Biology Unit 5 Study Guide PDF

-​ Neonicotinoids bind to acetylcholine receptors, preventing acetylcholine from binding and initiating a signal in the postsynaptic neuron. Because neonicotinoids are not degraded by acetylcholinesterase, their binding is irreversible. -​ Neonicotinoids selectively bind to insect acetylcholin...

-​ Neonicotinoids bind to acetylcholine receptors, preventing acetylcholine from binding and initiating a signal in the postsynaptic neuron. Because neonicotinoids are not degraded by acetylcholinesterase, their binding is irreversible. -​ Neonicotinoids selectively bind to insect acetylcholine receptors with higher affinity than to mammalian receptors, making them more effective insecticides with lower risk to non-target species. -​ Cortisol, testosterone, and estrogen are examples of steroid hormones, which are lipid-derived molecules synthesized from cholesterol. -​ Antidiuretic hormone (ADH) and insulin are examples of protein hormones, composed of chains of amino acids. -​ Acetylcholinesterase is responsible for breaking down acetylcholine, terminating its action at the synapse. If it is destroyed, acetylcholine will remain bound to its receptors for an extended period, causing continuous stimulation. -​ Acetylcholinesterase breaks down acetylcholine in the synaptic cleft, ensuring the termination of the muscle contraction signal. -​ Nitric oxide (NO) modulates synaptic activity via cGMP signaling pathways. Therefore disrupting cGMP synthesis would directly affect NO signaling. -​ Water-insoluble ligands must cross the plasma membrane to bind and activate intracellular receptors in the cytoplasm or nucleus. -​ Adenylate cyclase converts ATP into cyclic AMP (cAMP), which acts as a second messenger in the epinephrine signaling pathway. -​ Decreased water permeability of the collecting ducts, often due to ADH inhibition, would prevent water reabsorption, thus producing more dilute urine. The options involving increased ADH, aldosterone, or RAAS would all promote water retention and more concentrated urine. -​ Protein kinases amplify signals by adding phosphate groups to other proteins, creating a phosphorylation cascade. -​ Glutamate and GABA are both amino acids; glutamate is excitatory, while GABA is inhibitory. -​ The active transport of sodium ions in the ascending limb creates a high osmotic concentration in the kidney medulla, driving osmosis in the descending limb and collecting ducts. -​ If the alpha subunit cannot hydrolyze GTP, it remains active, continuously activating adenylate cyclase and prolonging PKA activation. -​ When an action potential reaches the axon terminal, it causes calcium channels to open, and the influx of calcium ions triggers the release of neurotransmitters. -​ The three subunits of hormones, which are secreted by endocrine cells, are amines (ex. melatonin, epinephrine, and norepinephrine), peptide hormones (ex. Insulin, oxytocin, FSH, and growth hormones), and steroid/lipid hormones (ex. Oestradiol, testosterone, cortisol) -​ Amino acids – glycine, glutamate and GABA (Gamma-aminobutyric acid) are involved in fast synaptic transmission, allowing neurons to communicate with each other in a matter of milliseconds. -​ Peptides – Neuropeptide Y is an example of a peptide neurotransmitter. It is responsible for a number of physiological and homeostatic processes. It increases the motivation to eat food. -​ Amines – Biogenic amines are modified amino acids. For example, serotonin regulates mood, dopamine is involved both in reward-seeking behavior and in regulation of movement, and norepinephrine (noradrenaline) controls the fight or flight response. -​ Gases – Nitrous oxide (NO) is a gas that acts as a neurotransmitter. It modulates the way neurons communicate with each other by regulating the release of other neurotransmitters. NO, commonly referred to as laughing gas, is used as a sedative by dentists. -​ G proteins are specialized proteins with the ability to bind the nucleotides guanosine triphosphate (GTP) and guanosine diphosphate (GDP). Like ATP, GTP is involved in energy transfer within the cell. -​ G proteins act like molecular switches when bound to G protein-coupled receptors (GPCRs) present in the plasma membrane. There are around 800 GPCRs, and each GPCR is specific to a particular function. Their ligands range from neurotransmitters and hormones to odors and light-sensitive compounds. In addition to