Biyofizik Full PDF

## Active Transport - Active processes use energy (ATP) to move substances across a membrane and often up a concentration gradient. - Active transport uses solute pumps to move substances against a concentration gradient. The two kinds of active transport are primary active transport and secondary...

## Active Transport - Active processes use energy (ATP) to move substances across a membrane and often up a concentration gradient. - Active transport uses solute pumps to move substances against a concentration gradient. The two kinds of active transport are primary active transport and secondary active transport. - Primary active transport directly uses ATP to transport the substance. ### Primary Active Transport #### Sodium-Potassium Pump 1. The sodium-potassium pump binds three sodium ions and a molecule of ATP. 2. The splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel. 3. The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind. 4. Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane. ### Secondary Active Transport - Secondary active transport uses a gradient to co-transport solutes and that gradient is set up by a primary active transport process, like the sodium-potassium pump. - **Primary Active Transport** - The ATP-driven Na+-K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. - **Secondary Active Transport** - As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell. ## Ion channels - **mechanically gated (ion) channel** - An integral membrane protein which is an ion channel within an excitable cell's outer cell membrane which opens and closes in response to a stimulus which is a mechanical pressure or vibration; such channels are primarily responsible for impulse initiation = initial depolarization of an excitable cell such as a mechanoreceptor (sensory cell responding to touch, vibration, compression or stretch). - **light-gated (ion) channel** - An integral membrane protein which is an ion channel within a photosensitive excitable cell's outer cell membrane which opens in response to a stimulus which is the arrival of a photon of light energy; such channels are primarily responsible for impulse initiation = initial depolarization of an excitable cell such as a photoreceptor (sensory cells, rods and cones responding to light in the retina of the eye). ## Action Potential - Action potential is the change in membrane potential which occurs because of the movement of ions across the neuronal membrane. - This potential is a wave of electrical activity that travels along the axon to the synapse. - There are several types of ion channels in the neuronal membrane, which open and close in response to different stimuli. - The opening and closing of these channels causes the changes in membrane potential that are responsible for the action potential. - The opening of sodium channels causes the membrane potential to become more positive (depolarization). - The opening of potassium channels causes the membrane potential to become more negative (repolarization). ## Resting Membrane potential Results from the fact that positively and negatively charged ions become distributed unequally on the two sides of the neural membrane: 1. The concentration of Na+ is higher outside 2. The concentration of Cl is higher outside 3. The concentration of K+ is higher inside 4. Various negatively charged protein ions are trapped inside ## Nerst Equation The Nerst Equation is a mathematical equation that describes the electrical potential difference across a membrane for a single ion. It is used to calculate the equilibrium potential for each ion. - Eion = (61/z) log ([ion]out/[ion]in) - E = membrane potential (V is sometimes used as well) - R = Universal Gas constant (1.98 calories per mole Kelvin) - T = Temperature (Kelvin) - z=charge on the ion - F = Faraday's Constant (2.3x10 calories per mole voltage) - In = natural log base e - Co = Concentration of ion outside the cell - Ci = Concentration of ion inside the cell ## Goldman Equation The Goldman Equation is a mathematical equation that describes the electrical potential difference across a membrane for multiple ions. It is used to calculate the resting membrane potential. - E(mV) = RT/F * ln(PNa+(CNa+) + PK+(CK+) + PCI-(CCI-))/(PNa+(CNa+)o + PK+(CK+)o + PCI-(CCI-)o) ## Driving Forces Acting on Molecules - **Chemical Driving Force** = Diffusion Force - **Electrical Driving Force** - If the inside of the cell is negative and the outside of the cell is positive, then the electrical driving force will favor the movement of cations into the cell and anions out of the cell. - if the inside of the cell is positive and the outside of the cell is negative, then the electrical driving force will favor the movement of cations out of the cell and anions into the cell. - **Electrochemical Driving Force** is the sum of the chemical driving force and the electrical driving force. ## Factors that Affect Resting Membrane Potentials 1. Negative anions inside of the cell 2. K permeability is high and it diffuses out easily 3. Na-K pumps ## Action Potential - **Action Potential** is a rapid change in membrane potential that occurs when a neuron is stimulated. - **Excitatory postsynaptic potentials (EPSPs)** are depolarizations; i.e. they increase the likelihood that a neuron will fire. - **Inhibitory postsynaptic potentials (IPSPs)** are hyperpolarizations; they decrease the likelihood that a neuron will fire. - **Action potentials** are all-or-none events, meaning that they either occur or they do not. - The amplitude of an action potential is always the same, regardless of the strength of the stimulus. - **Action potential** has a threshold, meaning that a certain level of stimulation is required to trigger an action potential. ## Types of Summation - **Spatial Summation** occurs when multiple synapses are activated simultaneously. - **Temporal Summation** occurs when multiple synapses are activated in rapid succession. ## Skeletal Muscle - **Skeletal Muscle** is responsible for voluntary movement. - **Skeletal Muscles** are connected to bones by tendons. - **Skeletal Muscle** cells are multinucleated and have a striated appearance. - **Skeletal Muscle** cells contain a large number of mitochondria. - **Skeletal Muscle** cells are able to contract quickly and forcefully. - The action potential in a skeletal muscle cell causes the release of calcium from the sarcoplasmic reticulum. - The calcium ions bind to troponin, causing the actin and myosin filaments to slide past each other and the muscle to contract. ## Cardiac Muscle - **Cardiac Muscle** is responsible for the pumping action of the heart. - **Cardiac Muscle** cells are striated and are interconnected by intercalated disks. - **Cardiac Muscle** cells are able to contract rhythmically and automatically. - **Cardiac Muscle** cells have a long refractory period, which prevents tetany. - **Cardiac Muscle** contraction is regulated by the autonomic nervous system. - **Cardiac Muscle** cells have a high density of mitochondria. ## Nerve-Muscle terminal 1. Acetylcholine released from the axon terminal binds to receptors on the sarcolemma. 2. An action potential is generated and travels down the T tubule. 3. Ca2+ is released from the sarcoplasmic reticulum in response to the change in voltage. 4. Ca2+ binds troponin; Cross-bridges form between actin and myosin. 5. Acetylcholinesterase removes acetylcholine from the synaptic cleft. 6. Ca2+ is transported back into the sarcoplasmic reticulum. 7. Tropomyosin binds active sites on actin causing the cross-bridge to detach. ## Electroretinography (ERG) - **ERG** is a technique used to measure the electrical activity of the retina. - **ERG** is a non-invasive test. - **ERG** is used to diagnose retinal diseases and disorders. - **ERG** is performed by placing electrodes on the skin around the eye. - The electrodes record the electrical signals produced by the retina in response to light stimulation. ## Electrocardiogram (ECG) - **ECG** is a non-invasive test that measures the electrical activity of the heart. - **ECG** is used to diagnose heart conditions. - **ECG** is performed by placing electrodes on the skin around the chest, arms, and legs. - The electrodes record the electrical signals produced by the heart, which are then displayed on a computer screen. - **ECG** can be used to identify heart rhythm abnormalities, heart attacks, and heart valve problems. ## Electromyography (EMG) - **EMG** is an electro-diagnostic medicine technique for evaluating and recording the electrical activity produced by skeletal muscles. - **EMG** is used to diagnose muscle and nerve disorders. - **EMG** is performed by inserting needle electrodes into the muscles. The electrodes record the electrical signals produced by the muscles, which are then displayed on a computer screen. - **EMG** can be used to identify muscle weakness, muscle spasms, and nerve damage.