Chapter 9 (Notes) Flashcards
Living cells require energy from
outside sources.
Some animals, such as the chimpanzee, obtain energy be eating plants, and some animals feed on other organisms that eat plants.
Energy flows into an ecosystem as
sunlight and leaves as heat.
Photosynthesis generates O2 and organic molecules, which
are used in cellular respiration.
Cells use chemical energy stored in organic molecules to
regenerate ATP, which powers work.
Several processes are central to
cellular respiration and related pathways.
The breakdown of organic molecules is
exergonic.
Three ways cells make ATP
Fermentation
Aerobic respiration
Anaerobic respiration
Fermentation is a
partial degradation of sugars that occurs without O2
((do this as last resort???))
Aerobic respiration
consumes organic molecules and O2 and yields ATP
tons of ATP) (need a lot of oxygen
Anaerobic respiration
is similar to aerobic respiration but consumes compounds other than O2.
(doesn’t need O2 but makes tons of ATP?)
Cellular respiration includes both
aerobic and anaerobic respiration but is often used to refer to aerobic respiration.
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to
trace cellular respiration with the sugar glucose.
Chemical equation for Cellular Respiration
C6H12O6 + 6 O2 —> 6 CO2 + 6 H2O + Energy (ATP + heat)
1 glucose + 6 Oxygen –> 6 molecules of Carbon Dioxide + 6 Water molecules + Energy in the two forms of ATP and Heat.
((2 things in and three things out))
(((glucose is oxidized. Oxygen is reduced(gains electrons))))
The transfer of electrons during chemical reactions releases
energy stored in organic molecules.
This released energy is ultimately used to synthesize ATP.
Chemical reactions that transfer electrons between reactants are called
oxidation-reduction reactions, or redox reactions.
In oxidation,
a substance loses electrons, or is oxidized.
In reduction,
a substance gains electrons, or is reduced (the amount of positive charge is reduced)
LEO GER
LEO (the lion) (says) GER
Oxidation:
L- Loses
E- Electrons
O- Oxidized
Reduction:
G-Gains
E- Electrons
R- Reduced
The electron donor is called the
reducing agent.
The electron receptor is called the
oxidizing agent.
Some redox reactions do not transfer electrons but
change the electron sharing in covalent bonds.
An example is the reaction between methane and O2.
-One way to follow electron movements is to watch the hydrogens.
- **Look for hydrogens.
- **Things that have hydrogens have a lot of electrons.
During cellular respiration, the fuel (such as glucose) is
oxidized, and O2 is reduced.
Cellular respiration allows us to break off
energy into small amounts.
(???)
Organic molecules that have lots of H (hydrogen) are good fuels because
they have e- (electrons) that can be transferred to oxygen.
This must happen stepwise.
Glucose burning releases 686 kcal/mol glucose.
In cellular respiration, glucose and other organic molecules ae
broken down in a series of steps.
Electrons from organic compounds are usually first transferred to
NAD+, a coenzyme.
As an electron acceptor, NAD+ functions as an
oxidizing agent during cellular respiration.
Each NADH (the reduced form of NAD+) represents
stored energy that is tapped to synthesize ATP.
NADH passes the electrons to the
electron transport chain.
Unlike an uncontrolled reaction, the electron transport chain passes electrons in a
series of steps instead of one explosive reaction.
O2 (oxygen) pulls electrons down the electron transport chain in an
energy-yielding tumble.
The energy yielded is used to regenerate ATP.
Food»_space; NADH»_space; Electron Transport Chain»_space; Oxygen (((» water)))
Most electrons follow this “downhill route” ^^
Harvesting of energy from glucose has three stages
- Glycolysis
- The Citric Acid Cycle
- Oxidative Phosphorylation
Glycolysis
-breaks down glucose into two molecules of pyruvate.
- Location it occurs: Cytoplasm
- How ATP is made: Substrate-Level Phosphorylation (SLP)
The Citric Acid Cycle
Pyruvate Oxidation
completes the breakdown of glucose.
- Location it occurs: Matrix Mitochondria
- How ATP is made: Substrate-Level Phosphorylation (SLP)
Oxidative Phosphorylation
accounts for most of the ATP synthesis.
- Location it occurs: Inner Membrane of Mitochondria
- How ATP is made: Oxidative Phosphorylation (OP)
The process that generates most of the ATP is called
oxidative phosphorylation because it is powered by redox reactions.
Oxidative phosphorylation accounts for almost 90% of the
ATP generated by cellular respiration.
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by
substrate-level phosphorylation.
For each molecule degraded to CO2 and water by respiration, the cell makes up to
32 molecules of ATP.
Glycolysis (“splitting of sugar”) breaks down glucose into
two molecules of pyruvate.
Glycolysis occurs in the cytoplasm and has two major phases
- energy investment phase
- energy payoff phase
Glycolysis occurs whether or not
O2 is present.
Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate.
After pyruvate is oxidized, the citric acid cycle completes the
energy-yielding oxidation of organic molecules.
In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the
oxidation of glucose is completed.
Before the citric acid cycle can being, pyruvate must be converted to
acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle.
This step is carried out by a multienzyme complex that catalyses three reactions.
The citric acid cycle, also called the Krebs cycle, completes the
breakdown of pyruvate to CO2.
The citric acid cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn.
-2 turns per 1 original glucose molecule.
The acetyl group of acetyl CoA joins the citric acid cycle by
combining with oxaloacetate, forming citrate.
