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Cellular Respiration

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Cellular Respiration

1. Glycolysis

2. Oxidation of Pyruvate

3. Krebs Cycle

(2)

Glycolysis is only the start

Glycolysis

Pyruvate has more energy to yield

◆ 3 more C to strip off (to oxidize)

◆ if O

2 is available, pyruvate enters mitochondria

◆ enzymes of Krebs cycle complete oxidation of

sugar to CO2

2x

6 C

3 C

glucose → → → → → pyruvate

3 C

1 C

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(4)

Step 2: Oxidation of pyruvate

Pyruvate enters mitochondria

◆ 3 step oxidation process

◆ releases 1 CO2 (count the carbons!) ◆ reduces NAD → NADH (stores energy) ◆ produces acetyl CoA

Acetyl CoA enters Krebs cycle

where does CO2 go?

NAD NADH 3 C 2 C 1 C

pyruvate acetyl CoA + CO2

[

(5)

Pyruvate oxidized to Acetyl CoA

Yield = 2C sugar + CO2 + NADH

reduction

(6)

Krebs cycle

aka Citric Acid Cycle

in mitochondrial matrix8 step pathway

each catalyzed by specific enzyme

step-wise catabolism of 6C citrate molecule

Evolved later than glycolysis

does that make evolutionary sense?

bacteria →3.5 billion years ago (glycolysis)

free O2 →2.7 billion years ago (photosynthesis)

eukaryotes →1.5 billion years ago (aerobic respiration (organelles)

1937

|

1953

(7)

Step 3: Kreb’s Cycle

This happens twice for each glucose

molecule

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4C 6C 4C 4C 4C 2C 6C 5C 4C CO2 CO2 citrate acetyl CoA

Count the carbons and electron carriers!

x

2

3C pyruvate reduction of electron carriers NADH NADH FADH2 NADH ATP This happens twice for each glucose

(9)

So we fully oxidized

glucose

C6H12O6

CO2

& ended up with 4 ATP!

(10)

Krebs cycle

produces large quantities of

electron carriers

NADHFADH2

stored energy!go to ETC

(11)

Energy accounting of Krebs cycle

Net gain = 2 ATP

= 6 NADH + 2 FADH2

3 NAD + 1 FAD 3 NADH + 1 FADH2

1 ADP 1 ATP

2x

acetyl - CoA → → → → → → → → →

CO2

]

(12)

ATP accounting so far…

Glycolysis

2 ATP

Kreb’s cycle

2 ATP

Life takes a lot of energy to run, need to

extract more energy than 4 ATP!

(13)
(14)

Mitochondria

Double membrane

outer membraneinner membrane

highly folded cristae*

intermembrane space

matrix

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STAGE 4: Oxidative Phosphorylation

the very controlled breakdown of

glucose to produce ATP

(17)

PART A. Electron Transport Chain

a)

In the presence of oxygen, a series of (mostly) transport proteins built into the inner membrane is used to link electron transport to ATP synthesis.

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Electron transport chain

Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron flow Electron carrier

NADH NAD+

FADH2 FAD

H2O ADP ATP ATP synthase

H+ H+ H+

H+

H+ H

+ H+ H+ H+ H+ H+ H+ H+ H+ + P O2

Electron Transport Chain Chemiosmosis

(19)

b) The electrons arrive using electron carriers NADH and FADH2

◆ NADH is oxidized at NADH dehydrogenase, releasing

2 electrons

◆ FADH

2 is oxidized at ubiquinone (Q) releasing 2

(20)
(21)

But what “pulls” the

(22)

Electrons flow downhill

Electrons move in steps from carrier to carrier downhill to O2

each carrier more electronegative

controlled oxidation AND controlled release of

(23)

H2O NAD+ NADH ATP H+ H+ Controlled release of energy for synthesis of ATP Electron transport chain

2 O2

2e− 2e−

+

(24)
(25)

as they travel through, the pairs of

electrons are releasing energy which is used to move H+ from the matrix to the intermembrane space

- 3 protons for every NADH

(26)

At the end

the electrons have to reduce something! oxygen

◆ oxygen is reduced as it picks up 2 e and 2

protons (from matrix) to make _____

(27)

there are fewer protons in the matrix than in the intermembrane space

(28)

PART B: OXIDATIVE PHOSPHORYLATION

a) A proton-motive force (PMF) is set up

(29)

inner membrane is impermeable to H+

the electrochemical gradient is used to synthesize ATP as H+ move through the ATP synthase channel protein

(30)

b) Protons (H+) travel along the

concentration gradient through the ATP synthase

◆ ATP synthase turns and releases energy to

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(32)

ATP synthase

enzyme in inner membrane of

mitochondria

only channel permeable to H+

flowing H+ cause change in

shape of ATP synthase

enzyme and powers bonding of Pi to ADP

(33)

c) At the end

For every H+ proton through the ATP synthase channel 1 ATP is formed

◆ NADH yields 3 ATP

◆ FADH

2 yields 2 ATP

(34)
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How efficient is cellular respiration?

