The Cell: Cytosol and Cytoskeleton

A cell’s cytoskeleton is a network of intracellular protein fibers that provides structural support, anchors organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles, and aids AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS intra- and extracellular movement. The cytosol is the liquid inside the cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane that surrounds the organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles and cytoskeleton. The cytosol is a complex solution where many biochemical processes take place.

Last updated: Aug 15, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Contents

Cytoskeleton

The cytoskeleton is composed of different protein fibers that extend through the cytosol. Three different types of fiber proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis provide the framework along which molecular motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis move.

Protein fibers

  • Microfilaments ( actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction filaments): 
    • Structure:
      • Smallest
      • Most common intracellular protein
      • 2 filaments made of approximately 7 nm actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction polymers (F-actin) coiled around each other (double helix)
      • Growth is directional (positive and negative end).
    • Function: 
      • Disassembles and reassembles rapidly (treadmilling), allowing cell to move
      • Provides track for motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology protein myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction 
      • Provides some structural support to cell
    • Examples:
      • Muscle contractions
      • Assemble along the circumference of a cell during cytokinesis Cytokinesis The process by which the cytoplasm of a cell is divided. Meiosis and tighten to pinch it into 2 daughter cells
      • Macrophage movement within body
      • Cytoplasmic streaming (movement of cytoplasm within the cell)
  • Intermediate filaments: 
    • Structure:
      • Medium
      • 10 nm in diameter
    • Composed of several different fibrous proteins Fibrous proteins Simple proteins characterized by their insolubility and fibrous structure. Within the body, they perform a supportive or protective function. Proteins and Peptides
    • Function:
      • Maintenance of cell shape
      • Anchor organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles
      • Structural components of nuclear lamina
    • Examples:
      • Keratin Keratin A class of fibrous proteins or scleroproteins that represents the principal constituent of epidermis; hair; nails; horny tissues, and the organic matrix of tooth enamel. Two major conformational groups have been characterized, alpha-keratin, whose peptide backbone forms a coiled-coil alpha helical structure consisting of type I keratin and a type II keratin, and beta-keratin, whose backbone forms a zigzag or pleated sheet structure. Alpha-keratins have been classified into at least 20 subtypes. In addition multiple isoforms of subtypes have been found which may be due to gene duplication. Seborrheic Keratosis protects against mechanical stress.
      • Cell–cell connection and intercellular communications
      • More stable than microfilaments
      • Stronger tensile strength Tensile strength The maximum stress a material subjected to a stretching load can withstand without tearing. Wound Healing
  • Microtubules
    • Structure:
      • Largest
      • 25–100 nm spiral Spiral Computed tomography where there is continuous x-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures. Computed Tomography (CT) made up of alpha and beta tubulin Tubulin A microtubule subunit protein found in large quantities in mammalian brain. It has also been isolated from sperm flagellum; cilia; and other sources. Structurally, the protein is a dimer with a molecular weight of approximately 120, 000 and a sedimentation coefficient of 5. 8s. It binds to colchicine; vincristine; and vinblastine. Flucytosine, Griseofulvin, and Terbinafine
    • Function:
      • Anchor on centriole near nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles
      • Directional growth: addition and subtraction of tubulin Tubulin A microtubule subunit protein found in large quantities in mammalian brain. It has also been isolated from sperm flagellum; cilia; and other sources. Structurally, the protein is a dimer with a molecular weight of approximately 120, 000 and a sedimentation coefficient of 5. 8s. It binds to colchicine; vincristine; and vinblastine. Flucytosine, Griseofulvin, and Terbinafine subunits
      • Highways for transportation within cell by molecular motors
    • Examples:
      • Assemble and provide framework for chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics movement during cell division Cell Division A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle
      • Form cilia and flagella Flagella A whiplike motility appendage present on the surface cells. Prokaryote flagella are composed of a protein called flagellin. Bacteria can have a single flagellum, a tuft at one pole, or multiple flagella covering the entire surface. In eukaryotes, flagella are threadlike protoplasmic extensions used to propel flagellates and sperm. Flagella have the same basic structure as cilia but are longer in proportion to the cell bearing them and present in much smaller numbers. Helicobacter, allowing movement through extracellular matrix Extracellular matrix A meshwork-like substance found within the extracellular space and in association with the basement membrane of the cell surface. It promotes cellular proliferation and provides a supporting structure to which cells or cell lysates in culture dishes adhere. Hypertrophic and Keloid Scars

Molecular motors

Specialized proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis “walk” along the microtubule highways, transporting organelles Organelles A cell is a complex unit that performs several complex functions. An organelle is a specialized subunit within a cell that fulfills a specific role or function. Organelles are enclosed within their own lipid bilayers or are unbound by membranes. The Cell: Organelles, substrates, or chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure within the cell. 

