5.1.6 Respiration

Question 1

What is respiration and why does it occur?

Answer 1

-energy stored in glucose is transferred to ATP, which provides immediate energy source for biological processes (by breaking C-H bonds in glucose to release energy used in synthesising ATP during chemiosmosis)
-one glucose molecule= net 32 ATP molecules

Question 2

Why do plants and animals need to respire?

Answer 2

-animals require energy for muscle contractions, cytokinesis, homeostasis etc
-plants require energy for active transport, photosynthesis, DNA replication, cell division etc

Question 3

Explain the structure of a mitochondrion

Answer 3

• outer mitochondrial membrane= separate the contents of the mitochondrion from the rest of the cell–} cellular compartment with ideal conditions for aerobic respiration
• inner mitochondrial membrane= contains electron transport chains and ATP synthase, folds of the membrane are cristae(increases SA available for oxidative phosphorylation)
• inter membrane space = proteins are pumped into it via ETC, small area so conc builds up quickly
• matrix= granular area, contains enzymes for Krebs cycle + link, contains mitochondria DNA
• ribosomes= protein synthesis
• mitochondrial DNA(contains 37 genes which are maternally inherited)

Question 4

What are the 4 stages of aerobic respiration?

Answer 4

-glycolysis= in the cytoplasm of the cell, also anaerobic as it doesn’t require oxygen
-link reaction= in the matrix of mitochondria
-Krebs cycle= in the matrix
-Oxidative phosphorylation= inner mitochondrial membrane

Question 5

Summary of what happens in glycolysis

Answer 5

-hexose, 6C glucose is split into 2 smaller, 3C pyruvate molecule
-ATP and reduced NAD also produced

Question 6

Glycolysis: Activation of glucose by phosphorylation

Answer 6

-2 phosphate molecules are released from 2 molecules of ATP–} attach to glucose to form hexose bisphosphate
(prvents glucose from being transported to plasma membrane and leaving cell= HB is more reactive than glucose)
-ATP is reduced to ADP and inorganic phosphate in this step

Question 7

Glycolysis: Lysis of the phosphorylated hexose

Answer 7

-hexose bisphosphate(6C) is very unstable
-causes it to split into 2 molecules of triose phosphate/TP(3C)

Question 8

Glycolysis: Phosphorylation of TP

Answer 8

-another phosphate group is added to to each molecule of TP to form two molecules triose bisphosphate
-the phosphate groups are free inorganic phosphate ions from the cytoplasm

Question 9

Glycolysis: Dehydrogenation and formation of ATP

Answer 9

-two TP molecules are oxidised by the removal of hydrogen atoms to from two pyruvate molecules
-hydrogen atoms are transferred to NAD coenzymes which then become reduced NAD
-two phosphate groups(from TP molecules) are transferred to ADP to form ATP–} substrate level phosphorylation(formation of ATP without ETC)

Question 10

What are the net and gross product and why are they different?

Answer 10

-the gross product of glycolysis is 4 ATP molecules but the overall net product is 2 ATP molecules
-because two ATP molecules are used to activate glucose at the beginning of glycolysis

Question 11

What is the link reaction?

Answer 11

-first step in aerobic respiration that links glycolysis(anaerobic) to the Krebs cycle(aerobic)

Question 12

The link reaction: pyruvate transporting

Answer 12

-pyruvate enters mitochondrial matrix through active transport via specific carrier proteins
-undergoes series of reactions catalysed by multienzyme complex pyruvate dehydrogenase

Question 13

The link reaction: Decarboxylation

Answer 13

-CO2 is removed from pyruvate(3C)

Question 14

The link reaction: Dehydrogenation

Answer 14

-hydrogen atoms are removed
-accepted by NAD, which becomes reduced to NADH

Question 15

The link reaction: combination with coenzyme A

Answer 15

-the resulting 2 carbon acetyl group is combined with coenzyme A to form 2 AcetylCoA

Question 16

What are the products of the link reaction for 1 glucose molecule?

Answer 16

-2 AcetylCoA molecules–} to the Krebs cycle to deliver acetyl group
-2 CO2–} released as waste product
-2 reduced NAD–} goes to oxidative phosphorylation stage

Question 17

What is the importance of AcetylCoA?

Answer 17

-CoA is an enzyme that is used as a carrier for acetyl group(from pyruvate to Krebs)
-most respiratory substances can be converted into AcetylCoA:
- carbohydrates
-fats-} fatty acids-} glycerol-} glycerol-3-phosphate
-fatty acids-} 2C fragments
- reactions are reversible

Question 18

What is the Krebs cycle?

Answer 18

-series of oxidation-reduction reactions that produces reduced coenzymes(NAD + FAD) + ATP
-takes place in the matrix of mitochondria
-cycle happens twice for every glucose molecule(once for every pyruvate molecule)

Question 19

Krebs cycle: formation of citrate

Answer 19

-Acetyl CoA(2C) enters Krebs cycle + combines with Oxaloacetate(4C) to form Citrate(6C)

Question 20

Krebs cycle: Formation of 5-C compound

Answer 20

-citrate molecule undergoes decarboxylation + loses a carbon in the form of CO2
-dehydrogenation occurs–} hydrogen is transferred to produce reduced NAD from NAD
-5C compound produced i.e Ketoglutarate

Question 21

Krebs cycle: Regeneration of oxaloacetate

Answer 21

-5C compound undergoes another decarboxylation to form oxaloacetate
-NAD reduced to NADH(twice to lose 2 hydrogen atoms)
-FAD reduced to FADH(once to lose 2 hydrogen atoms)–} dehydrogenation produces 4 more hydrogen atoms
-ATP is also produced from ADP and inorganic phosphate

Question 22

What are differences between NAD and FAD?

