Name: cell cycle regulators that control division
Uploaded: 2023-06-23T15:38:45.000Z
Duration: 1 min 27 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-4

molecular-factors-affecting-cell-division

Molecular Factors Affecting Cell Division

חלוקת התא, או השלב המיטוטי של מחזור התא, נשלטת על ידי גירויים כימיים חיצוניים, כגון גורמי גדילה והורמונים, וגורמים פנימיים, כגון מווסתי מחזור התא.
מחזור התא מווסת על ידי שילוב של חלבונים הנקראים ציקלינים וקינאזות תלויות ציקלין או Cdks. ריכוזים של ציקלינים שונים משתנים עם שלבי מחזור התא השונים.
כאשר התא מתקרב לסוף שלב G2, רמת הציקלין B עולה. בריכוזים גבוהים, ציקלין B יוצר קומפלקס עם Cdk1 שנקרא גורם מקדם שלב M או MPF.
פעילות MPF מווסתת על ידי אירועי זרחן ודפוספורילציה הקובעים אם התא עובר חלוקה או לא.
עד סוף G2, Wee1 קינאז פוספורילטים טירוזין שאריות על MPF ושומר אותו לא פעיל. פעולה זו מונעת כניסה למחזור התא ועוצרת את התא בשלב G2/M.
פעם Cdc25 dephosphorylates MPF, קינאז מפעיל Cdk phosphorylates threonine שמור על MPF ומפעיל אותו.
כעת התאים עוברים מיטוזה ומייצרים שני תאי בת.

גורמים מולקולריים המשפיעים על חלוקת התא

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מספר גורמים חיצוניים ופנימיים משפיעים על התחלת חלוקת התא ועיכובם. לדוגמה, מוות של תאים סמוכים או שחרור הורמון גדילה אנושי (hGH) מעודדים חלוקת תאים. לעומת זאת, חוסר ב-hGH או צפיפות של תאים יכולים לעכב את חלוקת התאים.

מספר חלבונים מתפקדים כמווסתים פנימיים כדי להבטיח שכל שלב במחזור התא יושלם נאמנה לפני שתמשיך לשלב הבא. מולקולות מווסתות עשויות לפעול ישירות או להשפיע על הפעילות או הייצור של חלבונים מווסתים אחרים. מולקולות רגולטוריות אלו מקדמות את התקדמות התא לשלב הבא (ויסות חיובי) או עוצרות את המחזור (ויסות שלילי).

מולקולות הרגולטור החיוביות כוללות את הציקלין והקינאזות התלויות בציקלין (Cdks) החיוניים להתקדמות מחזור התא. בעוד שרמת ה-Cdks נשארת קבועה, הרמות של ארבעה ציקלינים (ציקלין D, E, A, B) משתנות במהלך השלבים השונים של מחזור התא. לאחר קשירה איתנה עם Cdk, ציקלין עובר פוספורילציה לצורך הפעלה. רמות ציקלין D עולות בשלב G1, נשארות גבוהות לאורך כל הדרך ויורדות בשלב M. רמת ציקלין E מגיעה לשיא בנקודת המפגש של שלב G1-S, בעוד שציקלין A גבוה בשלבי S ו-G2. כשהתא מתקרב לשלב M, רמת ה-Cyclin B עולה ומעודדת חלוקת תאים.

המולקולות הרגולטוריות השליליות כוללות את חלבון הרטינובלסטומה (Rb), p53 ו-p21, אשר עוצרים את מחזור התא. לדוגמה, כאשר p53 מזהה נזק ל-DNA, מגויסים אנזימי תיקון DNA כדי לתקן את הנזק. אם ה-DNA נשאר ללא תיקון, p53 מתחיל אפופטוזיס או מוות של תאים ומונע שכפול כרומוזומים פגום. רמת ה-p53 המוגברת בתא עשויה גם לעורר סינתזה של p21. ה-p21 נקשר לקומפלקס Cdk/cyclin ועוצר את התקדמות המחזור. הצטברות של p53 ו-p21 מונעת מהתאים לעבור לסינתזת ה-DNA (שלב S).

הטקסט הזה מותאם מ <a href="https://openstax.org/books/biology-2e/pages/10-3-control-of-the-cell-cycle">Openstax, Anatomy and Physiology 2e, Section 10.3: Control of the Cell Cycle</a>
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מספר גורמים חיצוניים ופנימיים משפיעים על ייזום ועיכוב חלוקת התא. למשל, מוות של תאים סמוכים או שחרור של ...

Education

JoVE Core

Anatomy and Physiology

אנטומיה ופיזיולוגיה

Unit 1

יחידה 1

Essential Cellular Processes

תהליכים תאיים חיוניים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

cell cycle regulators that control division

Cell division is controlled by outside signals and by internal cell cycle regulators. Nearby cell death can encourage division, and human growth hormone (hGH) can also promote it. In contrast, too little hGH or crowded cells can slow or stop division.

Inside the cell, regulator molecules help each stage finish correctly before the next stage begins. Some regulators act directly on the cycle, while others affect the activity or production of other regulatory proteins. These molecules can either push the cell forward, which is positive regulation, or stop the cycle, which is negative regulation.

