Bio-150 Group Questions

Describe the nucleus of a neuron

An organelle located in the centre of the neuronal cell body (soma).

Houses and protects genetic information used in cell development and maintenance.

Serves as a command centre and regulates cellular functions (i.e. metabolism, cell division)

Surrounded by a nuclear envelope (continous with the ER, which is involved in protein synthesis) made up of outer nuclear membrane, inner nuclear membrane, and nuclear lamina.

Describe the mitochondria of a neuron

“Powerhouse of the cell“

Generates energy in the form of ATO and stores calcium, generates heat (especially necessary in infants, higher SA:V ratio), and mediates cell growth/death

Describe the Endoplasmic Reticulum and Golgi Apparatus of a neuron

Rough Er:

Has ribosomes on outer surface

Produces proteins wirh signal sequences which tell the cell where to put a protein (some remain in ER, some sent to Golgi)

Smooth ER:

Produces lipids (i.e. cholesterol, phospholipids) which are used to produce new membrane of cells

Golgi Apparatus:

Modifies, packages proteins for further transport (sends proteins throughout the cell to perform designated tasks)

Describe the dendrites of a neuron

Only found in neurons

Receives chemical/electrical signals from outside the cell and transfers it to the soma

“Dendritic arbor“

Describe the axon of a neuron

Only found in neurons

Uses info from the soma and transmits it out of the cell

Axon terminal located opposite in the neuron

Describe the axonal transport of a neuron

Moves lipids, vesicles, proteins, and organelles to the cellular body of a neuron

Occurs throughout the life of a neuron; essential to its sustenance

Describe the synapse of a neuron

Transmits electrical nerve impulses either between 2 neurons or between a neuron & muslce cell

On the end of the axon

Describe the overall structure of the cell membrane and explain why it is referred to as a fluid-mosaic

Hydrophobic inside and hydrophillic inside made of phospholipids

A mosaic of proteins and other parts that can move to serve different functions

What are phosphoglycerides (phospholipids) and how are they arranged in the cell membrane? Why are they arranged as such?

2 hydrocarbon chains and a phosphate group attatched to glycerol for the head

Membrane can be soft and flexible rather than hard and rigid due to viscous unsaturated fats without hydrogen, instead saturated fats without double bonds which can move around less

What is a protein? How are proteins arrange in the cell membrane?

One of 3 main macroneutrients (carbs, fats, proteins)

Made up of amino acids (themselves made of C and H)

Necessary to maintain muscle tissue and repair

In the phospholipid bilayer of the cell membrane

Integral (embedded in the bilayer) and peripheral membrane proteins (outside of lipid bilayer)

Also have hydrophobic/phillic interactions (ones interacting with the inside of the bilayer are phobic, outside are phillic)

What are some functions of these membrane proteins?

Allow molecules to pass through using active or passive transport

Catalyze some chemical reactions

Allow cells to identify the type of other cells based on proteins on their surface

What are ions?

Atoms with fewer/more elctrons than in neutral elemental form (more electrons:negative, anions, less=positive, cations)

Generally dissolved in water

What are ion channels and what is their function in the cell membrane?

Proteins located within the cell membrane

Pores/holes in the lipid layer made of hydrophillic amino acids allow ions to pass through

Alpha helices orients so every 4th is hydrophilic

What does it mean to be a sodium channel, or a potassium channel or a chloride channel?

Na+ channels allow Na+ into the cell: trigger

K+ channels are concentrated more inside the cell and let ions flow out of the cell naturally: rest

Cl- channels allow Cl- into the cell through the membrane: break

What does it mean to say that ion channels have gates?

Some channels open and close

Mechanism that open and close are “gates”

Some channels “leak“ and are always open

What ways can channel gates be opened or closed?

“Mechanically gated“- pushed open by physical pressure

Ligand-gated- use specific chemicals called ligands as keys to open and close channels

Voltage-gated- Not ohmic, controlled by changing voltage between inside and outside of cell

What is the Na+/K+ pump?

A trans-membrane protein pump (active transport) specific for Sodium and Potassium in animal cells

What type of molecule is the Na+/K+ pump?

A large integral transmembrane protein made up of folded chains of amino acids ca;lled Na+/K+ ATPase

P-type ATPase pump eznyme

What does the Na+/K+ pump do?

It helps establish the resting membrane potential of neurons by utilising ATP to move 3Na+ out of the cell for every 2k+ it brings in against the concentration gradient, contributing to the electrical potential difference between the inside and outside of the cell.

Keeps the inside of the cell negatively charged compared to the inside, important for resting membrane potential

Why is the Na+/K+ pump needed by neurons?

It maintains cell membrane potential and ionic concentration gradients required to send nerve impulses by transporting Na+ out and K+ into the cell.

The drug digitalis stops the Na+/K+ pump from working. Describe what will happen to a neuron poisoned with digitalis. How quickly will changes occur. Why?

The neuron will no longer be able to signal because it will lose its electrical potential difference as Na+ flows back into the neuron and K+ flows back out. The changes will occur gradually (4-6 hours for accute exposure or for chronic exposure like digoxin toxin, which is used to treat heart conditions, can take months) because it takes a long time for the ions to passively move across the membrane and to get rid of the initial gradient. In a lab, electrogenic effect will be stopped immediately, but over time, (hours), [Na+] grows and [K+] lessens and the Na +Nernst will get smaller, the K+ larger