Prof Study Guide Flashcards
plasma membrane
phospholipid bilayer + all the associated proteins and other molecules. Many of these are transmembrane proteins
what does the plasma membrane and its components collectively do?
confer selective permeability to ions, glucose and other molecules
nucleus
hosts the genome and is the site of transcription which produces mRNAs that
are exported.
ribosomes
sites of protein synthesis (translation)
found studded on ER or FREE IN CYTOPLASM
how is a vesicle-based system (budding and fusion) used by the ER/Golgi complex
used to sort new
proteins to either the PM, the outside of the cell (soluble proteins released by exocytosis) or
lysosomes. ONLY THESE THREE
where to the cytoplasm and other organelles get their proteins from
from free ribosomes
(mitochondria make a few proteins from their own mini-genome and
transcription/translation apparatus).
how do mitochondria produce ATP
from glucose or fatty acids (it can use amino acids in a pinch)
lysosomes digest debris by…
fusing with intracellular vesicles often derived from endocytosis
peroxisomes
DETOXIFY free radicals
cytoplasm
consists of the semi-liquid cytosol, an aqueous compartment in which intermediate metabolism occurs, the organelles and the cytoskeleton
microtubules
dynamic polymers of tubulin
microtubules form…
highways for movement of transport vesicles via kinesin and dynein motor proteins, and cilia and flagella for generating movements.
microfilaments
dynamic polymers of actin. In association with myosin, a motor protein,
they produce cellular contraction e.g. muscle fibers
intermediate filaments
longer proteins produced by an array of different genes
why have specialized/different types of cells?
complex multicellular life, like humans, require cells SPECIALIZED FOR DIFFERENT TASKS
PROXimate cause of different cell types
differential gene expression
all cell types contain the
same DNA, but express unique subsets of ~10K genes for any given cell type (out of ~22K in
the genome).
tissue
aggregate of cells and extracellular material
-muscle (contraction)
-nervous (signals; electrical and chemical)
-connective (structural support)
-epithelial (exchange)
organ system
An organ system is a group of organs that work together to perform complex functions and maintain HOMEOSTASIS in an organism
organ
two or more primary tissues organized to perform a function
- heart, lungs, liver
homeostasis
maintain a stable internal environment despite changes in external conditions. This stability is crucial for the proper functioning of biological systems and is essential for survival
synaptic; extracellular chemical messaging
A chemical messenger is released very locally @ a synapse (there’s a very small gap)
Detected by only one part of one cell
hormonal; extracellular chemical messenger
Secreting cell going to release chemical messenger into bloodstream
Now it is exposed to virtually all cells in the body, but it only activates a subset of cells; the ones that express the cognate receptor for that signal
paracrine; extracellular chemical messaging
Chemical messenger released into local tissue environment & exposed via diffusion in the extracellular space or fluid to 10s-100s neurons in local neighborhood
nuclear receptors
(intracellular) that activate gene expression
Many receptors can be found pre bound to DNA @ nucleus; hormones slip through PM and get in to bind receptors that’ll activate patterns of gene expression
Initiate a new wave of transcription
Relatively slow
GPCRs
(‘metabotropic’ or ‘2nd messenger’ signaling)
Chemical messengers bind to cell surface receptors
Activates G protein cascade that leads to sequence of phosphorylation events that alter the protein shape and function of pre-existing proteins and get cellular response
enzyme-linked receptors
cell surface proteins that, upon ligand binding, activate intrinsic enzymatic activity or recruit enzymes, triggering intracellular signaling cascades.
induces conformational changes
ionotropic receptors
(cell surface) which themselves are ion channels
Neurotransmitter binds receptor; it opens the ion channel and allows ions to flow down their electrochemical gradient
Can bring about a response immediately/in milliseconds
what does the brain do with sensory signals
processes them and produces motor output
perception
what you can report
brain relies on
neurons specialized for chemical and electrical signaling
The 86 billion neurons in the human brain and
interconnected by 100+ trillion synapses where a chemical neurotransmitter is released by
one neuron and detected by another
ion movement across the plasma membrane is BASIS of…
electrical signaling in neurons
two types of transmembrane proteins for ion/molecule movement:
carriers and
channels
Carriers have binding site for the molecule to be transported:
(1) Facilitated diffusion uses a fixed affinity site and transports down the concentration gradient. (2) Pumps have variable
affinity sites and transport uphill, AGAINST the concentration gradient
Na+/K+ ATPase pump
transports 3 Na out and 2 K in with each turn of the cycle.
