#cellular respiration_the process

7/22/2019 #Cellular Respiration_the Process....

http://slidepdf.com/reader/full/cellular-respirationthe-process 1/24

Cellular Respiration

Chapter 9:

The Process



Objectives

• Understand that cellular respiration is a seriesof coupled metabolic processes

• Describe the role of ATP, NAD+ and FAD in

coupled reactions

• Know the start and end products of eachreaction

• Know the kind and quantity of energy

produced by each reaction• Understand the difference between substrate-

level phosphorylation and oxidative

phosphorylation



Objectives continued

• Understand the process of chemiosmosis

• Explain how the “slide” of electrons down the

electron transport chain is coupled to theproduction of ATP by chemiosmosis

• Describe the fate of pyruvate during

fermentation

• Understand how food molecules other than

glucose can be oxidized to make ATP

• Explain how ATP production is controlled



Overview • Aerobic cellular

respiration has 4 steps – Glycolysis

• in cytosol

– Transition reaction

• at mitochondrialmembrane

– Kreb’s cycle

• in mitochondrial matrix

– Electron TransportChain

• at inner membrane of

mitochondria

C6H1206 + 6O26CO2 +6H20 + ENERGY



Glycolysis• Start with

glucose(C6H1206)

• End product

is 2x

Pyruvate2(C3H4O3)

• Some steps

are

endergonic

while others

are exergonic



1 First obstacle

– make glucose reactive

• Increase free energy of

glucose by phosphorylation by ATP

2 Rearrange molecule

3 Increase free energy of

glucose by phosphorylation with ATP

phosphofructokinase is an

allosteric enzyme that

controls the rate ofglycolysis

• Result in reactive molecule



4 Now that our 6C sugar (fructose 1,6-biphosphate) is ready to

react, aldolase cleaves it into 2(3C) molecules that are isomers

(what kind) of each other.

5 Isomerase converts the unusable Dihydroxyacetone phosphate into Glyceraldehyde phosphate



6 Each glyceraldehyde phosphate is acted on by the enzyme Triose phosphate

dehydrogenase that oxidized the sugar by reducing NAD+ and sequentially

adding inorganic phosphate to the sugar

7 A molecule of ATP is made from each 1,3-biphosphoglycerate as the phosphate

added in step 6 is transferred to ADP

8 The molecule is reorganized through the relocation of the phosphate group



9 Enolase makes an enol (C=C-O) through the removal of

water resulting in an unstable molecule (prone to change)10 Terminal step in glycolysis results in the formation of

Pyruvate as the enzyme Pyruvate kinase transfers the

phosphate group of phosphoenolpyruvate to ADP

forming ATP



Glycolysis summarized

• Glucose converted into 2 pyruvate• Energy requiring and energy releasing steps

• Energy net yield is 2ATP and 2NADH

• 2 molecules of water are produced

• Enzymes involved at each step

– Kinase: conversion of ATP to ADP or ADP to ATP

– Dehydrogenase: reduces NAD+ to NADH while

oxidizing sugar

• Regulated by phosphofructokinase activity (step

3) and the rate of isomer formation of

glyceraldehyde phosphate (step 5)



Mitochondria

Transition reaction

• at mitochondrial

membrane

Kreb’s cycle • in mitochondrial

matrix

Electron Transport

Chain

• at inner membrane of

mitochondria



Transition Reaction

• Pyruvate is converted into Acetyl-CoA as it is

transported into the mitochondrion from the

cytosol

• NAD+ converted into NADH

• CO2 produced during reaction



Kreb’s Cycle • Each molecule of

Acetyl- CoA entersthe Krebs cycle

• the 2C of acetyl

CoA are exchanged

for 2 C inoxaloacetate

• Each turn of the

cycle produces – 3 NADH

– 1FADH2

– 1ATP

– 2CO2



1 Acetyl CoA enters the kreb’s

cycle by attaching to a 4

carbon sugar (Oxaloacetate)

forming a six carbon sugar

(Citrate)

2 An isomer of citrate is created

through

condensation/hydrolysis

reactions resulting in isocitrate

3 Isocitrate loses CO2 forming

-ketoglutarate as oxidation of

the compound occurs NADH

is formed4 -ketoglutarate (C5) is

converted to Succinyl CoA

(C4). Along the way, CO2 is

released, and NAD+

is reduced



5 Succinyl CoA is converted

into Succinate. Reaction

starts as inorganic phosphate

attaches to Succinyl CoAdisplacing CoA. The

phosphate is picked up by

GDP forming GTP. The

terminal phosphate of GTP

is transferred to ADP

forming ATP

6 Succinate is oxidized to

Fumarate Reducing FAD to

FADH2

7 The addition of H2

0 to

Fumarate produces Malate

8 Oxaloacetate is reformed

through the oxidation of

Malate. NADH is formed

during the process



Summary of Transition Reaction and Kreb’s cycle

Each glucose that enters

Glycolysis is converted into

2 Pyruvate molecules

Transition Reaction

1 NADH/pyruvate

1 CO2 /pyruvate

Kreb’s Cycle

3 NADH/ Acetyl CoA

1FADH2 / Acetyl CoA1ATP / Acetyl CoA

2CO2 / Acetyl CoA



Electron Transport Chain

• Each NADH enters the electron

transport chain with enough free

energy to fuel formation of 3 ATP

• Each FADH2 will yield 2 ATP

Electron shuttling proteins

are called flavoproteins,

iron-sulphur proteins,

and cytochromes

Each protein in the series

is more electronegative

than its predecessor



ETC

• Some electron carriers

of the transport chain

carry only electrons – Ubiquinone

– Cytochrome c

• Some electron carriers

accept and release protons along with

electrons



Chemiosmosis

Chemiosmosis:coupling of exergonic electron flow down an ETC to

endergonic ATP production by the creation of a proton gradient across a

membrane (proton-motive force)



ATP Formation

• ATP synthase couples

inorganic phosphate to

ADP as H+

return tothe matrix (utilizes

potential energy of

proton gradient)

• 1ATP is formed foreach H+ diffusing

across the membrane



Substrate-level Phosphorylation: ATP production coupled by direct enzymatic

transfer of phosphate from an intermediate in catabolism to ADP

Oxidative Phosphorylation: ATP production that is coupled to the exergonic

transfer of electrons from food to oxygen



Variations of Glycolysis• In the absence of oxygen, liberation of energy can occur through

fermentation pathways yielding a max of 2 ATP/glucose• Fermentation is similar to glycolysis except that the end product

is not pyruvate because of the addition of a few steps necessary

to regenerate NAD+



What about the other foods?

• Proteins, Carbo’s and Fats can

all be utilized for energy

following hydrolysis

• Amino Acids are converted to

intermediates including

pyruvate, acetyl CoA, and -ketoglutarate

• Carbo’s enter glycolysis at the

beginning or as Fructose 6

phosphate• Fats components

– glycerol enters as glyceraldehyde

phosphate

– Fatty acids enter as Acetyl CoA



Feedback Mechanisms

• Feedback inhibition

– ample product switches off

product

• Regulation of enzymeactivity

• allosteric regulation of

phosphofructokinase

– ADP and AMP activate

enzyme

– Citrate inhibits enzyme

#cellular respiration_the process

Documents