LS 7C Midterm 1 Study Guide PDF

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Study Guide for Midterm 1. For review purposes ...

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Week

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Why are smaller cells are more effective than larger cells? - Larger cell needs to eat more, needs more energy, produces more waste - All these are limiting factors on how quickly a cell can get things in and out - Cells are small because it is better to have many cells taking up the same volume than 1 big cell that requires more food, energy etc. Discuss how a signal can lead to both short- and long-term responses Signaling: - Receptor activation(signal binds to receptor and activates it)→ signal transduction(signal transmitted to interior of cell by transduction pathway, usually a chain reaction) → response(ok nothing crazy) → termination(response terminated so new signals can be received) - In multicellular organisms, when the two cells are far apart, the signaling molecule is transported by the circulatory system. When they are close, the signaling molecule simply moves by diffusion. When they are close together, the signaling molecule is not released from the signaling cell at all. - Endocrine signaling- signaling by means of molecules that travel through the bloodstream - FUN FACT: The endocrine system is a chemical messenger system consisting of hormones, the group of glands of an organism that carry those hormones directly into the circulatory system to be carried towards distant target organs, and the feedback loops of homeostasis that the hormones drive - Paracrine signaling- the signaling molecule can simply move by diffusion between the two cells involved, does not require circulatory system: the signal is usually a small, water-soluble molecule such as a growth factor. - Other short distance responses: neurotransmitters, neurons/muscle cells - Growth factors, and histamine are examples of paracrine chemical agents released in small amounts that act locally on neighboring cells. Describe the mechanism of action for a receptor tyrosine kinase pathway - A signal molecule binds to the extracellular portion of two receptors, causing the receptors to bind with each other - This partnering of two similar or identical molecules is called dimerization. Dimerization activates the cytoplasmic kinase domains of the paired receptors, causing them to phosphorylate each other at multiple sites on their cytoplasmic tails - The addition of these phosphate groups provides places on the receptor where other proteins bind and become active. bind

Receptor kinases bind signaling molecules, dimerize, phosphorylate each

o and activate intracellular signal molecules.

Define the role of kinases and phosphatases in cell signaling pathways - A kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to a substrate. A kinase transfers a phosphate group from ATP to a protein, typically activating the protein(phosphorylation). A phosphatase removes a phosphate group from a protein, typically deactivating the protein(dephosphorylation). - PHOSPHORYLATION DOES NOT ALWAYS MEAN ACTIVATION.

Week 1 Distinguish the potential for differentiation of totipotent, pluripotent, and multipotent stem cells - Totipotent- A fertilized egg (ZYGOTE) that can give rise to a complete organism - The fertilized egg is totipotent because it can differentiate into both the inner cell mass and supporting membranes, and eventually into an entire organism. - The cells of the inner cell mass(embryonic stem cells)  are pluripotent because they can give rise to any of the three germ layers, and therefore to any cell of the body.They cannot on their own give rise to an entire organism. - Cells further along in differentiation are multipotent; these cells can form a limited number of types of specialized cell; cells in the germ layer bc they can only give rise to cells in the specified germ layer - BASIC RUNDOWN OF THE 3: ● totipotent can form ALL CELL TYPES in an organism (zygote) ● Pluripotent can generate ALL DIFFERENT TYPES of cells in the body(embryonic stem cells) ● multipotent can produce some or all of the MATURE CELL TYPES within a particular tissue (neural progenitor cells) Describe the different types of cell-cell junctions - Cell junctions- A complex of proteins in the plasma membrane where a cell makes contact with another cell or the extracellular matrix. - The skin is a community of cells organized into two layers—the epidermis and dermis—that together provide protection for the underlying tissues of the body.

Define microtubule, microfilament, and intermediate filament. - provide internal support for cells - Microtubules and microfilaments enable the movement of substances within cells as well as changes in cell shape. - Microtubule- A hollow, tubelike polymer of tubulin dimers that helps make up the cytoskeleton. - Microfilament- A helical polymer of actin monomers, present in various locations in the cytoplasm, that helps make up the cytoskeleton. - Intermediate filament- ONLY ANIMAL CELLS HAVE THIS: A  polymer of proteins, which vary according to cell type, that combine to form strong, cable-like filaments that provide animal cells with mechanical strength. - In addition to providing structural support, microtubules and microfilaments enable the movement of substances within cells as well as changes in cell shape.

