1

CHAPTER 9 – CELLULAR RESPIRATION

Cellular Respiration → breaking down food to get ATP

2

MITOCHONDRIA

Intermembrane Space

The mitochondria is the organelle responsible for cellular respiration. The Krebs cycle and also the ETC take place here to produce ATP. It is a double membrane with the inner membrane highly folded (to increase surface area and make the mitochondria more efficient.

POWERHOUSE OF THE CELL!!

3

Organic compounds possess potential energy as a result of the arrangement of electrons in the bonds between their atoms.

Enzymes catalyze the systematic degradation of organic molecules that are rich in energy. Some of the released energy is used to do work; the rest is dissipated as heat.

Fermentation, leads to the breakdown of sugars without the use of oxygen (anaerobic.)

A more efficient catabolic process, aerobic respiration, consumes oxygen as a reactant.

Although cellular respiration technically includes both aerobic and anaerobic processes, the term is commonly used to refer only to the aerobic process.

4

CELLULAR RESPIRATION – BACKGROUND INFO Carbohydrates, fats, and proteins can all be used as

the fuel, but it is most useful to consider glucose: Equation - C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP + heat) The catabolism of glucose is exergonic, with G =

−686 kcal per mole of glucose.

5

OXIDATION AND REDUCTION

Reduction – Gaining an electron; becomes more negative (hint: usually it gains a H+ too to keep it neutral – so look for the one that got a hydrogen added to it)Oxidation – Loses an electron; becomes more positive

In Cellular Respiration, Glucose is oxidized and Oxygen is reduced. Reducing agent = the thing that gets oxidized (glucose!)Oxidizing agent = the thing that gets reduced (oxygen!)

Note: Look at the proximity of the electrons; they lose potential energy as they get closer to the electronegative atoms.

6

ELECTRONS “FALL” CLOSER TO OXYGEN USING THE ETC AND NADH

NADH shuttles electrons from the food to the ETC

Glucose → NADH → ETC → Oxygen

NAD+ = oxidized form NADH = reduced form (note the

H on the end!)

NADH = nicotinamide adenine dinucleotide (nicotinamide is a nitrogen base that is NOT found in DNA or RNA)

Controlled release of energy in steps via the ELECTRON TRANSPORT CHAIN (ETC)!

7

GENERAL OVERVIEW – CELLULAR RESPIRATIONGlycolysis → in cytosol; turns glucose to 2 pyruvate, net gain of 2 ATP and 2 NADH; anaerobicKrebs (Citric Acid Cycle) → in mitochondrial matrix; 1 glucose powers 2 turns of Krebs, makes little ATP, NADH, and FADH2 (electron taxis); passes e- to ETCETC → uses oxidative phosphorylation (concentration gradients and chemiosmosis) to make lots of ATP

Intermediate Step Pyruvate gets transported into the mitochondria and gets converted into Acetyl-CoA, thereby losing a Carbon and releasing CO2 during this step; Acetyl CoA enters the Krebs

8

OXIDATIVE PHOSPHORYLATION VS. SUBSTRATE LEVEL PHOSPHORYLATION

Substrate Level Phosphorylation → when the P from one molecule gets attached to ADP to make ATP; it gets directly added on; ATP is made this way in glycolysis and the Krebs

Oxidative Phosphorylation → uses a concentration gradient to power chemiosmosis; 90% of the ATP is made this way; very efficient; used in the ETC

9

GLYCOLYSISMain Goal of Glycolysis is to turn glucose into two pyruvate: - Series of 10 steps Two

phases: Energy Investment and Energy Payoff

- Produces a net gain of 2 ATP and 2 NADH (e- carriers)

- From here it can go to the Krebs cycle (aerobic respiration) or to Fermentation (anaerobic)

- Does NOT release any 02 - Occurs in the cytosolOverall: Glucose → 2 Pyruvate;

net gain 2 ATP and 2 NADH

Glycolysis is ANAEROBIC….does NOT require oxygen!!

10

GLYCOLYSIS – ENERGY INVESTMENT PHASE

Glucose → Glucose – 6 – phosphate → Fructose-6- phosphate → Fructose- 1, 6 – biphosphate → G3P

In the energy investment phase, 2 ATP are put into the process.

