Photosynthetic Algae, Thalassiosira weissflogii, Response to CO2 Change

Glossary

Biogeochemical Cycles-- describe the mechanisms by which solar energy is assimilated by living organisms and stored in the form of chemical energy. Organisms then store this chemical energy for later use. Green plants store sugar and starch. Also, biogeochemical cycles serve as huge recycling systems that allow the biosphere to use the same elements over and over again. If there were no biogeochemical cycles, the earth would die, literally suffocating in its own wastes.

Calvin Cycle -- is also called the light independent or dark reaction of photosynthesis. In the Calvin Cycle, ribulose 5-phosphate, a 5-carbon compound is converted to a 6-carbon compound by the addition of CO₂. Through several intermediate steps, this 6 carbon compound is converted to two 3-carbon glyceraldehyde 3-phosphate molecules, which are then converted to glucose. These steps require the addition of hydrogen supplied by NADPH from the light reaction.

Carbonic Anhydrase (CA)-- allows algae to convert HCO₃^- (bicarbonate) to CO₂ to allow transport of Carbon through their cell membranes. CA is a carbon concentrating mechanism which catalyses the following reaction:

CA

CO₂ + H₂O ß à H⁺ + HCO₃^-

Chains of amino acids in the protein interact and fold up in a 3D shape. In the center is a zinc complex, and it is this zinc that speeds up the reaction between bicarbonate and carbon dioxide. This is accomplished by removing the natural kinetic hindrance by bringing water and carbon dioxide closer together. When carbon is limiting (in low supply), CA production is triggered in the cell. CA is a very important and common enzyme throughout all organisms. Twelve different types have been found up to now in humans. It is also the first enzyme found to contain Zinc, (Zn).

Carbon Dioxide-- Carbon dioxide levels in the atmosphere have fluctuated over time and are currently a major environmental concern. Present levels are about 360 ppm. Forty thousand years ago, the CO₂ level was 320 ppm. During glacial/interglacial cycles, the CO₂ ranged between 180 ppm (ice age) to 270 ppm. There are estimates that within 100 years there may be a doubling of CO₂ in the atmosphere.

Elements-- There are six major elements in living matter: hydrogen, carbon, oxygen, nitrogen, phosphorous, and sulfur. Phosphorous in the form of phosphate ester acts to bind together individual nucleotides that make up DNA and is also a component of adenosine triphosphate, or ATP, the cell’s energy source produced in the mitochondria.

Glucose--is a monosaccharide, or simple sugar produced through photosynthesis. It is the building block of carbohydrates, which are long chains (polymers) of glucose. Glucose is broken down in respiration to produce ATP, the cell’s energy source. The chemical formula for glucose is C₆H₁₂O₆.

Ocean-- The world’s oceans comprise about 0.02% of the earth’s mass, but about 70% of the earth’s surface. Our ocean’s circulation is both wind driven and thermohaline (temperature and density) driven. Because of the Coriolis Effect, produced by the rotation of the Earth, the surface layer is dominated by large-scale gyres moving clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. However in the deep ocean movement is determined by the density of the ocean water as a function of temperature and salinity. Upwelling and downwelling currents move seawater in a global conveyor belt, circulating water from the equator to the poles and back.

Chemically our ocean is a briny aqueous solution with a 3.5% salt concentration. Most of the salts are chlorides and to a lesser extent sulfates. The major cations are Na+, Mg++, Ca++, and K+. The major nutrient elements are C, N, P, Si, and Fe. Phytoplankton require these nutrient elements to carryout photosynthesis and other metabolic functions. It is interesting to note that phytoplankon removal of these nutrient elements at the surface layer occurs at such a rapid rate, that if these nutrients were to be stored permanently, photosynthesis would deplete the surface layer of the ocean of all its nutrient elements in less than one year. The oceans would die.

Photosynthesis-- has basically two reactions called the light dependent and light independent. In the light dependent reaction, water molecules are split into H⁺ ions, electrons, and oxygen. In the dark reaction, also called the Calvin Cycle, carbon dioxide is fixed by the addition of hydrogen to produce, through several intermediate compounds, glucose. NADPH, an electron carrier, transports the hydrogen ions from the light reaction to the Calvin Cycle.

Phytoplankton – include all unicellular photosynthetic organisms and may live in the ocean or freshwater. Generally called "algae," phytoplankton are divided into seven groups, depending on their photosynthetic pigments, cell wall composition, and method of food storage. Phytoplankton are the food source for zooplankton, tiny, floating animals and thus are the base of the food chain.

Pigments--are molecules that trap the energy of sunlight for use in photosynthesis. In addition, pigments give plants and algae their colors by absorbing some wavelengths and reflecting others. The most common plant pigment is chlorophyll which absorbs red and blue light and reflects green, hence plants look green. Other pigments include carotenoids which are yellow/orange and phycobilins which are red/purple.

Respiration--essentially the reverse reaction of photosynthesis, respiration uses oxygen to break down glucose and produce ATP, the energy source for all cell activities. This releases CO₂ and H₂O, the same compounds used to produce glucose during photosynthesis. All organisms carry on respiration.

The two processes work together to cycle carbon through the earth’s plants and animals.

RubisCO--(1,5 bisphosphate carboxylase-oxygenase) is a key enzyme in the Calvin Cycle. It requires relatively high concentrations of CO₂, much higher than are found in the surrounding seawater. RubisCO may have formed about 3 billion years ago when life forms first began to emit oxygen. Different groups of phytoplankton show differential specificity to CO₂, with diatoms being relatively high. This suggests that changing CO₂ and O₂ levels in the atmosphere may have lead to the enzyme becoming more efficient in its use of CO₂ over geologic time.

Thalassiosira weissflogii--is a very common centric diatom. Diatoms contain chlorophylls a and c. The outside wall is composed of silica impregnated with pectin.