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Questions and Answers
What is the primary function of the Na*-K+ ATPase pump?
What is the primary function of the Na*-K+ ATPase pump?
Which characteristic distinguishes primary active transport from secondary active transport?
Which characteristic distinguishes primary active transport from secondary active transport?
In primary active transport via the Na*-K+ pump, what is the ratio of Na* being pumped out to K+ being pumped in?
In primary active transport via the Na*-K+ pump, what is the ratio of Na* being pumped out to K+ being pumped in?
What role does the Na* concentration gradient play in secondary active transport?
What role does the Na* concentration gradient play in secondary active transport?
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What enhances the activity of the Na*-K+ pump during cellular swelling?
What enhances the activity of the Na*-K+ pump during cellular swelling?
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Which statement defines the nature of the countertransport or antiport system?
Which statement defines the nature of the countertransport or antiport system?
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What is a key characteristic of secondary active transport?
What is a key characteristic of secondary active transport?
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What is one major consequence of maintaining cellular ion concentrations through active transport?
What is one major consequence of maintaining cellular ion concentrations through active transport?
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What is the role of local regulators in the process of paracrine signaling?
What is the role of local regulators in the process of paracrine signaling?
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What occurs during autocrine signaling?
What occurs during autocrine signaling?
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Which type of signaling is characterized by neurotransmitter molecules diffusing across a synapse?
Which type of signaling is characterized by neurotransmitter molecules diffusing across a synapse?
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What is a key difference between local signaling and long-distance signaling?
What is a key difference between local signaling and long-distance signaling?
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What happens to receptor sensitivity during down regulation?
What happens to receptor sensitivity during down regulation?
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What triggers the secretion of neurotransmitter molecules in synaptic signaling?
What triggers the secretion of neurotransmitter molecules in synaptic signaling?
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What can cause a decrease in receptor synthesis according to cellular needs?
What can cause a decrease in receptor synthesis according to cellular needs?
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Which of the following is NOT a mechanism of signaling discussed?
Which of the following is NOT a mechanism of signaling discussed?
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What is the primary function of receptor-mediated endocytosis?
What is the primary function of receptor-mediated endocytosis?
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What triggers the process of exocytosis in cells?
What triggers the process of exocytosis in cells?
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Which of the following accurately describes total body water distribution?
Which of the following accurately describes total body water distribution?
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Which ion is the major cation found in extracellular fluid?
Which ion is the major cation found in extracellular fluid?
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What is one potential fate of molecules released during exocytosis?
What is one potential fate of molecules released during exocytosis?
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What characterizes the fluid found in the intracellular compartment?
What characterizes the fluid found in the intracellular compartment?
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In receptor-mediated endocytosis, which occurs after a specific molecule binds to a receptor?
In receptor-mediated endocytosis, which occurs after a specific molecule binds to a receptor?
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What percentage of total body water is intracellular fluid?
What percentage of total body water is intracellular fluid?
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What role do anions play in Donnan's equilibrium?
What role do anions play in Donnan's equilibrium?
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What is the primary function of the receptors in homeostasis?
What is the primary function of the receptors in homeostasis?
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What determines the resting membrane potential (RMP)?
What determines the resting membrane potential (RMP)?
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How does the control center respond to changes detected by the receptors?
How does the control center respond to changes detected by the receptors?
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What is the function of the efferent pathways in the homeostatic mechanism?
What is the function of the efferent pathways in the homeostatic mechanism?
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What best describes homeostasis?
What best describes homeostasis?
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Which of the following components is NOT part of the homeostatic mechanism?
Which of the following components is NOT part of the homeostatic mechanism?
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What is the significance of the set point in homeostasis?
What is the significance of the set point in homeostasis?
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What is the primary mechanism involved in receptor down regulation?
What is the primary mechanism involved in receptor down regulation?
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What is the main purpose of the transduction stage in cell signaling?
What is the main purpose of the transduction stage in cell signaling?
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Which of the following is a characteristic of G protein-linked receptors?
Which of the following is a characteristic of G protein-linked receptors?
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What happens when a ligand binds to ion channel-linked receptors?
What happens when a ligand binds to ion channel-linked receptors?
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Which category of responses is NOT typically triggered by cell signaling?
Which category of responses is NOT typically triggered by cell signaling?
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In what location are intracellular receptors typically found?
In what location are intracellular receptors typically found?
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Which receptor type functions by catalyzing the transfer of a phosphate group to tyrosine?
Which receptor type functions by catalyzing the transfer of a phosphate group to tyrosine?
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What type of molecules typically bind to intracellular receptors?
What type of molecules typically bind to intracellular receptors?
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What initiates the release of Ca** from the endoplasmic reticulum or sarcoplasmic reticulum into the cytosol?
What initiates the release of Ca** from the endoplasmic reticulum or sarcoplasmic reticulum into the cytosol?
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What is the role of DAG in cellular signaling?
What is the role of DAG in cellular signaling?
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What happens when Ca** binds to calmodulin?
What happens when Ca** binds to calmodulin?
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What is meant by signal amplification in a signaling pathway?
