Chapter 13

How Cells Obtain Energy From Food

EssentialCell Biology

FOURTH EDITION

Copyright © Garland Science 2014

Alberts • Bray • Hopkin • Johnson • Lewis • Raff • Roberts • Walter

Enzymes Allow Energy to be Extracted from Food in Discrete Steps and Stored

in Activated Carrier Molecules

Fig. 13-1

ATPNADH

Fig. 13-3

Catabolism Occurs in Three Stages

Overview of Glycolysis

Fig. 13-4

Fig. 13-5

A little more detail….

ATP consumed

Set up forATP production

ATP productionexceedingATP consumption

NADH production(NAD+ regenerated by ETC of mitochondriain aerobic organisms)

NAD+ regenerated by fermentation in anaerobic cells

Fig. 13-6

Skeletal muscles contain both aerobic slow twitchand anaerobic fast twitch muscle fibers.

fastslow

Karp,CMB7

slow twitch: long duration, low intensity contractions (+ mitochondria)fast twitch: short duration, high intensity contractions (- mitochondria)

Step

6

Step

7

Focus on Steps Producing NADH and ATP

Panel 13-1

DG = +1.5

DG = - 4.5Co

mb

ined

DG

= -

3.0

Fig. 13-7

High-Energy Bond Created in Step 6 Provides Energy for ATP Synthesis in Step 7

can be used in OxPhos

substrate level phosphorylation

Step 6: -short-lived high energy thioester bond formed between Cys of enzyme and substrate

-electrons transferred fromsubstrate to NAD+

-high energy Pi bond displaces high energy thioester bond linking substrate to enzyme

Step 7: -high energy Pi transferredto ADP in ATP synthesis bysubstrate-level phosphorylation

Fig. 13-9a

Details of High Energy Bond

Fig-139b

Steps 6 & 7 Generate Products for ATP Synthesis by Two Mechanisms

Phosphate Bonds with Higher Energy Than Those in ATP Can Be Used to Produce ATP bySubstrate-LevelPhosphorylation

Ste

p 7

Ste

p 1

0

Fig. 13-8

energy investment: step 1

creatine phosphate(~10.0)stored in muscle

Step 10 Also Involves Substrate-Level Phosphorylation

Panel 13-1

Pyruvate Converted to Acetyl CoA and CO2 byPyruvate Dehydrogenase in Mitochondria

large complex contains multiple copies of enzymatic subunits 1 and 3 tethered to core subunit 2

Fig. 13-10

Fig. 13-12

Citric Acid Cycle

NADH used in ATP synthesisby OxPhos

Fats also entercycle as acetyl-CoA.

Electron transport generates H+ gradient during Oxidative Phosphorylation

Fig. 13-19

IMM OMM

matrix

ATP and NADHactivated carriers

produced

Two Other Activated Carriers Produced in Citric Acid Cycle

GTP (ATP equivalent)

FADH2 e- carrierFig. 13-13

produced by SDH embedded in IMM

Krebs Used SDH Inhibitor to Show Pathway is Cyclical

xMalonate Inhibits

SDH Step

Fig. 13-15

Addition of either A-D or F-H caused accumulation of E (Succinate) during inhibition.

Fig. 13-17

Glycolysis and Citric Acid Cycle Also Provide Entry Points to Anabolic Pathways

Fig. 13-14

also provideentry points for other C sources for catabolism

Big Picture of Metabolic Pathways in Cells

Glycolysis and Citric Acid Cycle in Red

Fig. 13-20

Regulating Catabolism vs. Anabolism:allosteric modulation of key enzymes by ATP & AMP

Catabolism

AnabolismFig. 13-21

ATPAMP

ATPAMP

starvation stimulates

starvation inhibits

Acetyl-CoA

Fig. 13-11 Fig. 13-22

Excess Glucose Stored in Form of Glycogen and Triacylglycerol