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

- [Verteller] De cyclus van een cel wordt positief gereguleerd, waardoor de vooruitgang in de stadia wordt bevorderd via de interactie van twee klassen van eiwitten die in het cytoplasma worden gevonden, cyclines en cycline-afhankelijke kinasen, of CDK. Standaard zijn CDK's altijd aanwezig in een cel in een geïnactiveerde vorm. Ze moeten zich binden aan een specifieke cycline om geactiveerd te worden.

Wanneer dit complex zich vormt, kan het CDK een doeleiwit fosforyleren dat zijn werking wijzigt en de cel initieert om door te gaan naar de volgende fase. In de meeste gevallen, wanneer een cycline wordt afgebroken, wordt de CDK geïnactiveerd, wat het einde van een bepaalde fase aangeeft. Bijvoorbeeld, tijdens G1, wanneer een type cycline, genaamd D, wordt gesynthetiseerd en zich bindt aan een CDK, gaat de cel over in de S-fase, omdat een andere cycline, E, piekt en een complex vormt met CDK om DNA-replicatie te stimuleren.

E wordt vervolgens afgebroken door cytoplasmatische enzymen en de cycline-A concentraties nemen gedurende de S-fase toe en blijven hoog in G2 om de toegang tot de M-fase te bevorderen wanneer het in een actief complex is. Nadat A is afgebroken, zullen de concentraties van cycline B pieken in de M-fase, en het complex zal de verschillende stadia van mitose activeren. Wanneer de concentraties van B dalen, zal de cel de mitose verlaten en zich verdelen.

Dus de concentraties van de vier verschillende cyclines variëren in voorspelbare patronen en worden gecombineerd met consistente CDK's op specifieke punten om een voorwaartse beweging te bereiken.

positieve regulerende moleculen

Om consistent gezonde cellen te produceren, moet de celcyclus – het proces dat dochtercellen genereert – nauwkeurig worden gereguleerd.

Interne regelgevende controlepunten zorgen ervoor dat de grootte, de energiereserves en de DNA-kwaliteit en volledigheid van een cel voldoende zijn om de celcyclus te doorlopen. Op deze controlepunten bevorderen of remmen positieve en negatieve regulatoren de voortzetting van de celcyclus van een cel.

Positieve regulatoren omvatten twee eiwitgroepen die ervoor zorgen dat cellen door regelgevende controlepunten kunnen passeren: cyclinen en cycline-afhankelijke kinasen (CDK's). Deze eiwitten zijn aanwezig in eukaryoten, variërend van gist tot mensen.

Cyclinen kunnen worden gecategoriseerd als G1-, G1/S-, S- of M-cyclinen, op basis van de celcyclusfase of -overgang waarbij ze het meest betrokken zijn. Over het algemeen zijn de niveaus van een bepaalde cycline laag gedurende het grootste deel van de celcyclus, maar stijgen abrupt aan het einde van het celcycluscontrolepunt waaraan zij het meest bijdragen (G1-cyclinen vormen een uitzondering, omdat ze gedurende de hele celcyclus nodig zijn). De cycline wordt vervolgens afgebroken door enzymen in het cytoplasma, waardoor de niveaus ervan afnemen, terwijl de cyclinen die nodig zijn voor de volgende controlepunten zich opstapelen.

Om de celcyclus te reguleren, moeten cyclinen worden gebonden aan een cycline-afhankelijke kinase (CDK), een type enzym dat een fosfaatgroep hecht om de activiteit van een doeleiwit te wijzigen. De CDK is alleen actief wanneer hij aan een cycline is gebonden. Afhankelijk van de cycline waaraan ze gebonden zijn, worden CDK's gericht op verschillende doeleiwitten die nodig zijn om door te gaan naar een bepaald celcyclusstadium.

Vergeleken met cyclinen blijven CDK's gedurende de celcyclus op relatief constante niveaus, maar hun activiteit en de eiwitten waarop ze zich richten veranderen afhankelijk van de verschillende niveaus van cyclines in de celcyclus.

Positieve regulerende moleculen

To consistently produce healthy cells, the cell cycle&mdash;the process that generates daughter cells&mdash;must be precisely regulated.

Internal ...

Education

JoVE Core

Biologie

Cellular Processes

Cellulaire processen

Cell Cycle and Division

Celcyclus en celdeling

KEY TERMS AND CONCEPTS

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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...

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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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Cyclins and CDKs in the Cell Cycle

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