BPK 205 Week 2: Principles of Cellular Physiology; Membrane Transport, Membrane Potentials Flashcards
Why are ion channels unevenly distributed across the cell membrane?
- ion channels and transporters in the plasma membrane move ions resulting in an unequal distribution of ions and net charge
- necessary for biological processes
Typically: there are more ____x3 within the cell
- proteins
- K+
- phosphate
Typically: there are more ____x3 outside the cell
- Cl-
- Na+
- Ca2+
Why is the inside of the cell ___ charged?
- negatively
- Negatively charged proteins
- Negatively charged phosphate
- Sodium potassium charge kicking out an excess charge every time it cycles
Potassium leak channels
resting membrane potential (RMP)
- net charge difference between the intracellular fluid and extracellular fluid at rest; Result of the unequal distribution of ions on each side of the membrane
- -70mV
Membrane potential symbol
Vm or Em
List and describe the 2 driving forces experienced by ions
- Chemical driving force: movement of a substance in or out of a cell based on concentration gradient
- Electrical driving force: attraction of a substance in or out of a cell based on charge; Net movement is based on electrochemical gradient
Equilibrium potential
the millivolt value at which the chemical driving force and electrical driving force are equal and opposite. results in no net ion movement
What is the equilibrium potential of potassium?
-94mV
Nernst equation
- define
- give equation
- used to calculate equilibrium potential of an ion
- see google doc
Goldman-Hodgkin-Katz Equation (GHK equation)
- define
- give equation
- predicts membrane potential that results from the contribution of all ions that can cross the membrane. Based on the combined contributions of concentration gradients and relative membrane permeability for each ion
- see google doc
Why is the cell almost always somewhat permeable to potassium?
- potassium leak channels
- cells are more permeable to K+ than any other ion
What is the primary contributor to resting membrane potential>
K+
- -90mV
If the cell’s permeability to an ion increases:
- Get an increase in flow of that ion
- Change in Vm towards that ion’s Ex
Hyperpolarization:
more negative than resting membrane potential
Depolarization
change in membrane potential that brings you closer to 0 is called depolarization
Describe the 2 physiological signals
- Electrical signals: changes in the membrane potential of a cell
- Chemical signals: molecules secreted by cells into ECF; Bind to specific receptors on or in target cells (usually on)
Describe local cell-cell communication (3)
- gap junctions: form direct cytoplasmic connections between adjacent cells
- contact-dependent signals: require interaction between membrane molecules on two cells (example: cells that touch each other stop growing in a petridish)
- autocrine signals: act on the same cell that secreted them. paracrine signals are secreted by one cell and diffuse to adjacent cells
Describe long distance communication
- example: action potential travelling along a neuron
- hormones: secretions that travel through the blood
- neurotransmitters: chemical secretions by neurons that diffuse across a small gap to the target cell (short distance)
- neurohormones: chemicals released by neurons into the blood for action at distant targets (long distance)
Define: hormones and give an example
- Hormones are secreted by endocrine glands or cells into the blood. Only target cells with receptors for the hormone will respond to the signal
- Example: insulin secreted from the pancreatic B cells and bind the insulin receptors on cells throughout the body enabling glucose to enter these cells
Define: neurotransmitters and give an example
- neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell (short distance)
- Example: acetylcholine (neurotransmitter) - used to elicit skeletal muscle contraction
Define: neurohormones and give an example
- Neurohormones: chemicals released by neurons into the blood for action at distant targets (long distance)
- Example: oxytocin is released by neurons in the posterior pituitary gland into the blood and stimulates uterine contractions during labour
What are the 4 major classes of chemical signalling molecules?
