Name: how protein shape determines function
Uploaded: 2023-04-30T18:28:47.000Z
Duration: 2 min 15 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

Protein and Protein Structures

As proteínas são polímeros de aminoácidos ligados entre si através de ligações de peptídeo. A maioria das proteínas dobra-se em específicas estruturas tridimensionais para desempenharem a sua função. A estrutura proteica é classificada em quatro categorias:primária, secundária, terciária, e quaternária.A sequência linear dos aminoácidos na proteína é a sua estrutura primária. Estas sequências são lidas na ordem de síntese dos polímeros, do terminal N, na extremidade do amino livre, para o terminal C, na extremidade carboxil livre. Forma de estruturas secundárias através da ligação de hidrogénio entre o oxigénio do grupo carbonilo de um aminoácido e o hidrogénio do grupo de aminoácidos de outro.Estruturas secundárias comuns incluem hélices α-e folhas plissadas β-Estas e outras estruturas de ligações, tais como voltas β-interagem ainda mais para formar o tridimensional da proteína conhecida como a estrutura terciária. A formação da estrutura terciária ocorre devido às interações entre os grupos R dos aminoácidos. Os grupos R com cargas opostas podem formar ligações iónicas, e o enxofre em duas cisteínas pode formar uma ponte de dissulfureto covalente.Outros colaboradores incluem interações hidrofóbicas entre as cadeias laterais hidrofóbicas e as ligações de hidrogénio entre as cadeias laterais polares. Além disso, algumas proteínas formam estruturas quaternárias, montagens de duas ou mais cadeias de polipeptídios. Por exemplo, a hemoglobina é uma proteína composta de quatro subunidades, duas α e duas β.Os cientistas podem utilizar o estrutura de uma proteína para prever a sua função e localização numa célula. As proteínas no citoplasma da célula têm aminoácidos hidrofílicos nas suas superfícies que interagem com a água no citoplasma e têm núcleos hidrofóbicos. Em contraste, as proteínas presente nas membranas celulares têm frequentemente aminoácidos hidrófobos na superfície que interagem com glicerofosfolípidos na membrana e têm núcleos hidrofílicos.

<ol>
	<li>Nelson, D. L., & Cox, M. M. (2008). Princípios de bioquímica de Lehninger (5ª ed.). W.H. Freeman. Pág. 113-140</li>
	<li>Estrutura cristalina da hemoglobina do estado T com oxigênio ligado em todos os quatro hems.Paoli, M., Liddington, R., Tame, J., Wilkinson, A., Dodson, G. (1996) J Mol Biol 256: 775</li>
</ol>

