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Cellular Respiration Introduction – all forms of life depend directly or indirectly on light energy captured during photosynthesis – glucose molecules.

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Presentation on theme: "Cellular Respiration Introduction – all forms of life depend directly or indirectly on light energy captured during photosynthesis – glucose molecules."— Presentation transcript:

1 Cellular Respiration Introduction – all forms of life depend directly or indirectly on light energy captured during photosynthesis – glucose molecules are broken down back into carbon dioxide and water (molecules the plant started with)

2 ATP – Adenosine triphosphate
most common energy carrier in cells nucleotide composed of adenine, the sugar ribose, and three phosphate groups synthesized from adenosine diphosphate (ADP) and inorganic phosphate – process is called phosphorylation during glucose breakdown, energy is release and stored in bonds of ATP


4 Summary of complete glucose metabolism:
Photosynthesis: 6CO2 + 6H2O + sunlight energy  C6H12O6 + 6O2 Complete glucose metabolism: C6H12O6 + 6O2  6CO2 + 6H2O + chemical and heat energies

5 Glycolysis first stage of aerobic respiration
does not require O2 (anaerobic) and proceeds in exactly the same way under both aerobic (with oxygen) and anaerobic (without oxygen) conditions Splits apart a single glucose molecule (6 carbon) into two molecules of pyruvate (3 carbon) under anaerobic conditions, pyruvate converted by fermentation to lactic acid or ethanol occurs in cytoplasm pyruvate may enter mitochondria if oxygen available – breaks pyruvate down completely to CO2 and water generating an additional 34 to 36 ATP – aerobic respiration each step (reaction) is catalyzed by an enzyme

6 products are 2 molecules of ATP and 2 molecules of NADH
nicotinamide adenine dinucleotide – an electron carrier that transports energy in form of energetic electrons - Coenzyme electrons are held in high-energy outer electron shells – NAD+ NADH donates the electrons and their energy to other molecules hydrogen ions are often picked up simultaneously

7 formed through oxidation/reduction reactions – involves two complementary reactions
oxidation – liberates energy from the oxidation substance; results from the removal of one more electrons, alone or with H+ reduction – stores energy in a reduced compound; reduction results from addition of one or more electrons, alone or with H+

8 Glycolysis consists of two major sets of reactions:
Step 1 - glucose activation 2 ATP are used to convert stable glucose into highly unstable fructose bisphosphate (6 C)

9 Step 2 – Energy harvest fructose bisphosphate splits into two 3 C molecules of glyceraldehyde 3-phosphate (G3P or PGAL) each G3P molecule goes through series of reactions that convert it into pyruvate (pyruvic acid) 2 ATPs are made per G3P for a total of 4 – however, net gain is only 2 ATPs During these reactions, 2 high energy electrons and a H+ are added to NAD+ to form “energized” carrier NADH – 2 NADH are made (one from each G3P)


11 Fermentation In the absence of oxygen, pyruvate acts as electron acceptor from NADH producing ethanol or lactic acid – this process is called fermentation NADH production is not used as method to capture energy – used to get rid of hydrogen ions and electrons made when glucose is broken down NAD+ is regenerated by pyruvate acting as final electron acceptor - pyruvate may be converted to lactic acid (lactic acid fermentation – occurs in human muscles during strenuous exercise) or ethanol and CO2 (alcoholic fermentation)


13 Aerobic Respiration In presence of oxygen, oxygen is the electron acceptor (in the electron transport system) allowing pyruvate to be fully broken down (back into CO2 and water) to make even more ATP Aerobic Cellular Respiration – series of reactions, occurring under aerobic conditions, in which large amounts of ATP are produced – pyruvate is broken down into carbon dioxide and water – oxygen serves as final electron acceptor – each step catalyzed by enzymes

