“Nothing in life is to be feared, it is only to be understood.  Now is the time to understand more, so that we may fear less”  Marie Curie.   

Fun Marie Curie facts:

• She was the first person to receive two Nobel awards
• She is one of only two people to receive Nobels in two different catagories
• Her daughter, Irene, also received a Nobel in Chemistry (smarts run in that family!)
• Her discoveries, Radium and Polonium, eventually killed her
• She was so radioactive, that if you put a piece of film in between the pages of her lab manual today, her fingerprints will expose the film!
• She was quite scandalous in her day… she would go to parties held by scientists and pull her male colleagues into dark closets to show them vials of glowing radiation (which did not make her popular among their wives!)

Dear Diary,

This week we talked about everyone’s favorite topic – Metabolism!  Nobody walked out of class, so I’ll consider that a “win”.  

We started off with nutritional classes… this is how we “categorize” organisms by what they take into their cells to fulfill their Carbon, Electron and Energy needs.

Requirement	Nutritional class	Source of requirement
Energy	Chemotroph	Food
	Phototroph	Sunlight
Electrons (reducing power)	Organotroph	Organic food
	Lithotroph	Inorganic food
Carbon	Heterotroph	Organic food
	Autotroph	CO2

So, as you can see…. a photosynthetic bacteria that takes in CO2 (for carbon), hydrogen sulfide (for electrons) and uses sunlight (for energy) would be a “Photo-litho autotroph”

We next focused pretty heavily on chemo-organo heterotrophs for a few reasons.  One, humans are COHs, as are all of the pathogens that infect them, and we know a LOT about these pathways.

We talked about the three major food sources (sugars, fats and proteins) and how they are catabolized through Stage 1, 2 and 3 of catabolism.

• Stage 1 = polymers into monomers (for example, polysaccharides (like starch) into monosaccharides (like glucose)
• Stage 2 = monomers into acetyl coA (for example, glycolysis and the bridge reaction)
• Stage 3 = complete oxidation of acetyl coA into the final waste product CO2, plus the production of ATP using oxidative phosphorylation

ATP synthesis is what makes the majority of ATP in these organisms, and boy, is it the star of the show….

Sometimes I get teary eyed watching this…

We next discussed what happens to COHs if they run out of oxygen.  BTW….. where is Oxygen needed?  What pathway?

• They shut off TCA cycle and ETC (for catabolic purposes) and just focus on glycolysis for ATP production… but this soon runs into a problem as NADH is no longer being converted to NAD+ by the electron transport chain.  So, fermentation steps in to regenerate NAD+… this keeps glycolysis running.
• OR…. they can use an electron transport chain that has a non-oxygen electron acceptor.  Only some bacteria can do this… they would have to have another terminal reductase, and some of us just don’t have the genes for that.

Next, we focused on the other guys: the phototrophs, autotrophs and lithotrophs.

Phototrophs use sunlight to make ATP in a process very similar to how oxidative phosphorylation works in chemotrophs, just that the electrons are excited into a higher energy state by photons of sunlight, rather than being delivered to ETC by NADH or FADH2.

Autotrophs use the Calvin (Dark) cycle to convert CO2 into organic carbon compounds that can then be used to make other things like sugar.

    Organic… not “organic”  

The calvin cycle actually uses up a lot of ATP… it takes 9 ATPs just to fix one CO2!  So, why would they do it like this?  What’s the upside?

Lithotrophs use the ETC like chemotrophs, but they use INORGANIC sources of electrons to donate to the chain, rather than organic sources.  

We talked a bit about anabolic reactions:

• gluconeogenesis – the creation of sugars from non-carbohydrate sources
• Fatty acid anabolism – the creation of fatty acids from acetyl coA
• Nucleic acid anabolism – the synthesis of RNA and DNA
• amino acid anabolism – construction of new amino acids

but most importantly for microorganisms is Nitrogen fixation.  Why is this important?  Because prokaryotes ARE THE ONLY ORGANISMS ON EARTH THAT CAN DO IT.  If they didn’t fix nitrogen, nothing else would exist – including us.  All of the nitrogen in your body was originally fixed for you by some measly little bacterium somewhere.  Respect.

Finally, we talked about enzymes.  The Match.com of the biochemical world.  They literally take two molecules that might never meet on their own, squeeze them into the same small place, and cause a bond to form between them.   So romantic!  

via GIPHY

Things to focus on for this lecture:

• Do you have a basic understanding of each pathway discussed?  Reviewing your homework and in class quiz might help here too.
  • Know what the input and output of each pathway is
  • Know in which stage of catabolism each pathway is involved in
  • Understand how the pathways flow from one to the next (for example, write the order of pathways for the catabolism of glucose)
  • Be able to articulate what the PURPOSE of each pathway is … why do we do it in the first place?  You can even relate this back to the nutritional class… which pathway is important for electron harvesting?  Carbon harvesting? Energy conservation?  Etc…
• Be able to predict the nutritional class of a bacteria, if given the type of pathways that it runs or the type “food” it eats
• Don’t neglect the Photo-auto trophs…. be familiar with what the Light and Calvin cycles do
• Be familiar with which pathways would be used under different oxygen concentrations.  For example, how would an obligate anaerobe make most of its ATP?
• How does lithotrophic electron transport differ from organotrophic?

Questions or concerns?  Leave’ em below!