Signal transduction pathways amplify the effect of a signal molecule. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways? Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways. Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers. Cyclic GMP, or cGMP, acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls. In the penis, this signaling pathway and the resulting dilation of blood vessels leads to an erection.
Select the correct statement about the effect of Viagra on this signaling pathway. The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells.
Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis.
An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin? As children and teens, they walk an average of 12, to 16, steps per day. Young females, on the other hand, get 10, to 12, This trend continues into adulthood, at least in the United States. A study looked at pedometer data for just over 1, adults.
Overall, males took an average of 5, steps per day, compared to 4, for females. What you do for a living may impact your average steps per day, too. Jenny Craig conducted a small research project in involving 10 participants from Australia, each with a different job. They were given pedometers to track their steps. People in certain countries tend to take more steps per day than those in other countries.
A study tracked activity levels of , people in countries over an average of 95 days using smartphones. A range of factors likely play a role, including:. The CDC recommends that adults, including older adults, get a minimum of minutes of aerobic activity, such as brisk walking, per week.
A brisk pace translates to roughly steps per minute. For more health benefits, the CDC recommends upping that goal to minutes. For example, prokaryotic organisms have sensors that detect nutrients and help them navigate toward food sources. In multicellular organisms, growth factors, hormones, neurotransmitters, and extracellular matrix components are some of the many types of chemical signals cells use.
These substances can exert their effects locally, or they might travel over long distances. For instance, neurotransmitters are a class of short-range signaling molecules that travel across the tiny spaces between adjacent neurons or between neurons and muscle cells.
Other signaling molecules must move much farther to reach their targets. One example is follicle-stimulating hormone, which travels from the mammalian brain to the ovary, where it triggers egg release. Some cells also respond to mechanical stimuli. For example, sensory cells in the skin respond to the pressure of touch, whereas similar cells in the ear react to the movement of sound waves. In addition, specialized cells in the human vascular system detect changes in blood pressure — information that the body uses to maintain a consistent cardiac load.
Cells have proteins called receptors that bind to signaling molecules and initiate a physiological response. Different receptors are specific for different molecules. Dopamine receptors bind dopamine, insulin receptors bind insulin, nerve growth factor receptors bind nerve growth factor, and so on.
In fact, there are hundreds of receptor types found in cells, and varying cell types have different populations of receptors. Receptors can also respond directly to light or pressure, which makes cells sensitive to events in the atmosphere. Receptors are generally transmembrane proteins, which bind to signaling molecules outside the cell and subsequently transmit the signal through a sequence of molecular switches to internal signaling pathways.
Membrane receptors fall into three major classes: G-protein-coupled receptors, ion channel receptors, and enzyme-linked receptors. The names of these receptor classes refer to the mechanism by which the receptors transform external signals into internal ones — via protein action, ion channel opening, or enzyme activation, respectively.
Because membrane receptors interact with both extracellular signals and molecules within the cell, they permit signaling molecules to affect cell function without actually entering the cell. This is important because most signaling molecules are either too big or too charged to cross a cell's plasma membrane Figure 1. Not all receptors exist on the exterior of the cell. Some exist deep inside the cell, or even in the nucleus. These receptors typically bind to molecules that can pass through the plasma membrane, such as gases like nitrous oxide and steroid hormones like estrogen.
Figure 1: An example of ion channel activation An acetylcholine receptor green forms a gated ion channel in the plasma membrane. This receptor is a membrane protein with an aqueous pore, meaning it allows soluble materials to travel across the plasma membrane when open. This change initiates the process of transduction. Signal transduction is usually a pathway of several steps.
Each relay molecule in the signal transduction pathway changes the next molecule in the pathway. Membrane receptors function by binding the signal molecule ligand and causing the production of a second signal also known as a second messenger that then causes a cellular response.
These type of receptors transmit information from the extracellular environment to the inside of the cell by changing shape or by joining with another protein once a specific ligand binds to it. Intracellular receptors are found inside the cell, either in the cytopolasm or in the nucleus of the target cell the cell receiving the signal. Chemical messengers that are hydrophobic or very small steroid hormones for example can pass through the plasma membrane without assistance and bind these intracellular receptors.
Once bound and activated by the signal molecule, the activated receptor can initiate a cellular response, such as a change in gene expression. Since signaling systems need to be responsive to small concentrations of chemical signals and act quickly, cells often use a multi-step pathway that transmits the signal quickly, while amplifying the signal to numerous molecules at each step.
Steps in the signal transduction pathway often involve the addition or removal of phosphate groups which results in the activation of proteins.
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