Name: measuring enzyme reaction rates
Uploaded: 2023-04-30T06:31:30.000Z
Duration: 8 min 7 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

Matter and Its Interactions

HS-PS1-5

Enzyme Assays and Kinetics

酶动力学描述了酶的催化作用，酶是一类促进生物体必需化学反应的生物大分子。酶作用于被称为底物的分子，生成产物。通过测定底物或产物浓度随时间的直接或间接变化，可以确定酶动力学参数。&#160;
本视频将介绍酶动力学的基本原理（包括反应速率方程）和动力学模型。还将讨论酶活性测定的相关概念，并演示一种典型的比色法测定实验。应用部分介绍了通过荧光共振能量转移（FRET）分析进行酶活性测定、环境中外切酶活性的表征，以及利用分子探针研究DNA修复动力学。

酶活性测定与动力学

酶动力学描述了酶的催化作用，酶是一类促进生物体必需化学反应的生物大分子。酶作用于被称为底物的分子，生成产物。通过测定底物或产物浓度随时间的直接或间接变化，可以确定酶动力学参数。&#160;
本视频将介绍酶动力学的基本原理（包括速率方程）和动力学模型。还将讨论酶活性测定的相关概念，随后介绍一种典型的比色法测定。应用部分将讨论通过荧光共振能量转移（FRET）分析进行酶活性测定、表征环境中胞外酶活性，以及利用分子探针研究DNA修复动力学。
<div class="chapter_text" id="script_0">
酶是生命所必需的生物催化剂。酶活性测定用于研究酶促反应的动力学特性，阐明酶的催化作用。本视频将介绍酶动力学和酶活性测定的基本原理，概述一般实验步骤，并展示一些应用实例。
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<div class="chapter_text" id="script_1">
酶是蛋白质，或较少情况下为RNA，它们作用于特定的反应物，该反应物被称为底物。酶能够降低启动生化反应所需的活化能，从而使反应以更快的速率进行。
酶促反应可分为三个基本步骤。第一步是酶-底物复合物的形成，即底物与酶的活性位点结合。该复合物可分解为原始组分，这是第二个基本反应。或者，该复合物可生成产物并释放出酶，这是第三个基本反应。
基本反应的动力学由基本速率定律方程描述。速率定律方程以反应物浓度和速率常数来表示反应速率。每个基本反应都有其独立的速率定律方程，并具有各自的速率常数。这些方程可简化为一种称为米氏方程（Michaelis-Menten equation）的动力学模型。该模型以底物浓度表示反应速率，可通过实验测定。利用米氏方程可以识别酶反应的一些普遍趋势。在高底物浓度下，反应速率达到一个饱和点，称为Vmax。此时，反应速率受限于总酶浓度以及单位时间内每个酶分子转化底物为产物的数量，后者也称为kcat。在米氏动力学中，kcat是决定反应速率的两个常数之一。另一个常数KM被称为亲和常数。KM也等于反应速率达到Vmax一半时的底物浓度。亲和力较高的酶具有较低的KM值，并能更快地达到Vmax；而亲和力较低的酶则具有较高的KM值，达到Vmax所需时间更长。已知kcat和KM后，便可对不同酶进行比较。为此我们使用一个称为酶催化效率的比值。较高的kcat和较低的KM对应更高的催化效率，而较低的kcat和较高的KM则导致更低的催化效率。
用于阐明酶动力学的参数必须通过实验确定。这些测定通常在受控环境中将酶溶液与底物溶液混合后进行。通过测量底物、产物或副产物浓度随时间的变化来进行观察。
浓度随时间的变化用于确定反应速率。为了确定动力学参数，必须在多个不同底物浓度下获取速率数据。如果以初始速率的倒数对初始浓度的倒数作图（即Lineweaver-Burk图）呈线性关系，则表明该反应遵循米氏动力学。通过该直线的斜率和截距可确定动力学参数KM和Vmax，进而用于计算kcat和酶催化效率。
在讨论了酶动力学的基本原理之后，接下来让我们看看典型的酶活性测定是如何进行的。
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<div class="chapter_text" id="script_2">
本实验演示了一种比色测定法。第一步是建立标准曲线，以关联吸光度与底物浓度。配制已知浓度的溶液，并设置对照样品。加入与底物发生反应的显色剂溶液，生成有色化合物。测定各溶液的吸光度，并将其对浓度作图，从而绘制出标准曲线。
进行测定时，需配制已知浓度的底物以及适量的酶。将酶与底物混合，并在设定的时间间隔内进行孵育。使用缓冲溶液和加热块控制 pH 值和温度。加入终止剂以停止反应。然后向反应体系中加入显色剂溶液并混匀。将溶液转移至比色皿中，测定其吸光度。通过将测得的吸光度与标准曲线比较，确定消耗的底物量。利用所收集的数据，通过绘制浓度随时间变化的曲线来确定初始反应速率。最后，结合反应速率数据与浓度数据，绘制米氏-门顿（Michaelis-Menten）曲线。由此可确定酶的动力学参数，如转换数和酶催化效率。
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<div class="chapter_text" id="script_3">
在回顾了一种检测方法的流程后，让我们来看看其他检测方法的实施方式及其应用。
在此流程中，采用FRET分析来研究蛋白酶水解蛋白质肽键的动力学过程。这些发射信号可以被测量，从而实现对底物消耗和产物生成的连续且定量的分析，有助于确定反应动力学参数。
酶活性检测可用于环境科学中，以测定环境中胞外酶活性的水平。可从自然环境中采集水体、土壤和沉积物样品，并在实验室中进行处理。随后可利用酶活性检测来表征这些样品中的胞外酶活性。该方法对于理解环境如何降解有机物质具有重要意义。
通过研究细胞核内酶的动力学，可以评估细胞的DNA修复机制。利用仅在结合特定DNA序列时才会产生荧光的荧光分子信标，可测量酶切除DNA损伤位点的速率。通过检测带有荧光标记的切割产物，可实时测定DNA修复水平。
</div>
<div class="chapter_text" id="script_4">
您刚刚观看了 JoVE 关于酶动力学和酶活性检测的视频。该视频讲解了酶动力学的基本原理，介绍了检测方法的相关概念，概述了一般实验步骤，并描述了一些应用实例。
感谢观看！
</div>

