Transcript Chapter 5: capturing and releasing energy

CHAPTER 5: CAPTURING
AND RELEASING
ENERGY
Part 4
FERMENTATION
 Fermentation is an anaerobic pathway that can release energy
from carbohydrates.
 It occurs in the absence of oxygen, thus anaerobic.
 Bacteria and single-celled protists that live under anaerobic
conditions such as those in the human gut, in sea sediments,
mud, sewage treatment plants, etc. use this pathway.
 Most of these anaerobic cells cannot tolerate oxygen and die
when exposed to it.
 Other single-celled organisms, such as yeast, can perform
either fermentation or aerobic respiration.
 Animal muscle cells can also use both pathways.
 Generally, however, multicellular organisms cannot rely on
this pathway alone to produce the ATP needed for survival
since this process yields only the 2 ATP from glycolysis.
FERMENTATION
 Both aerobic respiration and fermentation begin with the
same reaction, glycolysis.
 After glycolysis, fermentation yields two pyruvate molecules ,
two NADH, and 2 ATP, just like in aerobic respiration.
 However, after this, fermentation continues to occur in the
cytoplasm, while aerobic respiration occurs in the
mitochondrion.
 Also, in fermentation, pyruvate is not cleaved to produce
carbon dioxide like it is aerobic respiration.
 In addition, electrons don’t flow through an electron transport
chain during fermentation and this is the reason why only 2
ATP form.
 Instead electrons are moved away from the the NADH to
regenerate NAD+ so that glycolysis can continue to happen
over and over (because glycolysis requires NAD+ to continue).
ALCOHOLIC FERMENTATION
 During this kind of fermentation, the pyruvate from glycolysis is
converted to ethyl alcohol (or ethanol).
 This happens when the 3 -carbon pyruvate is cleaved into a 2 -carbon
molecule called acetaldehyde and the carbon that is cut off leaves
as carbon dioxide.
 This process is taken advantage of when bakers use yeast to make
bread.
 The carbon dioxide released by the yeast as they break down the
carbohydrates in the dough during alcoholic fermentation is what
causes cakes and breads to rise.
 This process is also used to produce wine.
 Crushed grapes are left in vats with large populations of yeast
cells, which convert the sugars in the grapes to ethanol.
 However, once the concentration of alcohol in the vat reaches 12%,
it kills the yeast.
 Therefore, wines naturally will never have more than 12% alcohol.
LACTIC ACID FERMENTATION
 In this kind of fermentation, the electrons/H+ carried by
NADH are transferred directly to pyruvate.
 This converts 3-carbon pyruvate to 3 -carbon lactate (lactic
acid).
 It also converts NADH back to NAD+, which is needed for
glycolysis to continue.
 A special bacterium used in milk performs lactic acid
fermentation, producing buttermilk, cheese, and yogurt.
 Some yeast that do this reaction are used to preserve pickles
and sauerkraut, among other foods.
LACTIC ACID FERMENTATION
 Animal skeletal muscles contain two types of fibers: slow
fibers and fast fibers.
 These fibers dif fer in how they make ATP.
 Slow fibers have many mitochondria and use aerobic
respiration.
 They are used by your muscles during extended periods of
activity, such as a long run or swim.
 They also have an abundance of myoglobin, an oxygen storing
protein much like the hemoglobin in your blood which causes
them to appear red and allows them to do aerobic respiration.
LACTIC ACID FERMENTATION
 Fast muscle fibers contain few mitochondria and no myoglobin,
so they cannot carry out aerobic respiration and appear white
instead of red.
 They make most of their ATP using lactic acid fermentation.
 This pathway makes ATP quickly but not for very long, since the
lactic acid actually causes the muscle to cramp and fatigue
quickly.
 Therefore, these fibers are used for quick, strenuous activities
such as sprinting or weightlifting, rather than sustained
activities.
 This is the main reason chickens can’t fly very far; their breast
and wing muscle contain almost all white, fast fibers.