affecting our taste, smell, behaviour and mood, they are also targets of many medicinal drugs. -​ G proteins consist of three subunits – 𝛼, β and γ. In its inactive state, the alpha subunit is bound to GDP. When a ligand binds to a GPCR, the alpha subunit separates from the beta and gamma subunits and transitions between an inactive state (bound to GDP) and an active state (bound to GTP). This activated alpha subunit is able to activate downstream effectors of various transduction pathways in the cell. The beta/gamma subunit is also able to activate other transduction pathways. -​ Epinephrine (aka adrenaline) prepares the body for a “fight or flight” response. When our bodies anticipate intense physical activity, such as running away from a predator, we need our skeletal muscles to be supplied with lots of glucose for energy. -​ Recall that glycogen, a polysaccharide of glucose, is stored in the liver. Epinephrine receptors in the liver are GPCRs. When epinephrine binds to this receptor, the activated alpha-GTP complex activates multiple copies of a downstream enzyme (adenylate cyclase) embedded in the membrane. These embedded enzymes convert multiple ATP molecules to cAMP molecules (cyclic adenosine monophosphate) which act as second messengers, activating multiple protein kinase A enzymes. These kinases phosphorylate an enzyme in the liver that hydrolyzes stored glycogen into glucose. This glucose can enter the bloodstream and then be used by skeletal muscle for cellular respiration and the production of ATP. -​ Glucose moves from the filtrate in the nephron into the bloodstream during normal kidney function through active transport. This occurs in the proximal convoluted tubule. -​ The hormone ADH influences movement of water into blood. -​ ADH stimulates reabsorption of water in the collecting duct in the kidney. -​ Neurons with free nerve endings in the skin, known as nociceptors, detect and transmit pain signals in response to potentially harmful stimuli. These specialized sensory neurons have receptors that respond to mechanical, thermal, or chemical stimuli that may indicate tissue damage. When activated, nociceptors generate action potentials that travel along their axons to the spinal cord, where they synapse with secondary neurons in the dorsal horn. Neurotransmitters such as glutamate and substance P facilitate signal transmission to higher brain centers, including the thalamus and somatosensory cortex, where pain is processed and perceived. This system allows the body to detect, localize, and react to noxious stimuli, playing a crucial role in protective reflexes and injury avoidance. -​ Excitatory neurotransmitters, such as glutamate, depolarize the postsynaptic membrane by opening ion channels that allow positive ions (e.g., Na⁺) to enter, bringing the neuron closer to the threshold for action potential generation. Inhibitory neurotransmitters, like GABA and glycine, hyperpolarize the postsynaptic membrane by opening channels for negative ions (e.g., Cl⁻) or causing K⁺ efflux, making it less likely for the neuron to fire. In the process of summation, the postsynaptic neuron integrates multiple excitatory and inhibitory signals. Spatial summation occurs when multiple synapses release neurotransmitters simultaneously, while temporal summation results from rapid, successive signals from the same synapse. If excitatory inputs surpass inhibitory influences and reach the threshold, an action potential is triggered; otherwise, inhibition can prevent firing, regulating neural activity and maintaining balance in the nervous system. -​ Neonicotinoids are a class of insecticides that disrupt synaptic transmission by acting as agonists of nicotinic acetylcholine receptors (nAChRs) in the nervous systems of insects. These chemicals mimic acetylcholine, binding irreversibly to nAChRs and causing prolonged receptor activation. This leads to continuous depolarization of the postsynaptic membrane, resulting in excessive nerve firing, paralysis, and ultimately death. Unlike acetylcholine, neonicotinoids are not easily broken down by acetylcholinesterase, prolonging their toxic effects. While they are highly effective against insect pests, neonicotinoids can also impact non-target organisms, such as pollinators like bees, by impairing their neural function, leading to disorientation, reduced foraging efficiency, and colony decline. -​ Ion channels play a crucial role in