Topic 2/8 - Part 3 Flashcards

Question

Give an overview of the process of oxidative phosphorylation

Answer 1

- Hydrogen carriers donate high energy electrons to the electron transport chain (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 - The 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) - The de-energised electrons are removed from the chain by oxygen, allowing new high energy electrons to enter the chain - Oxygen also binds matrix protons to form water – this maintains the hydrogen gradient by removing H+ ions from the matrix

Answer 2

The structure of the mitochondrion is adapted to the function it performs: 1. Outer membrane – the outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol 2. Inner membrane – contains the electron transport chain and ATP synthase (used for oxidative phosphorylation) 3. Cristae – the inner membrane is arranged into folds (cristae) that increase the SA:Vol ratio (more available surface) 4. Intermembrane space – small space between membranes maximises hydrogen gradient upon proton accumulation 5. Matrix – central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur

Answer 3

- electron tomography has allowed 3D images of the interior of mitochondria to be made

Answer 4

the production of carbon compounds in cells using light energy

Answer 5

6 water + 6 carbon dioxide + solar energy --> glucose + 6 oxygen

Answer 6

- chromatography guidance: - paper chromatography can be used, but thin layer chromatography gives better results

Answer 7

- 400 - 700 nm - Red light has the longest wavelength - Violet light has the shortest wavelength

Answer 8

- Chlorophyll is more efficient at absorbing red and blue light, and least efficient at green light - Therefore most plants are green (because they reflect green light)

Answer 9

- the splitting of water molecules to release electrons needed in other stages - all of the oxygen generated in photosynthesis comes from photolysis of water - generates electrons for use in light-dependent reactions water --> 4 electrons + 4 protons (hydrogen ions) + oxygen

Answer 10

- Only one significant source of oxygen gas exists in the known universe – biological photosynthesis - Before the evolution of photosynthetic organisms, any free oxygen produced was chemically captured and stored - Approximately 2.3 billion years ago, photosynthetic organisms began to saturate the environment with oxygen - This led to changes in the Earth’s atmosphere, oceans, rock deposition and biological life

Answer 11

- Earth’s oceans initially had high levels of dissolved iron (released from the crust by underwater volcanic vents) - When iron reacts with oxygen gas it undergoes a chemical reaction to form an insoluble precipitate (iron oxide) - When the iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere

Answer 12

- For the first 2 billion years after the Earth was formed, its atmosphere was anoxic (oxygen-free) - The current concentration of oxygen gas within the atmosphere is approximately 20%

Answer 13

- The reaction between dissolved iron and oxygen gas created oceanic deposits called banded iron formations (BIFs) - These deposits are not commonly found in oceanic sedimentary rock younger than 1.8 billion years old; this likely reflects the time when oxygen levels caused the near complete consumption of dissolved iron levels - As BIF deposition slowed in oceans, iron rich layers started to form on land due to the rise in atmospheric O2 levels

Answer 14

Free oxygen is toxic to obligate anaerobes and an increase in O2 levels may have wiped out many of these species Conversely, rising O2 levels was a critical determinant to the evolution of aerobically respiring organisms

Answer 15

- endothermic because photosynthetic reactions requires an input of energy (solar energy)

Answer 16

1. Temperature 2. Light intensity 3. Carbon dioxide concentration

Answer 17

- boiling and cooling the water

Answer 18

- 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 photosynthesizing rapidly, then there may be starch grains or liquid droplets in the stroma

Answer 19

- intermembrane space of the thylakoids, which is located in the chloroplast

Answer 20

- reduced NADP and ATP, which serve as energy sources for the light-independent reactions

Answer 21

- the stroma, which is located in the chloroplast

Answer 22

Note: the light indepndent reactions are collectively known as the Calvin cycle Steps: 1. Carboxylation of ribulose bisphosphate 2. Reduction of glycerate-3-phosphate 3. Regeneration of ribulose bisphosphate

Answer 23

The Calvin cycle outlines the events that result in the formation of organic molecules from inorganic sources (CO2) - Ribulose bisphosphate (RuBP) is carboxylated by carbon dioxide (CO2) to form a hexose biphosphate compound - The hexose biphosphate compound immediately breaks down into molecules of glycerate-3-phosphate (GP) - The GP is converted by ATP and NADPH into molecules of triose phosphate (TP) - TP can be used to form organic molecules or can be recombined by ATP to reform stocks of RuBP

Answer 24

- acts as a catalyst for the carboxylation of RuBP (RuBP reacts with carbon dioxide to produce two molecules of glycerate 3-phosphate) - the stroma contains large amounts of rubisco to maximize carbon fixation

