Cell Biology Signal Transduction Quiz

Signal Transduction Pathways

• Signal transduction pathways are processes where cells receive and respond to signals.
• A ligand is a molecule that binds to a receptor on another molecule, initiating a signal.
• Quorum sensing is a process where cells communicate with each other by releasing and receiving chemical signals. This allows them to coordinate their behaviors in response to population density.
• Direct contact communication involves physical interaction between cells like gap junctions in animal cells. Cell-cell recognition with surface molecules plays a signaling role. Cell-cell recognition can involve membrane-bound signal receptors.

Local Signaling

• Local signaling includes paracrine signaling (signals act on nearby cells) and synaptic signaling (signals travel across synapses in neurons).
• Paracrine signaling uses secreted messenger molecules to affect target cells close to the emitting cell.
• Synaptic signaling involves the release of neurotransmitters across synapses, which bind to receptors on target cells.

Long-Distance Signaling

• Long-distance signaling involves hormones (chemical signals that travel through the circulatory system).

Stages of Cell Signaling

• Reception: A signaling molecule (ligand) binds to a receptor protein on the cell surface (or inside the cell).
• Transduction: The binding of the ligand changes the receptor protein's shape, initiating a cascade of intracellular events.
• Response: The final step may involve changes in gene expression, enzyme activity, protein activation, cellular movement, etc.

Receptor Types

• Membrane receptors: Located on the cell surface; typically bind to large, polar signaling molecules that cannot readily cross the membrane.
  • Example: G protein-coupled receptors (GPCRs).
• Intracellular receptors: Located within the cell; typically bind to small, hydrophobic signaling molecules that can cross the plasma membrane, like steroid hormones.
  • Example: steroid hormone receptors.

Cascades & Protein Kinases

• Cascades are a series of enzyme activation reactions (and other changes), amplifying each step to boost the signal.
• Protein kinases are enzymes that transfer phosphate groups from ATP to other proteins (phosphorylation/dephosphorylation), changing protein activity—often involved in cascades.

Secondary Messengers

• Secondary messengers are small molecules that relay signals from receptors to target molecules inside the cell.
  • Examples: Cyclic AMP (cAMP) and calcium ions (Ca²⁺).

Cellular Communication Responses

• Cellular responses can range from changes in gene expression (protein synthesis), altering enzyme activity, or inducing cell movement.

Receptor Proteins

• G protein-coupled receptors (GPCRs): Activated when a ligand binds, triggering a change in the receptor's shape. This activates a G-protein, which then activates an enzyme—which then activates a final response.
• Receptor tyrosine kinases (RTKs): Ligand binding causes dimerization and autophosphorylation of the receptor, which initiates signal transduction pathways.
• Ion channel receptors: Ligand binding opens or closes ion channels, changing ion flow across the plasma membrane.

Signal Transduction Pathway Problems/Defects

• Receptor defects affect signal activation, and pathway malfunctions cause various diseases.

Apoptosis

• Apoptosis is programmed cell death; it is regulated by cell signaling pathways. Apoptotic signals can trigger cellular destruction.

Interphase

• Interphase is the stage in the cell cycle that precedes mitosis/meiosis.

Chromatin

• Chromatin is a complex of DNA and protein; it condenses to form chromosomes during cell division.

Phases of Interphase

• G1 phase: Cell growth and preparation for DNA replication.
• S phase: DNA replication occurs.
• G2 phase: Cell growth and synthesis of proteins needed for mitosis/meiosis.

Interphase Checkpoints

• G1 checkpoint: Checks if the cell is large enough, has sufficient resources, and if the DNA is undamaged.
• G2 checkpoint: Checks if the DNA replication is complete and and if the DNA is undamaged.
• M checkpoint: Checks if all chromosomes are correctly attached to the mitotic spindle. These checkpoints ensure accurate cell division and prevent the propagation of damaged cells.

Cell Division Inhibition

• Cells might not divide due to lack of growth factors, DNA damage, or external signals.

G0 Phase

• G0 phase is a non-dividing state that cells enter when they're not actively preparing for division. This phase can be temporary or permanent.

