Metabolism questions

Malaria is a disease caused by parasitic protozoans of the genus Plasmodium the disease is transmitted via mosquito bites

-maturation and development of the parasite in both human and mosquito host is coordinated by specific enzymes -targeting these enzymes for inhibition, new anti-malarial drugs and medications can be produced

Scientists have sequenced the genome of infectious species of Plasmodium and used it to determine the parasite's proteome -enzymes involved in parasitic metabolism have been identified as potential targets for inhibition -enzymes may be screened against a bioinformatic database of chemicals to identify potential enzyme inhibitors

-promising compound identified -> chemically modified to improve its binding affinity and lower its toxicity

An alternative method by which potential new anti-malarial medications can be synthesised is via rational drug design -involves using computer modelling techniques to invent a compound that will function as an inhibitor -using combinatorial chemistry, a compound is synthesised that is complementary to the active site of the target enzyme

-most chemical changes in a cell result from a series of reactions (pathways), with each step controlled by a specific enzyme

-metabolic pathways allow for a greater level of regulation, as the chemical change is controlled by numerous intermediates

-some metabolic pathways form a cycle rather than a chain.

-in this type of pathway, the end product of one reaction is the reactant that starts the rest of the pathway.

Substances that bind to enzymes and lower their activity.

• Enzyme inhibitors can be competitive or non-competitive

enzyme inhibitor: a molecule that disrupts the normal reaction pathway between an enzyme and a substrate -prevent the formation of an enzyme-substrate complex and hence prevent the formation of product

**may be either reversible or irreversible depending on the specific effect of the inhibitor being used

Competitive Inhibition -involves a molecule, other than the substrate, binding to the enzyme's active site -inhibitor is structurally and chemically similar to the substrate (hence able to bind to the active site) -competitive inhibitor blocks the active site and thus prevents substrate binding -as the inhibitor is in competition with the substrate, its effects can be reduced by increasing substrate concentration

Noncompetitive Inhibition -involves a molecule binding to a site other than the active site (an allosteric site) -binding of the inhibitor to the allosteric site causes a conformational change to the enzyme's active site -the active site and substrate no longer share specificity, meaning the substrate cannot bind -as the inhibitor is not in direct competition with the substrate, increasing substrate levels cannot mitigate the inhibitor's effect

• Metabolic pathways can be controlled by end-product inhibition

End-product inhibition: a form of negative feedback by which metabolic pathways can be controlled -the final product in a series of reactions inhibits an enzyme from an earlier step in the sequence -product binds to an allosteric site and temporarily inactivates the enzyme (non-competitive inhibition) -enzyme can no longer function -> reaction sequence is halted -> rate of product formation is decreased

**functions to ensure levels of an essential product are always tightly regulated -product levels build up -> inhibition -> decreases the rate of further product formation -product levels drop -> reaction pathway proceeds -> the rate of product formation will increase

• End-product inhibition of the pathway that converts threonine to isoleucine

Isoleucine: an essential amino acid = not synthesised by the body in humans (and hence must be ingested)

-in plants and bacteria, isoleucine may be synthesised from threonine in a five-step reaction pathway -in 1st step: threonine is converted into an intermediate compound by an enzyme (threonine deaminase) -isoleucine can bind to an allosteric site on this enzyme and function as a non-competitive inhibitor -excess production of isoleucine inhibits further synthesis, it functions as an example of end-product inhibition -feedback inhibition ensures that isoleucine production does not cannibalise available stocks of threonine

• Enzymes lower the activation energy of the chemical reactions that they catalyse

-enzyme binds to a substrate -> stresses and destabilises the bonds in the substrate

-the substrate binds to thee active site and is altered to reach the transition state

-it is then converted into the products, which separate from the active site.

-reduces the overall energy level of the substrate's transitionary state

-the activation energy of the reaction is therefore reduced. (The net amount of energy released by the reaction is unchanged by the involvement of the enzyme.)