11

GLYCOLYSIS – ENERGY PAYOFF PHASE

In the energy payoff phase, 4 ATP are produced (net gain of 2) and 2 NADH are made (to be shipped to the ETC).

G3P → 1, 3 – biphosphoglycerate → 3-phosphogylcerate → 2- phosphoglycerate → Phosphoenolpyruvate → Pyruvate

12

INTERMEDIATE STEP Pyruvate (made in the cytosol via glycolysis) gets transferred into the mitochondria (active transport!). As it comes in, it loses a carbon (goes from 3C to 2C) when it produces one molecule of CO2. This new 2C molecule is acetyl CoA. Acetyl CoA is what goes into the Krebs cycle. Also, 1 molecule of NADH is made per pyruvate (so….2 per glucose). Specific Steps of the Intermediate Step:

1. A carboxyl group is removed from the pyruvate as CO2.

2. The remaining two-carbon fragment is oxidized to form acetate. An enzyme transfers the pair of electrons to NAD+ to form NADH.

3. Acetate combines with coenzyme A to form acetyl CoA. This is what enters the krebs cycle.

So…summary of intermediate is - 1 glucose 2 acetyl CoA

- 2 CO2 made for each glucose (b/c 2 pyruvate)

- 2 NADH made for each glucose

13

KREBS/ CITRIC ACID CYCLEMain Function of the Krebs → to make electron carriers (NADH and FADH2) to send to the ETC

Series of 8 steps; Occurs in the mitochondrial matrix

So…1 glucose produces: 2 ATP6 NADH2 FADH2

(remember: 1 glucose = 2 pyruvates)

**Also 2 CO2 released per turn (so 4 for one glucose)Acetyl CoA becomes acetate and that enters the Krebs and combines with oxaloacetate for form citrate (hence citric acid cycle)

14

Krebs →Makes 1 ATP, 3 NADH, and 1 FADH2 per turn

The acetyl group of acetyl CoA joins the cycle by combining with the compound oxaloacetate, forming citrate.The next seven steps decompose the citrate back to oxaloacetate.

15

ELECTRON TRANSPORT CHAIN (ETC)

Occurs on the inner membrane of the mitochondria (highly folded to increase SA); Energy from NADH and FADH2 power ATP synthesis

The ETC is a series of proteins throughout the membrane; the electrons lose energy every time they get passed down the chainElectron carriers in the chain:

FlavoproteinIron-Sulfur ProteinLipids (Ubiquinone Q)Cytochromes (iron prosthetic

group)

OXYGEN IS THE FINAL ELECTRON ACCEPTOR!!! → oxygen combines with the electrons and H+ to make WATER

Electron carriers flip between reduced and oxidized versions as they accept and donate electrons.

16

Main Goal of the ETC → it’s a stepwise free energy drop from food to oxygen; it creates a proton gradient that powers chemiosmosis to create ATP via oxidative phosphorylation (the ETC makes no ATP directly)

Note: NADH drops off its electrons at a higher level than FADH2 because their electrons carry more energy. The ETC uses energy from the electrons and pumps the protons OUT of the matrix into the intermembrane space; it then diffuses back in via ATP synthase.

17

CHEMIOSMOSIS

Definition → energy coupling mechanism that uses energy stored in the form of a H+ gradient across a membrane to drive workHow it works → as the electrons move down the ETC, the proteins pump H+ OUT of the matrix and then they use ATP Synthase to allow the H+ to diffuse back in. As the H+ diffuse back in, the ATP Synthase proteins make ATP

As electrons flow down the ETC, H+ are pumped FROM THE MATRIX into the INTERMEMBRANE SPACE, and the H+ diffuse BACK INTO the matrix via the ATP SYNTHASE

18

ATP SYNTHASEATP Synthase is a protein that is powered by the H+ gradient and converts ADP to ATP. It works like a water wheel and forces a conformational change which activates the catalytic sites on ADP to bond with P to form ATP.