Explain how motor proteins actively move material around the cell - Plus ends of microtubules and microfilaments assemble quickly, while the minus end assembles slower and this is due to the concentration of o  f tubulin and actin in that region of the cell. - Dynamic instability:The plus ends of microtubules undergo cycles of rapid disassembly followed by slow assembly. - Microtubules and microfilaments have some capacity to lengthen and shorten by polymerization and depolymerization BUT motor proteins amplify this! - Kinesin transports cargo toward the plus end of microtubules, while dynein carries its load away from the plasma membrane toward the minus end. Both powered by ATP. Explain how cell-cell junctions and the extracellular matrix (ECM) contribute to cells’ ability to form tissues and organs - Cell adhesion molecule- A cell-surface protein that attaches cells to one another and to the extracellular matrix. - Cadherins are calcium-dependent adherence proteins, that connect cells to other cells. - Integrins are transmembrane proteins that connect cells to the extracellular matrix. - Adherens junction- actin microfilaments are attached to the plasma membrane by cadherins. Cell communication through t he cadherins in the adherens junction of one cell which attach to the cadherins in the adherens junctions of adjacent cells. - Desmosomes- A button-like point of adhesion that holds the plasma membranes of adjacent cells together, cadherins are the primary cell adhesion molecules. - Hemidesmosome- allows for attachment of epithelial cells to the extracellular matrix, integrins are the primary cell adhesion molecules  complex that establishes a seal between cells so that the - Tight junctions-  junctional only way a substance can travel from one side of a sheet of epithelial cells to the other is by moving through the cells by a cellular transport mechanism. - Gap junction- A type of connection between the plasma membranes of adjacent animal cells that permits materials to pass directly from the cytoplasm of one cell to the cytoplasm of another. - Plasmodesmata- Connections between the plasma membranes of adjacent plant cells that permit molecules to pass directly from the cytoplasm of one cell to the cytoplasm of another.

Week 2 Describe the general structure of a neuron. - Neurons: basic functional units of nervous systems - Animal nervous systems have three types of nerve cell: sensory neurons, interneurons, and motor neurons - Each one has a diff function - Sensory neurons: receive and transmit information about an animal's environment or its internal physiological state - ^respond to physical features such as temp, light, touch, odor, taste - Interneurons: process the information received by sensory neurons and transmit it to diff body regions, communicating with motor neurons at the end of the pathway - Motor neuron: produces suitable responses, eg. stimulate a muscle to contract to produce movement or constricting blood vessels to adjust blood flow - Nervous system function is fundamental to homeostasis which is the ability of animals, organs, and cells to actively regulate and maintain a stable internal state - Ganglia: groups of nerve cell bodies that process sensory information received from a local, nearby region, resulting in a signal to motor neurons that control some physiological function of the animal - ^ can be thought of as relay stations or processing points in nerve cell circuits - Ganglia serve to regulate key processes in local regions and organs of the animal’s body. - Nerve cells form a circuit - Sponges are the only multicellular animals that lack a nervous system - Cephalization: the concentration of nervous system components at one end of the body, defined as the “front” Describe the general structure of a neuron & Relate the structural features of a neuron (i.e., dendrites, axons) to their functions.

