Biology

Discreet units of light energy

measured as the distance between two consecutive wave crests/throughs

use light energy to perform carbon fixation

use energy from the oxidation of inorganic molecules to perform carbon fixation

use light energy to produce some atp but cannot perform carbon fixation

cannot use light and cannot perfom carbon fixation

an endergonic metabolic pathway that converts light energy into chemical bond energy through the process of carbon fixation

an energonic metabolic pathway that converts inorganic carbon (CO2) into organic carbon (carbohydrate)

addition of a carboxyl group

removal of a carboxyl group

addition/transfer of a phosphate group

removal of hydrogens

catalyzed by an enxyme called "Dehydrogenase" which removes two electrons and two hydrogens from some substrate molecule and then trasfers both electrons and either one or both hydrogens to a coenzyme

NADP+ (oxidized form) --> NADPH (reduced form)

• NAD+ (oxidized form) --> NADH (reduced form)
• FAD (oxideized form) --> FADH2 (reduced form)

• Chlorophyll-a
• Chlorophyll-b
• Xanthrophyll
• Carotens

The photosynthetic pigments are located embedded in the phospholipic bilayer of the thylakoid membranes and are organized into clusters called photosystems.

a complex of light-gathering "antemae" molecules and a "reaction center" which is a special chlorophyll-a molecule located in close proximit to a "primary electron acceptor" molecule.

There are two photosystems (1 and 2).

Has a reaction center chlorophyll-a molecule called P700.

Has a reaction center chlorophyll-a molecule called P680.

When the energy from a photon of light is absorbed by the reaction center chlorophyll-a molcule, it makes it possible for an electron to go from its normal "ground state" to a higher energy "excited state" orbital.

Before the electron can give off the energy and return it to its more stable lower-energy ground state, the elctron is stolen by the primary electron acceptor an entered into an electron trasport chain.

a series of membrane protens, each one being more electronegative than the previous one.

as electrons are pulled exergonically down the ETC the energy is used to actively pump hydrogen ions (H+) from the stroma into the Thylakoid space to establish a proton gradient.

The potention energy of the proton gradient is converted to kinetic energy as the H+ spill back into the stroma through membrane protein cores called ATP-Synthase.

uses the kinetic energy from the flow of H+ to phosphorylate ADP and from ATP.

• Involves only photosystem-1 (PS1)and P700
• Photooxidation of PS1 (P700) electrons into an ETC that terminates with P700
• The exergonic form of e^- from P700 back to P700 is used to generate ATP
• NADPH is formed
• No O₂ is formed

• Involves both PS-1 (P700) and PS-2 (P680)
• Photooxidation of PS-1 (P700) sends e^- into an ETC that terminates with NADP⁺ reducing it to NADPH
• Photooxidation of PS-2 (P680) sends e^- into an ETC that terminates with P700 and generates ATP in the process
• Through a process known as "Photolysis" , a photon of light is used to split a water molecule into 2H⁺, 2e^-, and oxygen.
• The 2H⁺ are released into the stroma, the 2e^- are given to P680 to replace the electrons lost to P700, and the oxygen atom combines with another oxygen atom to form O₂ which is realsed as waste

• The dark reactions begin when Ribulose Biphosphate Cazboxylase (or "rubP carboxylase" or "Rubisco") picksup a molecule of CO₂ from the leaf air spaces and fixes (attatches) it to a 5-carbon compound already in the calvin cycle called ribulose biphosphate (or "RuBP")
• The resukting 6-carbon molecule is unstable and immediately spilts into two stable 3-carbon molecules called 3-Phosphoglycerate
• Atp is used to phosphorylate each 3-Phosphoglycerate to Glyceraldehyde-3 Phosphate (or "G3P") which is the actual product of the calvin cycle
• At this point, one molecule of G3P leaves the calvin cycle as a product and additional ATP is udes to convert any remaining G3P molecules back into RuBP to complete the cycle

an ineffective metabolic pathway that consumes O₂ and ATP, evolves CO₂, does not produce any carbohydrate and robs the calvin cycle

• It occurs because Rubisco's active site will accept either O₂ or CO₂ with equal affinity.
• When Rubisco picks up O₂ and attatches it to RuBp, the resulting unstable 5-carbon compound splits into a 3-carbon molecule called 3-phosphoglycerate and 2-carbon compound called glycolate.
• 3-phosphoglycerate remains in the calvin cycle but glycolate exits the cycle and goes to a peroxisome and then to a mitochondrion where it completely oxidized to two molecules of CO₂.
• C₄ and CAM photosynthesis both evolved as a way to by-pass photorespiration
• Photorespiration typically occurs under dry conditions when plants are forced to close their leaf stromata (openings) prematurely.
• When this occurs, the O₂ concentration in the leaf air spaces increases while the CO₂ concentration decreases, favoring rubisco picking up O₂