What is meant by signal amplification in a signaling pathway?
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Which of the following describes a mechanism for signal termination?
Which of the following describes a mechanism for signal termination?
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Why is signal termination important in cellular signaling?
Why is signal termination important in cellular signaling?
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What effect does the cholera toxin have on cellular signaling?
What effect does the cholera toxin have on cellular signaling?
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What is the consequence of failed signal termination in cellular pathways?
What is the consequence of failed signal termination in cellular pathways?
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Study Notes
Transport Across Cell Membranes
- The plasma membrane acts as a barrier between the extracellular fluid (ECF) and the cytosol of cells.
- Substances continuously exchange between the cytosol and ECF.
- ECF contains nutrients (glucose, amino acids, fatty acids), water, ions, oxygen, vitamins, and macromolecules needed by the cell.
- Cytosol contains waste products (carbon dioxide) and manufactured substances that need to exit the cell.
- Cell and body survival depend on the transport of these substances.
- Membrane transport is the process substances use to enter and exit the cell.
- Membrane transport is categorized into passive and active processes, based on the cell's energy expenditure.
Passive Processes
- Do not require cellular energy.
- Substances move down their concentration gradient.
Diffusion
- Simple diffusion: movement of small, nonpolar solutes across the phospholipid bilayer (e.g., oxygen, carbon dioxide, steroids).
- Facilitated diffusion: the movement of small polar or charged solutes facilitated by transport proteins (e.g., ion channels or carrier proteins).
Osmosis
- Special case of diffusion; the movement of water across a selectively permeable membrane from a region of high water concentration to a region of low water concentration.
Active Processes
- Require cellular energy (ATP).
- Substances move against their concentration gradient.
Active Transport
- Primary active transport: uses ATP directly to move substances against their concentration gradient (e.g., Na+-K+ pump).
- Secondary active transport: uses the electrochemical gradient established by primary active transport to move substances against their concentration gradient (e.g., Na+-glucose cotransporter).
Vesicular Transport
- Involves vesicles, small membranous sacs.
- Endocytosis: taking substances into the cell.
- Exocytosis: releasing substances from the cell.
Passive Diffusion
- No energy is required.
- Movement is down the concentration/electrochemical gradient.
- Solutes that are small or nonpolar move into/out of a cell passively.
Facilitated Diffusion
- Movement is down the concentration/electrochemical gradient.
- Requires a transport protein.
- Small polar or charged solutes move across the membrane with help of protein channels.
- Carrier-mediated diffusion: A solute binds to a carrier on one side of the membrane; the carrier changes shape, moving the solute to the other side before returning to its original shape.
Saturation
- In simple diffusion, the rate increases proportionally to the concentration.
- In facilitated diffusion, the initial increase is proportional, but the rate reaches a limit (transport maximum, Tm) when all transport proteins are occupied.
Competition
- In facilitated diffusion, similarly shaped molecules can compete for the same binding site on the carrier protein.
- When molecule A increases, it decreases B's transport, and vice versa.
- No competition in simple diffusion.
Specificity
- Carrier proteins show high specificity, transporting only certain molecules (e.g., a glucose transporter doesn't carry fructose).
Types of carrier proteins
- Uniport: carries one substance.
- Co-transport (symport): carries two substances in the same direction.
- Counter-transport (antiport): carries one substance in one direction and another substance in the opposite direction.
Active Transport - Primary
- Direct expenditure of energy (ATP).
- Establishes and maintains concentration gradients.
- Example: Na⁺-K⁺ pump
Active Transport - Secondary
- Uses electrochemical gradients created by primary active transport to move substances against concentration gradient.
- Example: glucose transport in intestine.
Vesicular Transport
- Bulk transport using membrane-bound vesicles.
- Endocytosis: taking in material.
- Exocytosis: releasing material from the cell.
Membrane transport
- Includes passive and active processes
- Passive processes (diffusion and osmosis) do not require energy expenditure
- Active processes (active and vesicular transport) require energy.
- Cell survival, function, and appropriate responses to outside stimuli depend on membrane transport.
Body Fluids
- Water is essential for all life.
- About 60% of an adult's weight is water.
- Water is distributed between intracellular and extracellular compartments.
Cellular Communication
- Cells communicate to maintain homeostasis (internal stability) by sending and receiving signals.
- Cells communicate with each other through direct and/or long distance signaling methods.
- Types of communication:
- Direct contact (Gap junctions): adjacent cells have channels connecting cytoplasms.
- Local signaling (paracrine and autocrine): signals travel short distances.
- Long distance signaling (hormones): signals travel through the circulatory system.
Stages of Cell Signaling
- Reception: signaling molecule (ligand) binds to a receptor protein.
- Transduction a series of changes to convert the signal (e.g., activating enzymes).
- Response: resulting cellular action (e.g., altering gene expression).
- Signal termination: the signal in the cell must be terminated.
Homeostasis
- Cells and organisms need internal stability.
- Homeostatic mechanisms are important for survival.
- Receptors, Afferent pathways, Control centers, Efferent pathways and Effectors are components of the homeostasis mechanism.
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