Kreb cycle + ETC & efficiency: 1/2 4.2 + 4.3

Who discovered the Krebs Cycle

Sir Hans Krebs

What does the citric acid cycle consist of?

8 enzyme-catalyzed reactions

• 7 in the mitochondrial matrix

• 1 that bind to the matrix side of the inner mitochondrial membrane

What is produced from the Krebs Cycle?

• oxidation of acetyl groups to CO2

• Synthesis of ATP, NADH, & FAD (Flavin adenine dinucleotide, gets reduced to FADH2)

What is produced when an acetyl-CoA enters the Krebs cycle?

3NADH, 1 FADH2, & ATP (substrate-level phosphorylation)

In a complete turn of the kerb cycle what happens?

2-carbon acetyl is consumed & 2CO2 molecules released 2CO2

• all glucose carbon turn to CO2

Net reactant and products of Krebs cycle:

acetyl-CoA + 3NAD+ + FAD + ADP + Pi → 2CO2 + 3NADH + 3H+ + FADH2 + ATP + CoA

Krebs cycle reaction 1:

Acetyl-CoA transferred to oxaloacetate

• 2-carbon acetyl group carried by CoA tranfers it to oxaloacetate to make citrate helped by citrate synthase

• H2O released

Krebs cycle reaction 2:

Isomerization

• Citrate is rearranged to its isomer isocitrate w/the help of aconitase

Krebs cycle reaction 3:

Redox, CO2 released, 1st NADH produced

• isocitrate oxidized to α-ketoglutarate

• 1 carbon removed & released as CO2

• NAD+ is reduced to NADH + H⁺

• helped by isocitrate dehydrogenase

Krebs cycle reaction 4:

Redox, CO2 released, 2nd NADH made

• α-ketoglutarate oxidized to succinyl CoA (CoA group gets added back)

• 1 carbons removed and released as CO2

• NAD+ reduced to NADH+ + H⁺

• helped by α-ketoglutarate dehydrogenase

Krebs cycle reaction 5:

CoA released, only ATP made

• CoA released from succinyl CoA makes succinate

• Energy released converts GDP(+ Pi) to GTP

• GTP converts to ADP to (Pi transfered) ATP by substrate-level phosphorylation

• helped by succinyl CoA synthetase

Krebs cycle reaction 6:

redox, FADH2 produced

• succinate oxidized to fumigate

• 2 e- & 2p removed from succinate transferred to FAD to make FADH2

• Helped by succinate dehydrogenase

Krebs cycle reaction 7:

adding water

• Fumerate converted to malate by adding a water molecule

• helped by fumarase

Krebs cycle reaction 8:

Redox, 3rd NADH made

• Malate oxidized to oxaloacetate

• Reduce NAD+ to NADH+ + H⁺

• oxaloacetate can react w/acetyl-CoA to re-enter the cycle

At the end of the Krebs cycle…

• orignal glucose completely dismantled

• original carbon & oxygen atoms are CO2 waste

• Only Hydrogen remains go original glucose molecules that new carried by NADH & FADH2

Purpose of the electron transport chain

extracts the energy in NADH & FADH2 and makes it available for making more ATP

• transferring e- from NADH & FADH2 to O2

4 protein complex in the electron transport chain:

1. Complex 1: NADH dehydrogenase

2. Complex 2: succinate dehydrogenase (made of a single proteins)

3. Complex 3: cytochrome complex

4. Complex 4: cytochrome oxidase

2 mobile electron shuttles that facilitate the flow of electrons:

1. Ubiquinone (UQ): hydrophobic molecules in the core of the membrane

   • transfer e- form complex 1 & 2 to complex 3

2. Cytochrome c (cyt c): in the intermembrane space side of the membrane

   • transfer e- form complex 3 to complex 4

Driving force behind electron transport

• complexes arranged in increasing electronegativity

  • cofactors in complex pull e- form upstream molecules and give to more electronegative downstream molecules

• O2 drives ETC by causing a chain reaction

  • e- carriers organized from high to low free energy, each component more electronegative than before

• electron carriers arranged from high to low free energy

terminal e- acceptor in the ETC?

Oxygen

• first carriers and NADH reduced til stable

• Oxygen interact with complex 4 & removes 2 e-

  • reacts with protons in matrix to produce 2 water

O2 & NADH

O2 stronger pull on e-

NADH weaker pull, more free energy which is used to pump protons from the matrix to intermembrane space across the inner membrane

Result of proton pumping across the inner membrane?

H+ conc. in the inter membrane space higher than in the matrix called proton gradient

Proton gradient DEF.

difference in proton concentration across a membrane, form of potential energy

What drives the complex proton pumps ?

electrons flowing though complexes

role of ubiquinone

• accept electrons form complex 1 & 2 & pick up protons form matrix

• after donating electrons to complex 3, UQ releases protons into he inter membrane space to become neutral

the difference in proton concentration across a membrane possesses ____

potential energy

The potential energy by a proton gradient is derived from 2 factors:

1. concentration of protons on either side of a membrane not equal

2. protons repel each other and attracted to the negative charge in matrix

called a proton-motive force

Proton-motive force def.

AKA electrochemical gradient

a force that moves protons because of a chemical gradient of protons across a membrane

• combination of a concentration gradient & an electrical potential gradient

chemisomosis def.

A process that makes ATP using the energy of an electrochemical gradient and ATP synthase

Where does the energy for chemiosmosis come from?

the electron transport chain that oxidizes energy-rich molecules like NADH

• proton-motive force also that pumps substances across membranes

Oxidative phosphorylation def.