depolarization and repolarization during an action potential. Depolarization occurs when voltage-gated sodium (Na⁺) channels open in response to a stimulus, allowing Na⁺ ions to rush into the neuron, making the inside of the cell more positive. Once the membrane potential reaches the threshold, more Na⁺ channels open, rapidly driving the membrane potential toward a peak positive value. Repolarization follows as voltage-gated potassium (K⁺) channels open while Na⁺ channels inactivate. K⁺ ions exit the neuron, restoring the negative resting membrane potential. In  some cases, hyperpolarization occurs due to prolonged K⁺ efflux before the neuron returns to its resting state via the sodium-potassium pump (Na⁺/K⁺ ATPase), which restores ion balance and prepares the neuron for another action potential. -​ Progesterone exerts its effects on target cells by binding to intracellular progesterone receptors, which then act as transcription factors to regulate gene expression. In the female reproductive system, progesterone is crucial for maintaining the uterine lining, preparing it for potential embryo implantation, and inhibiting uterine contractions during pregnancy. In mammary gland cells, it stimulates the development of milk-producing structures. Progesterone also influences the hypothalamus and pituitary gland, suppressing the release of gonadotropins to prevent ovulation during pregnancy. Additionally, it affects smooth muscle cells by relaxing the uterine and gastrointestinal muscles, which can slow digestion. Through these mechanisms, progesterone plays a vital role in reproductive health, pregnancy maintenance, and overall hormonal balance. -​ The acetylcholine receptor (AChR) is a classic example of a ligand-gated ion channel that alters membrane potential in response to neurotransmitter binding. When acetylcholine (ACh) is released into the synaptic cleft, it binds to nicotinic AChRs on the postsynaptic membrane, causing a conformational change that opens the receptor's ion channel. This allows sodium ions (Na⁺) to flow into the cell and potassium ions (K⁺) to exit, leading to depolarization of the membrane. If the depolarization reaches the threshold, it triggers an action potential, propagating the signal. In contrast, muscarinic AChRs, which are G-protein-coupled receptors, indirectly influence membrane potential by activating intracellular signaling pathways that regulate ion channels. These receptor mechanisms enable neurotransmitters to modulate neural excitability and synaptic transmission effectively. -​ Transmembrane receptors in the plasma membrane and intracellular receptors differ in their locations, activation mechanisms, and types of signaling molecules they respond to. Transmembrane receptors, such as G-protein-coupled receptors and ligand-gated ion channels, are embedded in the cell membrane and bind hydrophilic signaling molecules, like neurotransmitters and peptide hormones, which cannot cross the lipid bilayer. Upon activation, these receptors trigger intracellular signaling cascades that alter cell function. In contrast, intracellular receptors, located in the cytoplasm or nucleus, bind hydrophobic signaling molecules, such as steroid hormones, that diffuse through the cell membrane. Once activated, intracellular receptors often act as transcription factors, directly regulating gene expression by binding to DNA. While transmembrane receptors mediate rapid, short-term cellular responses, intracellular receptors typically induce longer-lasting changes by modifying gene transcription. -​ Quorum sensing is a bacterial communication process that allows populations to coordinate gene expression based on cell density. In Vibrio fischeri, a marine bacterium, quorum sensing regulates bioluminescence through the production and detection of signaling molecules called acyl-homoserine lactones (AHLs). At low cell densities, AHLs diffuse away, and bioluminescence genes remain inactive. As the bacterial population grows, AHLs accumulate and bind to the LuxR transcriptional regulator, activating the lux operon, which encodes enzymes like luciferase responsible for light production. This coordinated response ensures that bioluminescence occurs only when enough bacteria are present, optimizing energy use. In nature, V. fischeri exhibits this behavior in symbiosis with the Hawaiian bobtail squid, providing camouflage by mimicking moonlight in exchange for nutrients.