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Related Concept Videos

Titration of a Polyprotic Acid02:08

Titration of a Polyprotic Acid

A polyprotic acid contains more than one ionizable hydrogen and undergoes a stepwise ionization process. If the acid dissociation constants of the ionizable protons differ sufficiently from each other, then the titration curve for such polyprotic acid generates a distinct equivalence point for each of its ionizable hydrogens. Therefore, titration of a diprotic acid results in the formation of two equivalence points, whereas the titration of a triprotic acid results in the formation of three...
Acid-Base Titration Curves02:23

Acid-Base Titration Curves

A titration curve is a plot of some solution property versus the amount of added titrant. For acid-base titrations, solution pH is a useful property to monitor because it varies predictably with the solution composition and, therefore, may be used to monitor the titration’s progress and detect its endpoint. Acid-base titration can be performed with a strong acid and a strong base, a strong acid and a weak base, or a strong base and a weak acid.
For a titration carried out for 25.00 mL of 0.100...
Solution Composition During Acid/Base Titrations01:17

Solution Composition During Acid/Base Titrations

The titration of a weak acid with a strong base results in the formation of water and the conjugate base of the acid. For instance, titrating acetic acid with sodium hydroxide leads to the formation of water and sodium acetate. A solution of acetic acid and sodium acetate constitutes a buffer whose relative concentration at different stages of the titration is indicated by the α values, which represent percentages of the weak acid and its conjugate base.
The α0 and α1 values represent the...
Titration of Polyprotic Base with a Strong Acid01:18

Titration of Polyprotic Base with a Strong Acid

The titration of a polyprotic base such as sodium carbonate with a strong acid such as hydrochloric acid results in two equivalence points on the titration curve. At the first equivalence point, the carbonate ions in the base are completely converted to bicarbonate ions. The second equivalence point corresponds to the complete conversion of bicarbonate ions to carbonic acid, which dissociates into carbon dioxide and water. The region before the first equivalence point corresponds to the...
Titration of a Weak Acid with a Strong Base01:30

Titration of a Weak Acid with a Strong Base

In titrating a weak acid with a strong base, different calculation methods are applied at various stages. Initially, the pH of a weak acid like acetic acid is calculated using its dissociation constant (Ka) and an ICE table. Upon addition of a strong base such as sodium hydroxide, a buffer forms, and its pH is determined using the Henderson-Hasselbalch equation. As more base is added and the titration reaches the halfway point, the pH becomes equal to the pKa of the acid, indicating equal...
Titration of Polyprotic Acids with a Strong Base01:23

Titration of Polyprotic Acids with a Strong Base

Titration of a polyprotic acid, which contains multiple ionizable protons, involves distinct dissociation steps, each with its own dissociation constant (Ka). Each successive Ka is weaker than the previous one. In the titration of a polyprotic acid like sulfurous acid with a strong base such as sodium hydroxide, the base first neutralizes the initial ionizable proton, forming an intermediate species (e.g., hydrogen sulfite ions). This step's titration curve resembles that of a weak monoprotic...

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Related Experiment Video

Updated: Jul 5, 2026

Development of Sulfidogenic Sludge from Marine Sediments and Trichloroethylene Reduction in an Upflow Anaerobic Sludge Blanket Reactor
15:19

Development of Sulfidogenic Sludge from Marine Sediments and Trichloroethylene Reduction in an Upflow Anaerobic Sludge Blanket Reactor

Published on: October 15, 2015

Multisite phosphorylation and the countdown to S phase.

R J Deshaies1, J E Ferrell

  • 1Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. deshaies@its.caltech.edu

Cell
|January 10, 2002
PubMed
Summary
This summary is machine-generated.

The SCF(Cdc4) ubiquitin ligase specifically targets Sic1 with six phosphates, not five. This finding reveals a molecular counting mechanism, converting analog signals into digital outputs for protein nanoprocessors.

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Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte
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Quantification of Site-specific Protein Lysine Acetylation and Succinylation Stoichiometry Using Data-independent Acquisition Mass Spectrometry
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Related Experiment Videos

Last Updated: Jul 5, 2026

Development of Sulfidogenic Sludge from Marine Sediments and Trichloroethylene Reduction in an Upflow Anaerobic Sludge Blanket Reactor
15:19

Development of Sulfidogenic Sludge from Marine Sediments and Trichloroethylene Reduction in an Upflow Anaerobic Sludge Blanket Reactor

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Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte
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Quantification of Site-specific Protein Lysine Acetylation and Succinylation Stoichiometry Using Data-independent Acquisition Mass Spectrometry
12:49

Quantification of Site-specific Protein Lysine Acetylation and Succinylation Stoichiometry Using Data-independent Acquisition Mass Spectrometry

Published on: April 4, 2018

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Cellular Regulation

Background:

  • Sic1 is a cell cycle inhibitor regulated by phosphorylation.
  • SCF(Cdc4) is an E3 ubiquitin ligase involved in cell cycle progression.
  • Phosphorylation levels often dictate protein function and degradation.

Purpose of the Study:

  • To investigate the precise phosphorylation threshold recognized by SCF(Cdc4) for Sic1 ubiquitination.
  • To elucidate the mechanism by which SCF(Cdc4) distinguishes between different phosphorylation states of Sic1.
  • To understand how analog phosphorylation signals are converted into digital outputs in a biological context.

Main Methods:

  • In vitro binding assays using purified SCF(Cdc4) and Sic1 variants with defined phosphorylation states.
  • Ubiquitination assays to monitor Sic1 modification by SCF(Cdc4).
  • Mass spectrometry to confirm phosphorylation sites and stoichiometry on Sic1.

Main Results:

  • SCF(Cdc4) selectively binds and ubiquitinates Sic1 phosphorylated at six sites, but not five.
  • This phosphorylation-dependent ubiquitination triggers Sic1 degradation.
  • The study demonstrates a clear "digital" switch based on an "analog" input (number of phosphates).

Conclusions:

  • SCF(Cdc4) acts as a molecular counter, utilizing a precise phosphorylation threshold for substrate recognition.
  • This mechanism provides a digital output (ubiquitination/degradation) from an analog input (varying phosphorylation levels).
  • Understanding this protein nanoprocessor architecture offers insights into precise cellular regulation and signal transduction.