algae/notes/efficiency.html

Efficiency

We describe the metabolism, adapataion, growth and other characteristics as being "efficient."

These can all be related to the general concept of specific rates, the rate of processing an element compared to the amount of that element in the cell. The following are all examples of efficiency:

growth efficiency	specific growth rate new cells per time per cell (new cells)/(cells*time)
nitrogen uptake efficiency	specific nitrogen uptake rate nitrate uptake per cell nitrogen per time (NO3 taken up)/(cell N * time)
photosynthetic efficiency	this term is used in many ways in the literature one way is: carbon uptake rate/(cell_carbon * time)
metabolic efficiency	processing rate of carbon and energy per cell_carbon per time carbon and energy can be interconverted (see below)

Steady State Cell Composition

When cells are in steady state, or in "balanced growth", the cell specific efficiencies for all elements and processes are the same. This means that the specific growth rate, in terms of cells, nitrogen, phosphorus or any other element are all equal. If any of these element growth efficiencies are greater, then that element would be accumulating in the cell relative to the other elements.

Efficiency of cellular components

In this course we will be comparing the efficiency and regulation of ** cellular components:

PMEMB	photosynthetic membranes thylakoid membranes chlorophyll phycobilin pigments PSII, cytb6f complex, PSI coupling factor
PENZ	Photosynthetic enzymes RuBisC/O all other enzymes of the reductive pentose phosphate pathway (Calvin Cycle)
ENZ	Enzyme and Biosynthetic machinery all cell respiration machinery, such as mitochondria all enzymes for biosynthesis of lipids, nucleic acids, pigments, amino acids, and sugars all transcription machinery, ribosomes, tRNA and mRNA
NASSIM	Nitrogen uptake and assimilation membrane embedded transport sites enzymes for assimilating NO3- into NH4+
RES	Reserves and storage carbon and energy stored as glycogen or starch nitrogen stored in non-catalytic compounds such as cyanophycin, arginine
STRUCT	Structure Cell wall Cell membrane cytosol DNA and portions of the nucleus that have a nearly constant composition in algae

 

The molecular efficiency of individual components (such as the photosynthetic membrane or photosynthetic carbon fixation enzymes) is expressed as the rate of carbon processing per carbon in that component per time. In order for the efficiency of the different cellular components to be compared, all of these will be expressed in terms of the efficiency relative to one mole of carbon flowing through metabolism. This is straight forward for the photosynthetic enzymes and the respiration and biosynthetic machinery because they actually process carbon.

The molecular efficiency of NASSIM or PMEMB can be expressed in terms of an equivalent flow of carbon per carbon in the machinery per time. Each N atom taken up across the membrane and prepared for incorportation into the cell (via the ENZ) is equivalent to 6 C atoms because the cell C:N ratio is 6:1. The molecular efficiency of the PMEMB is calculated from the yield of ATP and NADPH produced. It takes 2 NADPH and 3ATP to be transferred to the PENZ to provide the energy to fix one molecule of CO2 into carbohydrates.

Overall Cell Efficiency

The net cell efficiency at growth has to be less than the individual efficiencies of any one component. This is simply because each C that is eventually fixed into new cell material must be processed sequentially by all of the active components. For example, PMEMB has to tranduce one equivalent of energy (3ATP and 2 NADPH), these are used in PENZ to fix one C into carbohydrate building blocks, then these building blocks are passed to ENZ where the building blocks are used for both energy and biosynthesis. Even if all of these individual components had the same efficiency (which they don't) the net efficiency would be 1/3 of that efficiency because the same C had to be processed 3 times to create the cell.

Acclimitization is the process of changing the relative amounts of the cellular components in such a way to serve the organisms survival or competitiveness.