proteínas e estruturas proteicas

As proteínas são uma das moléculas orgânicas mais abundantes em sistemas vivos e têm a mais diversa gama de funções de todas as macromoléculas. As proteínas podem ser estruturais, regulatórias, contráteis, ou protetoras. Podem servir em transporte, armazenamento, ou membranas; ou podem ser toxinas ou enzimas. As suas estruturas, como as suas funções, variam muito. Todas elas são, no entanto, polímeros de aminoácidos dispostos em sequência linear.
A forma de uma proteína é crítica para a sua função. Por exemplo, uma enzima pode ligar um substrato específico no seu local ativo. Se este local ativo for alterado devido a alterações locais ou alterações na estrutura global das proteínas, a enzima pode não ser capaz de se ligar ao substrato. Para entender como a proteína recebe a sua forma ou conformação final, precisamos entender os quatro níveis de estrutura proteica: primária, secundária, terciária, e quaternária.
Estrutura Primária
A sequência única dos aminoácidos em uma cadeia polipeptídica é a sua estrutura primária. Por exemplo, a hormona pancreática insulina tem duas cadeias de polipeptídeos, A e B, e elas estão ligadas entre si por ligações de dissulfeto. O aminoácido do terminal N da cadeia A é a glicina; enquanto que o aminoácido do terminal C é a asparagina.  As sequências de aminoácidos nas cadeias A e B são exclusivas da insulina.
O gene que codifica a proteína determina, em última análise, a sequência única para cada proteína. Uma alteração na sequência de nucleótidos da região codificante do gene pode levar à adição de um aminoácido diferente à cadeia polipeptídica em crescimento, causando uma alteração na estrutura e função das proteínas. Na anemia falciforme, a cadeia β da hemoglobina apresenta uma única substituição de aminoácidos, causando uma alteração na estrutura e função proteicas. Especificamente, a valina na cadeia β substitui o aminoácido ácido glutâmico. Devido a esta alteração de um aminoácido na cadeia, as moléculas de hemoglobina formam fibras longas que distorcem as células sanguíneas bicôncavas, ou em forma de disco, vermelhas, e fazem com que elas assumam uma forma de lua crescente ou de “foice”, que obstrui os vasos sanguíneos. Isto pode conduzir a uma miríade de problemas sérios de saúde tais como falta de ar, tonturas, dores de cabeça, e dor abdominal para aqueles afetados por esta doença.
Estrutura Secundária
O enovelamento local do polipeptídeo em algumas regiões dá origem à estrutura secundária da proteína. As mais comuns são as estruturas de folha em α-hélice e β-pregueada. Ambas as estruturas mantêm a sua forma através de ligações de hidrogénio. As ligações de hidrogénio formam-se entre o átomo de oxigénio no grupo carbonilo em um aminoácido e outro aminoácido que está quatro aminoácidos mais longe ao longo da cadeia.
Cada dobra helicoidal em uma hélice alfa tem 3,6 resíduos de aminoácidos. Os grupos R do polipeptídeo (os grupos de variantes) projetam-se para fora da cadeia de α-hélice. Na folha β-pregueada, as ligações de hidrogénio entre átomos no esqueleto da cadeia polipeptídica formam as "pregas". Os grupos R estão ligados aos carbonos e estendem-se por cima e por baixo das dobras da prega. Os segmentos pregueados alinham-se de forma paralela ou antilparalela entre si, e as ligações de hidrogénio formam-se entre o átomo de hidrogénio parcialmente positivo no grupo amino e o átomo de oxigénio parcialmente negativo no grupo carbonilo do esqueleto do polipeptídeo. As estruturas das folhas em α-hélice e β-pregueadas estão na maioria das proteínas globulares e fibrosas, e desempenham um papel estrutural importante.
Estrutura Terciária
A estrutura tridimensional única do polipeptídeo é a sua estrutura terciária. Esta estrutura deve-se em parte a interações químicas sobre a cadeia polipeptídica. Principalmente, as interações entre os grupos R criam a complexa estrutura terciária tridimensional da proteína. A natureza dos grupos R nos aminoácidos envolvidos pode neutralizar a formação das ligações de hidrogénio que descrevemos para estruturas secundárias padrão. Por exemplo, grupos R com cargas semelhantes repelem-se uns aos outros, e aqueles com cargas diferentes são atraídos uns para os outros (ligações iónicas). Quando ocorre o enovelamento de proteínas, os grupos R hidrofóbicos dos aminoácidos não polares encontram-se no interior da proteína; enquanto isso, os grupos R hidrofílicos ficam no exterior. As interações entre as cadeias laterais da cisteína formam ligações de dissulfeto na presença de oxigénio, o único elo covalente que se forma durante o enovelamento de proteínas.
Todas essas interações, fracas e fortes, determinam a forma tridimensional final da proteína. Quando uma proteína perde a sua forma tridimensional, pode não ser mais funcional. 
Estrutura Quaternária
Na natureza, algumas proteínas formam-se a partir de vários polipeptídeos, ou subunidades, e a interação dessas subunidades forma a estrutura quaternária. Interações fracas entre as subunidades ajudam a estabilizar a estrutura geral. Por exemplo, a insulina (uma proteína globular) tem uma combinação de ligações de hidrogénio e de dissulfeto que fazem com que ela se compacte principalmente em uma forma de bola. A insulina começa como um único polipeptídeo e perde algumas sequências internas na presença de modificação pós-translacional após formar as ligações de dissulfeto que mantêm as cadeias restantes juntas. A seda (uma proteína fibrosa), no entanto, tem uma estrutura de folha β-pregueada que é o resultado de ligações de hidrogénio entre as diferentes cadeias.
Este texto foi adaptado de <a href="https://openstax.org/books/biology-2e/pages/3-4-proteins">Openstax, Biology 2e, Chapter 3.4: Proteins</a>.