Answer 25

- RuBP is both consumed and regenerated through the Calvin cycle - three RuBP react with carbon dioxide to form six glycerate 3-phosphate which will ultimately become six triose phosphate through the Calvin cycle, five of which can then be used for the regeneratation of RuBP and one for the production of carbohydrates

Answer 26

- reduced to triose phosphate using reduced NADP and ATP - hydrogen must be added by a reduction reaction - ATP provides the energy required to perform the reduction and NADP provides the hydrogen atoms resulting in triose phosphate

Answer 27

- used to regenerate RuBP and to to produce carbohydrates - if 3 RuBP are used, 6 triose phosphates are produced; 5 triose phosphates are required to regenerate the 3 RuBP - 1 triose phosphate is thus available for conversion to carbohydrates - therefore, 6 turns of the Calvin cycle is required to produce one molecule of glucose (which requires 6 triose phosphates)

Answer 28

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' - These excited electrons are transferred to carrier molecules within the thylakoid membrane 2. Production of ATP via an ETC - 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 - This build up of protons within the thylakoid creates an electrochemical gradient, or proton motive force - The 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) - This process is called photophosphorylation – as light provided the initial energy source for ATP production - The newly de-energised electrons from Photosystem II are taken up by Photosystem I 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+ - This forms NADPH – which is needed (in conjunction with ATP) for the light independent reactions - The electrons lost from Photosystem I are replaced by de-energised electrons from Photosystem II - The electrons lost from Photosystem II are replaced by electrons released from water via photolysis - Water is split by light energy into H+ ions (used in chemiosmosis) and oxygen (released as a by-product)

Answer 29

- The 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 - The 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) - The electrons lost from Photosystem I are replaced by the de-energised electrons from Photosystem II - The electrons lost from Photosystem II are replaced following the photolysis of water - The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions

Answer 30

- photosystem II is where the light-dependent reactions of photosynthesis begin, as it removes an electron from water molecules and break it down to oxygen and hydrogen - the excited electron produces ATP as it returns to its rest state - at this point, the electron is once again excited by the photosystem I to a much higher energy level and produces a NADPH molecule which is used by the Calvin cycle. - photosystem I is very receptive to light waves at the 700 nm wavelength whilst photosystem II is very receptive to light wavelengths of around 680 nm.

Answer 31

the activation or control of a chemical, chemical reaction, or organism by light, as the activation of chlorophyll by sunlight during photosynthesis

Answer 32

- an electron acceptor associated with Photosystem II in photosynthesis. - it accepts two electrons and is reduced to Plastoquinol - acts as an electron and energy carrier in the electron transport process; carries the pair of excited electrons from the reaction centre of Photosystem II to the start of the chain of electron carriers

Answer 33

- the production of ATP by the light dependent reactions - carried out by thylakoids - may be either a cyclic process or a non-cyclic process

Answer 34

- Cyclic photophosphorylation 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 - Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic) - As the electron returns to the photosystem, NADP+ is not reduced and water is not needed to replenish the electron supply

Answer 35

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

Answer 36

Cyclic phosphorylation - only PS I involved - water is not required - oxygen is not evolved - NADPH is not syntheiszed - used to produce additional ATP in order to meet cell energy demands Non-cyclic phosphorylation - PS I and PS II are both involved - photolysis of water is required - oxygen is evolved - NADPH is synthesized - products can be used for the light indepedent reactions

Answer 37

- photosystem II - photosystem I - ATP synthase - a chain of electron carriers

Answer 38

- excited electrons from photosystem II are used to create a proton gradient - photolysis, which occurs in the fluid inside the thylakoids, also contributes to the proton gradient

Answer 39

- similar to the chemiosmosis in cellular respiration - protons travel across the membrane, down the concentration gradient, by passing through the enzyme ATP synthase - the energy released by the passage of the protons through the ATP synthase is used to make ATP from ADP + inorganic phosphate - when the electrons reach the end of the chain of carriers, they are passed to plastocyanin which is a water-soluable electron acceptor in the fluid inside the thylakoids - reduced plastocyanin is needed to transfer the electron to photosystem I

Answer 40

- chlorophyll molecules within PS I absorb light energy and pass it to the special two chlorophyll molecules in the reaction centre - this raises an electron in one of the chlorophylls to a high energy level (photoactivation) - the excited electron passes along a chain of carriers in PS I, at the end of which it is passed to ferredoxin (a protein in the fluid outside the thylakoid) - two molecules of ferredoxin are used to reduce NADP to form reduced NADP - an electron carried by plastocyanin, which is obtained from PS II, replaces the electron that PS I donated to the chain of carriers

Answer 41

- needed for light-independent reactions of photosynthesis (Calvin cycle) - carries a pair of electrons that can be used to carry out reduction reactions

Answer 42

- the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms - ie. Calvin cylce of photosynthesis

Answer 43

- 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)