 Chickens usually walk or run with their legs.
 This is because their leg muscles contain mostly slow, red fibers.
 This is why chicken breast and wing are white and the leg and
thigh are dark.
LACTIC ACID FERMENTATION
 Unlike chickens, most human muscles contain a mixture of
both fast and slow fibers, but the ratio of fast to slow varies in
dif ferent muscles and in dif ferent individuals.
 For example, great sprinters have a higher proportion of fast
fibers, while great marathon runners have a higher proportion
of slow fibers.
THE FATE OF GLUCOSE
 When a cell takes in more than enough glucose, the rate of ATP
production increases dramatically.
 If this ATP is not used quickly, its concentration increases in
the cytoplasm.
 This high concentration of ATP causes glucose to be diverted
away from glycolysis, to stop respiration and ATP formation.
 Instead, glucose is diverted to another pathway, one that
makes glycogen, which is a polysaccharide used for longer
term storage of energy.
 Also, if you eat too many carbohydrates, your blood level of
glucose gets too high and the Acetyl C0 - A that is used during
the Kreb’s cycle is diverted away toward a pathway that makes
fatty acids.
 This is why excess carbohydrates in your diet end up as fat.
THE FATE OF GLUCOSE
 Hormones control how the glucose in your diet is used.
 When the amount of glucose in your bloodstream rises, your
pancreas releases a hormone called insulin to help your cells to
take up that glucose to be used for energy production or
storage as glycogen (a long -term storage carbohydrate) or fat.
 When the amount of glucose in your bloodstream declines, the
pancreas releases a dif ferent hormone called glucagon.
 Glucagon initiates the conversion of stored carbohydrates, such
as glycogen, to glucose, which is a carbohydrate that can be
used very quickly by a cell for energy.
 Glycogen makes up about 1% of an average adult’s total stored
energy, which is about the equivalent of 2 cups of pasta.
 If you don’t eat regularly, you will deplete your body’s glycogen
stores in less than twelve hours.
THE FATE OF GLUCOSE
ENERGY FROM FATS
 While glycogen makes up only 1% of the stored energy reserves
in an adult, 78% of that reserve if made up of fat and 21% is
made up of protein.
 How does the body tap into these reserves in order to retrieve
their stored energy?
 Special fats called triglycerides are the main fat storage
molecule in your body.
 Triglycerides consist of a glycerol molecule with three fatty acids
attached.
 The glycerol molecules can be converted to an intermediate of
glycolysis by liver enzymes.
 The fatty acids can be cut by enzymes into fragments, which can
then be converted to Acetyl Co - A so that they can be used in the
Kreb’s cycle.
 Fats provide more energy per molecule than carbohydrates and
this is why, during prolonged exercise, fatty acid breakdown
provides about half of the ATP that is needed by muscle, liver,
and kidney cells.
ENERGY FROM FATS
 Diets that are extremely low in carbohydrates force the body
to use fats for energy.
 The breakdown of fats produces ketones, which cells can use
for energy instead of glucose.
 The state produced in the body as a result of the use of
ketones for energy is associated with starvation.
 It causes the level of LDL (“bad” fats) to increase in the blood
and can damage the kidneys and liver.
ENERGY FROM PROTEINS
 Enzymes in your digestive system can break proteins down
into their amino acid subunits.
 These amino acids are then further broken down by removing
their amino group, which becomes ammonia and is eliminated
from the body as urine.
 The carbon portion of the protein is then split to form Acetyl
Co- A , pyruvate, or other intermediates used in the Kreb’s
cycle.
ALTERNATIVE ENERGY SOURCES IN THE BODY
HOMEWORK
 Compare and Contrast alcoholic fermentation with lactic acid
fermentation.
 Explain why chicken breast and wing are white, while their leg
and thigh are dark.
 Both fats and proteins can enter what reaction of respiration
after being broken down?