Aerobic Respiration

Question 1

describe respiration in three points

Answer 1

a catabolic process involving a series of enzyme-catalysed reaction in cells

energy-rich substrates (e.g. glucose & fatty acids) are hydrolysed to release energy; some trapped as chemical energy in ATP and some released as heat energy

during respiration, high energy C-C, C-H and C-OH bonds are broken by enzymes in a series of small steps;
these reactions provide the energy to produce ATP

Question 2

define aerobic respiration

Answer 2

the release of large quantities of ATP energy from glucose or another organic substrate in the presence of oxygen
CO2 is produced

Question 3

define anaerobic respiration

Answer 3

takes place in absence of oxygen and produces lactic acid (lactate?) in animal cells and carbon dioxide and ethanol in yeast cells, together with a small yield of ATP energy

Question 4

what are two substrates that could be used to release energy in respiration?

Answer 4

glucose and fatty acids

Question 5

what is most of the energy released during respiration used for and how is the rest of the energy released?

Answer 5

most - used to synthesise ATP

rest - released as heat energy

Question 6

what are similarities and differences of aerobic and anaerobic respiration?

Answer 6

sim:
both produce CO2
both produce ATP energy

diff:
anaerobic does not require oxygen - aerobic does
ATP yield is lower in anaerobic

Question 7

what is ATP and what does it stand for?

Answer 7

it is a nucleotide found in all living organisms

adenosine triphosphate

Question 8

draw and label structure of ATP

Answer 8

on page 3 in booklet

Question 9

describe chemical energy, respiration in the context of ATP

Answer 9

chemical energy is stored in lipids or carbohydrates like glucose

respiration oxidises glucose in a series of small reactions to release energy in the form of ATP

ATP is not an energy store but an energy source

ATP is involved in energy changes by carrying the energy to where it is needed and releasing the energy when ATP is broken down

Question 10

what is ATP often called and define it?

Answer 10

the ‘universal energy currency’ because ATP provides energy in all cells in all (biochemical) reactions in all organisms

Question 11

give 6 roles of ATP

Answer 11

protein synthesis
active transport
secretion
nerve transmission
muscle contraction
DNA replication

Question 12

explain protein synthesis in relation to ATP

Answer 12

ATP required for amino acid activation in the cytoplasm

Question 13

explain active transport in relation to ATP

Answer 13

ATP changes the shape of transport proteins to move molecules against a concentration gradient

Question 14

explain secretion in relation to ATP

Answer 14

packaging and transport of secretory products, like enzymes in vesicles

Question 15

explain nerve transmission in relation to ATP

Answer 15

sodium/potassium pumps actively transport ions across the axon membrane

Question 16

explain muscle contraction in relation to ATP

Answer 16

energy is required for contraction of muscle fibres

Question 17

explain DNA replication in relation to ATP

Answer 17

synthesis of DNA from nucleotides during DNA replication at interphase

Question 18

describe formation of ATP

Answer 18

the enzyme of ATP synthase combines ADP (adenosine diphosphate) and Pi (inorganic phosphate) in a condensation reaction

this requires an input of energy of (30.6KJ mol-1) in an endergonic reaction

the addition of this phosphate to ADP is called phosphorylation

ADP + Pi -> ATP

Question 19

describe hydrolysis of ATP

(formation and hydrolysis in helpful diagram on page 4)

Answer 19

the enzyme ATPase hydrolyses the terminal phosphate bond releasing a small packet of energy (30.6KJ mol-1) in an exergonic reaction

this forms ADP and Pi

Question 20

how are the properties, structure and formation of ATP linked to its role in cells?

Answer 20

the hydrolysis of ATP to ADP releases immediate energy
the hydrolysis of glucose takes much longer and involves many intermediate reactions

only one enzyme is needed to release energy from ATP, whereas many are needed in the case of glucose

ATP releases energy in small packets when and where it is needed

ATP is the universal energy currency in many reaction in all living organisms

ATP is easily transported across membranes

Question 21

the breakdown of a molecule of glucose to carbon dioxide and water in aerobic conditions involves what four stages?

Answer 21

glycolysis

link reaction

Krebs cycle

electron transport chain

Question 22

where are each of these four stages of respiration located?

(helpful diagram on page 5)

Answer 22

glycolysis - cytoplasm

link reaction - mitochondrial matrix

Krebs cycle - mitochondrial matrix

ETC - inner mitochondrial membrane (cristae)

Question 23

describe redox reaction in respiration

Answer 23

glucose is broken down in a series of reactions tp synthesis ATP

at various stages in this process, hydrogen atoms are removed from intermediate compounds and split into protons and electrons

when glucose is broken down, hydrogen atoms are released

Question 24

why are hydrogens removed during respiration?

