Name: cellular enthalpy and energy changes
Uploaded: 2023-04-30T10:40:59.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Biology

BIO.11

BIO.11.A

Enthalpy within the Cell

האנרגיה הפנימית, או E, היא האנרגיה המוכלת בתוך מערכת, כגון האנרגיה הכלולה בקשרים כימיים והתנועה האקראית של חלקיקיה. מערכת וסביבתה יכולות להעביר אנרגיה ביניהן.
השינוי באנרגיה הפנימית של מערכת, דלתא E, שווה לסכום של q, סך החום המועבר למערכת, ו-w, סך כל העבודה שנעשתה על המערכת.
ברוב התגובות הביוכימיות לא מתבצעת עבודה; לכן, השינוי באנרגיה הפנימית שווה ערך לפונקציה תרמודינמית אחרת הנקראת אנתלפיה.
השינוי באנתלפיה של מערכת או ∆H מלווה בשינוי שווה והפוך באנתלפיה של הסביבה.
תהליך אקסותרמי הוא כאשר המערכת משחררת חום לסביבה ומיוצגת על ידי אנתלפיה שלילית. תהליך אנדותרמי הוא כאשר המערכת צוברת חום, המיוצג על ידי אנתלפיה חיובית.
תאים חיים הם מערכות פתוחות שמחליפות חומר ואנרגיה עם סביבתם, באמצעות תהליכים אקסותרמיים ואנדותרמיים, בעקבות החוק הראשון של התרמודינמיקה.

אנתלפיה בתוך התא

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אנתלפיה (H) משמשת לתיאור התרמודינמיקה של תהליכים כימיים ופיזיקליים. אנתלפיה מוגדרת כסכום האנרגיה הפנימית של המערכת (U) והמכפלה המתמטית של הלחץ (P) והנפח שלה (V):

H = U + PV

אנתלפיה היא גם פונקציית מצב. לא ניתן למדוד באופן ישיר ערכי אנתלפיה עבור חומרים ספציפיים; ניתן לקבוע רק שינויים באנתלפיה עבור תהליכים כימיים או פיזיקליים. עבור תהליכים המתרחשים בלחץ קבוע (מצב שכיח לשינויים כימיים ופיזיקליים רבים), שינוי האנתלפיה (ΔH) הוא:

ΔH = ΔU + PΔV

החום המופרש בעת הפעלת מבער בונזן שווה לשינוי האנתלפיה של תגובת שריפת המתאן המתרחשת, מכיוון שהוא מתרחש למעשה בלחץ קבוע של האטמוספירה. ערך שלילי של שינוי אנתלפיה, ΔH < 0, מצביע על תגובה אקסותרמית; ערך חיובי, ΔH > 0, מצביע על תגובה אנדותרמית.

ה- ΔH והשינוי באנרגיה החופשית, הנקראת דלתא G (∆G), קשורים במשוואה הבאה, המכונה משוואת גיבס הלמהולץ;

ΔG = ΔH − TΔS

בדרך כלל אנו מחשבים תנאי pH, טמפרטורה ולחץ סטנדרטיים ב-pH 7.0 במערכות ביולוגיות, 25 מעלות צלזיוס ו-100 קילופסקל (1 בר), בהתאמה. שימו לב שהתנאים התאיים משתנים במידה ניכרת מהתנאים הסטנדרטיים הללו, ולכן ערכי ∆G מחושבים סטנדרטיים לתגובות ביולוגיות יהיו שונים בתוך התא.
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אנתלפיה (H) משמשת לתיאור התרמודינמיקה של תהליכים כימיים ופיזיקליים. אנתלפיה מוגדרת כסכום האנרגיה הפנימית של מערכת ...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Energy and Catalysis

אנרגיה וקטליזה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

cellular enthalpy and energy changes

Cellular enthalpy describes how heat and energy change during chemical and physical processes. Enthalpy is written as H and is defined as the sum of a system’s internal energy, U, and the product of pressure and volume, PV. It is a state function, which means its value depends on the state of the system, not the path taken.

Scientists cannot measure the enthalpy of a single substance directly. They can determine enthalpy changes, or ΔH, for a process instead. For reactions or changes that occur at constant pressure, which is common in many chemical and physical processes, ΔH equals ΔU + PΔV.

A simple example is the heat released when a Bunsen burner burns methane. That heat is equal to the enthalpy change of the combustion reaction because the reaction happens at essentially constant atmospheric pressure. A negative ΔH means the reaction is exothermic, while a positive ΔH means it is endothermic.

Enthalpy also connects to free energy through the Gibbs-Helmholtz equation, ΔG = ΔH − TΔS. In biology, standard conditions are usually pH 7.0, 25 degrees Celsius, and 100 kilopascals, or 1 bar. Cellular conditions often differ from these standards, so standard calculated ΔG values for biological reactions can change inside the cell.

Cellular Enthalpy and Energy Changes

the first law of thermodynamics

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enthalpy within the cell

Cellular enthalpy describes how heat and energy change during chemical and physical processes. Enthalpy is written as H and is defined as the sum of a system’s internal energy, U, and the product of pressure and volume, PV. It is a state function, which means its value depends on the state of the system, not the path taken. Scientists cannot measure the enthalpy of a single substance directly. They can determine enthalpy changes, or ΔH, for a process instead. For reactions or changes that...

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the equilibrium binding constant and binding strength

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free energy and equilibrium

Free Energy and Reaction Direction

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Cells Stay Out of Equilibrium

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Explore enthalpy, ΔH, and Gibbs free energy in cells. Learn how constant pressure, exothermic and endothermic reactions, and cellular conditions affect energy change.

Cellular Enthalpy and Energy Changes | JoVE K12

cell biology

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BIO.11.B

Science concepts--biological structures, functions, and processes. The student knows the significance of matter cycling, energy flow, and enzymes in living organisms. The student is expected to:

Cellular Enthalpy and Energy Changes

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