AP BIOLOGY

Detailed explanation-1: -The three steps to cell signaling are reception, transduction, and response. In reception, a cell signaling molecule binds to a receptor protein on the cell membrane or inside the cell if the signaling molecule is hydrophobic and can pass through the membrane.

Detailed explanation-2: -First messengers are the signaling molecules (hormones, neurotransmitters, and paracrine/autocrine agents) that reach the cell from the extracellular fluid and bind to their specific receptors. Second messengers are the substances that enter the cytoplasm and act within the cell to trigger a response.

Detailed explanation-3: -Examples of second messenger molecules include cyclic AMP, cyclic GMP, inositol triphosphate, diacylglycerol, and calcium. First messengers are extracellular factors, often hormones or neurotransmitters, such as epinephrine, growth hormone, and serotonin.