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Cell respiration and metabolism

Terms in this set (85)

Metabolism
is the complete set of chemical reactions that occur in living cells. These processes are the basis of life, allowing cells to grow and reproduce, maintain their structures, and respond to their environments.
The chemical reactions of metabolism
are organized into metabolic pathways, in which one chemical is transformed into another by a sequence of enzymes.
Enzymes allow the regulation of metabolic pathways
in response to changes in the cell's environment or signals from other cells.
Catabolic reactions
release energy, usually by the breakdown of larger organic molecules into smaller molecules.
The catabolic reactions that break down glucose, fatty acids, and amino acids
serve as the primary sources of energy for the synthesis of ATP. this means that some of the chemical-bond energy in glucose is transferred to the chemical bond energy in ATP. Since energy transfers can never be 100% efficient, some of the chemical-bond energy from glucose is lost as heat.
Anabolic reactions
require the input of energy and include the synthesis of large energy-storage molecules, including glycogen, fat, and protein.
Aerobic respiration
requires O2 in order to generate ATP. It is the preferred method of pyruvate breakdown from glycolysis & requires that pyruvate enter the mitochondrion to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP by substrate-level phosphorylation, NADH.
The energy transfer involves
oxidation-reduction reactions.
Oxidation of a molecule occurs when
the molecule loses electrons.This must be coupled to the reduction of another atom or molecule, which accepts the electrons.
In the breakdown of glucose
and other molecules for energy, some of electrons initially present in these molecules are transferred to intermediate carriers and then to a final electron acceptor.
When a molecule is completely broken down to carbon dioxide and water within an animal cell,
the final electron acceptor is always an atom of O2. Because of the involvement of O2, the metabolic pathway that converts molecules such as glucose or fatty acid to carbon dioxide and water (transferring some of the energy to ATP) is called aerobic cell respiration.
Glycolysis
is the metabolic pathway by which glucose-a six-carbon sugar is converted into to molecules of pyruvic acid,or pyruvate.
Each pyruvic acid molecule contains
three carbons, three oxygens, and four hydrogens.
Glucose molecule
C6H12O6- can thus be accounted for in the two pyruvic acid molecules.
In glycolysis,
four hydrogen atoms are removed from the intermediates. Each pair of these hydrogen atoms is used to reduce a molecule of NAD. In this process, each pair of hydrogen atoms donates two electrons to NAD, thus reducing it.
Starting from one glucose molecule glycolysis results in
the production of two molecules of NADH and two H+. The H+ will follow the NADH in subsequent reactions, so for simplicity we can refer to reduced NAD simply as NADH .
Glycolysis
is exergonic, and a portion of the energy that is released is used to drive the endergonic reaction ADP+ Pi =ATP.
At the end of the gycolytic pathway, there is a net gain of two ATP molecules per glucose molecule:
Glucose + 2NAD+2 ADP+ 2Pi= 2pyruvic acid +2 NADH+ 2ATP
NAD
Nicotinamide adenine dinucleotide. is an important coenzyme found in cells. It plays key roles as a carrier of electrons in the transfer of reduction potential. .
NADH
is the reduced form of NAD+, and NAD+ is the oxidized form of NADH
Fermentation of pyruvate
w/o O2, pyruvate is not metabolized by cellular respiration but fermentation.
In skeletal muscles, the waste product is
lactic acid. This type of fermentation is called lactic acid fermentation.
In yeast, the waste products are
ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation.
fermentation of pyruvate
Instead of mitochondrion it stays in the cytoplasm, where it is converted to waste products that may be removed from the cell. purpose: oxidizing the H+ carriers so that they can perform glycolysis again and removing the excess pyruvate. This waste product varies depending on the organism.
In order for glycolysis to continue, there must be adequate amounts of
NAD available to accept hydrogen atoms. Therefore, the NADH produced in glycolysis must become oxidized by donating its electrons to another molecule
When oxygen is not available in sufficient amounts, the NADH (H+)
produced in glycolysis is oxidized in the cytoplasm by donating its electrons to pyruvic acid. This results in the re-formation of NAD and the addition of two H+ atoms to pyruvic acid, which is thus reduced. This addition of two hydrogen atoms to pyruvic acid produces lactic acid.
Anaerobic respiration.
The metabolic pathway by which glucose is converted to lactic acid
Fermentation
a process of energy production in a cell under anaerobic conditions (no O2). In common usage fermentation is a type of anaerobic respiration, however a more strict definition exists which defines fermentation as respiration under anaerobic conditions with no external electron acceptor.
Example of fermentation
even in the presence of abundant oxygen, yeast cells greatly prefer fermentation, as long as sugars are readily available for consumption.
Sugars
are the common substrate of fermentation, and typical examples of fermentation products are ethanol, lactic acid, and hydrogen. However, more exotic compounds can be produced by fermentation, such as butyric acid and acetone.