14 Aerobic Respiration occurs in the mitochondria
double membrane – inner folds are called cristae inner compartment contains fluid matrix intermembrane compartment separates the two membranes Mitochondria have their own DNA (circular chromosome) and ribosomes (70s – smaller than eukaryotic ribosomes)

15 Aerobic Respiration Step 1 – Glycolysis
Step 2 – Oxidative Decarboxylation two molecules of pyruvate produced by glycolysis are transported across both mitochondrial membranes into matrix each pyruvate is split into CO2 and a 2 C acetyl group which immediately attaches to coenzyme A to form acetyl CoA – during this reaction NADH is produced


17 Step 3 – Krebs Cycle (Citric Acid Cycle)
the acetyl CoA enter Krebs cycle by briefly combining with oxaloacetate to form citrate – coenzyme A is released to be reused Kreb’s cycle rearranges citrate to regenerate oxaloacetate giving off 2 CO2, 1 ATP and four electron carriers (1 FADH2 and 3 NADH) per pyruvate molecule (x2 per glucose molecule)



20 Electron Transport System (Oxidative Phosphorylation)
energetic electrons from NADH and FADH2 are used to generate more ATP (3 ATP are generated per NADH and 2 ATP per FADH2) located in inner mitochondrial membrane electrons move from molecule to molecule along transport system – energy released by electrons is used to pump hydrogen ions from the matrix across the inner membrane into the intermembrane compartment (used for chemiosmosis) at the end of the ETS, oxygen and hydrogen ions accept the electrons to form water – clears out transport system for more electrons to run through



23 Chemiosmosis hydrogen ions pumped across the inner membrane generate a large H+ concentration gradient (high concentration in intermembrane compartment and low concentration in matrix) inner membrane is impermeable to hydrogen ions except at protein channels that are part of ATP-synthesizing enzymes (ATP synthase) - whole thing is called the F1 complex during chemiosmosis, hydrogen ions move down the concentration gradient from intermembrane compartment to matrix by means of the F1 complex the flow of hydrogen ions provides energy to synthesize 32 – 34 ATPs from ADP


25 Coupled Reactions Many steps involved in respiration are coupled - reactions in which exergonic reactions drive endergonic reactions Some reactions occur together with two reactions sharing a common intermediate molecule

26 Metabolism of Fats and Proteins
cells can extract energy from fats and proteins breakdown of fat and proteins creates products that can be fed into the enzyme pathways of respiration Fats starts with hydrolysis into glycerol and fatty acids glycerol is converted into G3P and enters pathway fatty acids are converted into acetyl-CoA and enter pathway Proteins amino acids are broken down in a number of ways the amino group is first removed (deamination) some amino acids are converted into pyruvic acid, some into acetyl-CoA, and some into other compounds in the Krebs cycle


28 Body Temperature and Metabolism
cellular respiration captures energy in the bonds of ATP however, much of the energy is lost as heat (approx 60% of energy available is lost) the majority of animals and plants quickly lose this thermal energy to the environment – referred to as poikilothermic (“of variable heat”) or ectothermic (“externally heated”) body heat comes from external sources, body temp fluctuates with environmental temp metabolic rate (organism’s rate of oxygen consumption or release of CO2) increases with temp (enzymes more active at higher temps) ectotherms are more active with higher temps and sluggish with lower temps many have behavioral adaptations to assist with temp control (basking)

29 Mammals and birds (and some other organisms) make use of heat produced during metabolism – have evolved mechanisms to conserve heat (insulation with fat, hair, feathers) endothermic (“internally heated”) – have fairly high body temps (higher than environment) tend to maintain fairly constant body temp – homeothermic even when environmental temp fluctuates metabolic rate stays fairly constant

30 metabolic rate is inversely related to body size in both endo and ectotherms
endothermic, smaller animals have a higher surface area-to- volume ratio and therefore a larger relative heat loss to the environment must have faster metabolism to replace heat – have to consume relatively large amounts of food metabolic rate is higher in smaller ectotherms too but has never been fully explained as to why

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