Transcript Cellular Respiration

Cellular Respiration
Core 3.7 & Option C3
3.7.1 Define cellular respiration.
Introduction:
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All forms of life depend directly
or indirectly on light energy
captured during photosynthesis
Photosynthesis is done by
plants to make glucose
In cellular respiration, glucose
molecules are broken down
back into carbon dioxide and
water (molecules the plant
started with)
Cell respiration is the
controlled release of energy
from organic compounds in
cells to form ATP.
ATP – Adenosine triphosphate
most common energy carrier in cells
 nucleotide composed of adenine, the
sugar ribose, and three phosphate groups
 synthesized from adenosine diphosphate
(ADP) and inorganic phosphate – process
is called phosphorylation
 during glucose breakdown, energy is
release and stored in bonds of ATP
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Adenine
Ribose
Summary of complete glucose metabolism:
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Photosynthesis:
6CO2 + 6H2O + sunlight energy  C6H12O6 + 6O2
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Complete glucose metabolism:
C6H12O6 + 6O2  6CO2 + 6H2O + chemical and heat energies
3.7.2 State that, in cellular respiration, glucose in the cytoplasm is
broken down by glycolysis into pyruvate, with a small yield of ATP.
Glycolysis
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First stage of aerobic respiration
Does not require O2 (anaerobic) and proceeds in exactly
the same way under both aerobic (with oxygen) and
anaerobic (without oxygen) conditions
Splits apart a single glucose molecule (6 carbon) into two
molecules of pyruvate (3 carbon). 2 ATP are yielded.
Occurs in cytoplasm
Under anaerobic conditions, pyruvate is converted by
fermentation to lactic acid or ethanol
Under aerobic conditions, pyruvate may enter the
mitochondria – breaks pyruvate down completely to CO2
and water generating an additional 34 to 36 ATP – aerobic
respiration
Each step (reaction) is catalyzed by an enzyme
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Products of glycolysis are 2 molecules of ATP
and 2 molecules of NADH
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Nicotinamide adenine dinucleotide (NAD) – an
electron carrier that transports energy in the form
of energetic electrons – It is a coenzyme
– electrons are held in high-energy outer electron
shells – NAD+ NADH
– donates the electrons and their energy to other
molecules
– hydrogen ions are often picked up simultaneously
NAD+ + 2H+ +2e-  NADH + H+
(NADH2)
C.3.1 State that oxidation involves the loss of electrons from an
element, whereas reduction involves a gain of electrons; and that
oxidation frequently involves gaining oxygen or losing hydrogen,
whereas reduction frequently involves losing oxygen or gaining
hydrogen.
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Products are formed through
oxidation/reduction reactions (redox) –
involves two complementary reactions
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Oxidation – liberates (releases) energy from the
oxidation substance; results from the removal of one
or more electrons, alone or with H+
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In biological oxidation, oxygen is frequently added to the
oxidized compound
Reduction – stores energy in a reduced compound;
reduction results from addition of one or more
electrons, alone or with H+
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In biological reduction, compounds frequently lose oxygen
OIL RIG = Oxidation Is Loss of electrons; Reduction Is Gain of electrons
OIL RIG = Oxidation Is Loss of electrons; Reduction Is Gain of electrons
C.3.2 Outline the process of glycolysis, including
phosphorylation, lysis, oxidation and ATP formation.
Glycolysis consists of two major sets of
reactions:
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Step 1 - glucose activation (phosphorylation)
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2 ATP are used to convert stable glucose into highly
unstable fructose bisphosphate (6 C)
Step 2 – Energy harvest (lysis & oxidation)
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fructose bisphosphate splits into two 3 C molecules of
glyceraldehyde 3-phosphate (G3P aka PGAL) *lysis
each G3P molecule goes through series of reactions that
convert it into pyruvate (pyruvic acid)
During these reactions, 2 high energy electrons and a
H+ are added to NAD+ to form “energized” carrier NADH
– 2 NADH are made (one from each PGAL) *oxidation
2 ATPs are made per G3P for a total of 4 –
however, net gain is only 2 ATPs
3.7.3 Explain that, anaerobic cellular respiration, pyruvate can be
converted in the cytoplasm into lactate, or ethanol and carbon
dioxide, with no further yield of ATP.
Fermentation
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In the absence of oxygen, pyruvate acts as electron
acceptor from NADH producing ethanol or lactic acid –
this process is called fermentation
NADH production is not used as a method to capture
energy – used to get rid of hydrogen ions and electrons
made when glucose is broken down
NAD+ is regenerated by pyruvate acting as final electron
acceptor - pyruvate may be converted to lactic acid
(lactic acid fermentation – occurs in human muscles
during strenuous exercise) or ethanol and CO2 (alcoholic
fermentation – occurs in plants, many yeasts & some
bacteria)
The only ATP produced from anaerobic respiration are
the 2 yielded in glycolysis, none is made in fermentation
In anaerobic conditions:
Without fermentation,
NADH would not be able
to be converted back to
NAD+ and no more
pyruvate would be made.