Ischemia
refers to inadequate blood flow to an organ, such that the rate of oxygen delivery is insufficient to maintain aerobic respiration.
myocardial ischemia
Inadequate blood flow to the heart may occur if the coronary blood flow is occluded by atherosclerosis, a blood clot or by an artery spasm. severe pain in the chest and left arm. elevated blood levels of lactic acid which are produced by the ischemic heart muscle.
Glycogenesis
the formation of glycogen from glucose. Cells cannot accumulate very many separate glucose molecules, instead, many organs, particularly the liver, skeletal muscles, and heart, store carbohydrates in the form of glycogen.
During the glycogenesis process,
glucose is converted to glucose 6-phosphate by utilizing the terminal phosphate group of ATP. Glucose 6-phosphate is then converted into its isomer, glucose 1-phosphate. Finally, the enzyme glycogen synthase removes these phosphate groups as it polymerizes glucose to form glycogen
Glycogenolysis
The enzyme glycogen phosphorylase catalyzes the breakdown of glycogen to glucose1-phosphate. The Glucose 1-phosphate is then converted to glucose 6-phosphate.
glycogenolysis and the liver
glycogen stored in the liver and muscles is converted first to glucose-1- phosphate and then into glucose-6-phosphate.
In most tissues, glucose 6-phosphate can then be
respired for energy (through glycolysis) or used to resynthesize glycogen.
Only in the liver,
can the glucose 6-phosphate also be used to produce free glucose for secretion into the blood.
The liver contains
an enzyme as glucose 6-phosphatase that can remove the phosphate can then be transported through the cell membrane. The liver, then, can secrete glucose into the blood. Liver glycogen can thus supply blood glucose for use by other organs
Skeletal muscles, which have large amounts of
glycogen, can generate glucose 6-phosphate for their own glycolytic needs, but they cannot secrete glucose into the blood because they lack the ability to remove the phosphate group.
Two hormones which control glycogenolysis are
a peptide, glucagon from the pancreas and epinephrine from the adrenal glands.
Glucagon is released from
the pancreas in response to low blood glucose and epinephrine is released in response to a threat or stress. Both hormones act upon enzymes to stimulate glycogen phosphorylase to begin glycogenolysis and inhibit glycogen synthetase (to stop glycogenesis).
Gluconeogenesis
reverse of glycolysis. The conversion of noncarbohydrate molecules (not just lactic acid but also amino acids and glycerol) through pyruvic acid to glucose.
In human and other mammals, much of the lactic acid produced in anaerobic respiration is...
later eliminated by aerobic respiration of the lactic acid to carbon dioxide and water. However, some of the lactic acid produced by exercising skeletal muscles is delivered by the blood to the liver.
Within the liver cells under these conditions, the enzyme lactic acid dehydrogenase (LDH)...
converts lactic acid to pyruvic acid. Un like most other organs, the liver contains the enzymes needed to take pyruvic acid molecules and convert them to glucose 6-phosphate, a process that is essentially the reverse of glycolysis.
During exercise, some of the lactic acid produced by skeletal muscles may transformed
through gluconeogenesis in the liver to blood glucose. This new glucose can serve as an energy source during exercise and can be used after exercise to help replenish the depleted muscle glycogen.
Cori cycle
Two-way traffic between skeletal muscles and the liver.. Through the Cori cycle, gluconeogenesis in the liver allows depleted skeletal muscle glycogen to be stored within 48 hours.
The aerobic respiration of glucose begins with
glycolysis
Glycolysis results in the production of
two molecules of pyruvic acid, two ATP, and two NADH+H+ per glucose molecule.
In aerobic respiration, pyruvic acid leaves the
cell cytoplasm and enters the interior of mitochondria.
Once pyruvic acid is inside a
mitochondrion, carbon dioxide is enzymatically removed from each three-carbon-long pyruvic acid to form a two-carbon-long organic acid-acetic acid.
acetyl CoA
acetic acid with a coenzyme A . serve as substrates for mitochondrial enzymes in the aerobic pathway, while the CO2 is a waste product that is carried by the blood to lungs for elimination.
Glycolysis converts one glucose molecule into two molecules of
pyruvic acid. These acetyl CoA molecules serve as substrates for mitochondrial enzymes in the aerobic pathway, while the carbon dioxide is a waste product that is carried by the blood to lungs for elimination.
Each pyruvic acid molecule is converted into
one molecule of acetyl CoA and one CO2, two molecules of acetyl CoA and two molecules of CO2are derived from each glucose.
Once acetyl CoA has been formed
the acetic acid (two carbon long) combines with oxaloacetic acid ( four carbons long) to form a molecule of citric acid (six carbons long). Co A acts only as a transporter of acetic acid from one enzyme to another.
