Name: cell chemistry: water and macromolecules
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 2 min 58 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.K

Chemistry of the Cell

Le cellule sono gli elementi costitutivi di base degli organismi viventi, sono composti prevalentemente da acqua, molecole organiche e ioni inorganici. L'acqua costituisce circa il 70 percento della cellula. Questo ambiente acquoso nel citoplasma è essenziale per la struttura della cellula e per molte delle reazioni che avvengono al suo interno.

L'acqua è una molecola altamente polare, quindi interagirà con altre molecole polari e ioni nella cellula, ma non con quelli non polari. L'ambiente idrofilo del citoplasma favorisce la formazione di strutture tridimensionali delle proteine, con amminoacidi non polari al centro e polari in superficie. Nel caso della formazione di membrane, i gruppi di teste polari dei fosfolipidi interagiscono con l'acqua.

Al contrario, le code non polari interagiscono fra loro creando una barriera idrofobica all'esterno della cellula. Il pH dei fluidi biologici nella cellula e nei suoi compartimenti è tamponato con precisione. Il pH del citoplasma è intorno a 7, 2 ed è regolato da molecole come gli ioni fosfato.

Al contrario, il pH nei lisosomi, compartimenti cellulari specializzati, è di circa 5. Questo perché i lisosomi contengono enzimi che funzionano in modo ottimale in ambienti acidi. Le molecole organiche nella cellula includono carboidrati, proteine, lipidi e nucleotidi.

Tutte queste varie macromolecole hanno una molteplicità di ruoli. I carboidrati sono una fonte primaria di energia per alimentare vari processi metabolici;tuttavia, la cellula può anche scomporre proteine e lipidi come carburante. Le proteine possono essere enzimi che catalizzano le reazioni, o possono contribuire alla struttura cellulare.

I lipidi sono una componente significativa delle membrane cellulari. Inoltre, queste macromolecole possono legarsi in modo covalente fra di loro per formare coniugati, come glicoproteine e glicolipidi, spesso presenti nelle membrane cellulari. I nucleotidi fungono da materiale genetico e si associano anche alle proteine per formare nucleoproteine, le quali impacchettano strettamente il DNA in una cellula.

Il nucleotide ATP è anche la fonte di energia per molti processi cellulari. Gli ioni inorganici fondamentali per la funzione cellulare includono sodio, potassio, magnesio, calcio, fosfato e cloruro. Benché questi ioni costituiscano meno dell'1 percento della massa cellulare, svolgono ruoli diversi all'interno della cellula.

Per esempio, gli ioni come il calcio sono usati per trasmettere segnali biologici in una cellula, mentre il magnesio è essenziale per l'attività catalitica di molti enzimi.

<ol>
	<li>Cooper GM. La cellula: un approccio molecolare. 2a edizione. Sunderland (MA): Sinauer Associates; 2000. Capitolo 2, La chimica delle cellule. Disponibile da: <a href="https://www.ncbi.nlm.nih.gov/books/NBK9884/">https://www.ncbi.nlm.nih.gov/books/NBK9884/</a></li>
	<li>Alberts B, Johnson A, Lewis J, et al. Biologia molecolare della cellula. 4a edizione. New York: Garland Science; 2002. I componenti chimici di una cellula. Disponibile da: <a href="https://www.ncbi.nlm.nih.gov/books/NBK26883/">https://www.ncbi.nlm.nih.gov/books/NBK26883/</a></li>
	<li>Cooper GM. La cellula: un approccio molecolare. 2a edizione. Sunderland (MA): Sinauer Associates; 2000. La composizione molecolare delle cellule. Disponibile da: <a href="https://www.ncbi.nlm.nih.gov/books/NBK9879/">https://www.ncbi.nlm.nih.gov/books/NBK9879/</a></li>
</ol>

chimica della cellula

La cellula è chimicamente composta da acqua, molecole organiche e ioni inorganici.