-so less energy is needed to convert it into a product and the reaction proceeds at a faster rate

Plasmodium falciparum strain 3D7 is a variety of the malarial parasite for which the genome has been sequenced

• Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions

metabolism: sum total of all reactions that occur within an organism in order to maintain life -chemical changes in a cell result from a series of reactions (pathways) -with each step controlled by a specific enzyme

Metabolic pathways allow for a greater level of regulation: -the chemical change is controlled by numerous intermediates -typically organised into chains or cycles of enzyme-catalysed reactions

Examples of chains: Glycolysis (in cell respiration), coagulation cascade (in blood clotting) Examples of cycles: Krebs cycle (in cell respiration), Calvin cycle (in photosynthesis)

Relenza (Competitive Inhibitor)

-a synthetic drug designed by Australian scientists to treat individuals infected with the influenza virus

-virions are released from infected cells when the viral enzyme neuraminidase cleaves a docking protein (hemagglutinin)

-relenza competitively binds to the neuraminidase active site and prevents the cleavage of the docking protein

-virions are not released from infected cells, preventing the spread of the influenza virus

Cyanide (Noncompetitive Inhibitor)

-cyanide is a poison which prevents ATP production via aerobic respiration -> eventual death

-it binds to an allosteric site on cytochrome oxidase - a carrier molecule that forms part of the electron transport chain

-by changing the shape of the active site, cytochrome oxidase can no longer pass electrons to the final acceptor (oxygen)

-the electron transport chain cannot continue to function and ATP is not produced via aerobic respiration

-allows the concentration of the end-product produced to be controlled, it would be wasteful to continue making a substance that is not needed.

-reactions often do not go to completion.

-instead, an equilibrium position is reached with a characteristic ratio of substrates and products.

-so, if the concentration of products increases, a reaction will eventually slow down and stop.

-this effect reverberates back through a metabolic pathway when the end product accumulates, with all the intermediates accumulating.

-end-product inhibition prevents this build-up of intermediate products.

-(Malaria is a disease caused by the pathogen Plasmodium falciparum.)

-the increasing resistance of P. falciparum to anti-malarial drugs such as chloroquine

-the dependence of all new drug combinations on a narrow range of medicines and increasing global efforts to eradicate malaria all drive the need to develop new anti-malarial drugs

-bioinformatics is an approach whereby multiple research groups can add information to a database enabling other groups to query the database.

-one promising bioinformatics technique that has facilitated research into metabolic pathways is referred to as chemogenomics.

-sometimes when a chemical binds to a target site, it can signifcantly alter metabolic activity.

-scientists looking to develop new drugs test massive libraries of chemicals individually on a range of related organisms.

-for each organism a range of target sites are identified and a range of chemicals which are known to work on those sites are tested.

As the concentration of isoleucine builds up, it binds to the allosteric site of the first enzyme in the chain, threonine deaminase, thus acting as a non-competitive inhibitor.

-measuring the rate of disappearance of a substrate or the rate of appearance of a product.

Example: use iodine to test the presence of starch as iodine turns blue/black if starch is present.

Have one drop of iodine into each well.

Every 30 seconds, place a drop of the starch buffer solution into the iodine solution.

Continue until there is no colour change of the iodine solution when combined with the buffer solution.

Electron carriers are molecules that can accept or donate electrons.

Oxidative phosphorylation is where energy originally released from the oxidation of glucose is used to produce ATP from ADP and Pi.

Chemiosmosis is the use of the energy held within the proton gradient (created by the transport of electrons by the electron transport chain) to produce ATP.

The addition of a phosphate group, typically from ATP. (catalysed by kinases)

• In glycolysis, glucose is converted into pyruvate in the cytoplasm

-a hexose sugar (6C) is broken down into two molecules of pyruvate (3C)

1. Phosphorylation -hexose sugar (typically glucose) is phosphorylated by two molecules of ATP (to form a hexose bisphosphate) -makes the molecule less stable and more reactive, and also prevents diffusion out of the cell -glucose + 2P

2. Lysis -hexose biphosphate (6C sugar) is split into two triose phosphates (3C sugars)

3. Oxidation -H atoms are removed from each of the 3C sugars (via oxidation) to reduce NAD+ to NADH (+ H+) -2 molecules of NADH are produced in total (one from each 3C sugar)

4. ATP formation -some energy released from the sugar intermediates is used to directly synthesise ATP -direct synthesis of ATP is called substrate level phosphorylation -in total, 4 molecules of ATP are generated during glycolysis by substrate level phosphorylation (2 ATP per 3C sugar)

