Transcript METABOLISM - Doctor Jade Main

Cellular
Respiration
Energy
Flow
• photosynthesis
– carried out by plants
• uses energy from
sunlight
• converts it into glucose
& oxygen
• used in cellular
respiration
• oxygen is consumed
• glucose is broken down
into CO2 & H2O
Respiration
• means breathing
• cellular respiration
– exchange of gases
• O2 from the
environment is used
and & CO2 is
released & removed
by blood
Cellular Respiration
• provides ATP for cellular work
• called oxidation
• oxidizes food molecules, like
glucose, to CO2 & water
• 6C6H12O2 + 6O2   6CO2 +
6H2O + ATP
• energy is trapped in ATP
Cellular Respiration-Oxidation
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electrons are transferred from sugar to
O2 making H2O
6C6H12O2 + 6O2   6CO2 + 6H2O + ATP
do not see electron transfer in equation
see changes in H ions
glucose molecule loses hydrogen
atoms as it is converted to CO2
O2 gains hydrogen atoms to form water
O2 is an electron grabber
– pulls harder than other atoms to get
electrons
these hydrogen movements represent
electron transfers
each hydrogen atom consists of one
electron and one proton
electrons move along with hydrogens
from glucose to O2
it is as if they are falling
energy is released in the process
process is possible only because of O2
if you stop breathingno ATP would be
madeall processes stopdeath
Complete Oxidation of Glucose
• C6H12O6 + 6O2 6CO2 + 6H2O
• for one thing to be oxidized-another must
be reduced
• oxidation & reduction reactions occur
together
• redox reactions
Oxidation/Reduction Reactions
• Oxidation
– H+ atoms are removed from
compounds
• Oxidized things lose electrons
• electron lostoxidized-loses
energy
• Reduction
– H+ atoms are added to
compounds
• gain electronreduced-gains
energy
• food fuels are oxidized-lose
energy transferred to other
moleculesATP
• coenzymes act as hydrogen or
electron acceptors
– reduced each time substrate
is oxidized
CoEnzymes
• needed in oxidation reactions
• NAD+-niacin-nicotinamide adenine dinucleotide
• FAD-flavin adenine dinucleotide-riboflavin
Glucose Oxidation Steps
• Glycolysis
– occurs in cytosol
– does not require oxygen
– also called anaerobic
• Kreb’s Cycle
– occurs in mitochondria
– require O2
– aerobic
• Electron Transport Chain
– occurs in mitochondria
– require O2
– aerobic
Glycolysis
• first step in complete oxidation of
glucose
• takes place in cytosol
• begins when enzyme
phosphorylates glucose
– adds PO4 group to glucose
Glu6PO4
• traps glucose
– most cells do not have enzyme
to reverse reaction & lack
transport system for
phosphorylated sugars
– ensures glucose is trapped
• Glu6PO4isomerizedFru6P+
ATP  fructose-1,6-bisphosphateFru 1,6diP
• reaction uses 2 ATPs
• Energy Investment Phase
Glycolysis
• Glyceraldehyde-3-P
dehydrogenase
catalyzes NAD+
dependent oxidation
of glyceraldehyde
3P2 pyruvates
Glycolysis
• removed H+
–picked up by
NAD+NADH + H+
• Glucose + 2NAD +
2ADP + pi2 pyruvic
acids + 2NADH + 2
ATP
Glycolysis
Pyruvate
• important branch point in
glucose metabolism
• fate depends on oxygen
availability
• not enough oxygen
– NAD+ is regenerated
by converting
pyruvatelactic acid
• anaerobic fermentation
• O2 available
• pyruvic acid enters
aerobic pathways of
Krebs cycle
• aerobic respiration
Anaerobic Fermentation
• not enough oxygen
• NAD+ regenerated by converting
pyruvatelactic acid
• limited by buildup of lactic acid
– produces acid/base problems
– degrades athletic
performances
– impairs muscle cell
contractions & produces
physical discomfort
• used for short bursts of high
level activity lasting several
minutes
• cannot supply ATP for long,
endurance activities
Alcohol Fermentation
• yeast without
oxygen
• provides ATP
• by productethanol
• regenerates
NAD+
Aerobic Respiration
• pyruvic acid enters
mitochondria
• once inside converted
acetyl CoA
• during conversion
• hydrogen atoms of pyruvate
are removed by coenzymes
• pyruvate is decarboxylated
(carbons removed) released
as CO2diffuses out of cells
into bloodexpelled by
lungs
• pyruvic acid + NAD + +
coenzyme A CO2 + NADH
+ Acetyl CoA
Acetyl CoA
• major branch
point in
metabolism
• 2 carbons can
be converted
into fatty acids,
amino acids or
energy
Krebs Cycle