Acqua

La polarità della molecola d'acqua e il conseguente legame a idrogeno rendono l'acqua una sostanza unica con proprietà speciali intimamente legate ai processi della vita. La vita originariamente si è evoluta in un ambiente acquatico e la maggior parte della chimica cellulare e del metabolismo di un organismo avvengono all’interno del contenuto acquoso del citoplasma della cellula. Le proprietà speciali dell'acqua sono la sua elevata capacità termica e calore di vaporizzazione, la sua capacità di dissolvere le molecole polari, le sue proprietà coesive e adesive e la sua dissociazione in ioni che porta alla base del pH. Comprendere queste caratteristiche dell'acqua aiuta a chiarire la sua importanza nel mantenimento della vita.

Una delle proprietà importanti dell’acqua è che è una molecola polare: l’idrogeno e l’ossigeno all’interno delle molecole d’acqua (H_2O) formano legami covalenti polari. Sebbene non vi sia alcuna carica netta su una molecola d'acqua, la polarità dell'acqua crea una carica leggermente positiva sull'idrogeno e una carica leggermente negativa sull'ossigeno, contribuendo alle proprietà di attrazione dell'acqua. L'acqua genera cariche perché l'ossigeno è più elettronegativo dell'idrogeno, rendendo più probabile che un elettrone condiviso si trovi vicino al nucleo dell'ossigeno rispetto al nucleo dell'idrogeno, generando così la carica negativa parziale vicino all'ossigeno.

Come risultato della polarità dell’acqua, ciascuna molecola d’acqua attrae altre molecole d’acqua a causa delle cariche opposte tra le molecole d’acqua, formando legami idrogeno. L'acqua attrae o è attratta anche da altre molecole e ioni polari. Una sostanza polare che interagisce facilmente o si dissolve in acqua è idrofila. Al contrario, le molecole non polari come oli e grassi non interagiscono bene con l’acqua. Questi composti non polari sono idrofobici.

Molecole organiche

Proteine, carboidrati, acidi nucleici e lipidi sono le quattro principali classi di macromolecole biologiche - grandi molecole necessarie per la vita che sono costituite da molecole organiche più piccole. Le macromolecole sono composte da singole unità chiamate dagli scienziati monomeri che sono unite da legami covalenti per formare polimeri più grandi. Il polimero è più della somma delle sue parti: acquisisce nuove caratteristiche e porta ad una pressione osmotica molto inferiore a quella formata dai suoi ingredienti. Questo è un vantaggio importante nel mantenimento delle condizioni osmotiche cellulari. Un monomero si unisce ad un altro monomero con il rilascio di molecole d'acqua, portando alla formazione di un legame covalente. Gli scienziati chiamano queste reazioni di disidratazione o condensazione. Quando i polimeri si scompongono in unità più piccole (monomeri), utilizzano una molecola d'acqua per ciascun legame rotto da queste reazioni. Tali reazioni sono reazioni di idrolisi. Le reazioni di disidratazione e idrolisi sono simili per tutte le macromolecole, ma ciascuna reazione monomerica e polimerica è specifica per la sua classe. Le reazioni di disidratazione richiedono tipicamente un investimento di energia per la formazione di nuovi legami, mentre le reazioni di idrolisi tipicamente rilasciano energia rompendo i legami.

Carboidrati

I carboidrati sono un gruppo di macromolecole che costituiscono una fonte di energia vitale per la cellula e forniscono supporto strutturale alle cellule vegetali, ai funghi e a tutti gli artropodi tra cui le aragoste, i granchi, i gamberetti, gli insetti e i ragni. I carboidrati possono essere classificati in monosaccaridi, disaccaridi e polisaccaridi. Lo stoccaggio del glucosio, sotto forma di polimeri come l'amido o il glicogeno, lo rende leggermente meno accessibile al metabolismo; tuttavia, ciò impedisce che fuoriesca dalla cellula o che si crei un'elevata pressione osmotica che potrebbe causare un assorbimento eccessivo di acqua da parte della cellula.