The formation of citric acid begins a cyclic metabolic pathway known as
the citric acid cycle, this cyclic pathway is called the Krebs cycle.
Kreb's cycle
Through a series of reactions involving the elimination of two carbons and four oxygens (as two CO2 molecules) and the removal of hydrogens, citric acid is eventually converted to oxaloacetic acid, which completes the cyclic metabolic pathway.
Kreb's cycle results
One guanosine triphosphate (GTP) is produced which donates a phosphate group to ADP to produce one ATP.
Three molecules of NAD are reduced to NADH 3, and one molecules of FAD is reduced to FADH2.
NAD: Nicotinamide adenine dinucleotide
(NAD) is an important coenzyme found in cells. It plays key roles as a carrier of electrons in the transfer of reduction potential. NADH is the reduced form of NAD+, and NAD+ is the oxidized form of NADH.
flavin adenine dinucleotide (FAD)
is the precursor molecule to FADH2. Upon bonding to two hydrogen atoms, FAD is then changed to FADH2 and is turned into an energy-carrying molecule).
NADH and FADH2 eventually donate their electrons to an
energy-transferring process that results in the formation of large number of ATP. (32)
Mitochondria structure
There is a smooth outer membrane, surrounding a very convoluted inner membrane.
cristae
convolutions form recognizable structures
Mitochondria membranes
Together they create two compartments, namely the intermembrane space (the comparment between the membranes), and the matrix (the very interior of the mitochondria).
Electron transport
In the cristae of inner mitochondrial membrane are a series of molecules that serve as an electron-transport system during aerobic respiration.
Components of the electron transport system include
complexes I, II, III, and IV, plus two individual molecules, coenzyme Q and cytochrome c
electron transport chain
series of electron acceptors and proton pumps in the membranes of mitochondrial cristae. accept energy from NADH and FADH2
As electrons pass through ETC,
their energy is used to pump H+ from matrix to outer compartment. H+ will later diffuse back into matrix and produce 32 ATP
Chemiosmosis
is the process where protons diffuse from the outer compartment (high concentration) through ATP Synthase in the Cristae to the Matrix (low H+ Concentration). The energy in the protons as they pass is used by ATP synthase to create 32 ATP.
purpose of the Electron Transport Chain
is to receive the high energy electrons carried by the coenzymes NADH &FADH2 and use the energy from these electrons to pump protons out of the matrix. A high concentration of protons results. As the protons diffuse back to the matrix, their energy is used by the ATP synthase to create ATP.
electron transport occurs..
at cristae (Inner membranes)
NADH & FADH2 deliver
H+ and e- to cristae.
Electrons "transport" along cristae through electron acceptors,
provide energy to pump H+ from matrix to outer compartment.Concentration of H+ is now higher in outer compartment. H+ pass through ATP synthases in cristae back to matrix. ATP are made. This is known as chemiosmosis. Last step involves H+ & e- added to oxygen. This frees NAD+ to return to glycolysis & Krebs Cycle to pick up more H+ & e-.
lipolysis
When fat stored in adipose tissue is going to be used as an energy source, lipase, enzymes hydrolyze triglycerides into glycerol and free fatty acids.These molecules serve as blood-borne energy carriers that can be used the liver, skeletal muscles, and other organs for aerobic respiration. `
Most fatty acids consist of
a long hydrocarbon chain with a carboxyl, or carboxylic acid group (COOH) at one end. In a process known as B-oxidation enzymes remove two-carbon acetic acid molecules from the acid end of a fatty acid chain.
The amount of brown fat in the body is greatest
at the time of birth. Brown fat is the major site for thermogenesis in the newborn.
Brown fat location
around the kidneys and adrenal glands and around the blood vessels of the chest and neck.
Brown fat produces
a unique uncoupling protein. This protein causes H+ to leak out of the inner mitochondrial membrane, so that less H+ is available to pass through the respiratory assemblies and drive ATP synthase activity.
Lower ATP concentrations
cause the electron-transport system to be more active and generate more heat from the respiration of fatty acids. This extra heat may be needed to prevent hypothermia in newborns.
The blood serves as
a common trough from which all the cells in the body are fed. If all cells used the same energy sources, such as glucose, this source would quickly be depleted and cellular starvation would occur.
The blood contains a variety of energy sources from which to draw:
glucose and ketone bodies that come from the liver, fatty acids from adipose tissue, and lactic acid and amino acids from muscles. Some organs preferentially use one energy source more than the others, so that each energy source is spared for organs with strict energy needs.
The brain uses blood glucose as
its major energy source.
Under fasting conditions
blood glucose is supplied primarily by the liver through glycogenolysis and gluconeogenesis.
In addition, the blood glucose concentration
is maintained because many organs spare glucose by using fatty acids, ketone bodies, and lactic acids as energy sources.
During serve starvation
the brain also gains some ability to metabolize ketone bodies for energy.
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