cells and energy

CELLS USE A LOT OF ENERGY

Life is an energy intensive process. It takes energy to operate muscles, extract wastes, make new cells, heal wounds, even to think. It's in an organism's cells where all this energy is spent. In some cells, as much as half of a cell's energy output is used to transfer molecules across the cell membrane, a process called 'active transport.'

ATP THE UNIVERSAL ENERGY CARRIER

Most cell processes use the same energy source, the rechargeable energy carrier, adenosine tri phosphate -- ATP. ATP has this arrangement: a molecular unit of adenosine coupled to a chain of three phosphate groups, thus the name, adenosine tri phosphate

PHOTOSYNTHESIS

Photosynthesis is the way plants make fuel molecules to feed their mitochondria. In terms of getting energy, the only real difference between plants and animals is that plants make their own fuel molecules, where as we animals, in order to get fuel for our mitochondria, must eat plants, or eat something that has

What specific pathway do cells use?

The particular energy pathway that a cell employs depends in large part on whether that cell is a eukaryote or a prokaryote. Eukaryotic cells use three major processes to transform the energy held in the chemical bonds of food molecules into more readily usable forms

How Do Cells Keep Energy in Reserve?

When energy is abundant, eukaryotic cells make larger, energy-rich molecules to store their excess energy. The resulting sugars and fats — in other words, polysaccharides and lipids — are then held in reservoirs within the cells, some of which are large enough to be visible in electron micrographs.

The light reaction of photosynthesis

When light hits a plant some of the light energy absorbed by its chloroplasts is used to split water molecules into hydrogen ions and oxygen. The oxygen, a waste product, enters the atmosphere. The hydrogen ions are used in making ATP, the same energy carrier produced by mitochondria

THE LIGHT INDEPENDENT REACTIONS

." This cycle produces a kind of molecule with the rather intimidating name of Phosphogyceraldehyde, pGAL for short. Some of the pGAL molecules keep the cycle rolling, and some of the three carbon pGALS enter an enzyme that unites them to form the six carbon sugar glucose.

MITOCHONDRIA, THE CELL'S POWERHOUSES 2

A mitochondrion consists of two sacs made of membrane. Folds in the inner sac increase the surface area for chemical reactions that produce ATP. By breaking up mitochondria and separating out the membranes, biochemists have discovered exactly where the chemical reactions involved in synthesizing ATP actually occur

MITOCHONDRIA, THE CELL'S POWERHOUSES 1

All nucleated cells contain mitochondria, the tiny bodies where ATP is produced. The best way to see mitochondria clearly is to squeeze the cell under a cover-glass until it ruptures, forming a thin membrane bubble, a little aquarium in which float a few of its mitochondria

Where Do Cells Obtain Their Energy? 1

Cells, like humans, cannot generate energy without locating a source in their environment. However, whereas humans search for substances like fossil fuels to power their homes and businesses, cells seek their energy in the form of food molecules or sunlight.

How Do Cells Turn Nutrients into Usable Energy?

Complex organic food molecules such as sugars, fats, and proteins are rich sources of energy for cells because much of the energy used to form these molecules is literally stored within the chemical bonds that hold them together. Scientists can measure the amount of energy stored in foods using a device called a bomb calorimeter. With this technique, food is placed inside the calorimeter and heated until it burns. The excess heat released by the reaction is directly proportional to the amount of energy contained in the food.

Where Do Cells Obtain Their Energy? 2

In fact, the Sun is the ultimate source of energy for almost all cells, because photosynthetic prokaryotes, algae, and plant cells harness solar energy and use it to make the complex organic food molecules that other cells rely on for the energy required to sustain growth, metabolism, and reproduction (Figure 1).

SUMMARY AND REVIEW

So the cell's two energy transforming organelles, mitochondria and chloroplasts, feed on the waste products of each other. CO2 given off by mitochondria is exactly what chloroplasts need to make pGAL the building block of sugars and other carbohydrates. The oxygen released by chloroplasts during the light reactions is exactly what mitochondria need to drive the electrons -- that pump in the hydrogen ions -- making it possible for ATP synthase to add that terminal phosphate to ADP, creating ATP, the universal energy carrier.