Name: cyclins and cdks in the cell cycle
Uploaded: 2019-03-11T09:21:14.000Z
Duration: 1 min 45 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Biology

BIO.3

BIO.3.c

Positive Regulator Molecules

Le cycle d'une cellule est régulé positivement,promouvant le progrès par étapespar l'interaction de deux classesde protéines trouvées dans le cytoplasme :les cyclines et les kinases cycline-dépendantes ou CDK. 
Par défaut, les CDK sont toujours présentesdans une cellule sous une forme inactive. 
Elles doivent se lier à un cycline spécifiquepour être activées. 
Quand ce complexe se forme,le CDK peut phosphoryler une protéine cible,qui altère sa fonctionet initie la cellule pour passer à la phase suivante. 
Dans la plupart des cas où une cycline est dégradée,la CDK est inactivée,signalant la fin d'une phase particulière. 
Par exemple, au cours de G1 quand un type de cycline,appelé D, est synthétisé et se lie à un CDK,la cellule passe en phase Squand une autre cycline, E,atteint des pics et forme un complexeavec CDK pour promouvoir la réplication de l'ADN. 
E est ensuite dégradée par les enzymes cytoplasmiqueset les concentrations de cycline A augmententtout au long de la phase Set restent élevés dans la phase G2pour favoriser l'entrée en phase Mlorsqu'il s'agit d'un complexe actif. 
Après la dégradation de A, les concentrations de cycline Bs'élèvent au maximum en phase M et le complexe activerales différents stades de la mitose. 
Quand les niveaux de B chutent,la cellule sort de la mitose et se divise. 
Ainsi, les niveaux des 4 cyclines différentsvarient selon des modèles prévisibleset les combiner avec des CDK cohérentsà des moments précis pour aller de l'avant.

Bai, Jingwen, Yaochen Li et Guojun Zhang. « Régulation du cycle cellulaire et découverte de médicaments anticancéreux ». Cancer Biology & Medicine 14, n° 4 (novembre 2017) : 348-62. [<a href="https://doi.org/10.20892/j.issn.2095-3941.2017.0033 » target="__blank">Source</a>]

Laphanuwat, Phatthamon et Siwanon Jirawatnotai. « Rôles immunomodulateurs des régulateurs du cycle cellulaire. » Frontiers in Cell and Developmental Biology 7 (2019). [<a href="https://doi.org/10.3389/fcell.2019.00023 » target="__blank">Source</a>]

régulateurs positifs

Pour produire constamment des cellules saines, le cycle cellulaire — le processus qui génère les cellules filles — doit être réglé avec précision.
 
 Les points de contrôle de régulation interne garantissent que la taille, les réserves d’énergie, la qualité et l’exhaustivité de l’ADN d’une cellule sont suffisantes pour progresser dans le cycle cellulaire. À ces points de contrôle, les régulateurs positifs et négatifs favorisent ou inhibent la progression d’une cellule dans le cycle cellulaire.
 
 Les régulateurs positifs comprennent deux groupes de protéines qui permettent aux cellules de franchir les points de contrôle de régulation : les cyclines et les kinases dépendantes de la cycline (CDK). Ces protéines sont présentes dans les eucaryotes, allant de la levure à l’homme.
 
 Les cyclines peuvent être classées comme des cyclines G1, G1/S, S ou M en fonction de la phase du cycle cellulaire ou de la transition dans laquelle elles sont le plus impliquées. En général, les niveaux d’une cycline donnée sont faibles pendant la majeure partie du cycle cellulaire, mais augmentent brusquement au point de contrôle auquel elles contribuent le plus (les cyclines G1 sont une exception car elles sont nécessaires tout au long du cycle cellulaire). La cycline est ensuite dégradée par des enzymes dans le cytoplasme et ses niveaux diminuent. Pendant ce temps, les cyclines nécessaires aux prochains points de contrôle s’accumulent. 
 
 Pour réguler le cycle cellulaire, les cyclines doivent être liées à une kinase dépendante de la cycline (CDK) — un type d’enzyme qui fixe un groupe phosphate pour modifier l’activité d’une protéine cible. La CDK n’est active que lorsqu’elle est liée à une cycline. Selon la cycline à laquelle elles sont liées, les CDK sont dirigées vers différentes protéines cibles qui sont nécessaires pour passer à une étape particulière du cycle cellulaire.
 
 Par rapport aux cyclines, les CDK restent à des niveaux relativement constants tout au long du cycle cellulaire. Cependant, leur activité et les protéines qu’elles ciblent changent en fonction des niveaux variables de cycline le long du cycle cellulaire.

Régulateurs positifs

Pour produire régulièrement des cellules saines, le cycle cellulaire, c’est-à-dire le processus qui génère les cellules filles, doit être régulé avec précision.

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cyclins and cdks in the cell cycle

Cyclins and CDKs help control the cell cycle, the process that produces daughter cells. Cells use internal checkpoints to make sure their size, energy reserves, and DNA are ready before they move forward. At these checkpoints, positive regulators help the cell continue, while negative regulators slow or stop it.

The main positive regulators are cyclins and cyclin-dependent kinases, or CDKs. These proteins are found in eukaryotes, from yeast to humans. Cyclins are grouped by the stage they help control: G1, G1/S, S, or M cyclins. G1 cyclins are unusual because they are needed throughout the cell cycle.

Cyclin levels usually stay low for most of the cycle. They rise sharply at the checkpoint where they are needed most, then enzymes in the cytoplasm break them down and their levels fall. At the same time, the next cyclins begin to build up for later checkpoints.

CDKs are enzymes that add a phosphate group to a target protein. A CDK becomes active only when it is bound to a cyclin. The cyclin it binds helps direct the CDK to the right target proteins for that stage of the cell cycle. CDK levels stay fairly constant, but their activity changes as cyclin levels rise and fall.

Cyclins and CDKs in the Cell Cycle

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positive regulator molecules

Cyclins and CDKs help control the cell cycle, the process that produces daughter cells. Cells use internal checkpoints to make sure their size, energy reserves, and DNA are ready before they move forward. At these checkpoints, positive regulators help the cell continue, while negative regulators slow or stop it. The main positive regulators are cyclins and cyclin-dependent kinases, or CDKs. These proteins are found in eukaryotes, from yeast to humans. Cyclins are grouped by the stage they help...

negative regulator molecules

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cancer

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key terms and concepts

Learn how cyclins and CDKs regulate cell cycle checkpoints, with cyclin types, changing levels, and how CDKs are activated to move cells forward.

Cyclins and CDKs in the Cell Cycle | JoVE K12

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

From Molecules to Organisms: Structures and Processes

HS-LS1-4

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BIO.6.A

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Cyclins and CDKs in the Cell Cycle

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