chapter 7 - cellular resipiration and fermentation

heterotrophic

animals obtain energy by eating plants or other organisms

redox reactions

the transfer of electrons between reactants

• transfer of electrons releases energy stored in organic molecules

  • this is used to synthesize ATP

principles of redox

• oxidation - when a substance loses electrons (oxidized)

• reduction - when a substance gains electrons (reduced →becomes negatively charged)

electron donor

the substance that loses electrons (oxidized)

• called the reducing agent

electron acceptor

the substance that gains electrons (reduced)

• called the oxidizing agent

In cellular respiration…

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP (energy)

1. which is reduced

2. which is oxidized

1. Oxygen becomes reduced (gains H)

2. Glucose becomes oxidized (loses H)

energy harvest via NAD+

electrons (H) that are stripped from glucose (during glycolysis) travel with protons

• they are first transferred to NAD+ (coenzyme)

  • NAD+ becomes reduced after accepting the electron (H)

    • this forms NADH, which stores energy that will used to synthesize ATP

      • NADH passes the electrons to the electron transport chain

stages of cellular respiration

1. Glycolysis

2. Pre-citric acid cycle

3. Krebs cycle

4. Oxidative phosphorylation

glycolysis

“splitting of sugar”

• the breakdown of glucose into two molecules of pyruvate (C6H12O6 → C3H6O3 × 2)

  • occurs in the cytoplasm and does not require oxygen (anaerobic)

    • has two major phases: energy investment phase & energy payoff phase

glycolysis - step 1

• first investment of ATP

  • ATP gets hydrolyzed becoming ADP, where the third phosphate gets transferred onto glucose

    • this turns glucose (the substrate) into glucose-6-phosphate

      • all this is done with the Hexokinase enzyme

glycolysis - step 2

the enzyme, phosphoglucoisomerase, turns glucose-6-phosphate into fructose-6-phosphate

glycolysis - step 3

• second investment of ATP

  • takes a phosphate from another ATP (hydrolyzed) and transfers it onto fructose-6-phosphate

    • turns it into fructose-1,6-biphosphate

    • done by phosphofructokinase (enzyme)

regulation and stimulation of phophofructokinase

• Citrate from Krebs Cycle can inhibit this enzyme

  • telling it to stop prouction because there is a lot of it already

• AMP (Adenosine Monophosphate) can stimulate the enzyme

  • telling it to produce more of it's product

glycolysis - step 4

• splits fructose-1,6-biphosphate into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate

  • done by the enzyme aldolase

glycolysis - step 5

• isomerase turns dihydroxyacetone phosphate into glyceraldehyde-3-phosphaste

  • glyceraldehyde-3-phosphate and dihydroxyacetone phosphate are isomers.

    • isomerase just turns it into it's isomer

glycolysis - step 6

both glyceraldehyde-3-phosphates loses their electrons

• both electrons get transferred onto 2 NAD+

  • turns it into 2 NADH and an additional 2 H

  • while both glyceraldhyde-3-phosphate turns into 1,3-biphosphoglycerate (after losing their electrons)

    • they gained inorganice phosphates (phosphates found in the system)

glycolysis - step 7

the payoff step (overall gain is 0 → invested 2 → got 2)

• 2 1,3-biophosphoglycerate loses one of their phosphates

  • those 2 phosphate lost gets transferred onto ADP creating 2 ATP

    • this turns them into 3-phosphoglycerate

      • done by phosphoglycerokinase

      • this reaction is substrate level phosphorylation

substrate level phosphorylation

where a phoshpate group is directly transferred from a substrate to an ADP to form ATP

glycolysis - step 8

phosphoglyceromutase moves the phosphate on both 3-phosphoglycerate to the 2nd carbon

• turns it into 2 2-phosphoeglycerate

glycolysis - step 9

produces 2 water

• enolase converts 2 2-phosphoglycerate into 2 phosphoenolpyruvate

  • by product is water

glycolysis - step 10

2 phosphoenolpyruvate loses it's phosphates, which gets directly transferred to ADP

• creates 2 ATP (substrate level phosphorylation)

  • pyruvate kinase performs this reaction

    • the 2 phosphoenolpyruvate then becomes 2 pyruvate

glycolysis net yield

• 2 pyruvate → goes to mitochondria

• 2 ATP (substrate level)

• 2 H2O

• 2 NADH (goes straight to Oxidative phosphorylation)

pyruvate oxidation (pre-citric acid cycle)

• In the presence of O2 (aerobic), pyruvate enters the mitohondria's matrix

  • before the acid cycle begins, pyruvate must be converted into Acetyl CoA

    • this links the citric cycle to glycolysis

Acetyl CoA…

• It is an highly reactive molecule and contains a unstable bond

  • this is used in the first step of Krebs Cycle

Conversion fo pyruvate into Acetyl CoA

• 2 Pyruvate enters the mitochondria with a transport protein

  • Coenzyme A then gets added to each Pyruvate

    • as this Co-A gets added..