At the end of glycolysis, the following reactions have occurred: -glucose (6C) has been broken down into two molecules of pyruvate (3C) -two hydrogen carriers have been reduced via oxidation (2 × NADH + H+) -net total of two ATP molecules have been produced (4 molecules were generated, but 2 were used)

• Glycolysis gives a small net gain of ATP without the use of oxygen

-no O2 = pyruvate is not broken down further and no more ATP is produced (incomplete oxidation) -pyruvate remains in the cytosol and is converted into lactic acid (animals) or ethanol and CO2 (plants and yeast) -this conversion is reversible and is necessary to ensure that glycolysis can continue to produce small quantities of ATP

-glycolysis involves oxidation reactions that cause hydrogen carriers (NAD+) to be reduced (becomes NADH + H+) -the reduced hydrogen carriers are oxidised via aerobic respiration to restore available stocks of NAD+In the absence of oxygen -glycolysis will quickly deplete available stocks of NAD+, preventing further glycolysis -fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks) -hence, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen

• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD

• In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide

-acetyl CoA transfers its acetyl group to a 4C compound to make a 6C compound

-coenzyme A is released and can return to the link reaction to form another molecule of acetyl CoA

-over a series of reactions, the 6C compound is broken down to reform the original 4C compound (hence, a cycle)

-2 carbon atoms are released via decarboxylation to form two molecules of carbon dioxide (CO2)

-multiple oxidation reactions result in the reduction of hydrogen carriers (3 × NADH + H+ ; 1 × FADH2)

-1 molecule of ATP is produced directly via substrate level phosphorylation

**the Krebs cycle occurs twice

Per glucose molecule, the Krebs cycle produces: 4 × CO2 ; 2 × ATP ; 6 × NADH + H+ ; 2 × FADH2

• In link reaction pyruvate is decarboxylated and oxidised, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction

1st stage of aerobic respiration is the link reaction, which transports pyruvate into the mitochondria.

-pyruvate is transported from the cytosol into the mitochondrial matrix by carrier proteins on the mitochondrial membrane

-pyruvate loses a carbon atom (decarboxylation), which forms a carbon dioxide molecule

-2C compound then forms an acetyl group when it loses hydrogen atoms via oxidation (NAD+ is reduced to NADH + H+)

-acetyl compound then combines with coenzyme A to form acetyl coenzyme A (acetyl CoA)

**the link reaction occurs twice per molecule of glucose -per glucose molecule, the link reaction produces acetyl CoA (×2), NADH + H+ (×2) and CO2 (×2)

• Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.

-hydrogen carriers donate high energy electrons to the ETC (located on the cristae)

-as the electrons move through the chain they lose energy, which is transferred to the electron carriers within the chain

-the electron carriers use this energy to pump hydrogen ions from the matrix and into the intermembrane space

-accumulation of H+ ions in the intermembrane space creates an electrochemical gradient (or a proton motive force)

-H+ ions return to the matrix via the transmembrane enzyme ATP synthase (this diffusion of ions is called chemiosmosis)

-as the ions pass through ATP synthase they trigger a phosphorylation reaction which produces ATP (from ADP + Pi)

• Oxygen is needed to bind with the free protons to maintain the hydrogen gradient, resulting in the formation of water

-de-energised electrons are removed from the chain by oxygen, allowing new high energy electrons to enter the chain

-O2 also binds matrix protons to form water - this maintains the hydrogen gradient by removing H+ ions from the matrix

• Phosphorylation of molecules makes them less stable

phosphorylation: the addition of phosphate to an organic compound.

-one ATP contains three covalently bonded phosphate groups (potential energy stored in bonds)

-phosphorylation makes molecules less stable and hence ATP is a readily reactive molecule that contains high energy bonds

-when ATP is hydrolysed (to form ADP + Pi), the energy stored in the terminal phosphate bond is released for use by the cell

ATP is synthesised from ADP using energy derived from one of two sources:

-solar energy - photosynthesis converts light energy into chemical energy that is stored as ATP

-oxidative processes - cell respiration breaks down organic molecules to release chemical energy that is stored as ATP ********

Glycolysis is an example of a metabolic pathway.

Peter Mitchell's proposal of the chemiosmotic hypothesis in 1961 lead to a major shift in our understanding of cellular processes.

-explains the coupling of electron transport in the inner mitochondrial membrane to ATP synthesis.