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Neurons all share some basic features They have a cell body from which two kinds of fiber like extensions emerge: dendrites and axons Both types of cellular extensions can be highly branched, enabling neurons to communicate over large distances with many other cells Dendrites: A  fiberlike extension from the cell body of a neuron that receives signals from other nerve cells or from specialized sensory endings; the input end of a nerve cell.\ Axon: transmits signals away from the nerve’s cell body; the output end of a nerve cell. Signals travel along dendrites of the neuron’s cell body dendrites---> axon hillock----> axon At the axon hillock,the junction of the nerve cell body and its axon, the signals are summed and if the sum is high enough, the neuron fires an action potential aka nerve impulse, which travels down the axon

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Axons generally transmit signals away from the nerve’s cell body The end of each axon forms an axon terminal which communicates with a neighboring cell through a junction called a synapse Synaptic cleft: separates the end of the axon of the presynaptic cell and neighboring postsynaptic cell Signals cross the synaptic cleft through neurotransmitters Neurotransmitters: convey the signal from the end of the axon to the postsynaptic target cell The arrival of a nerve signal at the axon terminal triggers the release of neurotransmitter molecules from vesicles located in the terminal. The vesicles fuse with the axon’s membrane, releasing neurotransmitter molecules into the synaptic cleft. The molecules diffuse across the synapse and bind to receptors on the plasma membrane of the target cell. The binding of neurotransmitters to these receptors causes a change in the electrical charge across the membrane of the receiving postsynaptic cell, continuing the signal in the second cell.

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Nerve signals are transmitted electrically (in the form of an action potential) from one end of a neuron to the other. They are transmitted chemically (by neurotransmitters) across a synapse from one neuron to another.

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FIG. 35.5Variation in neuron shape(above). Neurons display a diversity of shapes, reflecting their different functions. Neurons within the brain and in many body regions are supported by other types of cell that do not themselves transmit electrical signals Glial cells: A  type of cell that surrounds neurons and provides them with nutrition and physical support. Human brain has more glial cells that neurons!!!! SCIENCE IS COOL Glial cells surround neurons and provide them with nutrition and physical support Astrocytes: glial cells that support endothelial cells that make up blood vessels in the brain Endothelial cells are linked by tight junctions to form a blood-brain barrier which prevents toxic compounds and pathogens in the blood from entering the brain, but fortunately not alcohol which is why we get LIT

Explain membrane potential and how it arises in both neuronal and non-neuronal cells. - Membrane potential: charge difference between the inside and the outside of a neuron due to differences in charged ions - Only nerve and muscle cells respond to membrane potential - Resting membrane potential is negative - Resting membrane potential of the cell is said to be polarized: there is a buildup of negatively charged ions on the inside of the cell’s plasma membrane and positively charged ions on its outer surface - Resting membrane potential ranges from -40 to -85 millivolts and is most commonly -65 to -70 mV, results primarily from the movement of K+ ions out of the cell.

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Eg. A  t rest, nerve (and muscle) cells have a greater concentration of sodium (Na+) ions outside the cell than inside, and a greater concentration of potassium (K+) ions inside the cell than outside. This distribution of ions results in part from the action of the sodium-potassium pump. The sodium-potassium pump uses the energy of ATP to move three Na+ ions outside the cell for every two K+ ions moved in. The action of the pump makes the inside of the cell less positive, and therefore more negative, than the outside of the cell. K+ channels allow K+ ions to “leak” out of the cell, resulting in a negative resting potential on the inside of the cell compared to the outside. The relative proportion of ions does not by itself determine the resting membrane potential. This is because the number of charged ions that build up at the cell’s surface is a tiny fraction of the total number of charged ions and proteins located inside and outside the cell. It is the movement  of K+ ions relative to other ions, particularly Na+ ions, that largely determines the resting membrane potential.

Explain the process by which an action potential is generated and propagated. - Neurons are excitable cells that transmit information by action potential - When a nerve cells is excited, its membrane becomes less negative (inside) or more positive than the outside of the cell which is Increase in membrane potential aka depolarization of the membrane - Depolarization starts at the terminal end of the dendrite, in response to neurotransmitters binding to the membrane receptors - Then it travels to cell body, losing strength along the way - If the depolarization is still strong enough at the axon hillock of the cell body, the cell fires an action potential that carries the signal from the cell body to the terminal ends of the axon - How is the action potential generated? At the axon hillock, the summed membrane depolarization of the cell’s dendrites causes voltage-gated sodium channels to open, allowing Na+ ions to enter the cell. - Voltage-gated channels open and close in response to changes in membrane potential - If the excitatory signal is strong enough to depolarize the membrane of the nerve cell body to a voltage of approximately 15 mV above the resting membrane potential (about –55 mV), the nerve fires an action potential at the axon hillock. - An action potential is a rapid, short-lasting rise and fall in membrane potential - Threshold potential: the critical depolarization voltage of -55 mV required for an action potential - The rise in voltage that results causes additional voltage-gated Na+ channels to open. This is an example of positive feedback, in which a signal (depolarization) causes a response (open voltage-gated Na+ channels) that leads to an enhancement of the signal (more depolarization) that leads to an even larger response (more open voltage-gated Na+ channels).