酶动力学描述了酶的催化作用，酶是一类促进生物体必需化学反应的生物大分子。

酶是生命活动所必需的生物催化剂。酶活性测定用于研究酶促反应的动力学特性，阐明酶的催化作用。本视频将介绍酶动力学和酶活性测定的基本原理，概述一般实验流程，并展示一些应用实例。酶是蛋白质，或较少情况下为RNA，可作用于特定的反应物，该反应物被称为底物。酶能降低启动生化反应所需的活化能，从而使反应以更快的速率进行。酶促反应可分解为三个基本组分。第一步是酶-底物复合物的形成，即底物与酶活性位点结合而生成该复合物。该复合物可分解为原始组分，这是第二个基本反应。或者，该复合物可生成产物并释放出酶，这是第三个基本反应。基元反应的动力学由基元速率方程描述。速率方程以反应物浓度和速率常数来表示反应速率。每个基元反应都有其独立的速率方程，并具有相应的速率常数。这些方程可简化为一种称为米氏方程（Michaelis-Menten equation）的动力学模型。该方程以底物浓度表示反应速率，且可通过实验测定。利用米氏方程可以识别酶促反应的一些普遍规律。在高底物浓度下，反应达到一个饱和点，称为 Vmax。此时反应速率受限于总酶浓度以及单位时间内每个酶分子转化底物为产物的数目，后者也称为 kcat。在米氏动力学中，kcat 是决定反应速率的两个常数之一。另一个常数 KM 称为亲和常数。KM 也等于反应速率达到 Vmax 一半时的底物浓度。亲和力较高的酶具有较低的 KM 值，并能更快达到 Vmax；而亲和力较低的酶则具有较高的 KM 值，达到 Vmax 所需时间更长。已知 kcat 和 KM 后，即可对不同酶进行比较。为此我们使用一个称为酶催化效率的比值。较高的 kcat 和较低的 KM 导致更高的催化效率，而较低的 kcat 和较高的 KM 则导致更低的催化效率。阐明酶动力学所用的因素必须通过实验确定。这些测定通常在受控环境中通过混合酶和底物溶液来进行。通过测量底物、产物或副产物浓度随时间的变化来进行观察。浓度随时间的变化用于确定反应速率。为了确定反应动力学，必须在多个不同浓度下获取速率数据。如果以初始速率的倒数对初始浓度的倒数作图（即 Lineweaver-Burk 作图）呈线性关系，则该反应遵循米氏动力学（Michaelis-Menten 动力学）。通过该直线的斜率和截距可确定动力学参数 KM 和 Vmax，进而用于计算 kcat 和酶催化效率。在讨论了酶动力学的基本原理之后，让我们来看一下典型的酶活性测定是如何进行的。在此实验中演示了一种比色测定方法。第一步是绘制标准曲线，以关联吸光度与底物浓度。制备已知浓度的溶液以及一个对照样品。加入与底物发生反应的显色试剂，生成有色化合物。测定吸光度，并将其对浓度作图以绘制标准曲线。进行该实验时，需配制已知浓度的底物以及适量的酶。将酶与底物混合后，在设定的时间间隔内进行孵育。通过缓冲溶液和加热块控制反应体系的 pH 值和温度。加入终止剂以停止反应。随后向反应体系中加入显色剂并混匀。将溶液转移至比色皿中，测定其吸光度。通过将测得的吸光度与标准曲线比较，确定消耗的底物量。利用所收集的数据，通过绘制浓度随时间变化的曲线来确定初始反应速率。最后，结合反应速率数据与底物浓度绘制米氏（Michaelis-Menten）曲线，从而确定酶的动力学参数，如转换数和酶催化效率。在回顾了检测方法的流程后，让我们来看看其他检测的实施方式及其应用。在此实验中，采用FRET分析法研究蛋白酶水解蛋白质肽键的动力学过程。这些发射光信号可被检测，从而实现对底物消耗和产物生成的连续定量分析，有助于反应动力学参数的确定。酶活性测定可用于环境科学中测定环境中胞外酶活性的水平。可从环境中采集水体、土壤和沉积物样品，并在实验室中进行处理。随后可利用酶活性测定方法对这些样品的胞外酶活性进行表征。该方法是研究环境如何降解有机物质的重要工具。通过研究细胞核中酶的动力学，可以评估细胞的DNA修复机制。利用仅在结合特定DNA序列时才会发出荧光的荧光分子信标，可测定酶清除DNA损伤（即DNA病变）的速率。通过检测荧光标记的切割产物，可实时测量DNA修复水平。您刚刚观看了 JoVE 关于酶动力学和酶活性检测的视频。该视频讲解了酶动力学的基本原理，涵盖了检测方法的相关概念，介绍了一般的实验操作流程，并描述了一些应用实例。感谢观看！

