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Signal Transduction Pathway (STP)
A series of molecular events that relay a signal from the receptor to a specific cellular response.
What are the steps in a Signal Transduction Pathway?
1. Reception (signal received), 2. Transduction (signal relayed), 3. Response (cell reacts).
What happens during reception in an STP?
A signaling molecule binds to a receptor, causing a conformational change.
What are examples of signaling molecules?
Hormones, neurotransmitters, and local regulators.
What types of receptors are involved in reception?
Cell surface receptors and intracellular receptors.
What is the purpose of transduction in STP?
To amplify and relay the signal inside the cell.
What are second messengers?
Small molecules that relay signals within the cell, like cAMP, cGMP, IP₃, DAG, and Ca²⁺.
How is signal amplification achieved?
One signal molecule activates many molecules at each step of the pathway.
What are examples of cellular responses to signals?
Activation of genes for transcription/translation.
Activation/inactivation of proteins to regulate functions.
What is the purpose of cellular responses?
To carry out the intended function of the signaling molecule.
What is the role of scaffolding proteins in signaling?
They hold multiple relay proteins together, increasing signal efficiency.
How are signals terminated in the STP?
Deactivation of kinases by protein phosphatases, hydrolysis of GTP by GTPase, and conversion of cAMP to AMP.
Define homeostasis.
The steady-state of internal conditions maintained by living organisms.
What are feedback loops?
Mechanisms where the output of a process regulates itself.
How does a negative feedback loop work?
It reduces the stimulus, bringing the system back to homeostasis.
How does a positive feedback loop work?
It enhances the stimulus, moving the system away from equilibrium.
Give an example of a negative feedback loop.
Insulin regulation of blood sugar levels.
Give an example of a positive feedback loop.
Oxytocin release during childbirth for uterine contractions.
What are the two main types of cell division?
Mitosis (eukaryotic cells) and binary fission (prokaryotic cells).
What are the key functions of cell division?
Growth, repair, and reproduction.
What is the cell cycle?
A series of events where a cell grows, replicates its DNA, and divides.
What are the phases of the cell cycle?
G₁, S, G₂ (interphase), and M phase (mitosis + cytokinesis).
What happens in the G₁ phase?
Cell growth and preparation for DNA replication.
What happens in the S phase?
DNA replication.
What happens in the G₂ phase?
Further growth and preparation for mitosis.
What are the phases of mitosis?
Prophase, Prometaphase, Metaphase, Anaphase, Telophase.
Prophase
Chromatin condenses, mitotic spindle forms.
Prometaphase
Nuclear envelope breaks down, spindle attaches to kinetochores.
Metaphase
Chromosomes align on the metaphase plate.
Anaphase
Sister chromatids separate and move to opposite poles.
Telophase
Nuclei reform, chromosomes decondense.
What is cytokinesis in animal cells?
Cleavage furrow pinches the cell into two.
What is cytokinesis in plant cells?
A cell plate forms, which develops into the cell wall.
How does binary fission differ from mitosis?
Binary fission occurs in prokaryotes and is simpler, with no spindle fibers or nuclear envelope involvement.
What are the steps of binary fission?
1. DNA replication, 2. DNA segregation, 3. Cell splitting.
What regulates the cell cycle?
Cyclin and Cyclin-Dependent Kinases (Cdks).
What are cell cycle checkpoints?
G₁, G₂, and M checkpoints ensure proper progression of the cycle.
What happens if a cell doesn’t pass the G₁ checkpoint?
It enters G₀, a non-dividing phase.
What causes cancer at the cellular level?
Mutations in genes like p53, leading to loss of cell cycle control.
What is the difference between benign and malignant tumors?
Benign: Non-invasive, do not spread.
Malignant: Invasive, can metastasize.
What is metastasis?
The spread of cancer cells to new areas of the body.
What external factors influence cell division?
Growth factors, density-dependent inhibition, and anchorage dependence.
How do cancer cells differ from normal cells regarding these factors?
Cancer cells ignore density-dependent inhibition and anchorage dependence.
What role does p53 play in preventing cancer?
It halts the cell cycle when DNA damage is detected and can trigger apoptosis.
How does the immune system respond to cancer cells?
It identifies and attacks cancer cells unless they evade detection through mutations.
What is chromatin?
DNA packaged with proteins.
What is a sister chromatid?
Two identical copies of a chromosome connected at the centromere.
What is the mitotic spindle?
A structure made of microtubules that separates chromatids.
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