Metabolism II

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Metabolism II
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What is the purpose of cell respiration?

• Provides energy to do cell work
• Cell work means uphill cellular processes
• Would not be spontaneous (could not occur) if
  were not coupled to other highly spontaneous
  process that supplies energy

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What are cell work processes?

• Active transport through cell membranes
• Movement (especially animals)
• Assembly of macromolecules

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Macromolecules

• Food, and living things, are largely made of
  large molecules macromolecules
• Macromolecules are polymers chains of small
  units (building blocks)

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Molecular machinery of life
4 classes of organic macro-molecules that are
assembled from smaller building blocks
http//www.wmscnet.com/clecinchist1v.jpg
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Four types of organic macromolecules
1. Proteins (structural catalytic
enzymes) 2. Nucleic acids (DNA, RNA
instructions for inheritance as the structure of
proteins) 3. Polysaccharides (energy storage
structure) 4. Complex lipids (energy storage
cell membranes)
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Proteins
http//matcmadison.edu/biotech/resources/proteins/
labManual/chapter_2.htm
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Protein function depends on form
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Nucleic Acids (DNA, RNA)
Chains of nucleotide building blocks
http//www.stkate.edu/physics/Astrobiology/nucleot
ide.gif
www.molecularstation.com/images/DNA-structure.gif
http//www.swbic.org/products/clipart/images/nacol
lage.jpg
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Polysaccharides chains of sugars
Plant Cellulose
www.steve.gb.com/science/carbohydrates.html
www.DennisKunkel.com
www.whfreeman.com
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Complex lipids chains of fatty acids
http//www.chemistryland.com/ElementarySchool/Buil
dingBlocks/BuildingOrganic.htm
http//www.crisco.com/about/0_grams.asp
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Trans Fats

• trans fats ? same building blocks as non-trans
  fats, but have a completely different shape
• In trans fat molecules, the hydrogens on the
  doubly bonded carbon atoms are in the trans
  rather than the cis configuration, resulting in a
  straighter, rather than kinked, shape
• As a result, trans fats are less fluid and have a
  higher melting point than the corresponding cis
  fats

http//biology.clc.uc.edu/Courses/bio104/lipids.ht
m
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Digitalis purpurea
Digitoxin is a glycoside from foxgloves
(Digitalis purpurea) formed between a sugar and a
steroid Cardiac glycosides like digitoxin
stimulate heart beat (by affecting the K/Na pumps
in the heart), and are used for dropsy and
arrhythmia. A lethal dose is just three leaves
www.steve.gb.com/science/carbohydrates.html
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Digestion of Macromolecules

• When we digest food macromolecules, we break them
  down completely into their building blocks
• which are carried by the blood to the cells,
  where they are taken up and some are reassembled
  into new macromolecules

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Digestion is downhill
Dismantling macromolecules is a disordering
process that increases the entropy of the universe

heat
Macromolecule
?
building blocks
(random energy)
(ordered, non-random)
(disordered)

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Spontaneous processes can happen
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Assembly a reversal of digestion?

• NO - Digestion is downhill (increases entropy of
  universe)
• Assembly by simply reversing digestion would be
  uphill, and cant happen. (The Second Law Its
  the law!)

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How can macromolecule assembly (and other types
of uphill cell work) occur?
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By coupling cell work to downhill processes

• A spontaneous process can be reversed by coupling
  it to a MORE spontaneous process (such as a
  larger weight)
• The COMBINED process is then downhill, and
  increases the entropy of the universe
• We say The second, highly spontaneous, process
  supplies energy to drive the uphill process
  (which could not have occurred alone)

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Mechanical coupling
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What drives cell work?

• The highly downhill process that drives cell work
  is splitting ATP

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ATP Adenosine Tri-Phosphate
ATP consists of a nitrogenous base (red)
adenine, a 5-carbon sugar (magenta) ribose
and a phosphate chain (blue)

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Splitting ATP
ATP
?
ADP Phosphate

heat
(One large molecule)
(Two smaller molecules)
(random thermal energy)
Splitting ATP is very downhill, and so can drive
uphill cell work
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Example of coupling ATP-driving assembly of
protein
spontaneous?
no
Amino acids heat ? protein
YES
ATP ? ADP Phosphate heat
--------------------------------------------------
--------------------------
Amino acids ATP heat
YES
? protein ADP phosphate heat
(FOUR ATPs are split to add ONE amino acid to a
protein)
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We need to regenerate ATP

• Human cells contain only enough ATP to last 30
  seconds
• QUESTION How can we keep doing cell work?
• ANSWER Put phosphate back on ADP to make ATP
  again ( ATP synthesis)

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How can ATP synthesis occur?
Coupling
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What process is downhill enough to drive uphill
ATP synthesis?