Education

教育

JoVE Science Education

Chemistry

化学

Biochemistry

生物化学

酶活性实验及动力学

measuring enzyme reaction rates

Enzyme reaction rates can be measured with assays that track how substrate or product levels change over time. Enzymes are proteins, or sometimes RNAs, that speed up chemical reactions by lowering the activation energy needed to start them. They act on a specific substrate and help form a product that supports life processes.

Enzymatic reactions are often described in three steps. First, the substrate binds to the enzyme active site and forms an enzyme-substrate complex. That complex can fall apart again, or it can make product and release the enzyme. Each step has its own rate law and rate constant.

These steps are often simplified with the Michaelis-Menten equation. This model links reaction rate to substrate concentration and helps show general enzyme trends. At high substrate levels, the reaction reaches a saturation point called V max. The turnover number, or k cat, describes how many substrate molecules one enzyme converts per unit time. KM is the concentration where the rate is half of V max, and it also reflects affinity. A lower KM usually means higher affinity, while a higher KM usually means lower affinity. The ratio of k cat and KM is used as enzyme efficiency.

To find these values, scientists run assays in a controlled setting. They mix enzyme and substrate and measure changes in substrate, product, or byproducts over time. Reaction rates are collected at multiple substrate concentrations. If a Lineweaver-Burk plot, which graphs inverse initial rate against inverse initial concentration, is linear, the reaction follows Michaelis-Menten kinetics. The slope and intercept can then be used to determine KM and V max, and these values help calculate k cat and enzyme efficiency.

A common lab method is a colorimetric assay, which uses color to measure concentration. First, a standard curve is made from known concentrations and a control sample. A developer solution reacts with the substrate and creates a colored compound. Absorbance is measured and plotted against concentration to build the curve.

For the assay, a known amount of substrate and enzyme is prepared. The two are mixed and incubated for a set time. Buffer solutions and heating blocks keep pH and temperature controlled. A quenching agent stops the reaction, and developer solution is added. The samples are placed in cuvettes, and absorbance is measured. The amount of substrate used is found by comparing the result to the standard curve. Initial rates are then plotted over time, and the Michaelis-Menten plot is used to determine turnover number and enzyme efficiency.