    • each pyruvate (which has 3 carbons), loses one carbon that becomes CO2

    • NAD+ comes and pulls hydrogen ions off of each pyruvate to form 2 NADH’s and 2H+

Krebs Cycle - step 1(CITRATE)

• When Acetyl CoA enters the cycle it fuses with Oxaloacetate

  • They can fuse together by enzyme, Citrate Synthase, to create CITRATE

    • Citrate is a 6 cabron molecule used as a substrate with the next step.

Citrate Synthase Regulation/Regulators

• Can be regulated

  • ATP can inhibits this enzyme which tells it to stop the cycle because there is enough energy

    • NADH can also inhibit this enzyme which tells it there is enough energy supply to form lots of ATP

      • Citrate also inhibits the enzyme becuase there is a lot a citrate

        • Succinyl CoA inhibits the enzyme by basically saying there is already a lot of it.

          • These are regulators of Citrate Synthase

Citrate Synthase Stimulator

• When the body uses lots of ATP

  • this creates lots of ADP and inorganic phosphates

    • ADP can stimulate the enzyme to create more Citrate which begins the cycle to create more NADH & FADH supply, which makes more ATP (energy)

Krebs Cycle - step 2 (IS)

• Citrate from step 1 gets converted into Isocitrate

  • This is an isomerization reaction

    • shuffles the hydrogens and carbons around

      • Isocitrate can also turn back into Citrate when there is too much of it

      • All this is done by the enzyme Aconitase

Krebs Cycle - Step 3 (KREBS)

• Isocitrate gets converted into a-Ketoglutrate

  • The molecule loses one carbon which means it is released as CO2

    • a-Ketoglutrate is a 5 carbon molecule

      • This is done by an enzyme by Isocitrate Dehydrogenase

        • Dehydrogenase indicates that NAD+ is being reduced (making NADH) → Redox Reaction

Isocitrate Dehydrogenase Regulator

If there is a lot of ATP..

• It will inhibit the enzyme

Isocitrate Dehydrogenase Stimulators

• Presence of ADP will increase the production rate of this enzyme

  • Calcium is also a stimulator

    • Helps make more ATP because it is needed for contractions

Krebs Cycle - Step 4 (STARTING)

• a-Ketogluterate gets converted into Succinyl CoA which is a 4 carbon molecule with a CoA on it

  • means it releases CO2 and a CoA enzyme added to it

    • Done by a-Ketogluterate Dehydrogenase enzyme

      • which then means NAD+ gets reduced into NADH (Redox Reaction)

a-Ketogluterate Dehydrogenase Regulators

• Succinyl CoA can inhibit it if there is too much of it

• NADH can also inhibit it if there is too much NADH

a-Ketogluterate Dehydrogenase Stimulator

• Calcium will also stimulate this enzyme

Krebs Cycle - Step 5 (SUBSTRATE)

• Succinyl CoA loses it's CoA and turned into Succinate

  • When CoA is released it generates some energy

    • GDP and an inorganic phosphate fuses to form GTP

      • ADP comes by and takes a phosphate from GTP to form ATP

        • GTP then returns to GDP

          • This is Substrate Level Phosphorylation

          • This is all done by Succinyl CoA Synthetase

            • It stimulates the substrate level phosphorylation

Krebs Cycle - step 6 (FOR)

• Succinate gets converted into Fumarate

  • FAD gets reduced into FADH2

    • This is done by Succinate Dehydrogenase

Krebs Cycle - step 7 (MAKING)

• Fumerate gets converted into Malate

  • Fumerase adds water into the reaction to convert fumerate

Krebs Cycle - step 8 (OXALOACETATE)

• Malate gets converted into Oxaloacetate

  • Done by Malate Dehydrogenase

    • which means NAD+ gets reduced into NADH

How many times does Krebs Cycle happen?

• 2 times

  • this is because we put in two Acetyl CoA to go through the cycle, meaning it happens twice

    • Which means all the products are multiplied by 2

Krebs Cycle Net Yield

• 4 CO2

• 6 NADH + 6H ions

• 2 FADH

• 2 ATP (Substrate Level Phosphorylation)

Krebs Cycle Pneumonic for each substrate

Citrate - Citrate

Isocitrate - Is

a-Keto

2 process in Oxidative Phosphorylation

1. Electron transport Chain

2. Chemiosmosis

where is the electron transport chain and what is it?

in the cristae of the mitochondria

• it is a multiprotein complex

does the electron transport chain generate atp?

no

what carries electrns to the electron transport chain?

NADH & FADH2

electron transport chain consists of how many proteins?

4 protein complexes with smaller proteins inside each one.

how does the electron transport chain work?

