Lecture 10 Flashcards
how do Na+ ions get across the membrane?
Na+ ions move across a membrane by facilitated diffusion through an ion channel protein
ATP
adenosine triphosphate;
used to change the conformation of the Na+/K+ pump
what type of transport requires energy?
active transport
voltage
electrical potentail energy or a separationof opposite charges
plasma membrane voltage
polarized
Na+ ions moving in cause a change in voltage
depolarization
why dont Na+ ions cross all the time
ion channels are gated ( voltage gated channels)
Polarized
positive stays out
negative stays in
gate closed
depolarized
positive in
negative out
gate open
how do neurons send signals
ions move across membranes
What makes Na+ want to go from out to in
The Na+ concentration gradient (high to low)
Remember that the 2nd law of thermodynamics says that disorder should increase (entropy increases).
How do Na+ ions get across the membrane
Na+ ions move across a membrane by facilitated diffusion through an ion channel protein.
How can a neuron fire over & over without running out of Na+ or energy?
Without a [Na+] gradient, a neuron couldn’t fire.)
neuron firing
Sodium ion concentration gradient
Ions move across membrane when nerve fires
Ions pumped back across membrane to recharge neuron
when a neuron fires
Na+ ions move down their concentration gradient spontaneously
A neuron recharges when
Na+ ions are actively pumped against their concentration gradient
Fugu Poisoning
Tetrodotoxin is heat-stable and blocks sodium ion channels.
10-45 minutes after ingestion tingling of the tongue and inner surface of the mouth begins.
An ascending paralysis develops, and death can occur within 6-24 hours, after respiratory muscle paralysis.
What does the puffer fish neurotoxin tetrodotoxin inhibit?
Channel proteins involved in diffusion
Why would this lead to paralysis and death
Neurons can’t fire without a voltage change.
How do signals move from one neuron to the next?
Exocytosis is used to move large molecules out of a cell
Vesicles
Vesicles containing neurotransmitters move along the cytoskeleton and fuse with the plasma membrane during exocytosis
Release of neurotransmitters (NTs) from vesicles
Travel from one neuron & bind to the plasma membrane of the next
Acetylcholine
released at neuromuscular junctions
Norepinephrine
released from neurons usually to other neuron
Ligand-gated ion channel
opens/closes when a signaling chemical (its ligand) attaches,
allowing or blocking flow of specific ions
Stimulants
cocain, amphetamines, caffine
depressants
barbituates, valium
toxins
organophosphate pesticides) – inhibit the action of acetylcholinesterase, a neurotransmitter
Heart medications (beta blockers)
inhibit ephinephrine mediated sympathetic reactions
Reduce the effect of excitement on heart rate
Drugs funciton
Drugs often mimic neurotransmitters (analogs).Drugs bind to NT receptors to open or block them or alter the metabolism of NTs.
How do channel proteins, pump proteins, and neurotransmitter receptor proteins get into a cell membrane?
.
Nucleus
stores DNA
Endoplasmic reticulum
Rough ER makes membranes & secreted (secretory) proteinsSmooth ERlipid synthesis
Ribosomes
in the cytoplasm read the RNA instructions & synthesize proteins (manufacturing plants)
Golgi Apparatus
protein modification and sorting
The secretory pathway
- Protein is put into RER as ribosome makes it
- Vesicle buds off RER with protein cargo and delivers it to Golgi where the proteins are modified
- Vesicle buds off Golgi with protein cargo
- Vesicle fuses to plasma membrane
Secreted proteins are released by exocytosis
Membrane bound proteins become part of the cell membrane
The cytoskeleton
interior framework of the cell A dense network of protein fibers that 1. Supports the shape of the cell 2. Anchors organelles 3. Used in vesicle transport
Which of the following choices best describes the route of a Na+ channel protein from its production to its final destination in the membrane?
. Rough ER, transport vesicles, Golgi, transport vesicles, cell membrane
How does a transport vesicle move from the cell body to the nerve terminal?
Along the cytoskeleton
Acetylcholine
Acetylcholine is important in the brain, and at synapses between motor neurons and muscle cells.
Acetylcholine excites skeletal muscles.
Acetylcholine slows down the heart.
Toxins released by black widow spider venom cause an explosive release of acetylcholine from neurons. These toxins cause paralysis by…
Triggering increased exocytosis of the transport vesicles containing acetylcholine.
In contrast, toxins produced by Clostridium botulinum (botulism toxin) block the release of acetylcholine from neurons. These toxins work by…
Inhibiting exocytosis of the transport vesicles containing acetylcholine.
What is an enzyme?
A protein that catalyzes reactions
activation E
energy required to contort molecules so bonds will break
Exergonic reactions
release energy;delta G is negative
Endergonic reactions
require energy;delta G is positive
what lowers activation energy
Enzymes
what kind of energy is ATP
Potential
Activation energy vs. coupled reactions
Coupled reactions harness energy from an exothermic reaction to drive an endothermic reaction.
Activation energy is the energy required to get any reaction, exothermic or endothermic, to proceed.
Inhibitors
Enzymes are not always on.Inhibitors lower the activity (turning off).
Amino acid side chains in the center of a cytoplasmic protein will typically be
non-polar
The fatty acid tails on a phospholipid are
non-polar
What types of amino acids would you expect to find on the outside of a membrane protein?
non-polar
Na+ is a charged ion. What types of amino acids would you expect to find lining the channel it passes through?
polar uncharged and polar charged
Channel proteins
selective pores in the membrane; amino acids lining ht echannel only allow one type of ion through
Although animal cells are always hyperosmotic to fresh water, the [Na+] in an animal cell is about the same as the [Na+] in fresh water. The scud could avoid too much osmosis of water into its cells by
Pumping out Na+ ions by active transport
The plant can adapt to a hypotonic solution because its cell walls
Prevent the cell membrane from swelling until it bursts
Tay-Sachs Disease
Genetic disorder in which children become mentally retarded and suffer damage to their central nervous system.
Caused by a mutation in the lysosomal enzyme hexosaminidase which breaks down lipids called gangliosides in neurons.
Lysosomes
are organelles that break down molecules = recycling center
The enzyme hexosaminidase normally breaks down lipids called gangliosides found in the membranes of neurons.
smooth ER
The enzyme hexosaminidase normally breaks down lipids called gangliosides found in the membranes of neurons. What would happen to the levels of gangliosides in the neurons of children with Tay Sachs disease?
Gangliosides would increase