Only about 40% efficient.

In other words, a call can harvest about 40% of the energy stored in glucose.

(42)

Taking it beyond…

What is the final electron acceptor in

electron transport chain?

O

2

So what happens if O2 unavailable?

ETC backs up

ATP production ceases

cells run out of energy

(43)

Certain poisons interrupt critical events in cellular respiration

Various poisons

Block the movement of electrons

Block the flow of H+ through ATP synthase

Allow H+ to leak through the membrane

H+

H+

H+

H+

H+

H+ H+ H+ H+

H+ H+ H+ H+ O 2

H2O P ATP

NADH NAD+

FADH2 FAD

Rotenone Cyanide, carbon monoxide Oligomycin DNP ATP Synthase +2 ADP+

Electron Transport Chain Chemiosmosis

1 2

(44)

Peter Mitchell

Proposed chemiosmotic hypothesis

revolutionary idea at the time

1961

|

1978

1920-1992

(45)
(46)

Summary of cellular respiration

Where did the glucose come from?

Where did the O2 come from?

Where did the CO2 come from?

Where did the H2O come from?

Where did the ATP come from?

What else is produced that is not listed in this equation?

Why do we breathe?

(47)

Energy Yields

Glucose: 686 kcal/mol

ATP: 7.5 kcal/mol

7.5 x 36 = 270 kcal/mol for all ATP's

produced

270 / 686 = 39% energy recovered from

(48)
(49)

Anaerobic: Lactic Acid Fermentation

▪ occurs in humans and other mammals

◆ The product of Lactic Acid fermentation, lactic acid, is toxic to mammals

◆ This is the "burn" felt when undergoing strenuous activity

▪ The only goal of fermentation reactions is to convert NADH to NAD+ (to use in glycolysis).

▪ No energy is gained

▪ Note differences - anaerobic respiration - 2 ATP's produced (from glycolysis), aerobic respiration - 36 ATP's produced (from

glycolysis, Krebs cycle, and Oxidative Phosphorylation)

(50)

Carbohydrates, fats, and proteins can all

fuel cellular respiration

When they are converted to molecules that enter glycolysis or the citric acid cycle

OXIDATIVE PHOSPHORYLATION

(Electron Transport and Chemiosmosis)

Food, such as peanuts

Carbohydrates Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Amino groups

(51)
(52)

Beyond glucose: Other carbohydrates

Glycolysis accepts a wide range of

carbohydrates fuels

polysaccharides → → → glucose

ex. starch, glycogen

other 6C sugars → → → glucose

ex. galactose, fructose

hydrolysis

(53)

Proteins → → → → → amino acids

Beyond glucose: Proteins

hydrolysis

amino group = waste product

excreted as ammonia, urea,

or uric acid

(54)

enter

Krebs cycle as acetyl CoA

Beyond glucose: Fats

Fats → → → → → glycerol & fatty acids

glycerol (3C) → → PGAL → → glycolysisfatty acids →

hydrolysis 2C acetyl groups acetyl coA Krebs cycle glycerol enters glycolysis

as PGAL

(55)

Carbohydrates vs. Fats

fat

carbohydrate

Fat generates 2x ATP vs. carbohydrate

more C in gram of fat

more O in gram of carbohydrate

(56)

Coordination of

digestion & synthesis

by regulating enzyme

Digestion

digestion of

carbohydrates, fats & proteins

all catabolized through same pathways

enter at different points

cell extracts energy

from every source

Metabolism

CO

(57)

Metabolism

Krebs cycle

intermediaries → →

amino acids pyruvate → → glucose

acetyl CoA → → fatty acids

Coordination of digestion & synthesis

by regulating enzyme

Synthesis

enough energy?

build stuff!

cell uses points in glycolysis

& Krebs cycle as links to pathways for synthesis

run the pathways “backwards”

eat too much fuel, build fat

Cells are versatile &

(58)
(59)

Food molecules provide raw materials for biosynthesis

Cells use some food molecules and

intermediates from glycolysis and the citric acid cycle as raw materials

This process of biosynthesis

Consumes ATP

ATP needed to drive biosynthesis

ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl

CoA Pyruvate G3P Glucose

Amino groups

Amino acids Fatty

acids Glycerol Sugars

Carbohydrates Fats

Proteins

Cells, tissues, organisms

(60)

The fuel for respiration ultimately comes from photosynthesis

All organisms

Can harvest energy from organic molecules

Plants, but not animals

Can also make these molecules from inorganic sources by the process of photosynthesis

References

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