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As you can see from the figure, the rising phase of the action potential (rapid depolarization) is followed by the falling phase (rapid repolarization). What causes this sudden reversal of the membrane potential? There are two important factors. First, voltage-gated Na+ channels begin to close once the membrane potential becomes positive. Second, voltage-gated K+ channels continue to open in response to the change in voltage. Because they are slower to respond than the voltage-gated Na+

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channels, the membrane voltage peaks and then falls as K+ ions diffuse out of the axon through the open voltage-gated K+ channels. The voltage inside the axon does not return immediately to the resting membrane potential. Instead, it briefly falls below the resting potential (in what is known as hyperpolarization or undershoot), then returns to the resting potential after another few milliseconds as K+ channels close to restore the resting concentration of Na+ and K+ ions on either side of the cell membrane. The continuous action of the sodium-potassium pumps also helps to reestablish the resting membrane potential. The period during which the inner membrane voltage falls below and then returns to the resting poten  tial is the refractory period. During the refractory period, a neuron cannot fire a second action potential. The refractory period results in part from the fact that when voltage-gated Na+ channels close, they require a certain amount of time before they will open again in response to a new wave of depolarization. In addition, open voltage-gated K+ channels make it difficult for the cell to reach the threshold potential. The local membrane depolarization initiated at the axon hillock triggers the opening of neighboring voltage-gated Na+channels farther along the axon. The inward sodium current depolarizes the membrane above threshold, triggering the opening of nearby voltage-gated Na+ channels still farther along the axon. By this means, the depolarization—the location of the action potential spike—spreads down the axon. Neighboring voltage-gated K+ channels subsequently also open and close to reestablish a resting membrane potential after an action potential has fired. Action potentials are thus s  elf-propagating: ^potassium moves inside when voltage gated K+ channels open Action potentials propagate only in one direction, normally from the cell body at the axon hillock to the axon terminal.The refractory period following an action potential prevents the membrane from reaching threshold and firing an action potential in the reverse direction.

Compare and contrast ligand-gated and voltage-gated ion channels with respect to their role in signal transduction in a neuron. - Postsynaptic membrane receptors are called ligand gated ion channels because when the neurotransmitter binds to a ligand, it causes the ion channel to open

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This allows specific ions to enter the postsynaptic cell, changing its membrane potential Each neuron has both types of channels in their cell membrane. Voltage gated ion channels open in response to voltage (i.e. when the cell gets depolarized) where as ligand gated channels open in response to a ligand (some chemical signal) binding to them

Explain the process by which two neurons communicate at a synapse. - Electrical synapses provide direct electrical communication through gap junctions that form between neighboring cells - Enable rapid communication but limit the ability to process and integrate information - Chemical synapses are the more common type of synapse found in animal nervous systems - Once the action potential reaches the end of an axon, the resulting depolarization induces voltage gated Ca2+ ion channels to open - Ca2+ ions diffuse into the axon terminal bc of their high concentration outside the cell - In response to rise in Ca2+ concentration, the vesicles fuse with the presynaptic membrane and release neurotransmitter molecules into the synaptic cleft by exocytosis - The neurotransmitters diffuse across the cleft and bind to postsynaptic membrane receptors of the neighboring cell - The binding of neurotransmitters opens or closes ion channels, causing a change in the postsynaptic cell membrane potential that allows the signal to propagate to the next neuron Describe the global organization of the human nervous system. - Nervous system is organize...