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Related Concept Videos

Measuring Reaction Rates03:09

Measuring Reaction Rates

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Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical reaction. Optically active substances have the capability of rotating the plane of polarization of linearly polarized light passing through them—a feature called optical rotation. Optical activity is attributed to the molecular structure of substances. Normal monochromatic light is unpolarized and possesses oscillations of the electrical...
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Factors Influencing the Rate of Chemical Reactions01:22

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A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the repulsion between their electrons. This energy is called activation energy. Factors influencing the rate of reaction either lower the activation energy or increase the likelihood of a successful collision.
Concentration and Pressure:
The more particles present within a given space, the more likely those particles are to bump into one another....
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Concentration and Rate Law03:03

Concentration and Rate Law

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The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions describing the relationship between the rate of a chemical reaction and the concentration of its reactants.
For example, in a generic reaction aA + bB ⟶ products, where a and b are stoichiometric coefficients, the rate law can be written as:
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Reaction Rate02:53

Reaction Rate

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The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time dependence of some property that can be related to reactant or product amounts. Rates of reactions that consume or produce gaseous substances, for example, are conveniently determined by measuring changes in volume or pressure.
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Effect of Temperature Change on Reaction Rate02:28

Effect of Temperature Change on Reaction Rate

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The Arrhenius equation,
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Temperature Dependence on Reaction Rate02:55

Temperature Dependence on Reaction Rate

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The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. This premise is the basis for a theory that explains many observations regarding chemical kinetics, including factors affecting reaction rates.
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Single-Molecule Diffusion and Assembly on Polymer-Crowded Lipid Membranes
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How does cytoplasmic crowding affect reaction rates?

Jo-Hsi Huang1, James E Ferrell2

  • 1Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.

Molecular Cell
|December 31, 2025
PubMed
Summary
This summary is machine-generated.

Cellular crowding generally slows biochemical reactions due to reduced diffusion, impacting cytoplasmic dynamics. This finding has implications for understanding cellular processes and molecular interactions within the cell.

Keywords:
Phillies’s lawdiffusionexcluded volumein vivo biochemistrymolecular crowdingrate constantsscaled-particle theory

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Area of Science:

  • Cellular Biology
  • Biochemistry
  • Biophysics

Background:

  • Eukaryotic cytoplasm is densely packed with macromolecules.
  • Macromolecular crowding can influence biochemical reaction rates.
  • Theoretical models propose both positive and negative effects of crowding.

Purpose of the Study:

  • To review theories explaining crowding effects on reaction rates.
  • To survey experimental evidence measuring these effects in vivo.
  • To assess the impact of crowding on cytoplasmic biochemical dynamics.

Main Methods:

  • Literature review of theoretical models.
  • Survey of experimental studies using cell extracts and live cells.
  • Analysis of effective second-order rate constants.

Main Results:

  • Crowding generally decreases effective second-order rate constants.
  • The primary mechanism for this decrease is the slowing of diffusion.
  • Experimental evidence suggests a consistent trend across various reactions.

Conclusions:

  • Macromolecular crowding in the cytoplasm often slows biochemical reactions.
  • Reduced diffusion is a key factor in this rate reduction.
  • Findings necessitate a re-evaluation of cytoplasmic biochemical dynamics and trade-offs.