Transcript Cellular Respiration

Cellular
Respiration
Autotrophs
• Autotrophs are organisms that can use basic
energy sources (i.e. sunlight) to make energy
containing organic molecules from inorganic
raw materials.
• 2 Types
• Photosynthetic autotrophs
• Chemosynthetic autotrophs
Chemosynthesis
• Chemosynthesis is a process used by
prokaryotic organisms to use inorganic
chemical reactions as a source of energy to
make larger organic molecules.
Heterotrophs
• Heterotrophs require organic molecules as
food.
• They get their energy from the chemical bonds
in food molecules such as carbohydrates, fats,
and proteins.
Prokaryotic Cells
Prokaryotic Cells
• Prokaryotic cells have no nuclei.
• Prokaryotic cells lack mitochondria and
chloroplasts.
• They carry out photosynthesis and cellular
respiration within the cytoplasm or on the
inner surfaces of the membranes.
Eukaryotic Cells
Eukaryotic Cells
• Eukaryotic cells contain nuclei, mitochondria,
and in the case of plant cells chloroplasts.
• Plant cells, animal cells, fungi and protists are
all eukaryotic.
Cellular Respiration
• Cellular respiration is the controlled release of
chemical-bond energy from large, organic
molecules.
• This energy is utilized for many activities to
sustain life.
• Both autotrophs and heterotrophs carry out
cellular respiration.
Aerobic Vs. Anaerobic
• Aerobic respiration requires oxygen.
• Anaerobic respiration does not require
oxygen.
Aerobic Respiration
• Aerobic cellular respiration is a specific series
of enzyme controlled chemical reactions in
which oxygen is involved in the breakdown of
glucose into carbon-dioxide and water.
• The chemical-bond energy is released in the
form of ATP.
• Sugar + Oxygen  carbon dioxide + water +
energy (ATP)
Aerobic Respiration
• Simplified Reaction:
• C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) ΔHc 2880 kJ
• Covalent bonds in glucose contain large
amounts of chemical potential energy.
• The potential energy is released and utilized to
create ATP.
Glycolysis
• Glycolysis is a series of enzyme controlled
anaerobic reactions that result in the
breakdown of glucose and the formation of
ATP.
Glycolysis
• A 6-carbon sugar glucose molecule is split
into two smaller 3-carbon molecules which
are further broken down into pyruvic acid
or pyruvate.
• 2 ATP molecules are created during
glycolysis and electrons are released during
the process.
Krebs Cycle
• The Krebs cycle is a series of enzymecontrolled reactions that take place inside the
mitochondrion.
• Pyruvic acid formed during glycolysis is broken
down further.
• Carbon dioxide, electrons, and 2 molecules of
ATP are produced in this reaction.
Electron Transport
System
• The electrons released from glycolysis and the
Krebs cycle are carried to the electrontransport system (ETS) by NADH and FADH2.
• The electrons are transferred through a series
of oxidation-reduction reactions until they are
ultimately accepted by oxygen atoms forming
oxygen ions.
• 32 molecules of ATP are produced.
Aerobic Respiration
Summary
• Glucose enters glycolysis.
• Broken down into pyruvic acid.
• Pyruvic acid enters the Krebs cycle.
• Pyruvic acid is further broken down and carbon-dioxide
is released.
Aerobic Respiration
Summary
• Electrons and hydrogen ions from glycolysis and
the Krebs cycle are transferred by NADH and
FADH2 to the ETS.
• Electrons are transferred to oxygen to form oxygen
ions.
• Hydrogen ions and oxygen ions combine to form
water.
Anaerobic Cellular
Respiration
• Anaerobic respiration does not require oxygen
as the final electron acceptor.
• Some organisms do not have the necessary
enzymes to carry out the Krebs cycle and ETS.
• Many prokaryotic organisms fall into this
category.
• Yeast is a eukaryotic organism that performs
anaerobic respiration.
Fermentation
• Fermentation describes anaerobic pathways
that oxidize glucose to produce ATP.
• An organic molecule is the ultimate electron
acceptor as opposed to oxygen.
• Fermentation often begins with glycolysis to
produce pyruvic acid.
Alcoholic Fermentation
• Alcoholic fermentation is the anaerobic
pathway followed by yeast cells when oxygen
is not present
• Pyruvic acid is converted to ethanol and
carbon-dioxide.