Other assay methods can track reactions in real time. FRET, or Förster resonance energy transfer, can measure a protease breaking a peptide bond in a protein. The emitted signal can be monitored continuously, which helps quantify substrate consumption and product formation. Enzyme assays are also used in environmental science to measure extracellular enzyme activity in waters, soils, and sediments. These samples are processed in the lab to help explain how the environment breaks down organic material.

Enzyme kinetics can also be used to study DNA repair. Enzymes in the nucleus remove DNA lesions, or damage, and their activity can be followed with fluorescent molecular probes. These beacons fluoresce only when they bind specific DNA sequences. The fluorescent cleavage products make it possible to measure DNA repair in real time.

Measuring Enzyme Reaction Rates

dialysis: diffusion based separation

Dialysis for Buffer Exchange in Biochemistry

Dialysis is a common biochemistry technique for buffer exchange and desalting. It separates molecules by diffusion through a semipermeable membrane, which lets small molecules pass while holding larger biomolecules inside the sample. The membrane is the key part of the setup. Its pores create a molecular weight cutoff, so a membrane such as a 10 kDa membrane usually keeps molecules larger than 10 kilodaltons inside. This cutoff is not exact, because membranes have a range of pore sizes.

enzyme assays and kinetics

Enzyme reaction rates can be measured with assays that track how substrate or product levels change over time. Enzymes are proteins, or sometimes RNAs, that speed up chemical reactions by lowering the activation energy needed to start them. They act on a specific substrate and help form a product that supports life processes. Enzymatic reactions are often described in three steps. First, the substrate binds to the enzyme active site and forms an enzyme-substrate complex. That complex can fall...

maldi-tof mass spectrometry

How MALDI-TOF Reads Biomolecules

MALDI-TOF mass spectrometry reads biomolecules by using a laser, a matrix, and a time-of-flight analyzer. MALDI, or matrix-assisted laser desorption ionization, helps fragile molecules keep their structure while they are moved into the mass analyzer. The analyzer then separates compounds based on size and charge. In MALDI, the sample is mixed into a matrix, usually an organic compound with aromatic and conjugated double bonds. A laser pulse strikes the spot, and the matrix absorbs most of the...

tandem mass spectrometry

Tandem Mass Spectrometry for Biomolecule Analysis

Tandem mass spectrometry is used to isolate a biomolecule and break it into smaller pieces so its makeup can be studied. Because biomolecules often have large, complex structures, it can be hard to identify their molecular composition and sequence from a single measurement. By linking mass spectrometers in series, the technique first selects one ion and then analyzes the fragments it produces. The process starts with an ion source that converts the sample into ions. A mass analyzer then...

protein crystallization

Protein Crystals for Structure Analysis

Protein crystals help scientists study protein structure and function. A crystal is a solid lattice made from purified protein molecules. These crystals are useful in structural biology because they reveal details that methods like mass spectrometry and SDS-PAGE cannot show on their own. Protein crystallization is paired with recombinant protein expression and x-ray diffraction to support this work. The process starts with a large amount of very pure protein. Researchers often make that...

chromatography-based biomolecule purification methods

chromatography-based-biomolecule-purification-methods

Protein Purification with SEC and IMAC

Protein purification with size-exclusion chromatography and affinity chromatography helps isolate biomolecules from complex mixtures. These methods are common in biochemistry because purified samples are needed before a biomolecule’s properties and activity can be studied. The video focuses on the principles behind size-exclusion chromatography, affinity chromatography, and immobilized metal affinity chromatography, or IMAC. Size-exclusion chromatography, or SEC, separates molecules by size. A...

two-dimensional gel electrophoresis

Protein Mapping with 2D Gel Electrophoresis

Protein mapping with 2D gel electrophoresis separates complex protein mixtures across two steps. The method combines isoelectric focusing, or IEF, with sodium dodecyl sulfate polyacrylamide gel electrophoresis, or SDS-PAGE. Together, these methods can resolve thousands of biomolecules from a single sample by their isoelectric point and molecular weight. The first dimension is IEF. Each protein has an isoelectric point, or pI, which is the pH where its net charge is zero. Proteins are loaded...

