Malcolm Rivera
Cells are the basic unit of life and are composed of various biochemical constituents. The two key biochemical features that minimally constitute a cell are its membrane and nucleus. The cell membrane, or plasma membrane, forms a selective barrier that allows nutrients to enter and waste products to exit. It is composed of water, inorganic ions, and carbon-containing (organic) molecules. The cell's nucleus, on the other hand, contains the genetic information necessary for cell growth and reproduction. It houses nucleic acids, specifically DNA and RNA, which carry and express the cell's genetic code.
| Characteristics | Values |
|---|---|
| Organic molecules | Carbohydrates, lipids, proteins, and nucleic acids |
| Inorganic ions | Sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), phosphate (HPO42-), chloride (Cl-), and bicarbonate (HCO3-) |
| Water | 70% or more of total cell mass |
| Cell membrane | Plasma membrane |
| Nucleus | Contains DNA, the molecule with all the information required to build and maintain the cell |
| Organelles | Chloroplasts, mitochondria, cytosol |
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What You'll Learn
- Cells are composed of water, inorganic ions, and carbon-containing molecules
- The presence of a nucleus and membrane-bound organelles defines a cell as a eukaryote
- The absence of a nucleus and organelles defines a cell as a prokaryote
- Nucleic acids are molecules that contain and express a cell's genetic code
- Proteins are another type of intracellular organic molecule
Cells are composed of water, inorganic ions, and carbon-containing molecules
All cells are composed primarily of water, inorganic ions, and organic molecules containing carbon. Water is the most abundant molecule in cells, accounting for 70% or more of their total mass. The polarity of water molecules, which results from the slight positive charge on their hydrogen atoms and the slight negative charge on their oxygen atom, is of central importance to their biological function. Due to their polar nature, water molecules can form hydrogen bonds with each other and with other polar molecules, as well as interacting with positively or negatively charged ions. This property makes water a unique substance with special characteristics that are intimately tied to the processes of life.
The interactions between water and other constituents of cells are crucial in biological chemistry. For instance, the aqueous environment in the cytoplasm is essential for the cell's structure and the reactions that occur within it. Water's high heat capacity, heat of vaporization, ability to dissolve polar molecules, cohesive and adhesive properties, and its dissociation into ions that form the basis of pH are some of its other important properties.
Inorganic ions constitute less than 1% of the cell mass but are critical to cell function. These include sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), phosphate (HPO42-), chloride (Cl-), and bicarbonate (HCO3-). Ions and polar molecules are readily soluble in water (hydrophilic), while nonpolar molecules, which cannot interact with water, are poorly soluble in an aqueous environment (hydrophobic). Consequently, nonpolar molecules tend to minimize their contact with water by associating closely with each other.
Organic molecules in cells include carbohydrates, proteins, lipids, and nucleotides. Carbohydrates, such as glycogen and starch, are a primary source of energy for metabolic processes, but proteins and lipids can also be broken down for fuel. Proteins can act as enzymes that catalyze reactions or contribute to cell structure. Lipids are a significant component of cell membranes. Nucleotides, such as DNA and RNA, serve as the cell's genetic material and are involved in protein synthesis.
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The presence of a nucleus and membrane-bound organelles defines a cell as a eukaryote
The presence of a distinct nucleus and membrane-bound organelles defines a cell as a eukaryote. Eukaryotic cells are typically much larger than prokaryotic cells, with a volume around 10,000 times greater. They are a major group of life forms, including all animals, plants, fungi, seaweeds, and many unicellular organisms.
The nucleus is considered the most critical organelle in a eukaryotic cell. It is surrounded by a double membrane, known as the nuclear envelope, which has nuclear pores that allow material to move in and out. The nucleus contains the cell's DNA, divided into linear bundles called chromosomes, which store the genetic information necessary for cell growth and reproduction.
The other membrane-bound organelles in a eukaryotic cell include the mitochondrion, chloroplasts, the Golgi apparatus, the endoplasmic reticulum, and lysosomes. These organelles are enclosed by lipid bilayer membranes, similar to the cell's outer membrane, and work together in an integrated fashion to meet the cell's overall needs. For example, mitochondria transfer energy from fatty acids and pyruvate molecules into adenosine triphosphate (ATP), which is then used by the rest of the cell's organelles as an energy source.
The presence of a nucleus and membrane-bound organelles is a defining feature that categorizes cells as either prokaryotes or eukaryotes. The emergence of self-contained nuclei and other organelles is believed to represent a significant advancement in the evolution of cells. Theories suggest that early eukaryotes engulfed prokaryotic cells, leading to a symbiotic relationship where the engulfed cell functioned as an organelle within the larger eukaryotic cell.
