Block 1 Learning Objectives Flashcards
Mitochondria
generates most of the ATP (chemical energy) needed to power the cells biochemical reactions
Plasma membrane
cell membrane serves as a clear boundary between the internal and external environments of the cell
Nucleus
repository for genetic information and as the cells control center. DNA replication, transcription and RNA processing all take place within the nucleus
Golgi apparatus
helps to process and package proteins & lipid molecules. Especially proteins that are destined to be exported from the cell.
Ribosomes
main site of protein synthesis within the cell, reads the mRNA sequence and translates that genetic code into a specified string of amino acids which grow into long chains that fold to form proteins
Lysosomes
Primary function is to break down excess or worn out cell parts. They may also be used to destroy invading viruses and bacteria. They also aid in apoptosis as a self destruction mechanism
Peroxisomes
provide a compartment for oxidation reactions and are involved in lipid biosynthesis.
In animal cells, cholesterol and dolichol are synthesized here and in the ER.
In the liver, they are involved in the synthesis of bile acids, which are derived from cholesterol
homeostasis
self regulating process by which biological systems maintain stability while adjusting to changing external conditions
Endocrine communication
communication over long distances thru the bloodstream
Paracrine communication
neighboring cell communication
Autocrine communication
cell communicating within itself
Phospholipids (glycerophospholipids)
- Amphipathic (containing both hydrophilic and hydrophobic parts)
- MAIN constituent of plasma membrane
- Glycerol backbone … (see slides its all there)
- Carbon tail = hydrophobic
- Naturally form spheres that “hide: the hydrophobic tail from water
Sphingolipids
Amphipathic
Sphingosine backbone (1 tail) + 1 fatty acid tail in amide linkage and polar head group
Cholesterol
Sterol, impacts the fluidity of the membrane (ring structure) does not go all the way through, wedges in one of the leaflets in a particular orientation
Which part of the plasma membrane is hydrophobic?
Carbon tail of bilayer
Peripheral membrane protein
don’t go through the membrane, but they were anchored to another protein
Integral membrane protein
proteins that go all the way or part of the way through the lipid bilayer (aka part of their structure is hydrophobic and part of their structure is hydrophilic)
Explain the dimension of a plasma membrane and its relationship to lipid structure
The dimension of the lipid constituents determines the thickness of the bilayer
Potassium inside vs. outside cell
high inside, low outside
Calcium inside vs. outside cell
high outside, low inside
Sodium inside vs. outside cell
high outside, low inside
Cytoplasmic sodium vs extracellular sodium
Cytoplasmic sodium concentration is lower than extracellular concentration.
Cytoplasmic potassium vs extracellular potassium
Cytoplasmic potassium concentration is higher on the inside. At any given time the potassium channels are almost always open and therefore the cell’s membrane potential is based on the potassium ions more than the other ions.
Ion gradients
- Sodium-potassium pump makes these gradients happen (3 Na+ out, 2 in K in)
- The Na,K-ATPase develops and maintains steady state ion gradients for ALL cells.
- Ions are not in equilibrium bc this requires energy to maintain gradients
- Energy comes from hydrolyzing ATP
Membrane permeability
- Defined by ion channels (which ones are present or open; NOT by ion concentration)
- K+ channels are present in all cells so K+ ions leak out; if you ever have to guess, go with the potassium they are usually open and plentiful!
Steady state vs. equilibrium
- Steady state is when energy is put in to maintain a higher free energy state
- Equilibrium is when there is no energy put in to maintain balanced conditions
Energy cost of maintaining ion concentration gradients
The energy to maintain these concentration gradients comes from hydrolyzing ATP
Hyperpolarizing effect of closing/opening sodium or potassium channels
Hyperpolarizing is when the potassium channels open causing the membrane voltage to become more negative
Depolarizing effect of closing/opening sodium or potassium channels
Depolarizing is when the sodium channels open causing the membrane voltage to become more positive
Nernst equation
calculates the membrane potential when an ion is at equilibrium (ie when chemical and electrical forces are equal and opposite
Goldman equation reflects the real situation where…
- Sodium ions and chloride ions also contribute to the membrane potential
- Ion permeabilities determine the relative influence of each ion on the membrane potential
Two important parameters of the Goldman equation
ion permeabilities and ion gradients
Voltage-gated
Opened by depolarization (membrane becoming less negative).
Chemical “ligand” gated
Opened when a signal molecule binds to the channel protein
Mechanically-gated
Open when membrane get stretched
threshold for the neuronal action potential
Action potential is an all or nothing event. Must be depolarized to a specific threshold to occur.
Absolute refractory
Na channels need to be reset causing a period when the membrane CANNOT be re-stimulated to produce another AP
Relative refractory
K needs to be reset causing a period where another AP CAN be produced but it takes a larger than normal stimulus.
Origin of graded potential
Dendrites and cell body
Origin of action potential
Trigger zones and propagate along axon
Types of graded potential channels
Ligand or mechanical
Types of action potential channels
Voltage gated for Na and K
Conduction of graded potentials
Not propagated - localized and only permits a few micrometers of communication
Conduction of action potentials
Propagate → longer distance communication
Amplitude of graded potentials
Varies from less than 1 mV to over 50 mV
Amplitude of action potentials
All or none; about 100 mV
Duration of graded potentials
Ranges from msec to several minutes
Duration of action potentials
0.5 to 2 msec
Polarity of graded potentials
Hyperpolarizing or depolarizing
Polarity of action potentials
ALWAYS depolarizing phase followed by repolarization and return to resting MP
Refractory period of graded potential
Not present → allows for spatial and temporal summation
Refractory period of action potentials
Present → summation cannot occur
Explain the two factors that influence the velocity of an action potential
- Size diameter of the axon. Larger diameter axons have a higher conduction velocity, they send signals faster.
- Myelination speeds conduction velocity.