metabolic labeling

Tracking Cell Chemistry with Metabolic Labels

Metabolic labeling tracks cell chemistry by using chemical analogs that cells take up and build into biomolecules. These labels help scientists follow biochemical changes and modifications inside cells. The labeled products can then be studied with tools such as SDS-PAGE and NMR to learn more about metabolic pathways. Several labeling strategies are shown here. Isotopic labeling uses analogs that match the natural molecule but contain uncommon isotopes, such as carbon-13 and nitrogen-15 in an...

electrophoretic mobility shift assay (emsa)

electrophoretic-mobility-shift-assay-emsa

Detecting Protein-DNA Binding by EMSA

Electrophoretic mobility shift assay, or EMSA, is a biochemical method used to detect binding between proteins and nucleic acids. It is also called a gel shift assay. The test compares how a labeled nucleic acid moves through a gel before and after it binds a protein. EMSA is used to see whether a specific protein binds to a specific nucleic acid. First, the nucleic acid is labeled to make a probe. The transcript describes radioactive phosphorus-32 as a common label. The probe is then mixed...

photometric protein determination

Measuring Protein Concentration with Absorbance

Measuring protein concentration with absorbance is a key step in many biochemical assays. Photometric methods use the fact that samples with more light-absorbing material transmit less light. Because concentration and absorption are directly related, this makes it possible to measure an unknown sample. The core idea comes from the Beer-Lambert Law. This law states that the concentration of a light-absorbing species is proportional to its absorbance. The video also introduces the Bradford assay...

density gradient ultracentrifugation

Sucrose Gradient Separation in an Ultracentrifuge

Sucrose gradient separation in an ultracentrifuge is a lab method for isolating cell parts and biomolecules. It uses differences in density to make particles sink or rise in a liquid. A high-speed ultracentrifuge speeds up this process so components can be separated without destroying them. The basic idea starts with a suspension, which is particles mixed in a liquid solvent. Particles that are denser than the solvent sediment, while less dense particles float. A rotor inside the...

co-immunoprecipitation and pull-down assays

co-immunoprecipitation-and-pull-down-assays

Protein Interaction Capture Methods in Cells

Co-immunoprecipitation and pull-down assays are laboratory methods used to capture stable protein-protein interactions. Protein-protein interactions help control many biological functions, but many of them have not yet been identified. These assays are related to immunoprecipitation, which isolates a target protein from a mixed sample using an antibody. In co-immunoprecipitation, or CoIP, an antibody binds the target protein, and that protein is already attached to another protein that the...

reconstitution of membrane proteins

Membrane Proteins in Liposome Models

Membrane proteins can be moved into liposome models so their function can be studied outside a cell. Reconstitution means restoring an isolated biomolecule to a working form. For membrane proteins, that usually means placing a purified protein into an artificial lipid membrane. Cell membranes are made mainly of phospholipids and membrane proteins. The phospholipids form a bilayer with hydrophilic phosphate heads facing water and hydrophobic fatty acid tails facing inward. Some membrane...

f&#246;rster resonance energy transfer (fret)

FRET as a Molecular Ruler in Cells

Föster resonance energy transfer, or FRET, is a way to study close-range biochemical interactions using light-emitting molecules. A donor fluorophore can pass energy to an acceptor fluorophore when their emission and absorption spectra overlap. This transfer happens only when the pair is very close together, usually within 10 nm. Because FRET depends on distance, it is often called a molecular or spectroscopic ruler. The strength of the signal is measured as FRET efficiency, which describes...

surface plasmon resonance (spr)

SPR Biosensors for Tracking Binding Kinetics

Surface plasmon resonance, or SPR, is a way to track biomolecular binding on a label-free biosensor. It is used to measure molecular affinity, kinetics, specificity, and concentration. The method works with a thin metal layer on a prism, where changes in reflected light reveal interactions in real time. SPR sensors use a thin layer of a noble metal on the face of a prism. Light is reflected from the prism-metal interface into a photodetector. At one specific angle, called the surface plasmon...

biochemistry

本系列介绍了常用的纯化方法, 如亲和层析, 以及分析方法, 如 MALDI。此外, 视频展示了评估生物相互作用和功能的方法, 如 co-immunoprecipitation 和代谢标记。

Measure enzyme reaction rates with assays, standard curves, and Michaelis-Menten plots. Learn how kcat, KM, colorimetric assays, FRET, and DNA repair studies work.

Measuring Enzyme Reaction Rates | JoVE K12

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-5.

