cellular respiration Flashcards

Question

what is the electron transport chain and where is it located?

Answer 1

the electron transport chain (ETC) is made up of a sequence of **electron carriers**, that undergo temporary **reduction & oxidation** as electrons from NADH & FADH2 are passed down to the **final electron acceptor**, molecular oxygen. the electron transport chain is located in the **inner mitochondrial membrane**, which is **highly folded** to form **cristae** in all cells

Answer 2

**no ATP is directly generated** - energy from electrons carried by NADH & FADH2 are used to **pump protons** across the inner mitochondrial membrane to the intermembrane space, generating a **proton gradient** across the inner mitochondrial membrane - the flow of the protons back into the matrix along their concentration gradient through the **ATP synthase complex** allows for **ATP synthesis by oxidative phosphorylation**

Answer 3

- the ETC, embedded in the inner mitochondrial membrane, comprises of a sequence of **electron carriers** that have the ability to be **reversibly reduced & oxidised** as electrons from NADH & FADH2 are passed down the mitochondrial ETC. - several coenzymes & cytochromes in the ETC are bound to enzymes and other essential factors, forming functional groups known as **complexes**. there are 4 main complexes, complexes I-IV, in the ETC - each subsequent member ofthe ETC has a **higher affinity** for electrons than its predecessor, but a **lower affinity** than its successor. this ensures a **one-way transport of electrons down the ETC**, so theelectrons move along the sequence of electron carriers in order of **increasing electron affinity** - electrons are eventually passed to the **final electron acceptor** in the ETC, **molecular oxygen** that has diffused into the mitochondrion. oxygen is reduced in the **mitochondral matrix** to produce a molecule of **water** - energy released as electrons flow through the ETC is sufficient to power the **pumping of H+ ions** across the inner mitochondrial membrane into the intermembrane space, establishing an electrochemical **proton gradient** - as members of the ETC accept electrons from NADH & FADH2, the oxidised coenzymes NAD & FAD are **regenerated**. this allows them to be available to accept electrons & protons from substrates during glycolysis, link reaction & Krebs cycle again.

Answer 4

chemiosmosis takes place in the inner mitochondrial membrane. - energy is released as electrons are transferred along the ETC. this energy **drives proton pumps** to **actively pump H+ unidirectionally** across the inner mitochondrial membrane from the mitochondrial matrix to the **intermembrane space** - the proton pumping generates a **proton gradient** with two components, 1) **concentration gradient of H+** and 2) **electrical gradient** (higher conc of +vely charged protons on 1 side of membrane) - since the inner mitochondrial membrane is **impermeable to H+**, protons can only re-enter through the **ATP synthase complex** - the ATP synthase complex couples the **exergonic passage of H+** to the **endergonic phosphorylation of ADP** to **form ATP**

Answer 5

amount of ATP produced depends on no. of H+ pumped into the intermembrane space, which depends on no. of electrons contributed by reduced coenzymes for each pair of electrons stripped from **NADH/reduced NAD**, - 5 pairs of (10) H+ are pumped across the inner mitochondrial membrane into the intermembrane space - re-entry of H+ into the matrix provides the energy to generate **3 ATP molecules** for each pair of electrons stripped from **FADH2/reduced FAD**, - 3 pairs of (6) H+ are pumped across the inner mitochondrial mmbrane into the intermembrane space - re-entry of H+ into the matrix provides the energy to generate **2 ATP molecules**

Answer 6

total no. of NADH: **10** (2 from glycolysis, 2 from link reaction, 6 from krebs cycle) total no. of FADH2: **2** (from krebs cycle) 10 NADH x 3 ATP (electrons from each NADH produces 3 ATP) = **30 ATP** 2 FADH2 x 2 ATP (electrons from each FADH2 produces 2 ATP) = **4 ATP** substrate level phosphorylation in glycolysis produces **2 ATP** substrate level phosphorylation in the krebs cycle produces **2 ATP** 30 + 4 + 2 + 2 = **38 ATP** ## Footnote whether the cell produces 36 or 38 molecules of ATP depends on the shuttle systems (FYI) used in the mitochondrion.