- amino acids
- amines
- peptides or proteins
- steroids
- others
List the 4 categories of membrane receptors
- receptor channels/ ligand gated channels
- Enzyme-linked receptor
- G protein-coupled receptor
- Integrin receptor
Describe this membrane receptor: receptor channel/ligand gated channels
Ligand-gated channels: signalling molecule (ligand) binds to its receptor and the receptor is an ion channel that is gated by ligand binding (fast response)
Describe this membrane receptor: enzyme-linked receptor
ligand building to a receptor-enzyme which activates an intracellular enzyme
- example: tyrosine kinase (TK) transfers phosphate group from ATP to tyrosine (an amino acid) of a protein
Describe this membrane receptor: G protein-coupled receptor (GPCRs)
ligand binds to a receptor that is physically coupled to a Guanosine nucleotide-binding (G) protein. G protein activates. The type of G protein involved will determine which intracellular cascade is initiated. Some GPCRs when activated will modify the activity of an enzyme initiating or inhibiting intracellular cascade of events
- can open an ion channel or alters enzyme activity
- largest family of cell surface receptors
- G protein has 3 subunits (alpha, beta, gamma)
Describe this membrane receptor: integrin receptor
ligand binding to integrin receptors alters the cytoskeleton
Provide an overview of signal transduction
- see google doc
Describe kinase
phosphorylate proteins
- Enzyme that uses ATP to put phosphates on target proteins, channels, or enzymes
Describe phosphatases
dephosphorylate proteins
- Remove phosphate groups from target protein, channels or enzymes
Signal amplification
turning up the “volume” in every step of the signal transduction pathway
- Example: one ligand may activate many second messenger systems
Signal transduction cascade
ensures that cellular response only occurs when there’s a signal for it
List two pathways related to GPCRs
- adenylyl cyclase pathway
- phospholipase C pathway
Describe the adenylyl cyclase pathway
- see google doc
Describe the phospholipase C pathway
- see google doc
State which is faster and why: receptor gated channel vs G protein coupled receptor
- receptor gated channel; less intracellular signalling and response needed
State the Ca2+ levels in the cytosol
- really low
- [Ca2+]o = 1.8 mM; [Ca2+]i < 0.001 mM
Ca2+ enters the cell via what (4)
- Voltage-gated channels
- Ligand-gated channels
- Mechanically-gated channels
- Can also be released from stores by second messengers
State what Ca2+ is used for in the body
Released Ca2+ will bind with Ca2+ binding proteins to exert effects (example: muscle contraction)
Define and describe hormones
Hormones: Cell-to-cell communication molecules
- Chemical signals; usually v. low concentration
- May be secreted by a cell or group of cells (gland)
- Transported by blood to distant target tissues; may act on many tissue types, or just one
half life
Half-life = time for the [hormone] in blood to reduce by 1/2
- Essentially a measure of stability of the hormone
3 chemical classes of hormones
- peptide/protein
- steroid
- amine
Peptide/protein hormones
- lipophobic hydrophilic, lipophilic/hydrophobic
- synthesis
- storage
- release
- transport in blood
- half-life
- receptor location
- general cellular response
- Lipophobic, hydrophilic
- Synthesis: made in advance in endocrine cells all over the body as inactive preprohormone. Series of post-translational modifications (in the Golgi complex) convert it to prohormone then hormone. Only the final hormone in a vesicle is active
- Storage: stored in vesicles until needed
- Release: into ECF via exocytosis then diffuses from ECF into blood (carried away in solution)
- Transport in blood: in solution
- Half-life: short (seconds to minutes)
- Receptor location: tend to bind to membrane receptors since they’re so large and bulky
- General cellular response: alters activity of target proteins
steroid
- lipophobic hydrophilic, lipophilic/hydrophobic
- synthesis
- storage
- release
- transport in blood
- half-life
- receptor location
- general cellular response
- Synthesis: made from cholesterol and made on demand in the adrenal cortex, kidney, skin, gonads, placenta. Uses lipophobic precursors that could be stored in intracellular compartments (e.g. SER, cytoplasm)
- Storage: cannot be stored because the final product is lipophilic (hydrophobic)
- Release: simple diffusion into blood
- Transport in blood: bound to carrier proteins
- Half-life: hours
- Receptor location and general cellular response:
intracellular receptors → slow genomic response (=modulation/regulation of gene expression)
Membrane receptors → fast, non-genomic response
Amine
- lipophobic hydrophilic, lipophilic/hydrophobic
- synthesis
- storage
- release
- transport in blood
- half-life
- receptor location
- general cellular response
- Synthesis: made in the pineal gland, adrenal medulla, thyroid; derived from tyrosine
- Catecholamine are similar to peptide hormones in terms of characteristics
^ Lipophobic, stored for release, short half life, changes the activity of target protein, etc.
^ Includes adrenaline
^ neurohormone - Thyroid hormones are similar to steroid hormones
^ Lipophilic, made on demand from lipophobic precursors stored in the thyroid, requires carrier proteins, long half life, genomic responses, etc. - Storage:
- Release:
- Transport in blood:
- Half-life:
- Receptor location:
- General cellular response:
Gland
collection of secretory cells
endocrine gland
Endocrine gland: secretes something that will stay within the body
exocrine gland
Exocrine gland: secreting something that will leave the body
Describe the pancreas’ endocrine and exocrine functions
endocrine: - Alpha cell: secretes glucagon - Beta cell: secretes insulin exocrine: - Acinar cells and duct cells - Pancreatic enzymes are secreted by the pancreas, dumped into the small intestine, where it assists with digestion
list 3 cellular processes hormones regulate
- Rates of enzymatic reactions
- Transport of ions or molecules across cell membranes
- Gene expression and protein synthesis
Q: What determines what a hormone does?
A: always about if the target receptor is present, where it is, and the specific signalling pathway present
Pituitary gland:
- location
- structure
- Location: in the brain; under the frontal cortex
- Structure: 2 glands fused together (posterior pituitary, anterior pituitary)
Describe the posterior pituitary and the secretion of hormones from it
- Posterior pituitary: neural tissue and secretes 2 neurohormones (vasopressin and oxytocin)
- see google doc
Describe the anterior pituitary and the secretion of hormones from it
- Anterior pituitary: endocrine tissue and secretes six true hormones
- Release of hormones is controlled by neurohormones from the hypothalamus, the region of the brain just above
- Portal circulatory system: specialized modification where two sets of capillaries are connected in series by a set of small veins
- see google doc
Vasopressin
antidiuretic hormone or ADH