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The absence of a nucleus and organelles defines a cell as a prokaryote
All living organisms can be classified into two groups: prokaryotes and eukaryotes. The absence of a nucleus and membrane-bound organelles defines a cell as a prokaryote. Prokaryotes are single-celled organisms that are generally smaller and simpler in structure compared to eukaryotic cells. They include bacteria and archaea.
Prokaryotic cells do not have a "true" nucleus containing their DNA. Instead, their DNA is bundled together in the nucleoid region, located within the cytoplasm. The nucleoid is a DNA/protein complex that lacks a nuclear envelope. Eukaryotic cells, on the other hand, have a distinct membrane-bound nucleus that contains their genetic information. This genetic information is necessary for cell growth and reproduction.
In addition to lacking a nucleus, prokaryotic cells also lack membrane-bound organelles. Organelles are internal structures within cells that perform specific functions, such as energy production and protein synthesis. Examples of organelles include mitochondria, the Golgi apparatus, and chloroplasts. Eukaryotic cells contain these membrane-bound organelles, which help to organize and compartmentalize cellular functions.
The distinction between prokaryotes and eukaryotes is considered a significant difference among organisms. Eukaryotic cells are much larger than prokaryotic cells, with volumes approximately 10,000 times greater. It is believed that eukaryotes evolved from prokaryotes around 2.7 billion years ago. This evolution is theorized to have occurred through endosymbiosis, where an early eukaryotic cell engulfed a prokaryote, leading to a symbiotic relationship and the development of more complex cellular structures.
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Nucleic acids are molecules that contain and express a cell's genetic code
The two biochemical features that minimally constitute a cell are a plasma membrane and a nucleus. The plasma membrane acts as a selective barrier, allowing nutrients to enter and waste products to exit the cell. The nucleus, which contains the cell's genetic information, is essential for cell growth and reproduction.
Nucleic acids, one of the major classes of organic molecules found in cells, play a crucial role in containing and expressing a cell's genetic code. They are chemical compounds that carry, create, encode, and store information in every living cell of every life form on Earth. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two major classes of nucleic acids.
DNA, a nucleic acid, contains the genetic instructions necessary for the development and functioning of all known living organisms. It is composed of two long polymers of nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. The sequence of nucleobases along the backbone encodes genetic information, specifying the amino acid sequence within proteins. This genetic code is read through transcription, where stretches of DNA are copied into RNA molecules.
RNA, the other major class of nucleic acids, has multiple roles associated with expressing the information stored in DNA. It functions in converting genetic information from genes into amino acid sequences of proteins, with three universal types: transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA). mRNA carries genetic sequence information between DNA and ribosomes, directing protein synthesis. rRNA reads the DNA sequence and catalyzes peptide bond formation, while tRNA serves as the carrier molecule for amino acids in protein synthesis and decodes the mRNA.
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Proteins are another type of intracellular organic molecule
The fundamental units of life, cells are composed of several distinct classes of organic molecules, including nucleic acids, proteins, carbohydrates, and lipids. Proteins are another type of intracellular organic molecule. They are chains of amino acids that play a crucial role in the replication of the genome and the structural changes that occur during cell division. Proteins are also involved in a variety of catalytic and structural functions within the cell.
The diversity of amino acids gives rise to the wide range of three-dimensional conformations of folded proteins, making them a highly complex and versatile group of macromolecules. These conformations are determined by the distinct chemical characteristics of the amino acids involved. Proteins are essential for converting cellular molecules into forms that meet the cell's specific needs. For example, enzymes, a type of protein, can convert proteins, carbohydrates, lipids, or nucleic acids into other forms.
The presence of proteins in cells is indicative of their complexity and functionality. They are involved in various processes, including the replication and expression of genetic material. Proteins are necessary for the replication of the genome, which contains all the information required to build and maintain the cell. This replication process is a complex task that proteins are well-suited to perform due to their structural diversity.
Additionally, proteins facilitate the structural changes that occur during cell division. They contribute to the profound alterations in cell structure, ensuring the accurate division of genetic material and the formation of new cells. The presence of proteins in cells highlights their dynamic nature and adaptability, as they actively participate in processes that shape and transform the cellular environment.
The role of proteins in cells is multifaceted and essential for maintaining cellular integrity and functionality. Their involvement in both catalytic and structural functions underscores their importance in sustaining cellular processes and overall cell health. By understanding the role of proteins within cells, we gain insight into the intricate workings of life at its most fundamental level.
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