-his hypothesis was a radical departure from previous hypotheses and only after many years was it generally accepted.

Decarboxylation: -C atoms are removed from the organic molecule (glucose) to form carbon dioxide -2 in Link reaction and 4 in Krebs

Oxidation: -e- and H+ are removed from glucose and taken up by hydrogen carriers (NADH and FADH2) -2 NADH in glycolysis -2 NADH in link reaction -6 NADH and 2 FADH2 in Krebs

• The structure of the mitochondrion is adapted to the function it performs -eukaryotic cells possess mitochondria - aerobic prokaryotes use the cell membrane to perform oxidative phosphorylation

-outer membrane - the outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol -inner membrane - contains the electron transport chain and ATP synthase (used for oxidative phosphorylation) -cristae - the inner membrane is arranged into folds (cristae) that increase the SA:Vol ratio (more available surface) -intermembrane space - small space between membranes maximises hydrogen gradient upon proton accumulation -matrix - central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur

two turns of the Calvin Cycle are needs to produce one molecule of glucose.

Carbon fixation: the process by which inorganic carbon (particularly in the form of carbon dioxide) is converted to organic compounds by living organisms. e.g carbon dioxide is converted into another carbon compound

Carboxylation: a chemical reaction in which a carboxylic acid group is produced by treating a substrate with carbon dioxide. e.g. the reaction in which carbon dioxide reacts with RuBP to produce an unstable six carbon compound

• Photosystems are chlorophyll molecules and other accessory pigments which are organized into photosystems.

Reaction center: a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis

a. Calvin cycle is light-independent ✔ b. carbon fixation OR carboxylation of ribulose bisphosphate/RuBP occurs ✔ c. algae placed in thin glass container/"lollipop" apparatus ✔ d. given plenty of light and bicarbonate/ CO2 ✔ e. at start of experiment algae supplied radioactive carbon/HCO3 - / 14C ✔ f. samples taken at intervals / heat/alcohol killed samples ✔ g. C-compounds separated by chromatography ✔ h. 14C/radioactive-compounds identified by autoradiography ✔ i. showed that RuBP was phosphorylated ✔ j. after five seconds/immediately more glycerate-3-phosphate/3-PGA labelled than any other compound ✔ k. shows glycerate-3-phosphate/3-PGA first «carboxylated» compound/the first stable product ✔ l. next compound to be detected containing radioactive carbon was triose phosphate/G3P/glyceraldehyde 3 phosphate ✔ m. showed that a wide range of carbon compounds was quickly made in sequence ✔ n. showed that a cycle of reactions was used to regenerate RuBP ✔

-excitation of photosystems by light energy -production of ATP via an electron transport chain -reduction of NADP+ and the photolysis of water

-light dependent reactions use photosynthetic pigments (organised into photosystems) to convert light energy into chemical energy (specifically ATP and NADPH)

• Absorption of light by photosystems generates excited electrons • Transfer of excited electrons occurs between carriers in thylakoid membranes

Step 1: Excitation of Photosystems by Light Energy -photosystems are groups of photosynthetic pigments (including chlorophyll) embedded within the thylakoid membrane -photosystems are classed according to their maximal absorption wavelengths (PS I = 700 nm ; PS II = 680 nm) -when a photosystem absorbs light energy, delocalised electrons within the pigments become energised or 'excited' -excited electrons are transferred to carrier molecules within the thylakoid membrane

• Excited electrons from Photosystem II are used to contribute to generate a proton gradient • ATP synthase in thylakoids generates ATP using the proton gradient

Step 2: Production of ATP via an Electron Transport Chain -excited electrons from Photosystem II (P680) are transferred to an electron transport chain within the thylakoid membrane -as the electrons are passed through the chain they lose energy, which is used to translocate H+ ions into the thylakoid -build up of protons within the thylakoid creates an electrochemical gradient, or proton motive force -H+ ions return to the stroma (along the proton gradient) via the transmembrane enzyme ATP synthase (chemiosmosis) -ATP synthase uses the passage of H+ ions to catalyse the synthesis of ATP (from ADP + Pi) -above process is photophosphorylation - as light provided the initial energy source for ATP production -newly de-energised electrons from Photosystem II are taken up by Photosystem I