• NADH enters the first protein complex and becomes oxidized (NAD+) leaving behind electrons

• The second protein complex is where FADH2 enters becomes FAD leaving behind electrons

  • comes from Krebs Cycle and past steps

    • This area in the electron transport chain has the lowest electronegativity

• Electrons then are transported by a molecule to enter complex 3 and then exit through complex 4

  • when it exits the electrons get picked up by O2 and O2 combines with Hydrogen ions (from NADH) to create 4 H2O

    • This area is the most electronegative

what type of energy is released by electron transport chain

• it releases potential energy as electrons move through the transport chain

what is potential energy from the electron transport chain used for?

• It is used to create a hydrogen gradient

  • it pumps the hydrogen ions from the matrix (of the mitochondria) into the intermembrane space

    • high concentration of hydrogens gets moved into the intermembrane space

what is the overall purpose of the electron transport chain? is the reaction a burst or controlled?

to create a hydrogen gradient

• it is a controlled reaction meaning in a step wise action

what is the hydrogen gradient?

a difference in hydrogen concentration in the mitochondria

• crucial for cellular respiration/making ATP

  • it is also referred to as a proton-motive force → the capacity for it to do work (in chemiosmosis)

what is the net yield for electron transport chain?

• 0 ATP

• 4 H2O

what enzyme is used for chemiosmosis

ATP Synthase

what does ATP synthase do?

Synthesis of ATP

how does chemiosmosis work?

• Hydrogens that are present in the intermembrane space flows through the ATP synthase enzyme back into the matrix

  • the hydrogens is what pumps the enzyme to create ATP (like a water wheel for electricity)

    • While this happens ATP is synthesized

      • ADP and an inorganic phosphate get fused into ATP

        • This is oxidative phosphorylation

what is oxidative phosphorylation?

when an inorganic phosphate is added to ADP

• the phosphate is inorganic because it is just present someowhere in the mitochondria

how much ATP does chemiosmosis make?

either 26 ATP or 28 ATP

why can chemiosmosis create different amounts of ATP?

this is because it depends on the shuttle that carries the electrons

• Either 2 NADH or 2 FADH2

how much ATP do you get if the shuttle is NADH?

if the shuttle is NADH..

• 1 NADH = 2.5 ATP

  • because it enters the first complex it creates more ATP

    • So the 2 NADH shuttle would equal to; 2NADH x 2.5 = 5 ATP

      • this gets added to the ATP created from NADH's and FADH2's from Krebs Cycle, which is 23 ATP

        • So; 5 + 23 = 28 ATP (IF THE SHUTTLE IS NADH)

how much ATP would you get if FADH2 was the shuttle?

if FADH2 was the shuttle…

• 1 FADH2 = 1.5 ATP

  • it enters the second complex meaning it goes through less complexes, so less ATP

    • So the if FADH2 was the shuttle; 2FADH2 × 1.5 = 3 ATP

      • Which then gets added to 23 ATP we get from krebs cycle

        • 3 + 23 = 26 ATP

where do the electron shuttles come from?

they come from the 2 NADH that is formed in glycolysis

• the NADH cannot enter the mitochondria by itself, so it needs a shuttle to help it.

  • the shuttle can either be NADH or FADH2

overall how much ATP does cellular respiration make?

• 2 from glycolysis (Anaerobic)

• 2 from Krebs Cycle (Aerobic)

• 26 or 28 from Chemiosmosis

  • OVERALL: 30 or 32 ATP

what is fermentation?

the process of making ATP without O2 (Anaerobic)

• done through repeated glycolysis

what processes does fermentation consist of?

• glycolysis

• reactions that regenerate NAD+, which can be reused by glycolysis

two common types of fermentation

1. alcohol fermentation

2. lactic acid fermentation

what happens in alcohol fermentation and what is it used for?

• 2 pyruvate from glycolysis is converted into 2 Acetaldehyde into 2 ethanol

  • CO2 is released when pyruvate gets converted

  • this type of fermentation (by yeast) is used in brewing, winemaking, and baking

what is the acetaldehyde and what does it do?

it is a derivitave that comes from the pyruvate, which can accept electrons from NADH, formed in glycolysis, and oxidize it back to NAD+

• this allows for glycolysis to happen again

what happens in lactic acid fermentation and what is it used for?

• 2 pyruvate, from glycolysis, gets converted into lactate

  • this realese no CO2

    • this fermentation is done by some fungi and bacteria which is used to make cheese and yogurt

do humans use lactic acid fermentation?

yes they do!

• the human cells use this to generate ATP when O2 is scarce (low oxygen)

  • this is when muscles shift from cellular respiration during intense workouts when the body is using a lot of oxygen to create more ATP

how does lactic acid fermentation regenerate NAD+?

it regenerates NAD+ by using pyruvate itself as an electron acceptor

• which allows NADH to oxidize by to NAD+

  • this then turns pyruvate into lactate

how much ATP does fermentation produce?

2 per glucose molecule

• glycolysis creates 2 ATP each time