Biophysics written

Temperature vs Heat

Temperature —> is the average KE that molecules in a system or material possess. This is measured in Celcius, Kelvin, Farenheit and Rankine.

Heat —> is the transfer of thermal energy between molecules from one system to another. It is measured in Joules.

Entropy and internal energy

Entropy —> is the measure of the disorder (randomness) of particles within a system e.g. gases have higher entropy than solids or liquids

Internal energy —> is the total KE contained in a system due to the movement and collision of particles. It changes primarily with temperature.

Free energy and heat (enthalpy)

Free energy —> is the total energy able to perform thermodynamic work

Heat enthalpy —> gives the total energy of a system that can be converted to heat

Phospholipids and cholestrol

Phospholipids —> are building blocks of cell membranes which provide structure and stability. It consists of a hydrophilic phosphate head and 2 hydrophobic fatty acid tails.

Cholesterol —> is a steroid or lipid derivative that helps to maintain integrity and fluidity of cell membranes

Lateral vs transverse diffusion

Lateral diffusion —> is the movement of lipid or protein molecules within the same layer (leaflet) of the cell membrane and occurs rapidly.

Transverse diffusion —> (also called flip-flop) is the movement of these molecules from one leaflet to the opposite one, crossing the hydrophobic core of the membrane, and occurs very slowly unless assisted by enzymes like flippases.

1.      Transversal lipids diffusion and flip-flop lipids diffusion

There is no difference between transversal lipid diffusion and flip-flop lipid diffusion as both terms are used interchangeably to describe the movement of lipids from one leaflet of the lipid bilayer to the opposite leaflet. Both processes refer to the crossing of the hydrophobic core of the membrane by lipid molecules. No difference

Neuronal and skeletal muscles

Neuronal muscles —> action potential originates in motor neurones and propagates to muscle fibres. They are brief, rapid, and triggered by synaptic input or sensory stimuli.

Skeletal muscles —> action potential originates within muscle fibre themselves. They are slightly longer in duration and lead directly to muscle contraction by initiating calcium release.

Tropomyosin and troponin

Tropomyosin —> block the binding sites on actin, preventing contraction. It shifts position when troponin binds calcium, allowing muscle contraction to occur.

Troponin —> regulate the position of tropomyosin. When calcium binds to troponin, tropomyosin moves allowing muscle contraction to occur.

G - actin and F - actin

G -actin —> monomeric, globular form of actin that is soluble in the cytoplasm. It serves as the building block for polymerization into filamentous actin.

F-actin —> polymerized, fibrous form of actin composed of linked G-actin units. It forms the structural filaments involved in muscle contraction and cytoskeletal support.

Electrical and receptor mediated smooth muscle stimulation

Electrical —> occurs when smooth muscle cells generate spontaneous action potential due to pacemaker cell activity. This doesn’t require external signals leading to rhythmic contractions.

Receptor mediated —> involves external signaling molecules (like neurotransmitters or hormones) binding to specific receptors on the smooth muscle cell membrane. This triggers intracellular pathways that lead to contraction or relaxation.

Ionophores and ionophoresis

Ionophores —> are small molecules that facilitate the transport of specific ions across biological membranes by forming complexes with them. They are often used in research or antibiotics to disrupt ion gradients in cells.

Ionophoresis —> medical technique that uses a mild electrical current to deliver charged drugs or ions through the skin. It is commonly used for localized drug delivery in physical therapy and dermatology.

Action potential and trace potential

Action potential —> is the rapid polarization and depolarization that propagates along a cell, and is triggered when a threshold is reached. Allows cells like neurons and muscles to communicate or contract

Trace potential —> small, lingering change in membrane potential that occurs after an action potential. It does not reach the threshold and cannot trigger another action potential, but it reflects residual ionic activity as the membrane returns to resting state.

Trace Potential

• A small leftover change in membrane potential after an action potential.

• It’s not strong enough to trigger a new signal.

• Think of it like the echo or fading ripple after a big wave (the action potential).

• It gradually returns to the resting potential, but the cell is not fully back to normal yet.