N581 Patho Question set-1

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Biology

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Nov 24, 2024

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9/5/23 Questions -Finish individual sections by 9/1 -Coordinate discussion on Sat 9/2, 10am via Zoom Join Zoom Meeting https://us04web.zoom.us/j/73887498727? pwd=yzPlaXTZjTCizISnLFIbmEngD88zbG.1 Meeting ID: 738 8749 8727 Passcode: 1RBhT3 1. How do cells acquire and use energy? 2. How are substances transported across the cell membrane? Anne : Substances are transported across the cell membrane through various mechanisms. Small water- soluble molecules are transported by transporter proteins (ATP-driven pumps, carriers, or channel proteins), lipid-soluble substances can cross by simple diffusion, and other larger particles may transport across the cell membrane via endocytosis/exocytosis. Transport across the cell membrane via membrane proteins occurs through either passive transport (facilitated diffusion) or active transport. Passive transport does not require any metabolic energy and involves substances moving from an area of high concentration to an area of low concentration. Active transport requires transport pumps that move substances across the membrane against a concentration or ion-charged gradient. Haley: Substances are transported across the cell membrane via active or passive transport. Active transport involves specialized proteins that serve as channels, pumps or carriers to move solutes from an area of low to high concentration. Passive transport, which includes diffusion, facilitated diffusion, and osmosis requires no energy and involves solutes moving from high concentration, through the phospholipid bilayer into a lower concentration. Elizabeth: 1. Cells acquire energy in a process called cellular metabolism. Cellular metabolism involves complex sequences of controlled biochemical reactions known as metabolic pathways. These processes allow organisms to grow, reproduce, and respond to environmental changes. 2. Substances are transported across cell membranes utilizing active or passive transport. A ctive transport involves the movement of molecules from lower concentration to higher concentration with the use of energy. Passive transport consists of the movement of molecules from higher concentration to lower concentration and no amount of energy is required. Ce lls acquire Carol: Transportation across cell membranes occurs with and without the use of energy. Passive transport does not require the cell to expend any energy, and it includes osmosis, facilitated

diffusion and simple diffusion. When a cell expends energy and moves against a gradient, it is active transport Leanne: Large molecules are transported across the cell membrane via endocytosis and exocytosis. There are multiple methods of endocytosis to include phagocytosis, pinocytosis, caveolae-dependent endocytosis, and clathrin-mediated endocytosis. In endocytosis, surface receptors on the cell membrane bind to molecules and engulf them into the cell where they are processed and then used or recycled. In exocytosis, vesicles carry substances that are to be secreted to the inner part of the cell membrane. This then fuses with the plasma membrane and substances are secreted for various uses, either in the cell membrane, extracellular matrix, or other sites via extracellular fluid. Three kinds of membrane proteins transport small molecules across the membrane. Channel proteins allow specific ions (must be the right size and charge) in through the opening and closing of pores. This is a passive process. ATP-driven pumps and carriers use active transport and bind to the molecule being transported. Active transport occurs at a much lower rate than the passive transport of channel proteins. 3. Why is it that some cells can produce action potentials and others cannot? -Some cells (such as neurons and muscle cells) contain voltage-gated ion channels. Changes in the cell membrane potential facilitate the opening and closing of these channels. Subsequent electrochemical gradients across the cell membrane create action potentials that contribute to cell-specific processes such as neuronal firing or muscle cell contraction. -Cells that do not have voltage-gated ion channels cannot produce action potentials, as they cannot create electrochemical gradients across their cell membranes. 4. What are the normal mechanisms of cellular growth control? Anne: Specific protein mitogens and growth factors are needed for growth and replication in many cell types. Cell-cell contact elicits signaling from cell adhesion proteins to limit further growth and replication. Regulation within the cell cycle plays into cell growth control as well. To begin the cell cycle, proliferation-promoting signals on the cell surface initiate a cascaded signal transduction pathway that results in upregulation of cell replication-promoting genes. Within the cell cycle, the G1, G2, and spindle assembly check points also assist in regulating progression through the cell cyle. Haley: G1, G2 and spindle checkpoints that are stages in eukaryotic cell cycle that determine whether to continue with cell division. These checkpoints send molecular signals to regulators. Cell cycle regulators including cyclins, Cdks, and enzyme complex APC/C, ensure that the cell cycle continues in the right order. If cells become damaged/mutated, the cell would undergo apoptosis.

Elizabeth: 3. In neurons, the types of ion channels in the membrane usually vary across different parts of the cell, giving the dendrites, axon and cell body different electrical properties. 4. Some parts of the membrane of a neuron may be excitable (capable of generating action potentials), whereas others are not. Carol: The cells begin at G1 which is the restriction point and if they successfully pass G1, they pass to the synthesis phase where cells duplicate the DNA and prepare for cell division. Next is the Mitosis/M phase which has 6 stages that end with cytokinesis where the cell division process is completed. Leanne: Cell growth is initiated by cell signaling. For specific cell types to grow and increase, specific combinations of growth factors and protein mitogens are required. Also, signals from the extracellular matrix are needed to determine if there is enough room. If both of these conditions are met, cells continue through the growth cycle (mitosis for body cells and meiosis for germ cells). 5. What are the usual cellular responses to reversible injury? 6. How are reversible and irreversible cellular injuries differentiated? Anne: Reversible cell injury often leads to hydropic swelling due to Na/K pump dysfunction, as well as aggregation of excess substances (e.g. lipids, carbohydrates, glycogen, and proteins). However, the cell returns to its normal state once the stress or injury has resolved. In contrast, irreversible cell injury is categorized as apoptosis (programmed cell death), or necrosis (cell death due to irreversible injury). In apoptosis, cells typically die due to natural remodeling processes. The apoptotic cells are then typically ingested by other local cells, which occurs without inflammation. Necrosis involves rupturing of the cell and subsequent localized inflammation. Haley: With a reversible injury, hydropic swelling occurs and if the injurious agent is removed the cell will return to pre-injury state. For irreversible, the injury is too extensive to repair, the plasma membrane is disrupted which results in cell death. Elizabeth: 5. Cell injury is classified as reversible if the injured cell can regain homeostasis and return to a morphologically (and functionally) normal state. Acute cell swelling is the classic morphologic change in reversible injury; however, it is also the typical early change of irreversible cell injury. 6. When cells are injured, one of two patterns will generally result: reversible cell injury leading to hydropic swelling and adaptation of the cells and tissue, or irreversible cell injury leading to cell death and tissue damage . When cells adapt to injury, their adaptive changes can be atrophy, hypertrophy, hyperplasia, or metaplasia. Carol: Reversible injury leads to the cells adapting to the injury, and irreversible is when the cell dies and/or tissue damage and does not return to the normal state. Leanne: Reversible injury occurs when the injury is acute or mild and the cell can quickly return to normal. In instances where the cell can change to accommodate the injury and maintain homeostasis, the injury is also considered reversible. Irreversible injury occurs when cell death occurs through necrosis or apoptosis and is caused by chronic or severe injury. Apoptosis is programmed cell death and may occur due to pathology or an anticipated physiologic process. Necrosis occurs when an injury causes cell death through significant cellular tissue damage.

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