The main positive regulators are cyclins and cyclin-dependent kinases, or Cdks. Cdks stay at a constant level, while cyclin levels rise and fall during the cell cycle. The four cyclins are cyclin D, cyclin E, cyclin A, and cyclin B. When cyclins bind tightly to Cdks, the complex becomes active after phosphorylation.

Each cyclin acts at a different point in the cycle. Cyclin D rises in G1, stays high through most of the cycle, and drops in M phase. Cyclin E peaks at the G1-S transition. Cyclin A is high during S and G2, and cyclin B rises as the cell nears M phase and helps drive cell division.

Negative regulators help prevent damaged or uncontrolled division. These include retinoblastoma protein, or Rb, p53, and p21. When p53 detects DNA damage, it recruits DNA repair enzymes. If the damage is not repaired, p53 can trigger apoptosis, or cell death, and prevent damaged chromosomes from being copied.

p53 can also increase p21 synthesis. The p21 protein binds to the Cdk/cyclin complex and blocks cycle progression. Together, p53 and p21 can stop the cell from entering DNA synthesis, which is the S phase.

Cell Cycle Regulators That Control Division

cell-cycle-regulators-that-control-division

the central dogma

Central Dogma: DNA to Protein

The central dogma explains how genetic information flows in cells from DNA to RNA to protein. It is a core idea in molecular biology and helps show how genes influence cell function. DNA stores the instructions. During transcription, a cell copies a gene into RNA, which is a related nucleic acid. That RNA message can then be used in translation to build a protein. Proteins carry out many jobs in cells and help determine traits. The central dogma links the genetic code in DNA to the molecules...

replication in eukaryotes

Eukaryotic DNA Copying at the Replication Fork

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RNA Types in Gene Expression

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transcription

Transcription and RNA Synthesis

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translation

Translation: mRNA to Protein

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regulation of expression at multiple steps

regulation-of-expression-at-multiple-steps

How Cells Control Gene Expression

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Cell Cycle Stages in Cell Growth

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interphase

Interphase and Cell Growth

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mitosis and cytokinesis

Cell Division: Mitosis and Cytokinesis

Cell division depends on mitosis and cytokinesis. Mitosis is the stage when the cell’s nucleus divides and the copied chromosomes are separated into two sets. Cytokinesis is the step that follows and splits the cell into two daughter cells. These two processes work together to make sure each new cell receives genetic material and its own cytoplasm. Mitosis keeps the chromosome sets organized, while cytokinesis finishes the division of the whole cell. Together, they create two separate cells...

the cell cycle control system

Cell Cycle Checkpoints and Cyclin Control

The cell cycle is controlled by checkpoints that help a cell move from one phase to the next and begin mitosis. This control system uses internal regulatory molecules and outside signals to send stop or advance instructions. It makes sure each step is finished before the cell moves forward. Cyclins and cyclin-dependent kinases, or Cdks, are the main regulators of the cell cycle. They act during the G1, G2, and M phases. These regulators work at specific checkpoints to keep cell division...

molecular factors affecting cell division

Cell division is controlled by outside signals and by internal cell cycle regulators. Nearby cell death can encourage division, and human growth hormone (hGH) can also promote it. In contrast, too little hGH or crowded cells can slow or stop division. Inside the cell, regulator molecules help each stage finish correctly before the next stage begins. Some regulators act directly on the cycle, while others affect the activity or production of other regulatory proteins. These molecules can either...

what is meiosis?

Meiosis and the Formation of Gametes

Meiosis is the cell division process that forms gametes, or sex cells. It reduces the chromosome number so offspring can inherit the correct amount of genetic material. This process includes two successive divisions. First, one cell divides, and then the resulting cells divide again. These steps separate the genetic material in a controlled way. Meiosis helps explain how sexual reproduction passes traits from one generation to the next. It is a key topic in high school biology because it...

overview of cell signaling

Cell Signaling Pathways and Responses

Cell signaling pathways and responses help cells communicate and react to changes. Cells send signals to one another, and those signals can trigger a specific response in the target cell. A signal usually begins when a signaling molecule reaches a cell with the right receptor, which is a protein that receives the message. The receptor helps the cell recognize the signal and start the communication process. Inside the cell, the message can move through a signaling pathway. This pathway passes...

types of signaling molecules

Chemical Messengers in Cell Signaling

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g protein-coupled receptors

G Protein-coupled Receptor Signaling

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cellular differentiation

From Stem Cell to Specialized Cells

Cellular differentiation turns unspecialized cells into specialized cells with specific jobs. This process helps a complex organism, such as a human, develop from a single fertilized egg into a body with many cell types. Nerve cells, muscle cells, and epithelial cells are examples of the final cell types that appear during development. A zygote is the first cell after fertilization. It is a totipotent stem cell, which means it has very high differentiation potential and can form all cell types...

key terms and concepts

Learn how external signals, cyclins, Cdks, p53, and p21 control cell division and help cells decide when to divide or stop.

Cell Cycle Regulators That Control Division | JoVE K12

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HS-LS1-2

Cell Cycle Regulators That Control Division

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