Proteínas e Estruturas Proteicas

As proteínas são uma das moléculas orgânicas mais abundantes nos sistemas vivos e têm a mais diversificada gama de funções de todas as macromoléculas. As proteínas podem ...

Education

JoVE Core

Cell Biology

Biologia Celular

Unit 1

Unidade 1

Biochemistry of the Cell

Bioquímica da Célula

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

how protein shape determines function

Proteins are essential molecules in living things, and their shape affects how they work. Protein structure is described at several levels, including primary, secondary, tertiary, and quaternary structure. These levels help explain how a protein is built and how its final form supports its job.

Primary structure is the sequence of amino acids in a protein. Secondary structure forms when parts of the chain fold into regular patterns. Tertiary structure is the overall three-dimensional shape of one protein chain. Quaternary structure appears when more than one protein chain joins together to make a working protein.

The video also shows how protein structure can be represented in different ways. A simple line drawing can show the amino acid sequence. Other models can show folding and the full 3D shape. These visual forms help students compare levels of structure and see why protein shape matters.

How Protein Shape Determines Function

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Elements in the Human Body and Periodic Table

Elements are the smallest units of matter that cannot be broken down further by chemical processes. Scientists know 118 elements, but not all of them occur naturally. Only a small number are essential for life, and living matter depends mostly on carbon, nitrogen, hydrogen, and oxygen. The periodic table organizes elements by their physical and chemical properties. Each square shows the element name, chemical symbol, atomic number, and atomic weight. The atomic number is the number of protons...

functional groups

Functional Groups in Organic Molecules

Functional groups are the part of an organic molecule that gives it specific chemical behavior. They help explain why compounds with similar carbon skeletons can react in different ways. In organic chemistry, these groups are often used to classify compounds. A functional group can change the properties of a molecule and affect how it behaves in a reaction. Knowing functional groups helps students recognize patterns in organic compounds. It also makes it easier to compare molecules that share...

types of chemical bonds

Chemical Bonds and How Atoms Join

Chemical bonds hold atoms together and help explain how different substances form. In chemistry, the main bond types are ionic bonds, covalent bonds, and metallic bonds. Ionic bonds form when electrons move from one atom to another. Covalent bonds form when atoms share electrons. Metallic bonds occur in metals, where electrons are held in a shared arrangement that gives metals their characteristic behavior. Understanding these bond types helps students compare how atoms connect in different...

noncovalent attractions in biomolecules

Biomolecule Interactions Without Covalent Bonds

Biomolecules often stay together through noncovalent attractions instead of covalent bonds. These weaker interactions help molecules recognize each other and form structures needed for life. The main noncovalent attractions are hydrogen bonds, electrostatic interactions, van der Waals forces, and hydrophobic interactions. Each one works in a different way, but all of them can influence how biomolecules fold, bind, and behave in cells. Hydrogen bonds form when a hydrogen atom is attracted to...

polymers

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what are lipids?

