41 terms

KBB chapter 8 "Respiration"

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External Respiration
refers to the entrance of air into the lungs and the gas exchange between the alveoli and the blood
Internal Respiration
exchange of gas between the blood and the cells and the intracellular processes of respiration
photosynthesis
converts energy of the sun into chemical energy of bonds in compounds such as glucose.
Respiration
conversion of chemical energy in these bonds into usable energy needed to drive the processes of living cells
favored fuel molecules in living cells
carbohydrates and fats
c-h bond (about)
As hydrogen is removed, bond energy is made available. energy rich, compared with other bonds it is capable of releasing the largest amt of energy per mole.
is carbon dioxide more or less energy rich than c-h bond
it has little usable energy. stable, energy exhausted end product of respiration.
dehydrogenation
high energy hydrogen atoms are removed from organic molecules during respiration. oxidation reaction. reduction component of redox reaction is the acceptance of hydrogen by a hydrogen acceptor (oxygen in final step)
The energy released from the reduction of accepting a hydrogen acceptor goes to..
forming a high energy phosphate bond in ATP.
net result of this redox reaction
energy production
two stages of degenerative oxidation of glucose
glycolysis and cellular respiration
where does glycolysis occur
cytoplasm, mediated by specific enzymes
glycolysis
series of reactions that lead to the oxidative breakdown of glucose into two pyruvate molecules, the production of ATP, and the reduction of NAD+ and NADH.
step 1: glucose turns into glucose 6 phosphate when
ATP->ADP.
step 2: glucose 6 phosphate turns into fructose 6 phosphate
step 3: fructose 6 phosphate turns to fructose 1,6 diphosphate when ATP->ADP.
step 4: fructose 1,6 diphosphate forms glyceraldehyde 3 phosphate (PGAL) in equilibrium with dihydroxyacetone phosphate
dihydroxyacetone phosphate is isomerized into PGAL so that it can be used in subsequent reactions. Thus, 2 molecules of PGAL are formed per molecule of glucose and all subsequent steps occur twice for each glucose molecule.
step 5: the two in equilibrium turn to 1,3 diphosphoglycerate when NAD+->NADH
step 6: 1,3 diphosphoglycerate turns to 3-phosphoglycerate when ADP->ATP
step 7: 3 phosphoglycerate turns to 2 phosphoglycerate
step 8: 2-phosphoglycerate turns to phosphoenolpyruvate
step 9: phosphoenolpyruvate turns to pyruvate when ADP->ATP
steps 5-9 occur twice per molecule of glucose
biproducts of glycolysis
2 pyruvate molecules, net 2 ATP per glucose molecule, 2 NADH per glucose
substrate level phosphorylation
ATP synthesis is directly coupled with the degradation of glucose without the participation of an intermediate molecule such as NAD+
after glycolysis, pyruvate degradation can proceed in one of two directions:
anaerobic and aerobic
anaerobic conditions (fermentation)
In the absence of oxygen, pyruvate is reduced during the process of fermentation.
NAD+ must be regenerated for glycolysis to continue in the absence of oxygen (accomplished by reducing pyruvate into ethanol or lactic acid) this term refers to all of the reactions involved in this process-glycolysis and the additional steps leading to the formation of ethanol or lactic acid. produces only 2 ATP per glucose molecule.
alcohol fermentation
commonly occurs only in yeast and some bacteria. The pyruvate produced in glycolysis is converted to ethanol, NAD+ is regenerated and glycolysis can continue.
lactic acid fermentation
occurs in certain fungi and bacteria and in human muscle cells during strenuous activity. When O2 supply to muscle cells lags behind the rate of glucose catabolism, pyruvate generated is reduced to lactic acid and NAD+ is regenerated.
aerobic conditions
In the presence of oxygen, pyruvate is further oxidized during cell respiration in the mitochondria.
cellular respiration
Aerobic process, oxygen acts as the final acceptor of electors that are passed from carrier to carrier during the final stage of glucose oxidation. most efficient catabolic pathway used for organisms to harvest the energy stored in glucose. Cellular respiration can yield 36-38 ATP.
can be divided into three stages: pyruvate decarboxylation, citric acid cycle, electron transport chain
where does cellular respiration occur
in the mitochondrion, catalyzed by reaction specific enzymes.
pyruvate decarboxylation
pyruvate formed during glycolysis is transported from the cytoplasm into the mitochondrial matrix where it is decarboxylated (loses a CO2 and the acetyl group that remains is transferred to coenzyme A to form acetyl CoA.) NAD+ reduced to NADH.
citric acid cycle
AKA Krebs Cycle. Begins when the two carbon acetyl group from acetyl CoA combines with oxaloacetate, a four carbon molecule, to form the six carbon citrate. 2 CO2's are released after complicated series of reactions, and oxaloacetate is regenerated for use in another turn of the cycle.
For each turn, 1 ATP is produced by substrate level phosphorylation via a GTP intermediate. Electrons are transferred to NAD+ and FAD, generating NADH and FADH2. These coenzymes then transport the electrons to the electron transport chain, where there is more ATP produced via oxidative phosphorylation. Keep in mind for each molecule of glucose, 2 pyruvates are decarboxylated and channeled into CAC.
net reaction of the citric acid cycle per glucose molecule
4 CO2, 6 NADH, 2FADH2, 2ATP, 4H+ and 2CoA
electron transport chain
located on inner mitochondrial membrane.
