Question

Describe 3 general ways that cells use ATP (or its equivalent, GTP). For each of these general ways, explain 3 detailed examples (for a total of 9 examples)

Answer 1

Cells are the units of life. Hence , they perform a variety of functions which make life possible. They need energy to perform these functions and they get that from ATP molecules . Energy is liberated from an ATP molecule by a reaction that removes one of the phosphate-oxygen groups leaving ADP [adenosine di phosphate] .The ADP can also liberate energy and change into AMP [ adenosine mono phosphate] .

The cells spend energy in several processes which can be placed under 3 headings--

*Synthesis and breakdown of substances

  * Transport

* Life processes

1] Synthesis and breakdown of substances--

a] Photosynthesis -- This is a process by which plant cells synthesise glucose from CO2 and H2O. In this process an electron transport chain and associated proton pump is created. ATP is used to construct organic molecules from H2O and CO2 . In fact ATP provides the energy needed to carry out the 'Dark reaction' of photosynthesis .

b] Glycolysis-- Glycolysis is the first pathway of respiration and takes place in the cytoplasm of cells. In this process, ATP is required to break glucose into two molecules of pyruvate . [Although there is a net gain of 2ATP by the end of glycolysis but to start the process, ATP molecules are needed] .

c] Synthesis of proteins and other cellular products -- The cells work day and night to produce materials like proteins, lipids, hormones and other biomolecules which constitute life. All these processes need energy which is provided by ATP. For example, during protein synthesis, the formation of mRNA and its movement to the cytoplasm, the work of transferRNA in transporting amino acids, all need energy .

2] Transport --

a] Inter cellular transport-- In 'active transport ' of materials , ATP is used. In fact, ATP plays a crucial role in transport of macromaolecules such as proteins, lipids etc .The energy provided by ATP is used to transport such molecules across a concentration gradient.

b] Intra cellular transport-- Materials synthesized in the ER and elsewhere inside the cell need to be transported to storage vesicles like the golgi bodies and lysosomes. Product of photosynthesis is stored in a large vacuole within the plant cell. Aii these utilise energy provided by ATP.

c] Ion channels-- Ca and K ion channels are necessary for neural transmission.. The conduction of nerve impulses through neurotransmiitter molecules takes up energy .

Life processes--

a] Muscle contraction -- ATP binds to myosin , moving it to a high energy state and releasing the myosin head from the actin active site. Again , ATP can bind to the to the myosin, which allows the cross bridge cycle to start again, so that muscle contraction can occur.

b] Breathing-- Breathing is a physical process which includes two steps-- inhalation and exhalation . Both the steps involve movement of the lungs, diaphragm and associated muscles and the ribs. ATP is spent in this process.

c] Heart beat -- Heart is our pumping organ which contracts and relaxes systematically so that blood is pumped through the body. The movement of heart involves diastole and systole which are set up by electric signals generated by nodes on the cardiac muscles . The whole process requires energy provided by ATP molecules.

All the life processes, be it digestion, excretion ,movement, cognitive functions etc require energy which is provide by the ATP.