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structure of lipids

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chemistry of carbohydrates

Carbohydrate Structure and Bonding

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protein and protein structures

Proteins are essential molecules in living things, and their shape affects how they work. Protein structure is described at several levels, including primary, secondary, tertiary, and quaternary structure. These levels help explain how a protein is built and how its final form supports its job. Primary structure is the sequence of amino acids in a protein. Secondary structure forms when parts of the chain fold into regular patterns. Tertiary structure is the overall three-dimensional shape of...

ph regulation in cells

Cell pH and Organelle Balance

Cell pH and organelle balance are essential for normal cell function. pH affects protein shape and activity, the charge on cell membranes, and many metabolic reactions inside the cell. Cells also use the proton motive force, which is the energy stored in a proton gradient, to make ATP, the cell’s main energy molecule. The cytosol, or fluid inside the cell, is usually slightly more acidic than the fluid outside the cell. Even so, cells must stop the cytosol from becoming too acidic. They use...

chemistry of the cell

Cell Chemistry: Water, Ions, and Molecules

Cell chemistry explains the substances that make cells work. Water is the main component of cells, and it supports the chemical reactions that keep life going. Cells also contain organic molecules, which are carbon-based compounds, and inorganic ions, which are charged particles needed for cell function. Organic molecules in cells include carbohydrates, lipids, proteins, and nucleic acids. These molecules have different roles, but together they build cell structures, store energy, and carry...

key terms and concepts

Learn how proteins are built and folded through primary, secondary, tertiary, and quaternary structure, and how protein shape affects function.

How Protein Shape Determines Function | JoVE K12

cell biology

JoVE Core - Biologia Celular ilustra processos celulares complexos em vídeos de animação fáceis de entender e, ao mesmo tempo, abrangentes. Esta coleção foca nos componentes e funções essenciais das células, incluindo organelas e membranas, transporte celular e energia celular. É complementado por vídeos de Cientistas em ação que demonstram a aplicação da biologia celular em experimentos de pesquisa do mundo real.

Florida Department of Education

SC.912.L.18

SC.912.L.18.1

SC.912.L.18.4

new-york-state-science-learning-standards

New York State Science Learning Standards

Structure and Function

HS-LS1-1.

Georgia Standards of Excellence

9-12

Biology

SB6.c

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

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Cell Structure

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Cytoplasm

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The Nucleus

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The Central Dogma

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Nucleic Acids

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Globular and Fibrous Proteins

Translation

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Intrinsically Disordered Proteins

Ribosomes

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Protein Complex Assembly

Conjugated Proteins

Proteins: From Genes to Degradation

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Protein-Protein Interfaces

Protein Folding

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Conserved Binding Sites

Cofactors and Coenzymes

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Cooperative Allosteric Transitions

Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

protein-complexes-with-interchangeable-parts

Protein Complexes with Interchangeable Parts

Mechanical Protein Function

Structural Protein Function

Protein Networks

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

Levels of Organization

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Anatomy of the Intestines

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Lipid Digestion

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Protein Digestion

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Carbohydrate Digestion

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What is a Nervous System?

Overview

The nervous system is the collection of specialized cells responsible for maintaining an organism&rsquo;s internal environment and coordinating ...

The Parasympathetic Nervous System

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The Sympathetic Nervous System

Overview

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Fertilization

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What is the Skeletal System?

Overview

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An Introduction to the Zebrafish: Danio rerio

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Physiology of the Circulatory System

Homeostasis
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Anatomy of the Circulatory System

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Anatomy of the Heart

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Measuring Circulatory System Function in Humans
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Blood Flow

Blood is pumped by the heart into the aorta, the largest artery in the body, and then into increasingly smaller arteries, arterioles, and capillaries. The ...

What Are Osmoregulation and Excretion?

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. ...

Blood Withdrawal I

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN
Blood collection is a common requirement for ...

Kidney Structure

The kidneys are two large bean-shaped organs located in the upper abdomen. They filter the blood several times a day to remove toxins and rebalance water ...

Blood Withdrawal II

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN
The collection of blood from mice and rats for ...

What is the Immune System?

Overview

The immune system comprises diverse biological structures and processes that protect the body from disease. These processes can be classified ...

Bone Remodeling

Bone remodeling is a continuous and balanced process of bone resorption by osteoclasts and bone formation by osteoblasts. In adults, it helps maintain ...

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.]

HS-LS1-2

How Protein Shape Determines Function

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