• Excited electrons from Photosystem I are used to reduce NADP • Photolysis of water generates electrons for use in the light dependent reactions

Step 3: Reduction of NADP+ and the Photolysis of Water -excited electrons from Photosystem I may be transferred to a carrier molecule and used to reduce NADP+ -forms NADPH - which is needed (in conjunction with ATP) for the light independent reactions -electrons lost from Photosystem I are replaced by de-energised electrons from Photosystem II -electrons lost from Photosystem II are replaced by electrons released from water via photolysis -H2O is split by light energy into H+ ions (used in chemiosmosis) and oxygen (released as a by-product)

• Reduced NADP and ATP are produced in the light dependent reactions

-carboxylation of ribulose bisphosphate -reduction of glycerate-3-phosphate -regeneration of ribulose bisphosphate

• In the light independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate

Step 1: Carbon Fixation -Calvin cycle begins with a 5C compound called ribulose bisphosphate (or RuBP) -enzyme, RuBP carboxylase (or Rubisco), catalyses the attachment of a CO2 molecule to RuBP -resulting 6C compound is unstable, and breaks down into two 3C compounds - called glycerate-3-phosphate (GP) A single cycle involves three molecules of RuBP combining with three molecules of CO2 to make six molecules of GP

• Glycerate-3-phosphate is reduced to triose phosphate using reduced NADP and ATP

Step 2: Reduction of Glycerate-3-Phosphate -reduction by NADPH transfers hydrogen atoms to the compound, while the hydrolysis of ATP provides energy -each GP requires one NADPH and one ATP to form a triose phosphate - so a single cycle requires six of each molecule

• Triose phosphate is used to regenerate RuBP and produce carbohydrates • Ribulose bisphosphate is reformed using ATP

Step 3: Regeneration of RuBP -of the six molecules of TP produced per cycle, one TP molecule may be used to form half a sugar molecule -two cycles are required to produce a single glucose monomer, and more to produce polysaccharides like starch -remaining five TP molecules are recombined to regenerate stocks of RuBP (5 × 3C = 3 × 5C) -regeneration of RuBP requires energy derived from the hydrolysis of ATP

• Photophosphorylation may be either a cyclic process or a non-cyclic process

Cyclic: -involves the use of only one photosystem (PS I) and does not involve the reduction of NADP+ -when light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP -the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic) -electron returns to the photosystem, so NADP+ is not reduced and water is not needed to replenish the electron supply

Non-Cyclic -involves two photosystems (PS I and PS II) and the reduction of NADP+ -light is absorbed by Photosystem II, the excited electrons enter into an electron transport chain to produce ATP -photoactivation of Photosystem I results in the release of electrons which reduce NADP+ (forms NADPH) -photolysis of water releases electrons which replace those lost by Photosystem II (PS I electrons replaced by PS II)

-cyclic photophosphorylation can be used to produce a steady supply of ATP in the presence of sunlight -non-cyclic photophosphorylation produces NADPH in addition to ATP (this requires the presence of water) **only non-cyclic photophosphorylation allows for the synthesis of organic molecules and long term energy storage

-radioactive carbon-14 is added to a 'lollipop' apparatus containing green algae (Chlorella) -light is shone on the apparatus to induce photosynthesis (which will incorporate the carbon-14 into organic compounds) -after different periods of time, the algae is killed by running it into a solution of heated alcohol (stops cell metabolism) -dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds -any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X-ray film exposure) -by comparing different periods of light exposure, the order by which carbon compounds are generated was determined

Calvin used this information to propose a sequence of events known as the Calvin cycle (light independent reactions)

ATP (from the light dependent reaction) provides the energy for NADPH (from the light dependent reaction) to reduce G3P, forming a three carbon carbohydrate, triose phosphate.

ATP is used to regenerate RuBP from triose phosphate.

-carbon fixation occurs in the chloroplast stroma.