Mode of ATP synthesis linked to oxidation of energy-rich molecules by the ETC

• relies on ATP sythase

ATP synthase components and location

spans the inner mitochondrial membrane and the headpiece goes into the mitochondrial matrix

Function of ATP synthase

move electrons from the intermembrane space to the matrix by proton-motive forces down its concentration gradient

How and why does the ATP headpiece rotate?

3 protons bind to sites in the headpiece causing it to rotate to crate ATP from ADP + Pi

What happens when the ETC and ATP synthase are uncoupled

Energy released in ETC does not make ATP, instead thermal energy released when p rush back across the inner membrane without passing the ATP synthase

One way uncoupling achieved

regulating the expression of various uncoupling protein

What does uncoupling e- transport cause?

causes the free energy to be released as thermal energy to regulate body temperature

• ex. brown adipose fat → has high a concentration of uncoupling protein in mitochondria. The thermal energy produced maintains body temperature in hibernating mammals

Another way uncoupling can be achieved

Ionophores can act a uncouplers by forming channels across membranes where ions including protein can leak

• causes high rates of electron transport and reduces ATP synthesis

• ex. 2,4-dinitrophenol (DNP), reduces ATP production and cells respond y consuming stored fat rapidly. can cause overheating and other side effects

Protons produced when 1 NADH oxidized?

10 protons

How many proton make 1 ATP?

3-4 protons

How many ATP made for 1 NADH oxidized?

3 ATP

How many ATP made for 1 FADH2 oxidized?

2 ATP bc passes complex one and less protons are pumped across membrane

Products when glucose is completely oxidized & entire H+ gradient used for ATP synthesis

10 NADH, 10 H+, & 2 FADH2

2 Shuttles that transfer electrons from NADH across inner member to matrix

1. Malate-aspartate shuttle

   • NADH oxidized to NAD+, electron transfer across membrane, used to reduce NAD+ to NADH in matrix

2. Glycerol-phosphate shuttle

   • Transfer of electronss across membrane from NADH to FAD to form FADH2 in matrix

     • less free energy & only make 2 ATP

Cells that use malate-aspartate shuttle, etc & oxidative phosphorylation make how much ATP

34 ATP

10 NADH x 3 = 30 ATP

2 FADH2 = 4 ATP

Maximum ATP produced in cellular respiration:

38 ATP

glucose = 2 ATP

Krebs = 2 ATP

ETC = 34 ATP

Total ATP, NADH, & FADH2 made in each stage of aerobic respiration

Glycolysis: 2 ATP, 2NADH

Pyruvate oxidation: 2NADH, 2CO2

Krebs: 6 NADH, 2 FADH2, 4CO2

Reason cellular respiration may not produce Max # of ATP

Energy from H+ may be lost due to uncoupling protein or used for other mitochondrial processes

How much energy in glucose is converted to ATP in cellular respiration

41%

hydrolysis of ATP: 31 KJ/mol (hydolysis of ATP)x 38 ATP = 1178 KJ/mol

1178kj/mol/2870kj/mol (energy glucose contains) x 100 = 41%

How are fluctuated demands of ATP accommodated?

Excess ATP stored in cells to make phosphorylate creatine

Equation for making creatine phosphate

creatine + ATP → creatine phosphate + ADP

Reverse reaction equation of creatine phosphate

creatine phosphate → ATP + creatine

• generates ATP fast

What happens when creatine phosphate depleted?

regenerated by ATP

Metabolic rate def.

Amount of energy is expanded per unit time in an organism

• = to rate of aerobic/anaerobic respiration

Basal metabolic rate (BMR) def.

Metabolic rate in kj/m2/h of an organism at rest

• energy consumption is about 60-70% of total daily energy used by human body

BMR & adipose tissue

higher % of adipose tissue = reduced metabolic rate

• ex. skeletal tissue resting metabolic rate is 3x than adipose tissue

2 ways metabolic intermediates are controlled in aerobic respiration:

1. Feedback inhibition

   • regulate supply and demand where end product of a pathway stops enzymes from earlier paths

2. Allosteric control or enzymatic activity

   • in glycolysis: Excess ATP bind to enzyme phosphofructokinase to inhibit action

     • reduced fructose -1,6 -phosphate and stop respiration

     • increase glycolysis & ATP production when ATP converted to ADP

   • In krebs: NADH, ATP, & citrate inhibit phosphofructokinase

     • build up of these cause increase in ATP, downstream reaction not moving as fast

Which stage do carbs enter aerobic respiration

glycolysis

• disaccharides broken down to monosaccharide by hydrolysis

• starches broke down to glucose monomers with amylase and digestive tract enzymes

• glycogen a complex carb is hydrolyzed by liver enzymes,es to make glucose-6-phosphate

Which stage do fats enter aerobic respiration

fat broken down to glycerol and fatty acids

glycerol: turns to G3P and goes into glycolysis

fatty acids: split into 2-carbon fragment that enter Krebs cycles are acetyl groups attached to CoA by fatty acid oxidization (beta-oxidation)

Beta - oxidation definition

A process where fatty acids are broken down into acetyl-CoA through catabolism

Which stage do protein enter aerobic respiration

protein hydrolyzed into amino group and the Amino group removed. Protein enter cellular respiration depending on R-group

• alanine → pyruvate

• leucine → acetyl group

• phenylalanine → fumarate that enter Krebs

Mass associated with carbs

carbs are extremely hydrophobic and have lots of water bond to them by H-bonds

• need 1 or more grams of water when eat “dry” sugar

• heavier than lipids as fuel

Mass associated with fats

hydrophobic

• 1g fat = 1g fuel

Building blocks form aerobic respiration

intermediates of glycolysis and Krebs used to assemble compounds which is why flexibility is needed

• ex. fatty acids can be source of energy by being oxidized to acetyl-CoA

  • acetyl-CoA can be removed from pathway and make fatty acid