The next seven steps in the citric acid cycle decompose the citrate back to
oxaloacetate, making the process a cycle.
The NADH and FADH2 produced by the citric acid cycle relay electrons extracted from
the food to the electron transport chain.
During oxidative phosphorylation,
chemiosmosis couples electron transport to ATP synthesis.
Following glycolysis and the citric acid cycle, NADH and FADH2 account for
most of the energy extracted from food.
These two electron carriers (NADH and FADH2) donate electrons to the electron transport chain, which
powers ATP synthesis via oxidative phosphorylation.
The electron transport chain is in the
inner membrane (cristae) of the mitochondrion.
Most of the chain’s (electron transport chain) components are proteins, which
exist in multiprotein complexes.
The carriers (NADH and FADH2??) alternate reduced and oxidized states as they
accept and donate electrons.
Electrons drop in free energy as they go
down the chain and are finally passed to O2, forming H2O.
The first proteins have lower affinity for electrons (less electronegative)
the final electron acceptor O2 is very electronegative.
Electrons are transferred from NADH or FADH2 to the
electron transport chain.
Electrons are passed through a number of proteins including
cytochromes (each with an iron atom) to O2.
The electron transport chain generates
no ATP directly.
The electron transport chain breaks the large free-energy drop from food to O2 into
smaller steps that release energy in manageable amounts.
Chemiosmosis
the energy-coupling mechanism
Electron transfer in the electron transport chain causes proteins to
pump H+ from the mitochondrial matrix to the intermembrane space.
H+ then moves back across the membrane, passing through the proton, ATP synthase.
ATP synthase uses the
exergonic glow of H+ to drive phosphorylation of ATP.
This is an example of chemiosmosis, the use of
energy in a H+ gradient to drive cellular work.
The energy stored in a H+ gradient across a membrane couples the
redox reactions of the electron transport chain to ATP synthesis.
The H+ gradient is referred to as a
proton-motive force, emphasizing its capacity to do work.
During cellular respiration, most energy flows in this sequence
glucose –> NADH –> electron transport chain –> proton-motive force –> ATP
About 34% of the energy in a glucose molecule is transferred to
ATP during cellular respiration, making about 32 ATP.
Several reasons why the number of ATP is not known exactly.
Fermentation and Anaerobic respiration enable cells to
produce ATP without the use of oxygen.
Most cellular respiration require
O2 to produce ATP.
Without O2 as a final electron acceptor,
the electron transport chain will cease to operate.
In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP.
Anaerobic respiration uses an
electron transport chain with a final electron acceptor other than O2, for example sulfate.
Fermentation uses substrate-level phosphorylation instead of an
electron transport chain to generate ATP.
Fermentation consists of
glycolysis plus reactions that generate NAD+, which can be reused by glycolysis.
Two common types of Fermentation are
alcohol fermentation
and
lactic acid fermentation.
In alcohol fermentation, pyruvate is converted to
ethanol in two steps, with the first releasing CO2.
Alcohol fermentation by yeast is used in
brewing, winemaking, and baking.
2 Ethanol, 2 CO2, 2 ATP and 2NAD+ are the products generated from 1 glucose.
In lactic acid fermentation, pyruvate is
reduced to NADH, forming lactate as an end product, with no release of CO2.
Lactic acid fermentation by some fungi and bacteria is used to
make cheese and yogurt.
Human muscle cells use lactic acid fermentation to
generate ATP when O2 is scarce.
1 glucose makes 2ATP, 2 lactate, and 2 NAD+
Fermentation, Anaerobic respiration, and Aerobic respiration all use glycolysis (net ATP=2) to oxidize
glucose and harvest chemical energy of food.
In fermentation, Anaerobic respiration, and Aerobic respiration, NAD+ is
the oxidizing agent that accepts electrons during glycolysis.
The processes have different final electron acceptors:
an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration.
Cellular respiration produces 32 ATP per glucose molecule; and
fermentation produces 2 ATP per glucose molecule.
Obligate anaerobes carry out
fermentation or anaerobic respiration and cannot survive in the presence of O2.
Yeast and many bacteria are facultative anaerobes, meaning that
they can survive using either fermentation or cellular respiration.
In a facultative anaerobe, pyruvate is the
fork in the metabolic road that leads to two alternative catabolic routes.
Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere.
Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP.
Glycolysis is a very
ancient process.
Glycolysis and the Citric Acid Cycle connect to
many other metabolic pathways.
Glycolysis and the citric acid cycle are major intersections to
various catabolic and anabolic pathways.
Catabolic pathways funnel electrons from many kinds of organic molecules into
cellular respiration.
Glycolysis accepts a
wide range of carbohydrates.
Proteins must be digested to amino acids; amino groups can feed
glycolysis or the citric acid cycle.
Fats are digested to
glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)
Fatty acids are broken down by
beta oxidation and yield acetyl CoA.
An oxidized gram of fat produces more than
twice as much ATP as an oxidized gram of carbohydrate.
The body uses small molecules to
build other substances.
We don’t just eat to get ATP – portions of our diet go to building up molecules.
These small molecules may come directly from food, from glycolysis, or from the citric acid cycle.
Feedback Inhibition is the
most common mechanism for control.
The end product inhibits an enzyme used in the synthesis pathway.
If ATP concentration begins to drop, respiration speeds up;
when there is plenty of ATP, respiration slows down.
Control of catabolism is based mainly on
regulating the activity of enzymes at strategic points in the catabolic pathway.