• 4 ATPS are generated from this process, but
glycolysis costs 2 ATPs yielding a net gain of 2
ATPs.
Lactic Acid Fermentation
• In Lactic acid fermentation, the pyruvic acid
from glycolysis is converted to lactic acid.
• The entire process yields a net gain of 2 ATP
molecules per glucose molecule.
• The lactic acid waste products from these
types of anaerobic bacteria are used to make
fermented dairy products such as yogurt, sour
cream, and cheese.
Lactic Acid Fermentation
• Lactic acid fermentation occurs in the
human body in RBCs and muscle cells.
• Muscle cells will function aerobically as long
as oxygen is available, but will function
anaerobically once the oxygen runs out.
Lactic Acid Fermentation
• Nerve cells always require oxygen for
respiration.
• RBCs lack a nucleus and mitochondria and
therefore must always perform anaerobic,
lactic acid fermentation.
Fat Respiration
• A triglyceride (neutral fat) consists of a
glycerol molecule with 3 fatty acids attached
to it.
• A molecule of fat stores several times the
amount of energy as a molecule of glucose.
• Fat is an excellent long-term energy storage
material.
• Other molecules such as glucose can be
converted to fat for storage.
Protein Respiration
• Protein molecules must first be broken down
into amino acids.
• The amino acids must then have their amino
group (-NH2) removed (deamination).
• The amino group is then converted to
ammonia. In the human body ammonia is
converted to urea or uric acid which can then
be excreted.
Glycolysis
• Glycolysis is also known as the EmbdenMeyerhof Pathway.
• Glycolysis is a pathway for carbohydrate
metabolism that begins with the substrate Dglucose.
• All organisms can use glucose as an energy
source for glycolysis.
Glycolysis
• Glycolysis likely the first successful energy
harvesting pathway that evolved on earth.
• The pathway evolved at a time when the
Earth’s atmosphere was anaerobic; no free
oxygen was available.
• Glycolysis is an anaerobic process that requires
no oxygen.
Glycolysis
• Glycolysis evolved in very simple, single-celled
organisms much like bacteria.
• These organisms did not have complex
organelles in the cytoplasm to carry out
specific cellular functions.
• There are ten steps in glycolysis, catalyzed by
ten enzymes.
Glycolysis - Investment
Phase
• The first five steps of glycolysis involve an
energy investment.
• This is referred to as the preparatory (or
investment) phase.
• Energy is consumed to convert glucose into
two three-carbon sugar phosphates.
• 2 ATP are consumed.
Glycolysis – Pay-off Phase
• In the remaining steps of glycolysis, energy is
harvested to produce a net gain of ATP.
• This phase involves a net gain of the energy rich
molecules ATP and NADH.
• 2 triose sugars are produced in the preparatory
phase; therefore, each reaction in the pay-off
phase occurs twice per glucose molecule.
• This yields a total of 2 NADH molecules and 4 ATP
molecules.
Glycolysis
• The major products of glycolysis are:
• Chemical energy in the form of ATP.
• Chemical energy in the form of NADH.
• Two three-=carbon pyruvate molecules.
Preparatory Phase – Step 1
• The first step in glycolysis involves
phosphorylation of glucose to form glucose 6phosphate.
• The enzyme hexokinase catalyzes this reaction.
• This keeps glucose concentration in the cell low to
facilitate continual diffusion of glucose into the
cell.
• 1 ATP is consumed.
Preparatory Phase – Step 1
Glucose (Glc)
Hexokinase
(HK)
H+
ATP
ADP
Glucose-6-phosphate
(G6P)
Preparatory Phase – Step 2
• Glucose 6-phosphate is then rearranged into
fructose 6-phosphate.
• The enzyme glucose phosphate isomerase
catalyzes this reaction.
• No ATP is consumed.
Preparatory Phase – Step 2
Glucose 6phosphate (G6P)
Phosphoglucose
isomerase
Fructose 6-phosphate
(F6P)
Preparatory Phase – Step 3
• Fructose 6-phosphate is then converted to
Fructose 1,6-biphosphate.
• The enzyme phosphofructokinase catalyzes this
reaction.
• 1 ATP is consumed.
• This reaction destabilizes the molecule.
