids are the basic units of proteins. Each amino acid has a...

protein organization

Protein Folding Levels and Bonds

Proteins are built from amino acids and folded into shapes that support many cell jobs. They help with DNA replication, molecular transport, catalysis, and structural support. Their function depends on how their amino acids are arranged and folded. Protein structure is organized in levels. The primary structure is the amino acid sequence in a polypeptide chain. Amino acids are joined by peptide bonds, and the chain has two ends: the amino terminus, or N-terminus, and the carboxyl terminus, or...

protein folding

How Amino Acid Sequence Shapes Proteins

Proteins get their shape from the order of amino acids in a polypeptide chain. After a protein is made, the chain folds into a three-dimensional form that is needed for it to work. The way amino acids interact with one another guides this folding. Protein structure matters because proteins do many jobs in cells. They can speed up chemical reactions, help with immune defense, store materials, carry substances, send cell signals, support movement, and provide structure. A protein usually works...

protein families

Protein Families and Superfamilies

Protein families and superfamilies group proteins with shared features. These groups help scientists organize proteins by common structure, function, or evolutionary history. The classification can show how related proteins are connected across different organisms. A protein family usually includes proteins that are closely related. A superfamily is a broader group that can include several families with more distant relationships. These categories help explain why some proteins share similar...

conservation of protein domains

Protein Domains Shared Across Proteins

Protein domains are shared structural and functional parts of proteins. A domain is a region that can often be found in more than one protein, even when the full proteins are different. This conservation means that a protein domain may keep a similar shape or role across related proteins. Because of that, scientists can compare proteins by looking for domains that stay the same. Conserved domains help reveal how proteins are related and how they may work. The topic of protein domain...

globular and fibrous proteins

Protein Shapes: Globular vs Fibrous

Proteins can have globular or fibrous shapes, and these shapes help explain how they work in the body. Globular proteins are compact and usually fold into rounded forms. Fibrous proteins are long, extended molecules that often provide support and structure. The shape of a protein is tied to its function. Globular proteins often take part in chemical jobs in cells, while fibrous proteins are better suited for strength and stability. These structural differences make the two groups easy to...

intrinsically disordered proteins

Flexible Protein Regions and Disorder

Intrinsically disordered proteins have flexible regions that do not settle into one fixed shape. Instead, these proteins can remain dynamic and change form as they move through the cell. This flexibility is an important part of their structure and function. Many proteins need a stable folded shape to work properly. Intrinsically disordered proteins are different because they may lack a single rigid structure under normal conditions. Their shifting shape can help them take part in cell...

protein complex assembly

Protein Complex Formation and Function

Protein complex formation explains how proteins join together to carry out specific jobs in cells. These groups are called protein complexes, and they can form in more than one way. Some complexes are homomeric, which means they contain the same kind of protein subunit. Others are heteromeric, which means they contain different protein subunits. The assembly process helps show how protein shape and subunit choice affect function. When proteins combine, the resulting complex can behave...

conjugated proteins

Conjugated Proteins and Their Bound Groups

Conjugated proteins are proteins that include a nonprotein part called a prosthetic group. This added group helps give the protein its full structure or function. The video explains how the protein part and the bound group work together. Several common types of conjugated proteins are named by the kind of group attached. Nucleoproteins contain nucleic acids. Glycoproteins contain carbohydrate groups, and lipoproteins contain lipid groups. Other examples include phosphoproteins, which have...

amyloid fibrils

Amyloid Fibrils and Protein Aggregation

Amyloid fibrils are protein aggregates with a very specific structure. They are made when proteins misfold and stick together in long, ordered fibers. This structure makes them different from many other protein clumps. Amyloid fibrils are important in biology because they are linked to protein aggregation. Protein aggregation means proteins build up into groups instead of staying properly folded and separate. In many cases, this process is associated with disease and abnormal cell function. <br...

key terms and concepts

Learn how amino acids join to form proteins, how peptide bonds work, and how pH and side-chain interactions shape protein structure and function.

Protein Building Blocks and Folding | JoVE K12

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HS-LS1-2

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HS-LS1-3

Protein Building Blocks and Folding

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