Proteine

Le proteine sono una classe di macromolecole che svolge una vasta gamma di funzioni per la cellula. Aiutano nel metabolismo agendo come enzimi, trasportatori o ormoni e forniscono supporto strutturale. Gli elementi costitutivi delle proteine sono gli aminoacidi.

Lipidi

I lipidi sono una classe di macromolecole di natura non polare e idrofobica. I tipi principali includono grassi e oli, cere, fosfolipidi e steroidi. I grassi sono una forma di energia immagazzinata e sono noti anche come triacilgliceroli o trigliceridi. Il colesterolo è un tipo di steroide ed è un importante costituente della membrana plasmatica, dove aiuta a mantenere la natura fluida della membrana.

Acidi nucleici

Gli acidi nucleici sono molecole composte da nucleotidi che dirigono le attività cellulari come la divisione cellulare e la sintesi proteica. Esistono due tipi di acidi nucleici: DNA e RNA. Il DNA trasporta il progetto genetico della cellula e lo trasmette dai genitori alla prole. L'RNA è coinvolto nella sintesi proteica e nella sua regolazione.

Ioni inorganici

Gli ioni inorganici costituiscono meno dell'1% della massa cellulare ma sono fondamentali per la funzione della cellula. Quelli presenti in una cellula includono sodio, potassio, magnesio, calcio, fosfato e cloruro.

Questo testo è adattato da <a href="https://openstax.org/details/books/biology-2e">Openstax, Biology 2e, Unit 1: </a><a href="https://openstax.org/details/books/biology-2e">The Chemistry of Life</a>.

Chimica della cellula

La cellula è composta chimicamente da acqua, molecole organiche e ioni inorganici.
Acqua
La polarità della molecola d'acqua e l'idrogeno che ne deriva ...

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KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

cell chemistry: water and macromolecules

Cell chemistry includes water, organic molecules, and inorganic ions. These materials shape how cells store energy, build structures, and carry out life processes. Most cellular chemistry and metabolism happen in the watery cytoplasm.

Water is a key part of the cell because it has special properties tied to its polarity. In a water molecule, hydrogen and oxygen form polar covalent bonds, so the molecule has no net charge but does have a slightly positive end and a slightly negative end. Oxygen is more electronegative than hydrogen, so shared electrons spend more time near oxygen. This polarity lets water molecules attract each other and form hydrogen bonds.

Water also interacts with other substances in important ways. It can dissolve polar molecules and attract ions. A substance that mixes well with water is hydrophilic, while nonpolar substances such as oils and fats are hydrophobic. Water also has high heat capacity and a high heat of vaporization, and it shows cohesive and adhesive behavior. When water dissociates into ions, it helps form the basis of pH.

The cell also contains the four major classes of biological macromolecules: proteins, carbohydrates, nucleic acids, and lipids. Macromolecules are large molecules built from smaller monomers that join by covalent bonds to make polymers. Polymers have properties that are different from their building blocks, including lower osmotic pressure than the parts would create alone. Monomers join in dehydration, or condensation, reactions, which release water. Polymers break apart in hydrolysis reactions, which use water. Dehydration usually needs energy, while hydrolysis usually releases energy.

Carbohydrates provide energy and structural support. They can be monosaccharides, disaccharides, or polysaccharides. Cells store glucose in polymers such as starch or glycogen. This storage form is less available for metabolism, but it helps keep glucose from leaking out and helps prevent high osmotic pressure that could draw too much water into the cell.

Proteins have many jobs in the cell. They can act as enzymes, carriers, or hormones, and they also provide structural support. Their building blocks are amino acids. Lipids are nonpolar and hydrophobic. Major lipid types include fats and oils, waxes, phospholipids, and steroids. Fats, also called triacylglycerols or triglycerides, store energy. Cholesterol is a steroid that helps maintain the fluid nature of the plasma membrane.

Nucleic acids are made of nucleotides and direct cell activities such as cell division and protein synthesis. DNA stores the genetic blueprint and passes it from parents to offspring. RNA helps with protein synthesis and its control. Inorganic ions make up less than 1% of cell mass, but they are still essential. Important ions include sodium, potassium, magnesium, calcium, phosphate, and chloride.