Its role is to establish and maintain concentration gradients.
ion channels
do not have binding sites
have pores which allow for diffusion-like permeation
chemical driving
diffusion down a concentration gradient
electrical driving force
results from electrostatic
interactions at a distance.
net driving force
vector sum of each driving force (w direction and magnitude)
membrane potential results from
CHARGE separation across the membrane
polarity is referenced inside relative to outside e.g. at rest there is an excess of negative charges on the inside and excess of positive charges on the outside, for a resting potential of -70 mV
why do Na and K concentration gradients no run down during normal operation
amount of charge separation underlying biologically meaningful electrical signaling is extremely small compared to the total number of ions in bulk solution on both sides of the membrane
IONS DO HAVE
equilibrium potential
equilibrium potential
defined as the membrane potential at which there is no net charge movement for that ion.
RMP
depends on all the permeant ion
species weighted by their relative permeabilities.
At rest, K permeability dominates as there
are more K leak channels than Na leak channels
transient injection of current
leads to passive dissipation of current regardless of the
current source. This passive dissipation causes a graded potential, which always decreases in size as it flows away from the current source. Graded potentials are self-limited in time and space.
action potentials
all or none
electrical signals initiated AT THE AXON HILLOCK which rapidly propagate to the axon terminals (as far as 1 meter) where they trigger transmitter release
BRAIN IS SYNAPTIC NETWORK
what do action potentials depend on
VOLTAGE-GATED Na+ and K+ channels
net driving force on Na at AP onset
strong; but weak at AP peak
it begins when all Na channels have opened (occurs just after threshold is reached) and ends when
Na inactivation is removed
relative refractory period
a few ms in duration, during which the neuron can fire another AP but would require a larger than usual triggering event
begins when Na inactivation is removed and ends when the resting potential is restored following the K channel deactivation
speed and reliability of action potential propagation depends on
axonal diameter, membrane resistance, internal resistance and the presence or absence of myelin
contiguous conduction
relies on a continuous distribution of v-gated Na and v-gated K channels along the length of the axonal membrane.
One metaphor is the stadium wave.
This is an active process in the sense that it is not self-limited in time and space.
Saltatory conduction relies on
myelin (insulator) and clusters of v-gated Na and v-gated K channels found at the Nodes of Ranvier. This is an active process at the sites of initiation (axon hillock) and nodes of Ranvier, and a passive process (graded potential) underneath the myelinated stretches of axon.
How far current will flow down the axon before leaking out depends on
relative values
of membrane resistance (sometimes referred to as transverse path) and internal resistance
(the axial path).
internal resistance in giant axons
low; which favors AP propagation
Myelin increases membrane resistance such that the axial path is now
the lower resistance path.
myelin decreases
capacitance and therefore lowers the time constant which results in the membrane potential changing faster in response to current injection: it SPEEDS UP AP propagation.
Na channel inactivation ensures…
unidirectional spread of naturally occurring AP, and the annihilation of APs experimentally induced at either end of an axon when they collide.
Demyelinating diseases result in
slow and unreliable AP propagation. The autoimmune disease multiple sclerosis commonly affects the cerebellum, a brain structure which plays
an important role in calibrating ongoing movements. The symptoms = ‘action tremors’
intrinsic
LOCAL control systems built into an organ
Organ itself has a solution for its own problem
E.g. increased CO2 production leads to relaxation of smooth muscle and dilation of blood vessels
Increase the blood flow through the organ and it will be able to clear CO2 faster
extrinsic
External control system outside of an organ permitting coordinated regulation of several organs