Answer 22

-NAD takes part in all stages of respiration whereas FAD only in Krebs
-NAD accepts 1 H molecule and FAD accepts 2
-reduced NAD is oxidised at the start of the electron transport chain releasing protons + electrons while reduced FAD is oxidised further along the chain
-reduced NAD results in synthesis of 3 ATP molecules whereas reduced FAD results in 2

Question 23

Products of one Krebs cycle

Answer 23

(would be double for one glucose molecule)
-2 CO2 molecules(released as waste products)
-1 ATP(used for energy)
-3 reduced NAD(to oxidative phosphorylation)
-1 reduced FAD(to oxidative phosphorylation)

Question 24

What is oxidative phosphorylation?

Answer 24

-process where the energy carried by electrons, from reduced coenzymes is used to make ATP
-occurs in the inner mitochondrial membrane is highly folded to from cristae(increases SA)
-requires oxygen

Question 25

Steps of oxidative phosphorylation: complexes

Answer 25

-reduced NAD + FAD arrive at mitochondrial membrane(matrix)–} at complex I, reduced NAD is oxidised to NAD and the hydrogen splits into protons and electrons
-the electrons are transferred along the electron transport chain via series of oxidation-reduction reactions to complex II(2 is reduced and 1 being oxidised)
-as electrons move down the chain, they lose energy–} being used to actively transport protons up from matrix to intermembrane space
-at complex II, reduced FAD is oxidised to FAD, which releases 2 H ions
-electrons transferred to complex III and H ions are pumped into intermembrane
-electrons move to complex IV which is reduced(meaning III is oxidised)

Question 26

Steps of oxidative phosphorylation: forming water

Answer 26

-oxygen acts as the final electron acceptor and combined with protons and electrons to form water
-ee + 2H+ + 1/2 O2 = H2O

Question 27

Steps of oxidative phosphorylation: chemiosmosis + ATP production

Answer 27

-there is a higher proton conc in the intermembrane space than in the matrix due to protons being pumped there–} forms a proton gradient
-protons move down the gradient, diffusing back into the matrix via ATP synthase
-this movement supplies energy for the synthesis of ATP from ADP and Pi(chemiosmosis)

Question 28

What is anaerobic respiration?

Answer 28

-respiration that doesn’t require oxygen, resulting in smaller quantities of ATP being produced
-used when O2 cannot be supplied fast enough for respiring cells
-starts with glycolysis like aerobic respiration

Question 29

What are the 3 different types of respiratory categories?

Answer 29

-Obligate anaerobes= cannot survive in the presence of oxygen, mostly prokaryotes
-Facultative anaerobes= synthesise ATP by aerobic respiration if O2 is present, but can switch in the absence of O2
-obligate aerobes= can only synthesise ATP in the presence of O2

Question 30

What is fermentation?

Answer 30

-form of anaerobic respiration where complex organic molecules are broken down into simpler organic molecules
-small quantity of ATP produced is through substrate-level phosphorylation

Question 31

What is lactate fermentation?

Answer 31

-occurs in mammals + some bacteria and produces lactate
-is a survival technique for babies immediately after birth + aquatic organisms in water with fluctuating O2 levels
-lactate is toxic so must be broken down by the liver to CO2 + water for excretion

Question 32

Lactate fermentation

Answer 32

-pyruvate accepts hydrogen atoms from reduced NAD that was formed in glycolysis
-pyruvate is then converted into lactate and NAD is regenerated*
-catalysed by lactate dehydrogenase
*small quantity of ATP can be produced

Question 33

What happens to lactate/lactic acid?

Answer 33

-converted back to glucose in the liver via gluconeogenesis
-but oxygen is needed for this process–} oxygen debt

Question 34

Why can’t lactate fermentation occur indefinitely?

Answer 34

-small quantity of ATP produced would not be enough for vital processes long term
-accumulation of lactic acid causes a fall in pH which leads to proteins denaturing–} respiratory enzymes + muscle filaments will cease to function

Question 35

Why and where does alcoholic fermentation occur?

Answer 35

-to produce ethanol
-occurs in yeast cells, fungi + some plants

Question 36

Alcoholic fermentation

Answer 36

-pyruvate is first converted into ethanal via decarboxylation(catalysed by pyruvate decarboxylass)
-reduced NAD from glycolysis transfers hydrogen to ethanal to form ethanol and NAD(catalysed by ethanol dehydrogenase)
-the NAD can be reused in glycolysis

Question 37

Why is alcoholic fermentation irreversible whilst lactate fermentation is reversible?

Answer 37

-pyruvate is converted into lactate which is catalysed by lactate dehydrogenase—} reversible
-pyruvate is converted into lactate AND CO2–} is lost as waste product which means pyruvate decarboxylase cannot reverse the reaction