• Both evolved to by-pass/ avoid/ reduce photorespiration
• Both use two carbon fixation episodes instead of one

fixes CO₂ into an organic acid

fixes CO₂ into a carbohydrate and is the calvin cycle

Uses a "spartial" separation of primary and secondary carbon fixation episodes

• Occurs only in the mesophyll cells and uses pepcarbolase instead of Rubisco.
• Pep-Carboxylase (phosphoenyl carboxylase) picks up a molecule of CO₂ it attatches it to a 3-carbon molecule called phosphoenyl pyruvate (pep) which forms a stable 4-carbon intermediate called oxaloacatate.
• Oxaloacetate is then converted to another 4-carbon oraganic acid called malate which is shuttled from a mesophyll cell and into a bundle sheath cell via a plasmodesma.
• Once inside the bundle sheath cell, t he malate is broken down into a 3-carbon molecule called pyruvate and a 1-carbon molecule CO₂
• The CO₂ is picked up by Rubisco and fixed a second time into carbohydrates via the calvin cycle
• The pyruvate molecule is shuttled back into the bundle sheath cell where ATP is used to phosphorylate it into pep to complete the cycle

CAM plants use a "temporal" separtion of primary and secondary carbon fixation events

• fixes CO₂ unto organic acids like malate, occurs at night when the stomata are open
• The malate is stored in the central vacuole.

occurs in the datytime via the calvin cycle when the stored malate is broken down into pyruvate and CO₂ while the stomata are closed.

involves the direct transfer of a phosphate group from some molecule to ADP

involves using the kinetic energy from the exergonic flow of electrons down the ETC to pump H⁺ against their concentration gradient and then converting the potential energy of the H⁺ to phosphorylate ADP to form ATP.

• Glycolysis
• Oxidation of Pyruvate to Acetyl Coenzume-A (Acetyl CoA)
• Kreb's Cycle
• OP/ETC

• Occurs in the cytoplasm (cytosol) whether O₂ is present or absent.
• One 6-carbon glucose molecule is oxidized and split into 3-carbon pyruvate molecules
• 2 ATP are consumed
• 4 ATP are produced by SLP (2 net gain/yeild)
• 2 NAD⁺ are reduced to 2 NADH (each one is worth 2 ATP by OP/ETC)
• No FADH₂ are produced
• No CO₂ are formed/evolved released

• Depends on the presence/ absence of O₂
• If O₂ is absent (an aerobic) pyruvate remains in the cytosol and is reduced to either ethanol/locate through a metabolic process known as fermentation.
• If O₂ is present (Aerobic) pyruvate enters the mitochondrial matrix and is oxidized to Acetyl CoA. (2-C)

• Occurs in the mitochondrial matrix only f O₂ is present
• Each 3-carbon pyruvate is oxidized to a two carbon molecule called acetyl CoA
• One molecule of CO₂ is formed/evolved
• One molecule of NAD⁺ is reduced to NADH and is worth 3 ATP through OP/ETC
• No ATP is produced by SLP
• No FADH₂ is formed

• Occurs in the mitochondrial matrix if O₂ is present.
• For every 2 carbon acetly CoA that enters the cycle:
• -2 CO₂ are formed/evolved
• -1 ATP is formed by SLP
• -1 FADH₂ is formed (worth 2 ATP throguh OP/ETC)
• -3 NAPH are formed (each one is worth 3 ATP each through OP/ETC)

• Located embedded in the inner mitochondiral membrane (cristae)
• Occurs only if O₂ is present (aerobic)
• electrons are entered into the chain, from the matrix side, by both FADH₂ and NADH
• The exergonic flow of e^- down the ETC is used to pump H⁺ gradient in the intermembrane space is converted to kinetic energy as the H⁺ spill back into the matrix through membrane protein channels called ATP synthase
• The kinetic energy from the exergonic flow of H⁺ through ATP synthase is used to phosphorylate ADP to for ATP
• Since NADH enters its electrons into the beginning of the chain, enough H+ are pumped into the intermembrane space to perform 3 phosphorylation reactions (each NADH is worth 3 ATP)
• Since FADH₂ enters its electrons further down the chain, its electrons into the intermembrane space to perfom 2 phosphorylation reactions (each FADH₂ is worth 2 ATP)
• Exception:
• The NADH fromed during glycolysis are each worth only 2 ATP (because the inner mitochondrial membrane is impermeable to NADH, so NADH sends its electrons across the inner membrane and itno the matrix where they are picked up by FAD, reducing it to FADH₂, which enters the electrons into the ETC).

• If O₂ is absent, glycolysis sitll occurs and splits glucose into two molecules of pyruvate
• Instead of entering the mitochondrion and being oxidized to acytyl CoA, pyruvate remains in the cytosol and is reduced to either ehtanol or lactate as a way of regenerating NAD⁺ from NADH.
• The process is known as fermentation and the NADH formed during glycolysis serves as the reducing agent while pyruvate serves as the oxidizing agent
• No ATP are consumed/produced during the process and no NADH or FADH₂ are formed
• 2 carbon ethanol, no CO₂ is evolved if pyruvate is reduced to 3 carbon lactate/ lactic acid