Micro Exam 3 - Phototrophy, Autotrophy/Heterotrophy

What is phototrophy?

converting light energy into chemical energy

What is cyclic phototrophy?

reaction centers hold bacteriochlorophyll arrays where high energy electrons are passed from one bacteriochlorophyll to the next; bacteriochlorophyll are both electron donor and acceptor

How can phototrophy be enhanced?

invaginations or antenna

How do invaginations enhance phototrophy?

by adding more surface area for reaction centers to be mounted on

How do antennas enhance phototrophy?

by increasing the surface area in which light can be absorbed

How do antennas work?

light harvesting cofactors are attached to phycobiliproteins and absorb different wavelengths which are funneled to different reaction centers

What does cyclic phototrophy do?

recycle electrons to make PMF and ATP

What does acyclic phototrophy make?

NADH

How is NADH made in acyclic phototrophy?

electron is pulled out of circulation and used to reduce NAD+ to NADH, this breaks the cycle and only occurs when out of NADH

What are the different acyclic solutions?

energy sources either higher/lower than NADH on tower

In acyclic phototrophy, if an energy source lower than NADH on the tower is used, what happens?

reverse ETC to make NADH

In acyclic phototrophy, if an energy source higher than NADH on the tower is used, what happens?

direct donation to NAD+

What is oxygenic phototrophy?

light energy is used to get electrons from H2O releasing O2 by using two photosystems

What must the first photosystem used in oxygenic phototrophy have?

low enough resting potential to accept electrons from water

What must the second photosystem used in oxygenic phototrophy have?

A high enough activated potential to directly reduce NAD+

What does oxygenic phototrophy use?

Z scheme

What is autotrophy?

building sugars (reduced carbons) directly from CO2; turning inorganic carbon into organic carbon

Autotrophy is...

extremely energetically expensive

Describe the process of carbon fixation.

1 - carboxylation: addition of CO2 to end of 5 carbon sugar, 2 - reduction: carbon atom is fixed by electron donation from NADPH, 3 - rearrangement: 3 carbon products can be sent through pentose phosphate pathway (PPP) to be rearranged into chains with different numbers of carbons

Why is RuBiSCO toxic?

because when O2 is high, it can compete with CO2 for the enzyme and be incorporated instead, generating glycolic acid and leading to photorespiration

What is the solution to RuBiSCO being toxic?

carboxysomes: protein shells in cytoplasm that contain a lot of RuBiSCO, enrich for CO2, and exclude O2

What are the electron and carbon sources for organoheterotrophy?

electron - organics, carbon - organics

What are the electron and carbon sources for photoautotrophy?

electron - light, carbon - CO2