Centromere

• Centromere: A region of condensed chromosome where the two sister chromatids are joined.
• It is made of repetitive DNA sequences and proteins

Chromatids

• Chromatids are identical copies of a chromosome formed by DNA replication.
• They are joined at the centromere

Phases of Mitosis

• Prophase: Chromosomes condense, nuclear envelope breaks down, mitotic spindle forms.
• Prometaphase: Spindle fibers attach to kinetochores.
• Metaphase: Chromosomes align at the metaphase plate.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear envelope reforms, spindle apparatus breaks down.

Kinetochore

• Kinetochore is a protein complex on the centromere that attaches to spindle fibers.

Chromatids to Chromosomes

• A chromatid becomes a chromosome when the two sister chromatids are separated, creating independent chromosomes.

Plant vs. Animal Mitosis

• Plant cells form a cell plate during cytokinesis, whereas animal cells form a cleavage furrow.

Cytokinesis

• Cytokinesis is the division of the cytoplasm that follows mitosis to create two daughter cells.

Binary Fission

• Binary fission is a type of asexual reproduction where a cell divides into two roughly equal-sized daughter cells; common in prokaryotes. Binary fission is simpler than mitosis, and doesn't involve a nucleus.

Cell Cycle Regulatory Proteins

• Cyclins and cyclin-dependent kinases (CDKs) are major regulatory proteins involved in cell cycle control.

MPF

• Maturation-promoting factor (MPF) is a complex of cyclin and CDK that triggers the cell to progress through the cell cycle.

Growth Factors

• Growth factors are proteins that stimulate cell division and promote cell growth; important for wound healing, tissue repair, and development.
  • Example: Epidermal growth factor (EGF), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF).

Loss of Cell Cycle Control

• Loss of cell cycle control can lead to uncontrolled cell proliferation, a hallmark feature of cancer.

Proto-oncogenes and Tumor Suppressor Genes

• Proto-oncogenes code for proteins that promote cell cycle progression. Tumor suppressor genes code for proteins that inhibit cell cycle progression.
• They are crucial for regulating cell growth and preventing uncontrolled cell division.
• If they stop working, they can accelerate cancer progression.

Oncogenes

• Oncogenes are mutated forms of proto-oncogenes that promote cell division excessively.

Dominant vs. Recessive Cancer Genes

• Cancer genes are characterized as dominant or recessive based on how many copies of the mutated gene (allele) are needed to drive uncontrolled cell proliferation and thus cause cancer.
• Most cancer genes are dominant

p53

• p53 is a tumor suppressor protein that plays a crucial role in DNA repair, apoptosis and cell cycle arrest (halts cell division) when DNA damage is detected. It's a key player in the cellular response to stress.

Tumor Types

• Benign tumors: Do not invade surrounding tissues, usually not life-threatening.
• Malignant tumors: Invade surrounding tissues and can spread to other parts of the body (metastasis) and life-threatening.

Metastasis

• Metastasis is the spread of cancer cells from the primary tumor to other locations in the body.

Cancer Treatments

• Surgery: Removal of the tumor.
• Radiation therapy: Using high-energy radiation to kill cancer cells.
• Chemotherapy: Using drugs to stop cancer cell growth.
• Hormone therapy: Using drugs to block the effects of hormones that drive cancer growth.
• Targeted therapy: Drugs that target specific molecules involved in cancer cell growth.

Cancer and Cell Cycle Changes

• Accumulation of mutations: In multiple genes involved in cell cycle regulation leads to uncontrolled growth.
• Loss of tumor suppressor function: Prevents proper cell cycle arrest and repair mechanisms allowing mutations to take effect.
• Activation of oncogenes: Promotes uncontrolled cell division.
• Evasion of programmed cell death: Cancer cells resist apoptosis allowing them to escape normal cell death control mechanisms.

Cancer Treatment's Effect on Cell Cycle

• Surgery, radiation, and chemotherapy target different points of the cell cycle to slow cancer growth and/or kill cancer cells.

Cancer Eradication Difficulty

• Cancer's origin from complex somatic errors, genetic variations and adaptability, make it hard to eradicate.

Test your knowledge on signal transduction pathways and local signaling mechanisms within cells. Explore the roles of ligands, quorum sensing, and different types of cell communication. This quiz covers essential concepts in cell signaling processes and their biological significance.