Part 1: From chemical elements to cell membrane

Lecture 1

Part 1: From chemical elements to cell membrane

ElementSymbol % of human body weight OxygenO65 CarbonC18 HydrogenH10 NitrogenN3 CalciumCa2 PhosphorP1.1 PotassiumK0.35 SulfurS0.25 SodiumNa0.15 ChlorideCl0.15 MagnesiumMg0.05 Bonding element ➔Ionic bond(electrostatic force) ◆+ attract - → Na+ and Cl- ➔Covalent bond(sharingof electrons forms molecules) ◆eg: H2O: oxygen + hydrogen: inner shell can have 2 atoms and other shells can have 8 → oxygen has inner 2 and outer has 6 (8 in total) → hydrogen has only one on the inner shell → they form a bond ◆Sometimes there are 8 around oxygen and sometimes they go to hydrogen and then hydrogen has 2 ◆Oxygen has a stronger positive core (8 atoms) so the negative electrons are more likely to be attracted to the oxygen core than the hydrogen core → the oxygen core ismore negativethan the hydrogen core Carbon chains → ●Glucose is made by a covalent bonding ●Amino acid is also made by covalent bonding ○are important in our body → key structure for making proteins

●Protein: structure of amino acids (1000 amino acids)

○Peptides: are short protein chains (10 amino acids)

●Lipids (fat): long carbon chains by covalent bondings between carbon

●Phospholipids: carbon chains connected by an extraphosphate (P) group →

phosphate has a static negative charge (carbon chain with P element → has many protons and so it attracts electrons → net negative charge) and is consequently hydrophilic head ○Tails (chain of carbon) from the phospholipids are lipids →hydrophobic

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○Double layer of phospholipids forms cell membrane (tails to the inside heads to the outside) and for the outside of the cells in our body

Part 2: Nerve cells

Nerve cell ●= soma with extensions (dendrites) receive information from other cells ●the body than integrate the signals → can be excitatory or inhibitory ●Either action potential yes or no ●Action potential over the axon (sends signals) ○Axon is covered in fatty layer = myelin sheath around 100 billion neurons in the human brain = 100 hard-disks with 1TB capacity Global structure 1.In the soma is thecell nucleuswith little poresfor transport of messengermRNA

a.Nucleus contains chromosomes with genes (pieces of DNA: deoxyribonucleic

acid) 2.Endoplasmic reticulum(production, storage and transportof proteins):mRNAis read to produce proteins → is themRNAis produced it needsto be read →

3.Golgi apparatus: post office for packing (neurotransmitterin

vesicles for transport) 4.Mitochondria: power plant (ATP: adenosine Tri-Phosphate→ energy of the cell)

5.Lysosomes: waste processing

6.Road system:microtubuli: road system for transportation neurotransmitter through axon DNA →mRNA(transcription: genes are read from theDNA and converted to messenger RNA =mRNA) →mRNAleaves the nucleus through thepores, and is read out by ribosomes (complex proteins), to form a new protein → need to be transported → Axoplasmic transport

●Kinesin: anterograde transport from the cell body(soma) to

terminal buttons → walk along the microtubuli

●Dynein: retrograde transport from terminal buttonsto soma

○Pick up chemicals that are not used back to the soma

not only neurons in the brain, there are also:

Glial cells(support cells)

●Microglia: immunologic defense and removal dead cells

●Macroglia:

○Oligodendrocytes: they form the myelin sheath in the central nervous system

(can make more myelin sheaths for more axons).

○Schwann cells: also make myelin sheath, but in the peripheral nervous

system. One cell that wraps around an axon to form a sheet of myelin (one sheath of myelin).

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○Astrocytes (star shape): support → structure and solidity (glia = glue), isolate synaptic clefts, and can take out nutrients from the bloodstream and give it to the neurons → blood cannot contact brain cells directly ■Blood-brain barrier taken over ■Feeding neurons by converting glucose in the blood to lactate ■Astrocyte can also storage a little bit of nutrients

Part 3: Bioelectricity (Membrane potential)

Axon holds a charge (-90 in quids and -65 mV in humans in the cells) Membrane potential origin ●the membrane potential is caused by a balance between two forces

●Diffusion: due to random motion, particles will movefrom regions with high

concentration to regions with low concentrations ●Electrostatics: positively charged particles repealeach other, negatively charged particles repel each other, but oppositely charged particles attract each other ●The membrane on nerve cells is not completely closed → they have ion channels.the channels can be in an open or closed state.○To let sodium, potassium or chloride in or out Cell at rest→ -Inside the cell many proteins (A-) are made and they attract elections -According to law of attractions they attract positive proteins but they cannot get otu -Inside the cell is a lot of K, but this charge does not outway the negative charge of the proteins -Electrostatic pressure keep K in the cell -K can leak out, and so the inside will be more negative → more difficult for other electrons to leave the cell → eventually K cannot leave anymore = the exact membrane potential (-70 mV) -on the outside is a lot of Na and Cl, and because there is pressure (abundant) they want to move into the cell -For chloride this is not possible → they are retained by the electrostatic force -But Na, because of diffusion, is attracted to the inside -Membrane will lean in some Na -Then moved out by Na/K pump

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Sodium/Potassium pumpmaintains membrane potential ●Higher Na+ concentration outside the cell due to Na/K pump ○3 Na ions outward for 2 K ions inward ●The pumps requireenergyand are activeall day

Part 4: Bioelectricity (Action potential)

Electric stimulation of the axon induces an action potential All or none activation ●The axon generates an action potential only if the resting potential crosses a threshold ●The magnitude of the action potential is always the same → all or none Action potential mechanism ●Electrical stimulation causes the membrane potential to be less negative ●If the threshold is crossed (-70 mV to -60mV) a

cascade starts:

1.More Na+ channels are opened, Na+ flows into the cell, cell inside becomes less negative(depolarisation) 2.K+ channels open, K+ flows out the cell, will counteract the electrical effect of the Na+ inflow 3.Na+ channels close(refractory period),Na+ inflowis halted 4.K+ keeps flowing out, cell return to negative (repolarization) 5.K+ channels close, Na+ channels returns to their normal closed condition (can be opened again) 6.Following the massive outflow of K+, the membrane temporarily has an extra negative charge (hyperpolarization)

Part 5: Bioelectricity (Action potential conduction)

→ The first action potential triggers a dominion effect

But this type of conduction is:

1.Relatively slow→ new action potentials are generatedin neighboring regions 2.Energy consuming→ resting potential needs to be recoveredacross the whole axon, by means of the Na/K pumps

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