Cell Chemistry: Water and Macromolecules

functional groups

Functional Groups in Organic Chemistry

Functional groups in organic chemistry are groups of atoms that give molecules specific properties. When these groups attach to a carbon skeleton, they can change how the molecule behaves. Some functional groups make a molecule hydrophilic, or water-attracting. Others make it hydrophobic, or water-repelling. Functional groups are a key part of organic chemistry and are also found in major biological molecules. They appear in carbohydrates, proteins, lipids, and nucleic acids. Each functional...

structure of lipids

Lipids, Fats, and Cell Membranes

Lipids are nonpolar molecules that do not mix well with water. They are hydrophobic, which means “water fearing,” because they contain mostly nonpolar carbon-carbon and carbon-hydrogen bonds. In cells, lipids store long-term energy as fats, help insulate plants and animals, and form protective water-repellent layers on feathers and fur. They are also part of cell membranes and serve as building blocks for many hormones. Common lipids include fats, oils, waxes, phospholipids, and steroids. A...

chemistry of the cell

Cell chemistry includes water, organic molecules, and inorganic ions. These materials shape how cells store energy, build structures, and carry out life processes. Most cellular chemistry and metabolism happen in the watery cytoplasm. Water is a key part of the cell because it has special properties tied to its polarity. In a water molecule, hydrogen and oxygen form polar covalent bonds, so the molecule has no net charge but does have a slightly positive end and a slightly negative end. Oxygen...

dna base pairing

Chargaff’s Rules and DNA Pairing

Chargaff’s rules and DNA base pairing explain how DNA strands match up. In double-stranded DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Chargaff also found that A equals T, G equals C, and the total amount of purines (A and G) equals the total amount of pyrimidines (C and T). Watson and Crick later showed why these matches matter. A forms two hydrogen bonds with T, while G forms three hydrogen bonds with C. These pairings keep the DNA double helix a...

chemistry of carbohydrates

Carbohydrates as Energy and Storage Molecules

Carbohydrates are important energy sources in human and animal diets. Grains, fruits, and vegetables are natural sources of carbohydrates. They help provide energy to the body, especially through glucose, a simple sugar found in starch and many staple foods. Carbohydrates are identified by the stoichiometric formula (CH2O)n, where n is the number of carbons in the molecule. This means the ratio of carbon to hydrogen to oxygen is usually 1:2:1. The name carbohydrate comes from this pattern,...

protein and protein structure

How Protein Shape Controls Function

Proteins are a major class of organic molecules in living systems, and their shape helps determine what they do. They can act as structural, regulatory, contractile, or protective molecules. They also take part in transport, storage, membranes, toxins, and enzymes. All proteins are polymers of amino acids arranged in a linear sequence. A protein’s function depends on its three-dimensional form. For example, an enzyme works when its active site can bind a specific substrate. If local changes or...

amino acids

Amino Acids and Protein Building

Amino acids are the building blocks of proteins. Each amino acid has the same basic structure. A central carbon atom, called the alpha carbon, is bonded to an amino group, a carboxyl group, and a hydrogen atom. Each amino acid also has an R group, or side chain, attached to the central carbon. The R group is different for every amino acid. It helps determine whether an amino acid is acidic, basic, polar, or nonpolar. Scientists call these molecules amino acids because they contain both amino...

peptide bonds

Peptide Bond Formation and Shape

Peptide bonds join amino acids into peptides and polypeptides. They form when the carboxyl group of one amino acid reacts with the amino group of another. This dehydration reaction releases a water molecule and creates a covalent link. As more amino acids are added, the chain becomes a polypeptide. Each polypeptide has a free amino group at one end. This end is the N-terminal, or amino-terminal. The other end has a free carboxyl group. This end is the C-terminal, or carboxyl-terminal. The...

