Control of the Eukaryotic Cell Cycle 2 Flashcards
What are the 4 major forms of signal transduction in cells?
Endocrine, paracrine, neuronal, contact-dependent
What is endocrine signalling?
Occurs when endocrine cells release hormones that act on distant target cells in the body
What is paracrine signalling?
It is a form of cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells
What is neuronal signalling?
Neurons send electrochemical signals, and once a neuron has been stimulated by stimuli, it will generate an electric potential that travels down the length of the cell
What is contact-dependent signalling?
It is a type of cell/extracellular matrix signalling in multicellular organisms that requires close contact. A membrane ligant (protein, lipid, oligosaccharide) and a membrane protein of two adjacent cells interact
What are some biological outcomes?
Death; differentiation; cell cycle progression; cell movement
How does a cell in G0 re-enter the cell cycle?
It needs activity of G1-phase cyclin-CDK complexes
What do the G1-phase cyclin-CDK complexes do to help a cell re-enter the cell cycle?
Regulate progression through the restriction point and trigger a wave of genetic expression need to support commitment into a new cell cycle, S phase and DNA replication
What stimulates G1-phase cyclin-CDK complexes?
Mitogens
How do mitogens stimulate G1-phase cyclin-CDK complexes?
Mitogens release the breaks on CDK activity, thereby allowing cell cycle entry and progression
How is the Ras-MAPK signal transduction pathway triggered?
Mitogens bind to cell-surface receptors which triggers this pathway
What is the Ras-MAPK pathway?
The activation of Ras activates the MAP kinase cascade, which leads to increased expression of several immediate early genes (including the transcription regulatory protein Myc)
What is the function of Myc?
Increases transcription of many delayed response genes, including the G1 phase cyclin, Cyclin D
What does Cyclin D-Cdk4 activate?
A group of transcription regulatory factors called E2F proteins
How are E2F proteins released from their inactive site by Rb proteins?
Phosphorylation of Rb proteins by cyclin D-Cdk 4 releases active E2F proteins
What is the main function of Rb proteins?
Inhibit cell cycle progression until a cell is ready to divide
What do E2F proteins do once they are activated?
They activate expression of their target genes (G1/S phase cyclins and S phase cyclins)
What are 2 of the positive feedback loops?
Activate E2F proteins (phosphorylation of Rb) and active G1/S phase cyclin-CDK and active S phase cyclin-CDK (phosphorylation of p27)
What happens if mitogens are not available during G1?
The cells enter G0
What happens if mitogens are present during G1?
Mitogens stimulate expression of G1-phase cyclins
How does apoptosis occur?
DNA damaged is detected by detector enzymes (ATM ATR, Chk1 Chk2). Protein kinases become catalytically active which phosphorylates p53. Once p53 levels rise, it is able to induce the transcription of inhibitory proteins and these bind to/inhibit cyclin-cdk complexes which leds to cell cycle arrest
