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