nucleic acids

DNA and RNA: Genetic Instructions

DNA and RNA are the nucleic acids that store genetic information and help direct cell activity. These macromolecules carry the cell’s genetic blueprint and the instructions it uses to function. DNA is the genetic material in all living organisms, from single-celled bacteria to multicellular mammals. In eukaryotic cells, DNA is found in the nucleus and also in organelles such as chloroplasts and mitochondria. In prokaryotes, DNA is not enclosed in a membrane. The full genetic content of a cell...

dna replication

DNA Copying: Leading and Lagging Strands

DNA replication copies genetic material before a cell divides. Each original DNA strand serves as a template for a new complementary strand. The result is semiconservative replication, which means each new DNA molecule contains one old strand and one new strand. The two daughter cells then receive DNA with the same sequence. Replication starts when helicase separates the two strands of the double helix. This creates a Y-shaped replication fork. Primase then adds short RNA primers that give DNA...

from dna to protein

The Genetic Code and Codons

The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis. Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand.

polymers

Polymer Chains and How They Form

Polymers are long chains of molecules made from repeating units called monomers. The word polymer comes from the Greek words "poly," meaning many, and "mer," meaning parts. Polymers can be found in nature, such as DNA and proteins, or made synthetically, such as plastics. A polymer’s shape helps define its properties. Some polymers form linear chains, while others are branched or arranged in complex networks. Functional groups on a polymer also affect how it behaves. The repeating units in a...

key terms and concepts

Explore how water, macromolecules, and inorganic ions shape cell function. Learn about polarity, pH, carbohydrates, proteins, lipids, DNA, and RNA.

Cell Chemistry: Water and Macromolecules | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

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Biology

BIO.5

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3.3.9-12.H

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Students who demonstrate understanding can develop a model based on evidence of Earth's interior to describe the cycling of matter by thermal convection.  Clarification Statement: Emphasis is on both a one-dimensional model of Earth, with radial layers determined by density, and a three-dimensional model, which is controlled by mantle convection and the resulting plate tectonics.  Examples of evidence include maps of Earth's three-dimensional structure obtained from seismic waves, records of the rate of change of Earth's magnetic field (as constraints on convection in the outer core), and identification of the composition of Earth's layers from high-pressure laboratory experiments.  Assessment Boundary:

3.3.9-12.I

Role of Water in Human Biology

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Students who demonstrate understanding can plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes. [cite: 44] Clarification Statement: Emphasis is on mechanical and chemical investigations with water and a variety of solid materials to provide the evidence for connections between the hydrologic cycle and system interactions commonly known as the rock cycle. [cite: 45] Examples of mechanical investigations include stream transportation and deposition using a stream table, erosion using variations in soil moisture content, or frost wedging by the expansion of water as it freezes. [cite: 46] Examples of chemical investigations include chemical weathering and recrystallization (by testing the solubility of different materials) or melt generation (by examining how water lowers the melting temperature of most solids). [cite: 47] Assessment Boundary:

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3.3.9-12.L

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The Food Chain
Energy is one of the most important abiotic factors in an ecosystem and organisms in an ecosystem are connected by the flow of energy and ...

Students who demonstrate understanding can construct an argument based on evidence about the simultaneous coevolution of Earth's systems and life on Earth. [cite: 59] Clarification Statement: Emphasis is on the dynamic causes, effects, and feedbacks between the biosphere and Earth's other systems, whereby geoscience factors control the evolution of life, which in turn continuously alters Earth's surface. [cite: 60] Examples include how photosynthetic life altered the atmosphere through the production of oxygen, which in turn increased weathering rates and allowed for the evolution of animal life; [cite: 61] how microbial life on land increased the formation of soil, which in turn allowed for the evolution of land plants; [cite: 62] or how the evolution of corals created reefs that altered patterns of erosion and deposition along coastlines and provided habitats for the evolution of new life forms. [cite: 63] Assessment Boundary: Assessment does not include a comprehensive understanding of the mechanisms of how the biosphere interacts with all of Earth's other systems. [cite: 64]

3.3.9-12.N

Cell Chemistry: Water and Macromolecules

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