Cellular Metabolism Flashcards
heterotrophic organisms
derive energy by breaking down the organic molecules made by plants and using power held in the bonds of the molecules
autotrophs
organisms capable of using suns energy to create organic molecules like glucose that can store that energy in their bonds
- plants through anabolic process of photosynthesis
- take light energy, release heat to make organic compounds, which those compounds are taken in by heterotrophs (heat is released again) to make atp
energy flow for both autotrophs and heterotrophs
- autotrophs form glucose by breaking bonds (c-o) in CO2 and breaking bonds (o-h) in H2O
- atoms rearranged into glucose and energy is stored in chemical bonds being formed
- THE SUNS ENERGY POWERS PHOTOSYNTHETIC REACTIONS, THIS FORMATION OF GLUCOSE IS ENDOTHERMIC
- -> 6CO2 + 6H2O + energy -> glucose + 6O2
- heterotrophs free this energy in bonds by breaking bonds and using the energy to do work = cellular respiration (previous equation in reverse)
- ** energy is lost in the form of heat for both photosynthesis and cellular respiration
ATP (energy carrier)
- adenosine triphosphate is primary energy currency of cell
- generated during glucose catabolism (cellular respiration)
- consists of nitrogenous base adenine, sugar ribose, and 3 phosphate groups (ribose 2 degree carbon bound to a hydroxyl group
- -> actual energy is store in high energy phosphate bonds (covalent bonds, all very negatively charged, lots of energy stored in them)
- can be broken down into ADP and inorganic phosphate OR AMP and pyrophosphate (PP) -> release of energy is 7 kcal/mol
- glucose catabolism (breakdown) provides this energy needed to remake ATP
- -> ADP + P + 7 kcal/mol -> ATP
NAD+ and FAD (energy carriers)
- nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD) are coenzymes capable of ACCEPTING HIGH ENERGY ELECTRONS during glucose oxidation (these two are reduced RIG)
- by passing through the electron transport chain, ATP can be generated using their captured stored energy
- when accept hydride ions (H) during glycolysis and Krebs cycle, they are reduced to NADH and FADH2 —> carried to etc. in mitochondria and liberated t make ATP
glycolysis - glycolytic pathway
-series of reactions that break down glucose into two smaller organic molecules
-pathway occurs in CYTOPLASM in presence or absence of oxygen
-inputs: 6 carbon glucose
-outputs: 2 molecules of three-carbon pyruvate
-atp inputs: 2
-atp outputs: 4 —> NET OF 2 ATP OUTPUT
-direct generation of ATP from ADP and P is called substrate-level phosphorylation
-NAD+ is reduced twice to NADH
–>input: 2 NAD+ and output: 2 NADH
KEY: steps 5-9 occur twice per molecule of glucose
equation: glucose + 2 ADP + 2 P + 2 NAD+ -> 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
Pyruvate then has 2 potential outcomes
- aerobic env (with oxygen) pyruvate undergoes further oxidation in mitochondrial electron transport chain
- anaerobic env (w/o oxygen) pyruvate undergoes oxygen free process called fermentation
Fermentation
- a way to regenerate NAD+
- reduces pyruvate to either ethanol or lactic acid
- -> reduce pyruvate (gains electrons) and oxidize NADH (loses electrons) back to NAD+ so can recycle it for more glycolysis
Alcohol Fermentation
occurs in yeast and some pacteria
-pyruvate decarboxylated to acetaldehyde which then gets reduced by NADH to ethanol
Pyruvate (3C) -> CO2 + Acetaldehyde (2C)
Acetaldehyde (2C) + NADH + H+ -> Ethanol (2C) + NAD+
Lactic Acid Fermenation
- many glucose molecules put through glycolysis which gives 2x as many molecules of pyruvate and NADH
- pyruvate and NADH builds up (less and less NAD+ which we need)
- to keep muscles working pyruvate is reduced to lactic acid (gains electrons) and NADH is oxidized back to NAD+
Pyruvate(3C) + NADH + H -> Lactic acid + NAD+
cellular respiration
- most efficient way to do glucose catabolism
- generates 36-38 atp per molecule of glucose
- aerobic process using electron transport chain with oxygen being final electron acceptor
- occurs some in cytoplasm and in mitochondria
pyruvate decarboxylation
- first step in aerobic respiration
- does not require oxygen, but only occurs once the cell commits to aerobic respiration and that commitment made only in presence of pxygen
- pyruvate transported from cytoplasm into the mitochondrial matrix where it is decarboxylated (LOSES A CO2)
- the remaining acetyl (2C) group is bound to coenzyme A to form acetyl-CoA
- 2 NAD+ molecules are reduced per molecule of glucose
- **key: started with 6 carbons, 3 in each pyruvate, left with 2 acetyl-CoA molecules that have 2 carbons each, and release the other 2 carbons as CO2 molecules