Answer 24

because energy from hydrogen atoms used to create a proton gradient powering production of ATP

Question 25

describe OILRIG in terms of redox reactions in respiration

Answer 25

oxidation is the loss of electrons/hydrogen reduction is the gain of electrons/hydrogen A is oxidised, losing hydrogen - a catabolic process and energy is released B is reduced, gaining hydrogen - an anabolic process and energy is taken in

Question 26

give two examples of redox reactions in respiration

Answer 26

two co-enzymes act as hydrogen carriers: NAD+ is reduced to form reduced NAD (NADH/H+) FAD is reduced to form reduced FAD (FADH2) hydrogen is picked up by NAD & FAD so it is reduced NAD + 2H+ + 2e- -> NADH FAD + 2H+ + 2e- -> FADH2 (small helpful diagram on page 5 in booklet)

Question 27

how does glucose enter the cell cytoplasm?

Answer 27

active transport facilitated diffusion

Question 28

draw out the process of glycolysis and ANNOTATE

Answer 28

very important diagram on page 6

Question 29

describe how the ATP molecules are synthesised - happens in glycolysis what is this process known as?

Answer 29

synthesised using energy derived from the breakdown of a substrate which donates an inorganic phosphate this inorganic phosphate combines with ADP to form ATP substrate level phosphorylation

Question 30

what is produced per glucose molecule?

Answer 30

reduced NAD = 2 ATP gross produced = 4 used = 2 net total produced = 2

Question 31

what happens in glycolysis? written

Answer 31

takes place in the cytoplasm of cells, it is the initial biochemical pathway in both aerobic and anaerobic respiration glucose (6C) is phosphorylated, making it unstable, to form hexose phosphate (6C) (Pi is attached to this molecule) this requires the addition of 2 ATP molecules (provides the phosphate) hexose phosphate (6C) splits spontaneously into triose phosphate molecules (3C) each triose phosphate molecule is oxidised to pyruvate (3C) (a usable form for mitochondria). this means that hydrogen is removed by a dehydrogenase enzyme in a dehydrogenation reaction the hydrogen is accepted by NAD forming reduced NAD the production of pyruvate from triose phosphate also results in the phosphorylation of 2 ADP molecules to produce 2 ATP - this is substrate level phosphorylation overall, in glycolysis 2 reduced NAD and 2 pyruvate are produced there is also a net gain of 2 ATP molecules as 4 ATP molecules were produced but 2 ATP were required in the first stage of the pathway to phosphorylate glucose net products: 2 pyruvate molecules + 2NADH + 2ATP

Question 32

how does pyruvate enter the mitochondrial matrix?

Answer 32

(pyruvic acid) diffuses from the cytoplasm where the link reaction occurs

Question 33

draw and annotate the link reaction

Answer 33

page 8 in booklet IMPORTANT

Question 34

what molecules are produced per glucose molecule in the link reaction?

Answer 34

reduced NAD = 2 CO2 = 2

Question 35

why is pyruvate provided as a respiratory substrate for mitochondria and not glucose?

Answer 35

glucose can only be hydrolysed in the cytoplasm during glycolysis pyruvate can enter the mitochondrion (by facilitated diffusion) for the link reaction

Question 36

what happen in the link reaction? written (diagram on page 9)

Answer 36

in the presence of oxygen, pyruvate diffuses from the cytoplasm into the mitochondrial matrix where the link reaction takes place pyruvate (3C) is decarboxylated by a decarboxylase enzyme (one molecule of CO2 is removed) pyruvate is also oxidised to acetate; dehydrogenase enzymes remove hydrogen which is accepted by NAD to form reduced NAD acetate (2C) is produced acetate (2C) combines with coenzyme A to form acetyl coenzyme A which enters Krebs cycle (role of coenzyme A) overall in the link reaction 2 molecules of CO2, 2 molecules of reduced NAD and 2 molecules of acetyl coenzyme A are produced per glucose molecule

Question 37

draw and annotate the Krebs cycle

Answer 37

page 10 in booklet IMPORTANT

Question 38

what is produced per glucose molecule in the krebs cycle

Answer 38

reduced NAD = 6 CO2 = 4 reduced FAD = 2 ATP = 2 (substrate level phosphorylation) (divide each number by 2 for ONE krebs cycle)

