● Amplification: An effect that occurs when the original signal is strengthened by many domino-effect reactions within signal transduction.
● Apoptosis: can be termed as “cell suicide”, occurs as a result of cell signals
● Epinephrine: water soluble ligand molecule; signals the cell to convert glycogen into usable sugar/energy
o responsible for the onset of the fight or flight reaction
o also referred to as adrenaline
● G protein: Binds with GTP and works with a G-protein coupled receptor to relays signals from the outside to the inside of the cell
● Gap junction: intercellular junction common between animal cells, allows materials to pass through
● Glycogen: polysaccharide that acts as a storage for glucose; it is common in muscle and liver cells
● Ligand: a molecule that binds to a very specific receptor in the cell membrane; it’s binding to the receptor is the onset of signal transduction
o Water soluble ligands require an external receptor, while hydrophobic ligands usually have intracellular receptors
o Ligand-gated ion channel: channel in the plasma membrane that opens in response to the binding of a specific ligand
● Local regulator: type of cell signal that acts locally
o Common in short distance cell signaling
● Protein kinase: Enzyme that removes the phosphate from ATP and attaches it to the next protein kinase in a reaction cascade
o encourages the cascade of reaction during signal transduction
● Protein phosphatase: enzyme the removes the phosphate group from proteins kinases in signal transduction
o Often used to halt a certain signal that has been cascading
● Receptor tyrosine kinase: Another plasma membrane receptor that functions in cell signaling
o helps cells in their regulation of cell cycle and cell reproductive signals, as it is able to trigger numerous signal pathways at the same time
● Signal transduction: the processes that include how the cell responds an extracellular (or intracellular) signal
● Testosterone: steroid hormone that works as a ligand for multiple signals that aid in the process of male reproductive system development.
● Transcription factor: A regulatory protein that binds to DNA and affects transcription of specific genes.
● Stages of Cell Communication:
o reception - ligand binds to receptor
o transduction - original signal from ligand is amplified through a cascade of reactions
o response - cell responds when the end of the cascade is reached
● Hormone: chemical substance that acts as a ligand in signal transduction; common in long-distance communication
● Endocrine function: produces and sends hormones
● Neurocrine function: Hormones transmit the molecular signal from neuron to its axon and then into bloodstream to the distant target cells
● Paracrine function: hormonal signals that act on local cells
● Autocrine function: hormone acts back on the cells of their origin to modulate their own secretion or intracellular processes
● Steroid hormones are made from cholesterol
o aldosterone, progestins, vitamin D, estrogens
● Major classes of hormone receptors:
o Extracellular/membrane receptors: binding of hormonal ligand to an extracellular receptor causes a conformational change, which in turn activates more enzymes that continue the cascade effect of signal transduction. Some common ones are:
▪ Adenylyl cyclase
▪ cGMP phosphodiesterase
▪ Ca2+ and K+ channels
▪ Phospholipase-C, -A2 or D
o Nuclear receptors: water-fearing hormones bind to intracellular receptors, and their effect is dependent on the number of hormones/ligands present to kickstart the cell response
● Intracellular Signals: protein kinases or signal receptors inside the cell that bind to hydrophobic ligands
o Steroids, hormones
● Transduction: cascades of interactions between protein kinases and ATP that amplify the signal received by the binding of ligand
o Amplification occurs when a single kinase activates multiple kinases in the next level of the cascade reaction
o The multiple kinases allow places for control and regulation
o Signals are constantly transduced (translated) into a different form until another signal is sent to prevent phosphorylation of ATP.
▪ Kinases stimulate pathways
▪ Phosphatase shuts off pathways
● Dephosphorylation: Occurs when phosphatase enzymes remove the phosphates from the protein.
● Secondary Messengers: Small, non-protein, water-soluble molecules or ions that pass a signal; spread via diffusion.
o cyclic-AMP: responsible for activating the protein kinase cascade. Often works with adenylyl cyclase
o Calcium Ions: a common messenger and relays signals in G-Protein and Tyrosine Kinase Receptor pathways.
● Cell signaling leads to a cytoplasmic response or a change in the nucleus that leads to protein production, inciting a cellular response.
● Gene Expression: gene information is used to produce proteins through translation and transcription
o Transcription: copies DNA into RNA
o Translation: RNA used to make proteins
● Signal Termination: Signal response is terminated quickly by the reversal of the ligand binding.
● Quorum sensing: cellular communication method common in bacteria where bacteria inform each other of the excess of products in their environment
● Pheromone: chemical signal released externally by animals of the same species
● Antigen-presenting cell (APC): immune system cells that help in regulation
● Helper T lymphocyte (TH): CD4+ cells help in the adaptive characteristic of the immune system
● Plasmodesma: allow small molecules (including signaling molecules) to flow between neighboring cells
● Neurotransmitters: ligand for nerve cells
● Insulin: hormone produced to help the body use sugar
● Negative Feedback Loop: similar to homeostasis in which a system aims to stay at or close to a set point
● Positive Feedback Loop: signal pathways that move away from a set point; a signal in one direction activates and amplifies in that direction
● Feedback Mechanism: a system in which the products formed by a signal pathway help regulate and inhibit that pathway
● Purpose of Cell Division:
o Unicellular: to reproduce and have their kind continue on
o Multi-Cellular: growth, repair, replace dying/dead cells
● Parent and daughter cells are identical: DNA, organelles, etc.
● DNA in Cell Division
o Chromatin: coiled DNA
o Chromosomes: DNA that is wrapped tightly
o Mitotic chromosome: a chromosome that has duplicated, often referred to as sister chromatids
● Stages of Cell Cycle
o Interphase: cells are often in this phase; the longest phase
▪ NO division happens here
o 3 phases of interphase: G1 phase, S phase, G2 phase
▪ G0 phase of interphase: optional part of interphase where cells exit the cell cycle and no longer divide
▪ G1 of interphase: cells grow after they are "born"
▪ S phase of interphase: DNA replicates in preparation for division
● DNA replicates prior to cell division so each daughter cell gets a full set of DNA
▪ G2 phase of interphase: cell finishes growth; prepares to divide by making organelles, proteins, and membranes
● Mitosis: cell division of somatic cells that produces identical daughter cells
o Prophase: Chromosomes become visible, nuclear envelope dissolves, centrosomes form and spindle fibers attach to chromosomes
o Metaphase: Chromosomes line up in the middle of the cell; centrosomes move to opposite poles of cell
o Anaphase: sister chromatids are pulled to opposite sides of cell by spindle fibers and centrosome
o Telophase: centrosomes disassemble, nuclei reform, chromosomes start to uncoil back into chromatin
o Cytokinesis in animal cells: cleavage furrow
o Cytokinesis in plant cells: cell plate, which then becomes a cell wall that separates the resulting daughter cells
● Cancer: cell division that is uncontrolled and unregulated
● Benign: form of cancer that produces tumors, but does not metastasize
● Malignant: cancerous tumor that metastasizes
● Chemotherapy: chemical therapy used to treat cancer
● Radiation: another cancer therapy that targets cancer cells with radiation
● Regulatory Proteins: "signals that help the cell know when to duplicate, when to progress through the cell cycle, etc.