(finished) Botany - Cellular/Inter-Plant Processes

C2

“Carbon refixation” by delaying breakdown of photorespired glycine (an amino acid) and shuttling it from the mesophyll into bundle sheath. Then the glycine is converted to serine, releasing CO2 for surrounding Rubisco to calvin cycle.

C3

Most common. CO2 enters through stomata; fixed into sugar via enzyme Rubisco in Calvin cycle. First carbon compound produced has 3 carbon atoms. Has photorespiration (energy wasted). Good growth rates.

C4

aka Hatch-Slack Pathway.

Has distinct leaf anatomy called Kranz anatomy.

CO2 captured in mesophyll, turned into oxaloacetate (aka OAA) then malate (via PEP), and concentrated into “bundle sheath” cells (where O2 is low, to avoid photorespiration). CO2 is then removed from malate, and calvin cycle continues as normal.
First carbon compound produced has 4 carbon atoms.
Negligable photorespiration

CAM

Stands for Crassulacean Acid Metabolism.

Stomata only open at night to take in co2, which is converted into oxaloacetate (via PEP) then malate, and stored in vacuoles until day, where it’s broken down into co2 and undergoes Calvin cycle.

Water-efficient (therefore drought-tolerant), and negligible photorespiration. Most common in desert plants.

Calvin cycle

Uses CO2 and the ATP and NADPH from light-dependent reaction to turn CO2 into glucose
3 phases:
Carbon fixation: Rubisco catalyzes the attachment of a 3CO2 molecule onto 3RuBP. This then breaks down into 6 3-PGA’s.

Reduction: 6 3-PGA are converted into 6G3P via ATP (provides energy) and NADPH (gives electrons and H+)

Regeneration: 5 G3P’s regenerate stocks of RuBP (alongside ATP). Half a glucose molecule is produced by the remaining 1 G3P (so 2 calvin cycles needed to make 1 glucose); 1G3P doesn’t do much until another G3P (from another cycle) comes in.

Location: Stroma

Photosynthesis (overview definition)

Sunlight & water (in light-dependant reactions; energy stored in ATP and NADPH, with O2 byproduct) is used to turn CO2 into (mostly) glucose (Calvin cycle; uses energy from first part + CO2 = glucose)

Glucose for energy/to make substances like cellulose (used in building plant cell walls).

Location: Chloroplast (Thylakoid membrane, stroma)

Equation: 6CO2 + 6H2O + Light Energy -> C6H12O6 + 6O2

Photorespiration

When the enzyme RuBisCO oxygenates RuBP (instead of giving it CO2, for the Calvin cycle), wasting some of the energy made during photosynthesis.

Apoplastic vs symplastic pathway

#1: Transport of water by going through cell walls/intercellular spaces due to hydrostatic pressure

#2: Transport of water from cell to cell via osmosis (so slower), starting at cell sap and going through protoplasm via plasmodesmata.

Auxin vs cytokinin and effects

Auxin: Vertical elongation of stems/roots; suppression of lateral bud growth; phototropism

Cytokinin: Cell division, shoot/root branching, and fruit development

Light-dependent reactions of photosynthesis

Creates ATP and NADPH (for calvin cycle etc), and the byproduct O2.

Photosystems 2 and 1 (which have chlorophyll) catch sunlight, whose energy is gathered in a “reaction center chlorophyll molecule” while exciting electrons to a higher state.

The reaction center passes it to the electron transport chain. The electrons lost by the photosystem are replaced via photolysis (when an H2O molecule is oxidized, producing free electrons and O2.)

During the electron transport chain, the e- powers the travel of H+ from the stroma to the thylakoid, making a concentration gradient that allows the H+ to power ATP synthase (which turns ADP into ATP.).
The now-low-energy e- enter photosystem 1 to get re-energized, get back on the transport chain, and reduce NADP+ to NADPH via the enzyme FNR

Location: Thylakoid membrane

4 Interfering agents to phosphorylation

• Cyanide - electron transfer and cytochrome oxidase

• Amytal - electron transfer

• DCCD - ATP synthase

• FCCP - uncoupling of phosphorylation from electron transfer

Protein phosphorylation

The reversible addition of a phosphate group (serine, threonine, and to a lesser extent, tyrosine) from ATP to a protein, acting as a master on-off switch that regulates hormones, growth, etc

Oxidation phosphorylation

Photophosphorylation

Oxidation phosphorylation: Uses energy from nutrients instead. Doesn't use water but NADH. In mitochondria.

Photophosphorylation: The process where cells use sun energy to convert ADP into ATP during photosynthesis (in Thylakoid membrane)

Cyclic and non-cyclic photophosphorylation

Cyclic: Uses both photosystem 1 (ps1) and ps2. Produce ATP, nadph, and o2.

Non-cyclic: Uses only ps1. Produces ATP only.

2 types of CAM include…

Facultative/inducible: Can switch from C3 or C4 (never both, and c3 most often) to CAM reversibly, taking advantage of drought-resistance in CAM when needed.

Obligate/constitutive: Only uses CAM for any photosynthesis/is always active;

Chemiosmosis

The movement of ions across a semipermeable membrane via an integral membrane protein, down their electrochemical gradient.

It’s the main method of producing ATP during photosynthesis (movement of H⁺ through ATP synthase)

Strong vs weak CAM and 1 example for both

Two more types of CAM.

Strong: Associated with constitutive CAM. CAM strongly expressed, with high CO2 fixation capacity. e.g. aloe

Weak: Associated with facultative CAM. CAM weakly expressed, with low CO2 fixation capacity. e.g. snake plant

CAM cycling

Extremely weak CAM; stomata don’t open at night; plant instead gets CO2 via own respiration and/or storing some CO2 during daytime.