Respiration and Photosynthesis - Arif Sir's Handouts · 2018-09-06 · Photosynthesis and respiration are the reverse of each other, and you couldn’t have one without the other

International Turkish Hope School - Chittagong BranchAcademic Year 2014-2015

Advanced Level Biology – UNIT 05

Teacher in Charge: ARIF ULLAH - 01817721521

RespirationMetabolism refers to all the chemical reactions taking place in a cell. There are thousandsof these in a typical cell, and to make them easier to understand, biochemists arrangethem into metabolic pathways. The intermediates in these metabolic pathways arecalled metabolites.

· Reactions that release energy (usually breakdown reactions) are called catabolicreactions (e.g. respiration)

· Reactions that use up energy (usually synthetic reactions) are called anabolicreactions (e.g. photosynthesis).

Photosynthesis and respiration are the reverse of each other, and you couldn’t have onewithout the other. The net result of all the photosynthesis and respiration by livingorganisms is the conversion of light energy to heat energy.




Cellular RespirationC6H12O6 + 6O2à 6CO2 + 6H2O

Oxidation of glucosev Yield high energy but not easilyv Has a high activation energyActivation energy lowered by enzymes or by phosphorylating glucose

ATP- Adenosine Triphosphate (energy currency)

Why use ATP?à If all the energy released on oxidation is used at an instant, a lot of it will be

wasted as thermal energy.

ATP

1) 5 carbon sugar(Ribose)2) Nitrogenous base(Adenine)3) 3 Phosphate groups

The chemical bonds that link the phosphate groups together are high energy bonds.




When a phosphate group is removed to form ADP, small packets of energy are released.

How is ATP used?à Anabolic reaction – growth and reproductionà Active transportà Mechanical work

ATP acts an as intermediate between cell’s energy yielding and energy requiring reactionand hence called energy currency of a cell.

ATP is made in 2 ways1) Phosphorylation (glycolysis and Krebs cycle)2) Chemiosmotic phosphorylation (electron transport chain)

PHOSPHORYLATION

1) glycolysis (cytoplasm)2) Link reaction3) Krebs cycle

4) Electron transport chain (cristae of mitochondria)

Matrix of themitochondria




1) Glycolysis

· Glucose enters cell by facilitated diffusion· ATP activates glucose to produce 2 unstable compounds· Substrate-level phosphorylation produces 4ATP· Net yield of 2ATP and 2reducedNAD per glucose molecule

2) Link Reaction

· Pyruvate enters matrix of mitochondrion for further reaction· Net yield of 2reducedNADH per glucose




3) Krebs cycle

· Citrate is gradually broken down to re-form oxaloacetate· Substrate-level phosphorylation forms 2ATP· Removal of hydrogen from respiratory substrate· Net yield of 2ATP, 2reducedFADH, 6reducedNADH per glucose




4) Electron transport chain (cristae of mitochondria)

The respiratory chain (or electron transport chain) is an unusual metabolic pathway inthat it takes place within the inner mitochondrial membrane, using integral membraneproteins. These proteins form four huge trans-membrane complexes called complexesI, II, II and IV. The complexes each contain up to 40 individual polypeptide chains,which perform many different functions including enzymes and trans-membranepumps. In the respiratory chain the hydrogen atoms from NADH gradually release alltheir energy to form ATP, and are finally combined with oxygen to form water.

· Reduced coenzymes arrive at ETC· Split into coenzyme + 2H+ + 2e- by hydrogen carriers· 2e- are transferred to electron carriers (cytochrome)· Pass down ETC by redox reaction and release energy as they go· Energy produces ATP by oxidative phosphorylation· Final electron acceptor 1/2O2 is reduced by 2H+ and 2e- to produce H2O· Net yield of 34ATP (30NADH, 4FADH) per glucose







ATP made in Respiration

Stage molecules produced per glucoseFinal ATP yield

(old method)

Final ATP yield

(new method)

Glycolysis

2 ATP used -2 -2

4 ATP produced (2 per triose phosphate) 4 4

2 NADH produced (1 per triose phosphate) 6 5

Link Reaction 2 NADH produced (1 per pyruvate) 6 5

Krebs Cycle

2 ATP produced (1 per acetyl coA) 2 2

6 NADH produced (3 per acetyl coA) 18 15

2 FADH produced (1 per acetyl coA) 4 3

38 32




Anaerobic Respiration

Ethanol Pathway




· Absence of oxygen stops oxidative phosphorylation. The ETC therefore stopsworking

· In microorganisms such as yeast, and in some plant tissues, the hydrogen fromreduced NAD is passed onto ethanal. This releases NAD and allows glycolysis tocontinue

· Pyruvate from glycolysis is decarboxylated to ethanal, then ethanal is reduced toethanol(enzyme-alcohol dehydrogenase)

Lactate pathway

· In other microorganisms and mammalian muscles deprived of oxygen, pyruvateacts as the hydrogen acceptor and is converted to lactate(enzyme-lactatedehydrogenase)

· NAD is released which allows gycolysis to continue.




Ethanol and lactate are toxic. The reaction cannot continue indefinitely.The pathway leading to ethanol is irreversible and the chemical potential of ethanol isthus wasted.The lactate pathway is reversible. The lactate is carried by the blood plasma to the liverwhere it is converted back to pyruvate. The liver oxidizes abt 20% of the incoming lactateto carbon dioxide and water via aerobic respiration when oxygen is available. Theremainder of the lactate is converted to glycogen. The oxygen needed to allow removal oflactate is called oxygen debt.

Respiratory substrates

1. Fats and proteins can also be used to respire. When fats are about to be respired they arebroken down into fatty acids and glycerol. The glycerol is converted into triose phosphateand enters the glycolysis stage. The fatty acids are broken down into two carbon fragmentsand entered into the Krebs cycle via acetyl co-enzyme A.

2. Proteins cannot be stored by mammals so have to either be used or excreted.3. The respiration of proteins only occurs when there is a excess of them in the diet. To begin

their process the amino group is removed (called deamination). The amino group thencombines with CO2forming urea, later to be excreted. The remains of the amino acid,without an amino group, are organic acids and are is feed back into the Krebs cycle.




Respiratory Quotient

Respiratory Quotient, or RQ for short, is a number used in estimating carbon dioxideproduction. The equation to find the RQ is:

RQ = CO2 Released / O2 Used

For example the question might ask.The equation to calculate the oxidation of a lipid is:

C57H104O6 + 80O2 = 57CO2 + 52H2O + energy

Use the equation to calculate the respiratory quotient of this lipid. Show yourworkings.

And the answer?

Using the RQ equation you can see we need to know the amount of CO2 Releasedand the amount of O2 Used. This will be 57 for CO2 and 80 for O2. 57 / 80 = 0.71

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Respiration and Photosynthesis - Arif Sir's Handouts · 2018-09-06 · Photosynthesis and respiration are the reverse of each other, and you couldn’t have one without the other