Week 5 Flashcards
What is chemotaxis?
Chemotaxis is a biological process in which cells or organisms direct their movements according to chemical gradients in their environments. In the context of bacteria like E. Coli, chemotaxis involves the movement toward chemical attractants, such as food sources, or away from repellents, such as toxic substances.
How do bacteria use chemotaxis?
- Detection of Chemical Gradients: Bacteria use chemo-receptors, typically located on their cell surface, to detect and respond to chemical gradients in their environment.
- Signal Transduction: When a chemo-receptor binds to a molecule, it triggers a signal transduction pathway inside the bacterium, involving MCPs.
- Motor Response: Bacterial flagella can rotate in two ways: clockwise or counterclockwise. In a favorable chemical gradient (toward an attractant), the flagella rotate counterclockwise, causing the bacterium to swim in a straight line forward. In the presence of a repellent or when attractant concentrations decrease, the flagella rotate clockwise, causing the bacterium to tumble and randomly change its direction.
- Adaptation: Bacteria can adapt to constant levels of a chemical signal. This adaptation involves changes at the level of the chemoreceptor and associated signaling molecules, enabling the bacterium to reset its sensitivity to the chemical gradient. This process allows bacteria to continue to respond to changes in chemical concentrations over time, despite potentially high local concentrations of an attractant or repellent.
List the five types of sense receptors.
- Mechanoreceptor
- Thermoreceptor
- Electroreceptor
- Chemoreceptor
- Photoreceptor
What is a mechanoreceptor?
a transmembrane cation channel protein that is sensitive to pressure.
What is a thermoreceptor?
a transmembrane cation channel protein that is sensitive to temperature.
What is an electroreceptor?
An electric current opens a calcium channel.
What is a chemoreceptor?
a receptor binding initiates a G protein signaling cascade controlling an ion channel.
What is a photoreceptor?
light alters a receptor protein, initiating a signaling cascade that controls an ion channel.
Explain the difference between autocrine and paracrine signals.
Autocrine signals are chemical signals that act on the same cell that secretes them. These signals are important for self-regulation, often in the context of growth or immune responses.
Paracrine signals are released by cells and act on nearby cells to regulate their behavior. These signals help in communication between cells that are in close proximity but are distinct from the signaling cell.
What occurs to a cell when its insulin receptor is bound by insulin?
- The alpha subunits of the receptor bind insulin (the signal).
- A conformational change in the B subunits transmits a signal to the cytoplasm that insulin is present.
- The insulin signal activates the receptor’s protein kinase domain in the cytoplasm.
- which phosphorylates insulin response substrates, triggering a cascade of chemical responses inside the cell.
Overall, this triggers and uptake of glucose into the cell.
Where on the cell is the insulin receptor located?
On the plasma membrane.
What kind of cells are the stretch receptors of crustaceans?
Mechanoreceptors composed of specialized neurons that can detect stretching within muscles or other tissues.
What are the steps of the stretch response?
- stretching a muscle is the stimulus.
- that activates the ion channels in stretch receptor dendrites.
- the resulting depolarization is a receptor potential that spreads to the cell body.
- the spreading depolarization extending to the initial segment of the axon causes the generation of action potential.
- action potentials are conducted along the axon.
What basic type of sensory receptor is a stretch receptor?
Mechanoreceptors.
Compare the compound eye of insects with the mammalian eye
Compound eyes of insects are made up of many small units called ommatidia, each containing its own lens and photoreceptive cells, providing a wide field of view and excellent motion detection but poorer resolution.
Mammalian eyes have a single lens system that focuses light onto a photoreceptive layer called the retina, capable of high-resolution imaging and depth perception.