-the 5-carbon molecule ribulose bisphosphate (RuBP) is carboxylated by CO2, forming 2 3-carbon molecules called glycerate-3-phosphate (G3P). -the enzyme that catalyzes the carboxylation of RuBP is called ribulose bisphosphate carboxylase (rubisco).*

The light dependent reactions of photosynthesis include: *Photoactivation *Photolysis *Electron transport *Chemiosmosis *ATP synthesis *Reduction of NADP to NADPH + H+

• Light independent reactions of photosynthesis include:

• Carbon fixation

• Carboxylation of RuBP

• Production of triosphosphate

• ATP and NADPH as energy sources

• ATP used to regenerate RuBP

• ATP used to produce carbohydrates

-Calvin used algae suspended in a solution. -the vessel containing the algae had a lollipop shape; it was a thing, round, glass vessel. -this ensured all the algae had equal light. -air was bubbled through the vessel. -a short burst of 14CO2 was supplied. -every few seconds, samples of algae were taken and added to hot methanol. -khis kills the algae, stopping the light-independent reactions. -the samples were seperated by two-dimensional paper chromatography and visualized by autoradiography. -by analyzing autoradiograms of samples stopped at different times after the addition of 14CO2, Calvin could follow the pathway taken by 14C. -in the first sample, the most abundant compound was glycerate-3-phosphate, indicating this is the first product. -he determined the order of the complete cycle.

-if the structure of chloroplasts varied, those organisms with the chloroplast that absorbed light and converted it into glucose most efficiently would have the advantage. -they would have an increased chance of survival and would tend to produce more offspring. -these offspring would inherit the type of chloroplast that produces glucose using light energy more efficiently. -if this trend continued, the structure of the chloroplast would gradually evolve to become more and more efficient. -(Chloroplasts are quite variable in structure but share certain features): A double membrane forming the outer chloroplast envelope. An extensive system of internal membranes called thylakoids, which are an intense green colour. Small fluid filled spaces inside the thylakoids. A colourless fluid around the thylakoids called stroma that contains many different enzymes. In most chloroplasts there are stacks of thylakoids, called grana. If a chloroplast has been photosynthesising rapidly then there may be starch grains or lipid droplets in the stroma.

-light dependent reactions occur within the intermembrane space of the thylakoids -chlorophyll in Photosystems I and II absorb light, which triggers the release of high energy electrons (photo activation) -excited electrons from Photosystem II are transferred between carrier molecules in an electron transport chain -electron transport chain translocates H+ ions from the stroma to within the thylakoid, creating a proton gradient -the protons are returned to the stroma via ATP synthase, which uses their passage (via chemiosmosis) to synthesise ATP -excited electrons from Photosystem I are used to reduce NADP+ (forming NADPH) -electrons lost from Photosystem I are replaced by the de-energised electrons from Photosystem II -electrons lost from Photosystem II are replaced following the photolysis of water -products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions

Photosynthesis is a two-step process: • Light dependent reactions take place in the intermembrane space of the thylakoids • Light independent reactions take place in the stroma.

Step 1: LDR -light is absorbed by chlorophyll, which releases energised electrons that are used to produce ATP (chemical energy) -electrons are donated to carrier molecules (NADP+), which is used (along with ATP) in the light independent reactions -electrons lost from the chlorophyll are replaced by water, which is split (photolysis) to produce oxygen and hydrogen

Step 2: Light Independent Reactions -ATP and hydrogen / electrons (carried by NADPH) are transferred to the site of the light independent reactions -hydrogen / electrons are combined with carbon dioxide to form complex organic compounds (e.g. carbohydrates) -ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together

-a hydrophobic electron carrier -stays inside the thylakoid membrane to pass on the electrons to the next electron carrier; continuing all the way to photosystem I. -in photoactivation at Photosystem II, the reaction center chlorophyll is oxidized and the plastoquinone (Pq) is reduced -electrons pass from plastoquinone (Pq) through a chain of electron carrier molecules.

-chloroplasts are the 'solar energy plants' of a cell - they convert light energy into chemical energy

The structure of the chloroplast is adapted to the function it performs: -thylakoids - flattened discs have a small internal volume to maximise hydrogen gradient upon proton accumulation -grana - thylakoids are arranged into stacks to increase SA:Vol ratio of the thylakoid membrane -photosystems - pigments organised into photosystems in thylakoid membrane to maximise light absorption -stroma - central cavity that contains appropriate enzymes and a suitable pH for the Calvin cycle to occur -lamellae - connects and separates thylakoid stacks (grana), maximising photosynthetic efficiency

An insoluble form of glucose produced by photosynthesis. Starch is the form that glucose is transported around the plant as.