1 glucose => 2 Pyruvate (3c) +2 CoA + 2 NAD+ -> 2 NADH + 2 Acetyl-CoA (2c) + 2 CO2(1c)
energy: 2 atp (glycolysis) 2 NADH (glycolysis) 2 NADH (pyruvate decarboxy)
Citric Acid Cycle (Krebs Cycle)
- starts with combination of acetyl-CoA (2c) and oxaloacetate (4c) to generate citrate (6c)
- through 8 rxns 2 molecules of CO2 are released (lose 2 c) and oxaloacetate is regenerated
- each turn of cycle makes 1 ATP via substrate-level phosphorylation and a GTP intermediate
- value of cycle is its ability to make high energy electrons that are carried by NADH and FADH2
- for each molecule of acetyl-CoA that enters cycle, 3 NADH and 1 FADH2 produced
- KEY: the cycle turns twice for each molecule of glucose because 1 molecule of glucose creates 2 acetyl-CoA molecules
2x3 NADH = 6 NADH 2x1 FADH2 = 2 FADH2 2x1 GTP (ATP) = 2 ATP
these coenzymes then bring electrons to etc where more atp is created via oxidative phosphorylation
overall reaction for 2 rounds of cycle:
2 acetyl-CoA + 6 NAD+ + 2 FAD + 2 GDP + 4 H2O -> 4 CO2 + 6 NADH + 2 FADH2 + 2 ATP + 4 H + 2 CoA
energy: 2 atp (glycolysis) 2 NADH (glycolysis) 2 NADH (pyruvate decarbox) 6 NADH (TCA cycle) 2 FADH2 (TCA cycle) 2 ATP (TCA cycle)
carbon input of 4, 2 in each acetyl-CoA
carbon output of 4, 2 leave in each turn via CO2, 2 turns
NO useful organic products are leftover
Electron Transport Chain (etc) - electron transfer
- oxidation phosphorylation process that electrons from NADH and FADH2 are passed along an assembly line of carriers that release free energy with each transfer
- carriers are enzymes known as cytochromes, each contain central iron atom that can undergo reversible redox reactions as electrons bind and release
- 3 major complexes of cytochromes
1. nadh dehydrogenase (complex 1) - NADH gives its electrons directly to FMN in complex 1, then passed to carrier Q (small hydrophobic molecule) which passes electrons to complex 3
2. b-c complex (complex 3) - donates e to complex 4
3. cytochrome oxidase (complex 4)
NADH generates 3 ATP molecules
oxygen takes electrons from cytochrome a3, protein in complex 4, along with two protons to create water –> 2 H + 2 e- + 1/2 O2 => H2O (oxygen is the final electron acceptor in the etc and result is formation of water)
FADH2 only make 2 at molecules because electrons given directly to complex 2, which give to carrier Q, and rest of pathway is same as NADH
–> FADH2 electrons travel shorter distance to get to oxygen and less energy is extracted from them (only get 2 ATP)
MAIN FUNCTION OF ETC IS TO MOVE H OUT OF THE MITOCHONDRIAL MATRIX INTO THE INTERMEMBRANE SPACE
cyanide will block the final transfer of elecrons to O and DNP destroys the mitochondrions ability to generate useful proton gradient necessary for ATP generation
ATP generation and the proton pump
-a proton gradient across the inner mitochondrion membrane links the oxidation of NADH and FADH2 to ADP phosphorylation
-as carriers give up electrons, protons passed into mitochondrial matrix where they accumulate
-etc then pumps these ions out of the matrix into intermembrane space at each of the maor protein complexes
-the accumulation of H in the intermembrane space makes it both positively charged and acidic
-the electrochemicial gradient drives H passively back across the inner mitochondrial membrane into the mitochondrial matrix via ATP synthases -> known as the proton-motive force
~~as H ions pass through these specialized channels back into the matrix, the energy released allows for the phosphorylation of ADP back to ATP – known as oxidative phosphorylation
ATP synthase generates ATP from ADP and inorganic phosphate by allwing high-energy protons to move down the concentration gradient created by the ETC
Review
- overall generation of energy in glucose catabolism comes from substrate level phosphorylation and oxidative phosphorylation
- total amount of ATP generated depends on these wo processes and how much of each occurs
- substrate level phosphorylation: degradation of one molecule of glucose will yield a net of 4 atp (2 net atp from glycolysis and 1 atp per turn of the TCA cycle)
- oxidative phosphorylation: pyruvate decarbox yields 2 NADH (1 per pyruvate), each turn of TCA gives 3 NADH and 1 FADH2 -> 6 NADH and 2 FADH2 because do 2 turns per molecule of glucose
- EACH NADH can make 3 ATP per molecule except the two from glycolysis - these two cant enter mitochondrial membrane and instead give their electrons directly to carrier Q so they only generate 2 ATP each
NADP to ATP totals: 4 from glycolysis (2 NADH) 6 from pyruvate decarbox (2 NADH) 18 from TCA cycle (6 NADH, 3 per turn) 28 total
FADH2 TO ATP totals:
2 total formed, 2 atp each -> 4 ATP total
total: 36 atp