Life Science

Structure and Function

HS-LS1-1.

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

HS-LS1-6.

Inheritance and Variation of Traits

HS-LS3-1.

Overveiw

Principles of Enzyme Kinetics

Enzyme Assay

Applications

Summary

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Atomic Structure

All matter is composed of atoms, the smallest individual units of elements. Each atom is made up of three subatomic particles: protons, neutrons, and ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central&#160;core called the nucleus, with electrons present around the ...

Electron Behavior

Electrons are negatively charged subatomic particles that are attracted to an orbit around the positively-charged nucleus of an atom. They reside in ...

Electron Orbital Model

Orbitals are the areas outside of the atomic nucleus where electrons are most likely to reside. They are characterized by different energy levels, shapes, ...

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

Electron Configurations

Electron configurations and orbital diagrams can be determined by applying the Aufbau principle (each added electron occupies the subshell of lowest ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. [Clarification Statement: Examples of properties that could be predicted from patterns could include reactivity of metals, types of bonds formed, numbers of bonds formed, and reactions with oxygen.] [Assessment Boundary: Assessment is limited to main group elements. Assessment does not include quantitative understanding of ionization energy beyond relative trends.]

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Atomic Number and Mass Number

The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element. Its value determines the identity of ...

Chemical Reactions

A chemical reaction is a process by which the bonds in the atoms of substances are rearranged to generate new substances. Matter cannot be created or ...

Chemical Equations

Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are ...

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Predicting Reaction Outcomes

Kinetics describes the rate and path by which a reaction occurs. In contrast, thermodynamics deals with state functions and describes the properties, ...

Chemical Reactions in Aqueous Solutions

Chemical substances interact in many different ways. Certain chemical reactions exhibit common patterns of reactivity. Due to the vast number of chemical ...

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates ...

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates ...

Rate-Determining Steps

Relating Reaction Mechanisms
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest ...

Reaction Stoichiometry

A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and ...

Limiting Reactant

The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in ...

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The ...

stoichiometry-product-yield-and-limiting-reactants

Stoichiometry, Product Yield, and Limiting Reactants

Chemical equations represent how a chemical reaction proceeds from reactants to products through physical or chemical change using chemical formulas.
...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Preparation of 25% v/v Ethylenediamine in Deionized WaterExpand
	Here, we show the laboratory ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Synthesis of tris(ethylenediamine)nickel chlorideExpand
	In this lab, you will combine nickel ...

Balancing Redox Equations

Electrochemistry is the science involved in the interconversion of electrical and chemical reactions. Such reactions are called reduction-oxidation, or ...

Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. [Clarification Steatement: Examples of chemical reactions could include the reaction of sodium and chlorine, of carbon and oxygen, or of carbon and hydrogen.] [Assessment Boundary: Assessment is limited to chemical reactions involving main group elements and combustion reactions.]

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What is Matter?

The substance of the universe&#8212;from a grain of sand to a star&#8212;is called matter. Scientists define matter as anything that occupies space and ...

Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. [Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.] [Assessment Boundary: Assessment does not include Raoult’s law calculations of vapor pressure.]

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Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

types-of-chemical-reactions-anabolic-and-catabolic

Types of Chemical Reactions: Anabolic and Catabolic

The first law of thermodynamics holds that energy can neither be created nor destroyed&#8212;it can only change form. An organism&#39;s essential function ...

types-of-chemical-reactions-exchange-and-reversible

Types of Chemical Reactions: Exchange and Reversible

An exchange reaction is a chemical reaction in which both synthesis and decomposition occur, chemical bonds are both formed and broken, and chemical ...

Energy Transfer in Chemical Reactions

Chemical reactions require sufficient energy to cause the matter to collide with enough precision and force that old chemical bonds can be broken and new ...

Arrhenius Plots

The Arrhenius equation relates the activation energy and the rate constant, k, for chemical reactions. In the Arrhenius equation, k = Ae&#8722;Ea/RT, R is ...

Reaction Rate

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 ...

Measuring Reaction Rates

Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical ...

factors-influencing-the-rate-of-chemical-reactions

Factors Influencing the Rate of Chemical Reactions

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 ...

Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. [Clarification Statement: Emphasis is on the idea that a chemical reaction is a system that affects the energy change. Examples of models could include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.] [Assessment Boundary: Assessment does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products.]

HS-PS1-4

Measuring Enzyme Reaction Rates

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