During oxidative phosphorylation, ATP is produced when high energy potential electrons are transferred from NADH and FADH2 to oxygen by a series of carrier molecules located in the inner mitochondrial membrane. As electrons are transferred, free energy is released, which is used to form ATP. most of the molecules in this chain are cytochromosomes which are electron carriers that resemble hemoglobin in the structure of their active site. Cytochromosomes can be reduced and oxidized, and sequential redox reactions continue to occur as electrons are transferred from one carrier to the next, each reduced as it accepts an electron and oxidized when it passes it on to the next carrier. The last carrier passes its electron to the final electron acceptor, O2. In addition to the electrons it picks up a pair of hydrogen ions from surrounding medium forming water.
How many ATP's formed from substrate level phosphorylation overall in cellular respiration
degradation of 1 glucose molecule yields a net of 2 ATP from glycolysis and 1 ATP for each turn of the citric acid cycle. Thus a total of 4 ATP produced.
How many ATP's formed from oxidative phosphorylation overall in cellular respiration
two pyruvate decarboxylations yield 1 NADH each for a total of 2 NADH. Each turn of the citric acid cycle yields 3 NADH and 1 FADH2 , for a total of 6 NADH and 2 FADH2 per glucose molecule. Each FADH2 generates 2 ATP, each NADH generates 3 ATP except for the 2 NADH reduced during glycolysis which produce 2 ATP for each glucose molecule. Therefore, 4 ATP's from glycolysis, the other 8 NADH yield 24 ATP, and the 2 FADH2 produce 4 ATP, total of 32 ATP by oxidative phosphorylation.
This leads to a sum total of 36 ATP produced during eukaryotic glucose catabolism
Why do prokaryotes produce 38 ATP's instead of 36 as in eukaryotes?
the 2 NADH of glycolysis don't have any mitochondrial membranes to cross and therefore don't lose energy
carbohydrates as an alternative energy source
disaccharides are hydrolyzed into monosaccharides, most of which can be converted into glucose or glycolytic intermediates. Glycogen stored in the liver can be converted into a glycolytic intermediate when needed.
Fats as an alternative energy source
stored in adipose tissue in the form of triglyceride, however, when they're needed they are hydrolyzed by lipases into fatty acids and glycerol and are carried by blood to other tissues for oxidation. Glycerol can be converted into PGAL. A fatty acid must be activated in the cytoplasm which requires 2 ATP. Once activated, fatty acid is transported into mitochondrion and taken thru beta-oxidation cycles that convert it into 2 carbon fragments, which are then converted into acetyl CoA. Acetyl CoA then enters the citric acid cycle, with each round of b oxidation of a saturated fatty acid, 1 NADH and 1 FADH2 are generated.
Fats yield the greatest number of ATP per gram. Extremely efficient energy storage molecules. (stored fat reserves can meet long term energy needs for about a month)
Proteins as an alternative energy source
body degrades proteins in last resort. Most amino acids undergo transamination reaction in which they lose an amino group to form an alpha keto acid. The carbon atoms of most amino acids are converted into acetyl CoA, pyruvate, or one of the intermediates of citric acid cycle. These then enter their respective metabolic pathways, allowing cells to produce fatty acids, glucose, or energy in the form of ATP.
oxidative deamination- removes an ammonia molecule directly from amino acid, ammonia is a toxic substance in vertebrates, fish can excrete ammonia while insects and birds convert it to uric acid and mammals convert it to urea for excretion
Respiratory system of arthropod phylum
Consists of a series of respiratory tubules called tracheae whose branches reach to almost every cell. open to surface in openings called spiracles, permits intake distribution and removal of resp. gases directly between the air and the body cells by diffusion. No oxygen carrier is needed in the respiratory system and the efficiency of this system allows insects to have relatively inefficient open circulatory system (what is this sentence)
Respiration in humans
air enters lungs after traveling through respiratory airways. Air passages= nose, pharynx, larynx, trachea, bronchi, bronchioles, and the alveoli. Gas exchange bw the lungs and the circulatory system occurs in alveoli (air filled sacs at the terminals of the airway branches) Following gas exhange, air rushes back thru respiratory pathway and is exhaled.
ventilation
ventilation of the lungs (breathing) is the process by which air is inhaled and exhaled. Purpose of this is to take in oxygen from surroundings and eliminate carbon dioxide from the body.
inhalation
diaphragm contracts and flattens, and external intercostal muscles contract pushing the rib cage and chest wall up and out. This causes thoracic cavity to increase in volume, which in turn reduces the pressure causing lungs to expand and fill with air.
exhalation
generally a passive process in which the lungs and chest wall are highly elastic, and tend to recoil to their original positions following inhalation. Diaphragm and external intercostal muscles relax and the chest wall pushes inward. The consequent decrease in thoracic cavity volume causes the air pressure to increase. This causes lungs to deflate, forcing air out of the alveoli.
ventilation is regulated by
neurons (respiratory centers) located in medulla oblongata.
It's rhythmic discharges stimulate intercostal muscles and/or diaphragm to contract. When partial pressure of CO2 rises, medulla stimulates an increase in the rate of ventilation **
Increase in CO2 in the body causes...
ventilation (to decrease carbon dioxide and increase oxygen)
pulmonary capillaries
dense network of minute blood vessels that surround the alveoli. Gas exchange occurs by diffusion across capillary walls and those of alveoli. gases move from regions of higher partial pressure to regions of lower partial pressure
o2 diffuses from ___ to ____
and co2 diffuses from ____ to ____
O2 diffuses from alveolar air into the blood while carbon dioxide diffuses from the blood into the lungs to be exhaled.
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