• How can we drive ATP synthesis?
• Couple it to something even more downhill
  spontaneous
• But what?
• The slow combustion of food cellular
  respiration!

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Example of coupling ATP-driving assembly of
protein
spontaneous?
no
ADP Phosphate heat ? ATP
YES
Food O2 ? CO2 H20 heat
--------------------------------------------------
--------------------------
Food O2 ADP Phosphate heat
YES
? ATP CO2 H20 heat
The COMBINED process makes ATP and increases the
entropy of the universe
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The ATP Cycle

• ATP is renewable
• Transfers energy from exergonic to endergonic
  reactions

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Metabolic pathways

• Metabolism the chemical processes of cells
• Metabolic Pathway sequence of reactions by
  which chemical changes such as cell respiration
  are carried out in many small steps
• Cellular respiration using the sugar glucose as
  fuel takes place in three phases, involving 20
  separate reactions, and 20 different enzymes

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Enzymes protein catalysts
Enzymes are proteins that act as catalysts
enzymes speed up chemical reactions
Enzymes have no effect on directions of reactions
times arrow still points the same direction
whether an enzyme is present or not
(Oiling the pulley axle cant make the weight go
up)
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Structure of an enzyme
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3 Stages of glucose burning
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The ten steps of glycolysis
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1. Glycolysis occurs in the cytosol the cell
juice
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Glycolysis

• Occurs in cytosol
• Glucose ? pyruvic acid
• Supplies 3rd stage with electrons H
• 2 energy recovery
• No O2

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Mitochondrion
http//www.imtech.res.in/raghava/rslpred/mitochond
ria.jpg
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Krebs Cycle

• Occurs in mitochondria
• Completes glucose breakdown to CO2
• Supplies 3rd stage with electrons H
• 2 energy recovery

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Mitochondrion
http//www.imtech.res.in/raghava/rslpred/mitochond
ria.jpg
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Electron Transport Chain

• Inner membrane of mitochondria thylakoid
  membrane in Ps
• Uses electrons and H from previous steps to
  produce most of ATP
• O2 final electron acceptor

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Where does the food come from that is used as
fuel in cellular respiration?
Animals eat plants or they eat animals that have
eaten plants
Plants make their own food by photosynthesis
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Photosynthesis
spontaneous?
no
CO2 H2O ? Glucose O2
YES
Photons of light ? heat
--------------------------------------------------
--------------------------
YES
CO2 H2O Photons ? Glucose O2
heat
Light supplies the energy to drive synthesis of
glucose in photosynthesis
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Chloroplast
http//www.ualr.edu/botany/chloroplast.jpg
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Photosynthesis

• 2 main reactions each with multiple steps
• Light dependent
• - thylakoid membrane (light E ? ATP)
• Light independent
• - in stroma (sugars assembled)

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NOTE WELL Plant cells use the food they make in
the same way that animal cells do - by cellular
respiration
http//hawaii.hawaii.edu/laurab/generalbotany/imag
es/Plant20Cell.gif
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Energy Acquiring Pathways
Sunlight Energy drives reactions
?
Photosynthesis The Main Energy Acquiring Pathway
1. Sun Energy transformed to ATP Energy
2. ATP Energy ? glucose synthesis
CO2 H2O required
O2 released
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Energy Acquiring Pathways
Aerobic Respiration The Main Energy Releasing
Pathway
1. Energy released from breakdown of organic
compounds
2. Released energy transformed to ATP Energy
CO2 H2O released
O2 required
about 40 of glucoses energy banked 60
lost as heat
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Energy Flow
SUNLIGHT
GLUCOSE
O2
ATP
CELL WORK
(Photosynthesis)
(Cellular Respiration)
-Active transport
(Splitting ATP)
-Bio-synthesis
-Movement
heat
heat
Carbon Dioxide
ADP
heat


Inorganic Phosphate
Water
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