In other words, without
fermentation, glycolysis
could not continue and
ATP production would
stop.
3.7.4 Explain that, during aerobic cell respiration, pyruvate can be
broken down in the mitochondria into carbon dioxide and water
with a large yield of ATP.
Aerobic Respiration
In the presence of oxygen, oxygen is the
electron acceptor (in the electron transport
system) allowing pyruvate to be fully broken
down (back into CO2 and water) to make even
more ATP
Aerobic Cellular Respiration
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series of reactions, occurring under aerobic
conditions, in which large amounts of ATP are
produced
pyruvate is broken down into carbon dioxide and
water – oxygen serves as final electron acceptor
each step is catalyzed by enzymes
C.3.6 Explain the relationship between the structure of the
mitochondria and its function.
Aerobic Respiration
Occurs in the mitochondria
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double membrane – inner folds are called cristae
inner compartment contains fluid matrix
intermembrane compartment separates the two membranes
Mitochondria have their own DNA (circular chromosome) and
ribosomes (70s – smaller than eukaryotic ribosomes)
C.3.3 Draw and label a diagram showing the structure of a
mitochondria as seen in electron micrographs.
C.3.4 Explain aerobic respiration, including the link reaction, the
Kreb’s cycle, the role of NADH + H+, the electron transport chain and
the role of oxygen.
Aerobic Respiration
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Step 1 – Glycolysis
Step 2 – Oxidative Decarboxylation (Link
Reaction)
– two molecules of pyruvate produced by
glycolysis are transported across both
mitochondrial membranes into matrix
– each pyruvate is split into CO2 and a 2 C acetyl
group which immediately attaches to coenzyme
A to form acetyl CoA – during this reaction
NADH is produced (oxidative piece)
*Decarboxylation = loss of CO2
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Step 3 – Krebs Cycle (Citric Acid Cycle)
the acetyl CoA enter Krebs cycle by briefly combining
with oxaloacetate to form citrate – coenzyme A is
released to be reused
Kreb’s cycle rearranges citrate to regenerate
oxaloacetate giving off 2 CO2, 1 ATP and four electron
carriers (1 FADH2 and 3 NADH) per pyruvate molecule
(x2 per glucose molecule)
Electron Transport System (Oxidative Phosphorylation)
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energetic electrons from NADH and FADH2 are
used to generate more ATP (3 ATP are
generated per NADH and 2 ATP per FADH2)
located in inner mitochondrial membrane
electrons move from molecule to molecule along
transport system – energy released by electrons
is used to pump hydrogen ions from the matrix
across the inner membrane into the
intermembrane compartment (used for
chemiosmosis)
at the end of the ETS, oxygen and hydrogen
ions accept the electrons to form water – clears
out transport system for more electrons to run
through
C.3.5 Explain oxidative phosphorylation in terms of
chemiosmosis.
Chemiosmosis
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hydrogen ions pumped across the inner membrane
generate a large H+ concentration gradient (high
concentration in intermembrane compartment and
low concentration in matrix)
inner membrane is impermeable to hydrogen ions
except at protein channels that are part of ATPsynthesizing enzymes (ATP synthase) - whole thing
is called the F1 complex
during chemiosmosis, hydrogen ions move down
the concentration gradient from intermembrane
compartment to matrix by means of the F1 complex
the flow of hydrogen ions provides energy to
synthesize 32 – 34 ATPs from ADP
Metabolism of Fats and Proteins
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Cells can also extract energy from fats and proteins
Breakdown of fat and proteins creates products that can
be fed into the enzyme pathways of respiration
Fats
– starts with hydrolysis into glycerol and fatty acids
– glycerol is converted into G3P and enters pathway
– fatty acids are converted into acetyl-CoA and enter
pathway
Proteins
– amino acids are broken down in a number of ways
 the amino group is first removed (deamination)
 some amino acids are converted into pyruvic acid,
some into acetyl-CoA, and some into other
compounds in the Krebs cycle
Mammals and birds (and some other
organisms) make use of heat produced
during metabolism – have evolved
mechanisms to conserve heat (insulation
with fat, hair, feathers)
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Endothermic (“internally heated”) – have fairly
high body temps (higher than environment)
Homeothermic – tend to maintain fairly
constant body temp even when environmental
temp fluctuates
metabolic rate stays fairly constant