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?

Una proteina è una catena di amminoacidi, composti che contengono gruppi amminici e carbossilici, insieme a diverse catene laterali denominate R, attaccate a un nucleo di carbonio.
Gli amminoacidi sono legati attraverso legami peptidici covalenti e la serie ripetuta di atomi lungo il nucleo è chiamata spina dorsale polipeptidica.
La sequenza inizia all'N-terminale, con un gruppo amminico libero, NH3<span style="color: rgb(0, 0, 0); famiglia di caratteri: Arial; dimensione del carattere: 13px; stile del carattere: normale; legature-varianti-del carattere: normale; maiuscole varianti del carattere: normale; peso del carattere: 400; spaziatura delle lettere: normale; orfani: 2; allineamento del testo: sinistra; rientro del testo: 0px; trasformazione del testo: nessuno; spazio bianco: pre-involucro; vedove: 2; spaziatura delle parole: 0px; -webkit-larghezza-tratto-testo: 0px; colore di sfondo: rgb(255, 255, 255); spessore-decorazione-testo: iniziale; stile-decorazione-testo: iniziale; testo-decorazione-colore: iniziale; Display: in linea !important; galleggiante: nessuno;" >+, e termina con il capolinea C, un gruppo carbossilico libero, COO<span style="color: rgb(0, 0, 0); famiglia di caratteri: Arial; dimensione del carattere: 13px; stile del carattere: normale; legature-varianti-del carattere: normale; maiuscole varianti del carattere: normale; peso del carattere: 400; spaziatura delle lettere: normale; orfani: 2; allineamento del testo: sinistra; rientro del testo: 0px; trasformazione del testo: nessuno; spazio bianco: pre-wrap; vedove: 2; spaziatura delle parole: 0px; -webkit-larghezza-del tratto-testo: 0px; colore di sfondo: rgb(255, 255, 255); spessore-decorazione del testo: iniziale; stile-decorazione-testo: iniziale; testo-decorazione-colore: iniziale; Display: in linea !important; galleggiante: nessuno;" >-.
Ogni proteina è unica, a seconda del numero di aminoacidi e delle loro catene laterali.
Ci sono 20 diverse catene laterali, che rientrano in uno dei quattro gruppi. Gli amminoacidi acidi, come l'acido aspartico e l'acido glutammico, hanno catene laterali con un gruppo carbossilico. Per questo motivo, agiscono come acidi a pH fisiologico.
Gli amminoacidi basici hanno un gruppo amminico nella loro catena laterale e agiscono come basi.
Diversi amminoacidi sono polari ma non sono carichi. Tendono ad essere idrofili e costituiscono la porzione esterna di una proteina ripiegata, dove sono liberi di interagire con l'ambiente acquoso.
Infine, un ampio gruppo di amminoacidi contiene catene laterali non polari. Possono essere semplici, come la glicina, o complessi, come la prolina e il triptofano.

cosa sono le proteine?

Le proteine sono polimeri di amminoacidi legati tra loro da legami peptidici. Proteine e polipeptidi sono usati in modo intercambiabile per riferirsi a lunghe catene di amminoacidi. Tuttavia, i polipeptidi hanno un peso molecolare inferiore a 10.000 dalton, mentre le proteine hanno un peso molecolare maggiore. I polipeptidi con meno di 20 aminoacidi sono chiamati oligopeptidi o semplicemente peptidi. Le interazioni tra le catene laterali degli aminoacidi costituenti delle proteine le aiutano a ripiegarsi in una struttura tridimensionale stabile chiamata struttura nativa. La struttura nativa di una proteina è la sua forma funzionalmente attiva.

