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Chapter 5
Cell Respiration and Metaboli
sm
y
All reactions that involve energy transformatio
ns
Divided into 2 Categories
y
Catabolic
y
x Release energy
x Breakdown larger molecules into smaller molecules
y
Anabolic
b l
x Require input of energy
y
of large
g energy-storage
gy
g molecules
x Synthesis
Metabolism
y
Oxidation-reduction reactions
◦ Break down of molecules for energy
◦ Electrons are transferred to intermediate car
riers,
i
th
then tto the
th final
fi l electron
l t
acceptor:
t
ox
ygen
◦ Oxygen is obtained from the blood
Aerobic Cell Respiration
y
y
y
Breakdown of glucose for energy in the cytopl
asm
Glucose is converted to 2 molecules of pyruvic
acid
Each pyruvic acid contains
◦ 3 carbons
◦ 3 oxygens
◦ 4 hydrogens
y
4 hydrogens are removed from intermediates
Glycolysis
Gl
Glycolysis
l i
Each pair of H+ reduces a molecule of NAD
y Produces
y
◦ 2 molecules of NADH and 2 unbound H+
◦ 2 ATP
y
Glycolysis Pathway
Glucose + 2NAD + 2ADP + 2Pi
+ 2ATP
2 pyruvic acid + 2NADH
y
Glycolysis is exergonic
◦ Energy
gy released used to drive endergonic
g
reaction
◦ ADP + Pi
ATP
y
Glucose must be activated first before energy can be o
btained
◦ ATP consumed at the beginning of glycolysis
◦ ATP
ADP + Pi
Pi is not released but added to intermediate molecules (
p
phosphorylation)
p
y
)
y Phosphorylation of glucose, traps the glucose inside cell
y Net gain of 2 ATP and 2 NADH
y
Anaerobic respiration: Oxygen is not used in the process
y NADH + H+ + pyruvic acid
lactic acid and NAD
y Produce 2 ATP/ glucose molecule
y
Lactic Acid Pathway
y
S
Some
tissues
ti
adapted
d t d to
t anaerobic
bi metabolism
t b li
◦ Skeletal muscle: normal daily occurrence
◦ RBCs do not contain mitochondria and only use lactic a
cid pathway
y
C di muscle:
Cardiac
l iischemia
h
i
Glycogenesis and Glycogenolysis
Increase glucose intracellularly,
intracellularly would increase osmotic pr
essure
y Must store carbohydrates in form of glycogen
y
Glycogenesis: formation of glycogen from glucose
y Glycogenolysis: conversion of glycogen to glucose-6-phosphate
y
◦ Glucose-6-phosphate can be utilized through glycolysis
Glucose-6-phosphate cannot leak out of the cell
y Skeletal muscles generate glucose-6-phosphate for own glycolytic
needs
y Liver contains glucose-6-phosphatase that can produce free glucose
y
Lactic acid produced by anaerobic respiration delivered to the live
r
y LDH converts lactic acid to pyruvic acid
y Pyruvic acid converted to glucose-6-phosphate
◦ Intermediate for glycogen
◦ Converted to free glucose
y Gluconeogenesis:
g
conversion to non-carbohydrate
y
molecules thro
ugh pyruvic acid to glucose
y
Cori Cycle
y
y
y
y
y
Aerobic respiration of glucose, pyruvic acid is formed by glycoly
sis, then converted into acetyl coenzyme A (acetyl CoA)
Energy is released in oxidative reactions, and is captured as ATP
Pyruvic acid enters interior of mitochondria
Converted to acetyl
y CoA and 2 C02
Acetyl CoA serves as substrate for mitochondrial enzymes
Aerobic Respiration
Acetyl CoA enters the Krebs Cycle
y
y
y
y
y
Acetyl CoA combines with oxaloacetic acid to form citric acid
Citric acid enters the Krebs Cycle
Produces oxaloacetic acid to continue the pathway
1 GTP, 3 NADH, and 1 FADH2
NADH and FADH2 transport
p
electrons to Electron Transport
p
Cy
y
cle
Krebs Cycle
y
Cristae of inner mitochondrial membrane contain molec
ules that serve as electron transport system
y
Electron transport chain consists of FMN, coenzyme Q, a
nd cytochromes
Electron Transport
y
Each cytochrome transfers electron pairs from NADH and FAD
H2 to next cytochrome
y
Oxidized NAD and FAD are regenerated and shuttle electrons
y
to the ETC
from the Krebs Cycle
Cytochrome receives a pair of electrons
y Iron reduced
reduced, then oxidized as electrons are transferred
y
Cytochrome a3 transfers electrons to O2 (final electron accep
t )
tor)
y Oxidative phosphorylation occurs. Energy derived is used to pho
y
sphorylate ADP to ATP
ETC Chain
Chemiosmotic theory
y ETC powered by transport of electrons, pumps H+ from mit
ochondria matrix into space between inner and outer mitoc
hondrial membranes
y
y
Proton pumps
◦ NADH-coenzyme Q reductase complex: Transports 4H+ fo
r every
y pair
p
of electrons
◦ Cytochrome C reductase complex: Transports 4H+
◦ Cytochrome C oxidase complex: Transports 2H+
Coupling ETC to ATP
Higher
g
[[H+] in inter-membrane space
p
y Respiratory assemblies permit the passage of H+
y
y
Phosphorylation is coupled to oxidation,
oxidation when H+ diffuse
through the respiratory assemblies
ATP
◦ ADP and Pi
y
Oxygen functions as the last electron acceptor
◦ Oxidizes cytochrome a3
y
Oxygen accepts 2 electrons: O2 + 4 e- + 4 H+
H20
2
Metabolism of Lipids
y
When more energy is taken in t
han consumed,
consumed glycolysis inhibi
ted
y
Glucose converted into glycoge
n and fat
Lipogenesis
Formation of fat
y Occurs mainly in adipose t
i
issue
and
d li
liver
y
y
Acetic acid subunits from
acetyl CoA converted into
various lipids
y
Lipolysis: Breakdown of fat
Triglycerides
glycerol + fa
y
F
Free
f serve as blood-borne
fa
bl d b
energy carriers
i
y
lipase
Beta--oxidation
Beta
Enzymes remove acetic acid from
acid end of fa
y Forms acetyl CoA
y Acetyl CoA enters Krebs Cycle
y
y
y
y
y
y
Nitrogen is ingested primarily as protein
Excess nitrogen must be excreted
Nitrogen balance: Amount of nitrogen ingested minus amount
excreted
+ N balance: Amount of nitrogen
g
ingested
g
more than amount
excreted
- N balance: Amount of nitrogen excreted greater than ingested
Metabolism of Proteins
Adequate
q
amino acids are required
q
for g
growth and repair
p
y A new amino acid can be obtained by transamination: Amino
group (NH2) transferred from one amino acid to form another
y
Process by
P
b which
hi h excess amino
i
acids
id are eliminated
li i t d
y Amine group from glutamic acid removed, forming ammoni
a and excreted as urea
y
Deamination
Energy conversion: amino acid is deamin
ated
y Ketoacid can enter the Krebs Cycle
y