  • Structure:
    • Protein complexes:
    • Different complex based on direction of transportation:
      • Dynein (connector dynactin) moves from the periphery toward the nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles.
      • Kinesin moves from the nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles toward the periphery.
  • Function:
    • Convert chemical energy into kinetic energy
    • Transport substances along microtubule “highways”
    • Assembly walks down microtubule by ATP hydrolysis Hydrolysis The process of cleaving a chemical compound by the addition of a molecule of water. Proteins and Peptides.
  • Examples:
    • Walk along mitotic spindle to separate sister chromatids during cell division Cell Division A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle
    • Transport neurotransmitter-filled vesicles Vesicles Female Genitourinary Examination down neuron axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology 
Molecular motor moving along microtubule

Molecular motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology moving along microtubule

Image by Lecturio.

Cytosol

  • Cytosol is a liquid found inside cells (fluid matrix):
    • Water (70%)
    • Dissolved ions ( pH pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance 7.0–7.4)
    • Small proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis
    • Large, water-soluble macromolecules
  • Surrounded by cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane in prokaryotic Prokaryotic Prokaryotes are unicellular organisms that include 2 of the 3 domains of life: bacteria and archaea. Prokaryotic cells consist of a single cytoplasm-filled compartment enclosed by a cell membrane and cell wall. Cell Types: Eukaryotic versus Prokaryotic cells
  • Part of cytoplasm (all material within cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane except nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles)
  • Site of eukaryotic Eukaryotic Eukaryotes can be single-celled or multicellular organisms and include plants, animals, fungi, and protozoa. Eukaryotic cells contain a well-organized nucleus contained by a membrane, along with other membrane-bound organelles. Cell Types: Eukaryotic versus Prokaryotic cellular processes:
    • Signal transduction Transduction The transfer of bacterial DNA by phages from an infected bacterium to another bacterium. This also refers to the transfer of genes into eukaryotic cells by viruses. This naturally occurring process is routinely employed as a gene transfer technique. Bacteriology
    • Cytokinesis Cytokinesis The process by which the cytoplasm of a cell is divided. Meiosis
    • Glycolysis Glycolysis Glycolysis is a central metabolic pathway responsible for the breakdown of glucose and plays a vital role in generating free energy for the cell and metabolites for further oxidative degradation. Glucose primarily becomes available in the blood as a result of glycogen breakdown or from its synthesis from noncarbohydrate precursors (gluconeogenesis) and is imported into cells by specific transport proteins. Glycolysis
    • Pentose phosphate pathway Pentose phosphate pathway The pentose phosphate pathway (also known as the hexose monophosphate (HMP) shunt)) is an important physiological process that can occur in 2 phases: oxidative and nonoxidative. The oxidative phase utilizes glucose-6-phosphate to produce NADPH and ribulose-5-phosphate. Pentose Phosphate Pathway
    • Protein biosynthesis Biosynthesis The biosynthesis of peptides and proteins on ribosomes, directed by messenger RNA, via transfer RNA that is charged with standard proteinogenic amino acids. Virology
    • Gluconeogenesis Gluconeogenesis Gluconeogenesis is the process of making glucose from noncarbohydrate precursors. This metabolic pathway is more than just a reversal of glycolysis. Gluconeogenesis provides the body with glucose not obtained from food, such as during a fasting period. The production of glucose is critical for organs and cells that cannot use fat for fuel. Gluconeogenesis
    • Transport of metabolites and vesicles Vesicles Female Genitourinary Examination
  • Organizational areas within cytosol (components do not mix randomly):
    • Concentration gradients: (e.g., calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes) can be created near open channel
    • Protein complexes: form to pass substrate Substrate A substance upon which the enzyme acts. Basics of Enzymes along metabolic pathway
    • Protein compartments: form to separate contents from cytosol (e.g., proteasome enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes within proteasome)
    • Microdomains created by cytoskeleton: can prevent larger proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis from accessing areas of cytosol (sieving)

References

  1. Alberts B, Johnson A, Lewis J, et al. (2002). Molecular Biology of the Cell. 4th edition. New York: Garland Science. How Cells Regulate Their Cytoskeletal Filaments. https://www.ncbi.nlm.nih.gov/books/NBK26809/
  2. Alberts B, Johnson A, Lewis J, et al. (2002). Molecular Biology of the Cell. 4th edition. New York: Garland Science. The Cytoskeleton and Cell Behavior. https://www.ncbi.nlm.nih.gov/books/NBK26930/
  3. Lodish H, Berk A, Zipursky SL, et al. (2000). Molecular Cell Biology. 4th edition. New York: W. H. Freeman. Section 18.1, The Actin Cytoskeleton. https://www.ncbi.nlm.nih.gov/books/NBK21493/

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