• Unlike the previous reactions, this reaction is
essentially irreversible. A different chemical
pathway must be used for gluconeogenesis.
Preparatory Phase – Step 3
Fructose 6-phosphate
(F6P)
Phosphofructokinase
(a transferase)
H+
ATP
ADP
Fructose 1,6bisphosphate
(F1,6BP)
Preparatory Phase – Step 4
• The destabilization of the molecule from the
previous reaction allows for splitting of the
hexose ring.
• Fructose 1,6-bisphosphate is split into two
triose sugars.
• Glyceraldehyde 3-phosphate
• Dihydroxyacetone phosphate
• The enzyme fructose bisphosphate aldolase
catalyzes this reaction.
Preparatory Phase – Step 4
Fructose 1,6bisphosphate
(F1,6BP)
Fructose
Glyceraldehyde
bisphosphate
3-phosphate
aldolase
(GADP)
(ALDO)
+
Dihydroxyacetone
phosphate (DHAP)
Preparatory Phase – Step 5
• Dihydroxyacetone phosphate (DHAP) can be
interconverted to glyceraldehyde 3-phosphate
(GADP).
• The enzyme triosephosphate isomerase
catalyzes this reaction.
• GADP proceeds into the pay-off phase of
glycolysis.
Preparatory Phase – Step 5
Dihydroxyacetone
phosphate (DHAP)
Triesophosphate
isomerase (TPI)
Glyceraldehyde 3phosphate (GADP)
Pay-Off Phase - Step 1
• GADP is dehydrogenated and inorganic
phosphate is added to them forming 1,3bisphosphoglycerate.
• The enzyme glyceraldehyde phosphate
dehydrogenase catalyzes this reaction.
• Hydrogen is used to reduce two molecules of
NAD+ to give NADH and H+.
Pay-Off Phase - Step 1
Glyceraldehyde 3phosphate (GADP)
Glyceraldehyde 3phosphate
dehydrogenase
(GADPH)
Pi
H+
NAD+
NADH
1,3bisphosphoglycerate
(1,3-BPG)
Pay-Off Phase - Step 2
• In this step a phosphate group is transferred
from 1,3 bisphosphoglycerate to ADP to form
ATP and 3-phosphoglycerate.
• The enzyme phosphoglycerate kinase (a
transferase) catalyzes this reaction.
• 1 ATP is generated in this step.
Pay-Off Phase - Step 2
1,3bisphosphoglycerate
(1,3-BPG)
Phosphoglycerate
kinase (PGK) (a
transferase)
ADP
ATP
Phosphoglycerate
kinase
3-phosphoglycerate
(3-P-G)
Pay-Off Phase – Step 3
• 3-phosphoglycerate is converted to 2phosphoglycerate.
• The enzyme phosphoglycerate mutase
catalyzes this reaction.
Pay-Off Phase – Step 3
3-phosphoglycerate
(3PG)
Phosphoglycerate
mutase (PGM)
2-phosphoglycerate
(2PG)
Pay-Off Phase - Step 4
• 2-phosphoglycerate is converted to
phosphoenolpyruvate.
• The enzyme enolase catalyzes this reaction.
• This is a dehydration reaction. Water is
released.
Pay-Off Phase - Step 4
2-phosphoglycerate
(2PG)
Enolase (ENO)
H2O
Phosphoenolpyruvate
(PEP)
Pay-Off Phase - Step 5
• Phosphoenolpyruvate is converted to
pyruvate.
• ADP is phosphorylated to ATP.
• The enzyme pyruvate kinase (a transferase)
catalyzes this reaction.
• 1 ATP is generated in this reaction.
Pay-Off Phase - Step 5
Phosphoenolpyruvate
(PEP)
Pyruvate kinase (PK)
(a transferase)
Pyruvate (Pyr)
H+
ADP
ATP
Pay-Off Phase
• The payoff phase generates 2 ATP for each
triose sugar from the preparatory phase.
• 2 triose sugars are generated in the
preparatory phase from each molecule of
glucose that enters into glycolysis.
• Consequently, 4 ATP are generated during the
payoff phase for each molecule of glucose.
Pay-Off Phase
• 2 ATP are consumed for each molecule of
glucose during the preparatory phase.
• A net gain of 2 ATP per molecule of glucose is
obtained from glycolysis.