Question 39

what happens in the krebs cycle? written

Answer 39

krebs cycle also known as the citric acid cycle occurs in mitochondrial matrix krebs cycle liberates energy ('frees') from carbon-carbon bonds to make ATP, reduced NAD (NADH/H+) and reduced FAD (FADH2) CO2 is also released as a waste product the acetate (2C) from acetyl coenzyme A combines with a 4C compound to form a 6C compound coenzyme A is regenerated and returns to the link reaction to collect another acetate a series of enzyme-controlled reactions then takes place; there are two decarboxylation reactions and four dehydrogenation reactions per turn of the cycle the acetate which enters the krebs cycle is completely broken down to CO2 and water and the 4C compound is regenerated via 6C and 5C intermediates

Question 40

define a decarboxylation reaction

Answer 40

any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as CO2 catalysed by decarboxylase enzymes

Question 41

define a dehydrogenation reaction

Answer 41

a chemical reaction that involves the elimination of hydrogen catalysed by dehydrogenase enzymes

Question 42

describe the process of dehydrogenation e.g. of the 4C compound in Krebs cycle (helpful diagram on page 12)

Answer 42

the 4C substrate and NAD collide with the dehydrogenase enzyme the substrate is oxidised (loses hydrogen) NAD accepts the hydrogen and is therefore reduced the products are released the active site is unchanged and available for re use

Question 43

why is it an advantage for the inner mitochondrial membrane to be folded into cristae? (helpful diagrams on page 13)

Answer 43

increased SA for stalked particles so more ATP can be synthesised

Question 44

suggest 2 functions for mitochondrial DNA

Answer 44

codes for its own replication codes for enzymes involved in aerobic respiration

Question 45

draw and annotate the electron transport chain

Answer 45

diagram on page 14 IMPORTANT

Question 46

whats the number of ATP per NAD and FAD in the electron transport chain?

Answer 46

ATP - 3 FAD - 2

Question 47

how and why does the pH change in the ETC?

Answer 47

as protons (H+) are pumped into the space the pH becomes more acidic (lower)

Question 48

describe what happens to produce ATP in the inner mitochondrial membrane? (ETC) (12 points)

Answer 48

reduced NAD & reduced FAD deliver their pairs of hydrogen atoms to the electron transport chain at the inner mitochondrial matrix the hydrogen atoms split into protons (H+) and electrons (e-) the high energy electrons are transferred along carriers in the inner mitochondrial membrane along the ETC, moving from high energy levels to lower energy levels the energy released during electron transport fuels the proton pumps protons are pumped through channel proteins from the matrix to the intermembrane space the build-up of protons in the intermembrane space forms an electrochemical gradient stalked particles lining the cristae contain the enzyme ATP synthase protons flow down their conc. gradient through an ion channel in ATP synthase this is the only part of the membrane permeable to H+ the flow of protons releases enough energy for the synthesis of ATP from ADP and Pi (catalysed by ATP synthase) the production of an electrochemical gradient which results in diffusion of protons through a proton channel in ATP synthase, fuelling the synthesis of ATP, is known as chemiosmosis oxygen acts as the final electron acceptor; the electrons and protons combine with oxygen to form water 4H+ + 4e- +O2 -> 2H2O this method of producing ATP is called oxidative phosphorylation

Question 49

define electron transport chain

Answer 49

the movement of high energy electrons along electron carriers, releasing energy to fuel proton pumps / the chain of proteins in the membrane

Question 50

define chemiosmosis

Answer 50

production of an electrochemical gradient resulting in the diffusion of protons through a proton channel past ATP synthase, fuelling the synthesis of ATP

Question 51

define oxidative phosphorylation

Answer 51

the process by which ATP is produced at the electron transport chain on the inner mitochondrial membrane involves the oxidation of reduced NAD and reduced FAD

Question 52

how many molecules of ATP are produced from oxidative and substrate level phosphorylation altogether? (helpful table on page 17)

Answer 52

oxidative: 34 substrate level: 4

Question 53

suggest why cells may not actually produce 38 ATP molecules from one glucose molecule?

Answer 53

maximum yield is never quite reached due to losses (leaky membrane) as well as the cost of moving pyruvate and ADP into the mitochondrial matrix typical yield = 30-32 ATP per glucose molecule

Question 54

glucose catabolism during aerobic respiration is spread out over many reactions suggest an advantage of this

Answer 54

energy is released in small packets rather than all at once which could release too much heat excessive increases in temperature could lead to denaturation of proteins in cells