Answer 7

***occurrence*** - SLP occurs during **glycolysis** in the cytoplasm and during **krebs cycle** in the mitochondrial matrix - OP occurs during **ETC** in the inner mitochondrial membrane ***ATP production*** - SLP produces only a **small amount** of ATP - OP produces almost 90% of ATP generated in respiration ***process*** - SLP: the enzymatic endergonic phosphorylation of ADP with a 5' monophosphate coupled to **exergonic dephosphorylation** of an organic substrate - OP: the enzymatic endergonic phosphorylation of ADP to form ATP by ATP synthase, coupled to **exergonic electron transport** from a substrate to the final electron acceptor, oxygen. exergonic **passage of protons** along a proton gradient

Answer 8

***poisons that block electron flow*** - various poisons (eg carbon monoxide & cyanide) block the movement of electrons down the ETC - this **completely inhibits** ATP production ***poisons that inhibit ATP synthase*** - these poisons (eg oligomycin, an antibiotic) **directly inhibits** ATP synthase by **preventing the influx of protons** through ATP synthase - although the proton gradient becomes larger than normal, its potential energy cannot be tapped to make ATP ***poisons that make the inner mitochondrial membrane leaky to protons*** - these poisons (eg 2,4-dinitrophenol) are known as **uncoupling agents**. they carry protons back across the inner mitochondrial membrane. - this causes the **proton gradient to dissipate** - no proton gradient is formed, so **no ATP can be made** by oxidative phosphorylation. rather, the energy derived from electron transport is released as heat.

Answer 9

- glycolysis can take place in the absence of oxygen (so pyruvate is formed) - under anaerobic conditions, **no further oxidation of pyruvate occurs**, so **no acetyl CoA is formed**, and **no additional ATP can be generated** - because without oxygen, the link reaction, Krebs cycle and oxidative phosphorylation **do not occur** - the energy needs of the cell are met by the **2 ATP molecules per glucose** generated in glycolysis, so cells must consume glucose morerapidly to maintain steady-state cellular ATP levels

Answer 10

- anaerobic respiration, occuring in the **cytosol**, uses organic molecules as terminal electron acceptors for the regeneration of NAD the two common types of fermentation, where **pyruvate** is used as an **electron acceptor**, are: 1. **lactic acid fermentation**, where pyruvate is converted to lactate 2. **alcoholic fermentation**, where pyruvate is converted to ethanol & CO2

Answer 11

NADH + C3H4O3 (pyruvate) -> NAD + C3H6O3 (lactate) pyruvate is **reduced directly** by NADH to form **lactate** (ionised form of lactic acid) as a waste product, when **no release of CO2** lactic acid fermentation occurs in animals and in certain fungi & bacteria why need lactic acid fermentation? - in animals: to **regenerate NAD** so it can continue glycolysis - in certain fungi & bacteria: to make cheese and yoghurt in the dairy industry

Answer 12

NADH + C3H4O3 (pyruvate) -> NAD + C2H5OH (ethanol) + CO2 **CO2 is released** from pyruvate, and pyruvate is converted to acetaldehyde. then, acetaldehyde is **reduced by NADH to ethanol** occurs in fungi, eg **yeast**, and in most plant tissues CO2 is a waste product

Answer 13

***energy yield*** aerobic: max **38 ATP** produced per glucose molecule oxidised anaerobic: **2 ATP** per glucose molecule oxidised (only from glycolysis) ***oxidation*** aerobic: **complete oxidation** of glucose to CO2 & water anaerobic: **incomplete oxidation** of glucose ***condition*** aerobic: occurs in the **presence** of oxygen anaerobic: occurs in the **absence** of oxygen

Answer 14

- respiration rate (uptake of oxygen per unit time) can be measured using a **respirometer**. the manometer in the respirometer detects **changes in pressure/volume of a gas** - respiration by tiny organisms that are trapped in the respirometer chamber alters the composition of the gas - oxygen consumption per unit time can be measured by reading the **level of manometer fluid** against the scale - changes in temperature & pressure will alter the volume of air in the apparatus, so temperature of the surroundings must be kept constant while readings are taken, using a **thermostatically controlled water bath**. a control tube containing an equal volume of inert materials to the volume of organisms used helps **compensate for changes in atmospheric pressure** - once measurements have been taken at a series of temperatures, a graph can be plotted of oxygen consumption against temperature - the respirometer can also be used to measure the **respiratory quotient (RQ)** of an organism - find oxygen consumption at the same temperature (x), then do the same but remove the chemical to absorb CO2 so the manometer scale shows whether the volumes of oxygen absorbed and CO2 produced are the same. if they are the same, level of manometer fluid won't change and **RQ = 1**. if more CO2 is produced, the scale shows an increase in volume of air in the atmosphere (y) - RQ = CO2/O2 - (x+y)/x - if less CO2 is produced than oxygen absorbed, the volume of air in the respirometer decreases (z), so RQ = CO2/O2 - (x-z)/z