This is how ATP is produced = CHEMIOSMOSIS

19

-NADH and FADH2 drop off e- to the ETC-As the e- get passed down the chain, they lose energy; that energy is used to pump H+ OUT of the matrix into the intermembrane space-This creates a concentration gradient-The protons then diffuse back INTO the matrix via the ATP synthase (chemiosmosis); this creates ATP (oxidative phosphorylation)-Makes a TON of ATP!!!

Final e- acceptor after they go down the ETC is OXYGEN (from the atmosphere) …it combines with e- and H+ to make WATER

20

CELLULAR RESPIRATION OVERVIEW

ATP Summary → Substrate Level Phosphorylation – 4 ATP (2 from Glycolysis and 2 from Krebs); Oxidative Phosphorylation – 34 ATP (from ETC)

Efficiency of Respiration →34% efficient (66% of energy is lost as heat)

21

CELLULAR RESPIRATION VS. FERMENTATION

Oxygen Present → Aerobic Respiration (efficient!)

Oxygen NOT Present → Fermentation (not efficient)

22

FERMENTATION If there is no oxygen present

(anaerobic) the pyruvate (from glycolysis) goes to fermentation

The main goal of fermentation is to make NAD+ to put back into glycolysis; it makes NO ATP on its own (it just keeps glycolysis going so that it can make 2 ATP at a time)

Occurs in cytosol 2 types of fermentation: alcohol and

lactic acid

23

ALCOHOLIC FERMENTATION

- Pyruvate is turned into ethanol

- CO2 is released (bubbles!)

- Done by yeast for brewing, baking, wine-making

3C Pyruvate → 2C Ethanol

Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP

24

LACTIC ACID FERMENTATION- Pyruvate is turned into Lactate

(or lactic acid)- Lactate is eventually carried

away by the blood to the liver where it gets converted back into pyruvate

- The waste product, lactate, was previously thought to cause muscle fatigue and pain, but recent research suggests instead that it may be increased levels of potassium ions (K+)

- No CO2 is released

3C Pyruvate → 3C Lactate

Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP

25

LACTIC ACID VS. ALCOHOL FERMENTATION

Both start with pyruvate from glycolysis

Alcohol makes ethanol and gives off CO2

Lactic acid makes Lactic acid and does NOT give off CO2

Both create NAD+ to be sent back to glycolysis

Neither make any ATP on their own

26

FERMENTATION - OVERVIEWObligate Aerobes → needs oxygen; can do respiration only

Obligate Anaerobes → will not survive in the presence of oxygen; fermentation only

Facultative Anaerobes → can live with or without oxygen (if given the choice they will use the oxygen to do respiration because it is so much more efficient); can do cellular respiration or fermentation; ex. Human muscle cells

Respiration is 19 times more efficient than fermentation (38 ATP vs. 2 ATP)

27

The role of glycolysis in both fermentation and respiration has an evolutionary basis

Ancient prokaryotes likely used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere.

The evidence suggests that this pathway evolved very early in the history of life on Earth.

28

WHAT KINDS OF FOOD CAN GO INTO GLYCOLYSIS? A VARIETY OF MOLECULES CAN BE USED TO MAKE

ATPCarbohydrates → get broken down into their monomers and then those monomers get converted to glucose; glucose is then turned into pyruvate during glycolysis

Proteins → are broken down to their individual amino acids and then the amino groups are removed (called deamination – this nitrogen waste is then excreted as urea or ammonia); the remaining carbon skeletons are then put into glycolysis and the krebs cycle

Fats → glycerol is converted into glyceraldehyde phosphate (G3P) which is an intermediate of glycolysis; the FA chains are broken down into 2C components that enter the Krebs as acetyl CoA (called beta oxidation)

29

FEEDBACK MECHANISMS

OF RESPIRATION

Phosphofructokinase (PFK) sets the pace for respiration - It is STIMULATED by AMP and ADP - It is INHIBITED by ATP and by citrate (first product of Krebs)

This ensures that we are only making as much ATP as we need and not extra that is just getting wasted.

PFK is regulated allosterically by the above molecules.

30

CELLULAR RESPIRATION ANIMATION 6 minutes

https://www.youtube.com/watch?v=-Gb2EzF_XqA