I residui di aminoacidi sono gli elementi costitutivi delle proteine

Un amminoacido è una molecola che contiene un gruppo carbossilico (–COOH), un gruppo amminico (–NH2), una catena laterale, chiamata gruppo R, e un atomo di idrogeno attaccato allo stesso atomo di carbonio o al carbonio α. Le proprietà chimiche del gruppo R determinano la struttura finale della proteina poiché interagiscono tra loro e con le molecole di acqua polare. Ad esempio, l'amminoacido più semplice, la glicina, ha un singolo atomo di idrogeno come gruppo R. Altri amminoacidi portano gruppi R più complessi in modo tale che possano attrarre o respingere l'acqua (idrofili o idrofobici), portare una carica negativa (acida) o una carica positiva (basica) e formare legami idrogeno (polari).

L'identità di ciascun amminoacido è determinata anche dal suo specifico gruppo R. Il codice genetico eucariotico specifica solo 20 aminoacidi utilizzati nella sintesi proteica di tutti gli aminoacidi conosciuti. Ciascuno di questi 20 amminoacidi è rappresentato in modo univoco da abbreviazioni che utilizzano un codice di tre lettere (ad esempio, Gly, Val, Pro) o una lettera (ad esempio, G, V, P).

La sintesi delle proteine è una reazione di disidratazione.

Durante la sintesi polipeptidica, si formano legami peptidici covalenti tra il gruppo amminico (gruppo –NH2) di un amminoacido e il gruppo carbossilico (–COOH) dell’amminoacido adiacente rimuovendo l’acqua. La sintesi delle proteine è una reazione di disidratazione. Il legame covalente risultante è un legame peptidico. Il polipeptide appena formato è costituito da un gruppo amminico libero ad un'estremità, chiamato N-terminale, e un gruppo carbossilico libero all'altra estremità, chiamato C-terminale. La sequenza aminoacidica viene sempre letta dal terminale N al terminale C.

Il pH del mezzo circostante determina la funzione chimica degli amminoacidi.

Gli amminoacidi hanno sia un gruppo basico che uno acido. Possono quindi agire come una base (ricevitore di ioni idrogeno) o come un acido (donatore di ioni idrogeno). Tuttavia, le loro proprietà chimiche dipendono dal pH del mezzo circostante. A pH basso (ad esempio pH 2), sia il gruppo carbossilico che quello amminico sono protonati (–NH3, –COOH), quindi l'amminoacido agisce come una base. A un pH alcalino (ad esempio pH 13), sia i gruppi carbossilici che quelli amminici sono deprotonati (–NH2, –COO-) e l'amminoacido agirà come un acido. A pH neutro (ovvero, nella maggior parte degli ambienti fisiologici, ~pH 7,4), il gruppo amminico viene protonato (–NH3+) e il gruppo carbossilico viene deprotonato (–COO-), dando origine a uno zwitterione, una molecola con sia un carica positiva e negativa. Questa proprietà chimica degli amminoacidi a pH fisiologico consente loro di formare legami idrogeno con l'ambiente acquoso circostante e contribuisce quindi a strutture proteiche più complesse.

Le proteine mostrano un’enorme diversità nella loro struttura, composizione e, quindi, nella loro funzione. Aiutano a fornire supporto strutturale alla cellula (ad esempio, sotto forma di collagene), assistono nel movimento cellulare (ad esempio, sotto forma di proteine di actina e miosina nei muscoli), aiutano a catalizzare le reazioni biologiche (come enzimi), trasportano le molecole attraverso la membrana cellulare (come canali) e difende i vertebrati dagli invasori (come anticorpi).

Cosa sono le proteine?

Le proteine sono polimeri di amminoacidi legati tra loro da legami peptidici. Proteine e polipeptidi sono usati in modo intercambiabile per riferirsi a lunghe catene di ammino ...

Education

Didattica

JoVE Core

Cell Biology

Biologia cellulare

Unit 1

Unità 1

Protein Structure

Struttura delle proteine

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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Proteins: From Genes to Degradation

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protein-complexes-with-interchangeable-parts

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Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

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Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.]

HS-LS1-3

Protein Building Blocks and Folding

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