• Acetyl CoA enters Krebs Cycle
– also tricarboxylic acid cycle
or Citric Acid Cycle
• during cycle hydrogen atoms are
removed from organic
moleculestransferred to
coenzymes
• cycle begins & ends with same
substrate: oxaloacetate (OAA)
• acetyl CoA condenses with
oxaloacetate- 4 carbon
compoundcitrate-6 carbon
compound
• cycle continues around through 8
successive step
• during steps atoms of citric acid
are rearranged producing different
intermediates called keto acids
• eventually turns into OAA
Krebs Cycle
• complete revolution per acetyl
CoA includes 2
decarboxylations & 4
oxidations
• Yields
– 2 CO2
– reducing equivalents-3
NADH & 1 FADH2
• further oxidized in
electron transport chain
– 1 GTP-ATP equivalent
Since two pyruvates are
obtained from oxidation of
glucose amounts need to
be doubled for complete
oxidation results
Electron Transport Chain
• transfers pairs of electrons
from entering substrate to
final electron acceptoroxygen
• electrons are led through
series of oxidationreduction reactions before
combining with O2 atoms
• reactions takes place on
inner mitochondrial
membrane
• only permeable to water,
oxygen & CO2
Electron Transport Chain
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members of chain
FMN-flavin mononucleotide
Fe-S centers
copper ions
coenzyme Q
cytochromes
– Sequence- b,c, a & a3
Oxidative Phosphorylation/Electron
Transport Chain System
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responsible for 90% of ATP used by
cells
basis-2H + O22 H20
releases great deal of energy all at
once
cells cannot handle so much energy
at one time
reactions occur in series of steps
Oxidation reactions
– remove H+ atoms & lose energy (H+)
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Oxidized things lose electrons
compounds that gain electrons
reduced-gain energy
enzymes cannot accept H atoms
Coenzymes needed to accept
hydrogens
when coenzyme accepts hydrogen
atoms coenzyme reduced & gains
energy
Oxidative Phosphorylation
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Step 1: coenzyme strips pair of hydrogen
atoms from substrate
FADH2 is reduced
– FAD accepted 2 hydrogens & 2
electrons in TCA cycle
– NADH accepted 2 electrons
• bound one as hydrogen atom
Step 2: NADH & FADH2 deliver hydrogen
atoms to coenzymes in inner
mitochondrion membrane
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Step 3: conenzyme Q accepts hydrogen
atoms from FADH2passes electrons to
cytochromes
– hydrogen atoms released as
hydrogen ions-H+
Step 4: electrons passed along energy
lost at each step as passed from
cytochrome to cytochrome
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one of 2 paths can be taken depending on
donor
released as hydrogens
Step 5: oxygen atom accepts electron
creating oxygen ion O- which has strong
affinity for H+combinesH2O
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does not produce ATP directly
creates conditions needed for ATP production
Chemiosmosis
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ETC creates conditions needed for ATP
production by creating concentration gradient
across inner mitochondrial membrane
as energy is released-as electrons are
transferred  drives H ion pumps that move H
across membrane into space between 2
membranes
pumps create large concentration gradients for
H
H ions cannot diffuse into matrix because not
lipid soluble
channels allow H ions to enter matrix
Chemiosmosis
– energy released during oxidation of
fuels=chemi
– pumping H ions across membranes of
mitochondria into inter membrane space
=osmo
– creates steep diffusion gradient for Hs
across membrane
when hydrogens flow across membrane,
through membrane channel proteinATP
synthase attaches PO4 to ADP ATP
ATP
synthase
Oxidative Phosphorylation
• for each pair of
electrons removed
by NAD from
substrate in TCA
cycle6 hydrogen
ions are pumped
across inner
membrane of
mitrochondria
makes 3 ATP
• FAD4 hydrogens
pumped across2
ATP
Energy Yield
• aerobic metabolism generates
more ATP per mole of glucose
oxidized than anaerobic
metabolism
• Glycolysis
– net 2 ATPs
• Krebs Cycle
– 2 ATP
– 8 NADH + H+ X 3=24 ATP
– 2 FADH2 X 2=4 ATP
• 2 moles pyruvate2 NADH + H+glycolysis 2 X 2 = 4 ATP
• Total 36 ATP
Metabolism Overview