Chapter 8: Energy Metabolism Flashcards
metabolism
the chemical processes involved in maintaining life
metabolism is the chemical processes involved in maintain life by:
- enabling us to release energy from carbohydrates, fats, proteins, and alcohol
- permitting us to synthesize new substances and excrete waste products
metabolism process
glycolysis –> acetyl CoA –> TCA cycle –> electron transport chain
metabolic pathway
a group of biochemical reactions that occur in a progression
what compounds are formed during the steps of metabolism
intermediates
metabolism is sometimes termed as
the bioenergetics because it is how we get energy
energy is stored in
the bonds that connect the molecules that make up carbohydrates, proteins, and fats
energy is released when
the bonds are broken
the bonds are broken with
- aerobic reactions
- anaerobic reactions
glycolysis
the metabolism of glucose
aerobic reactions
with oxygen
anaerobic reactions
no oxygen
anabolic pathways
use small compounds to build larger ones
anabolic equals
building
anabolic pathways use
energy
anabolic pathways are used during
periods of growth; pregnancy and childhood/adolescence
anabolic pathways use what small compounds to build larger ones
glucose, fatty acids, cholesterol, and amino acids are building the blocks
how we use glucose to build glycogen is an example of what pathway
anabolic pathway
catabolic pathways
break down larger compounds into smaller ones
glycogen is broken down to make glucose is an example of what pathway
catabolic pathway
catabolic pathways results in the release of
CO2, H2O, and energy (ATP)
catabolic pathways produce
energy
catabolic pathways are more prominent during
weight loss, wasting disease, or cancer
Because of the catabolic pathway, when someone is trying to lose weight it is really difficult to
maintain muscle mass
metabolism takes place
within the cells
different cells perform different metabolic functions
each cell’s structure is similar
outside of cell
plasma membrane
plasma membrane of a cell
holds in the cell contents
inside of cell
organelles and cytosol
organelles
mitochondria
mitochondria
- generate most of the cell’s energy from carbohydrates, proteins, and fats
- most of the body’s energy is produced here
how is energy generated in the organelles
by aerobic metabolism
cytosol
fluid portion of the cell
what takes place in the cytosol
glycolysis and anaerobic metabolism
the most metabolically active organ
the liver
first organ to metabolize, store and distribute nutrients after absorption
the liver
the liver converts monosaccharides, amino acids, glycerol and fatty acids into
- new compounds
- energy
- and store for future use
when the compounds in the liver are stores for future use they are stored as
- triglycerides
- glycogen
glycogen stores in the liver are responsible for
distributing nutrients
glycogen stored in the liver is broken down when
our blood glucose levels are low
stored glycogen helps
regulate or maintain homeostasis in blood glucose levels
what is stored glycogen not used for
energy
before the body can use energy from food, it must first
disassemble the macronutrients into carbon dioxide and water while capturing the released energy as ATP
adenosine triphosphate (ATP)
a high energy molecule composed of adenine, ribose, and three phosphate molecules
any source of macronutrients can be used to generate
ATP
catabolism
the breaking down aspect of metabolism
three stages of catabolism
- digestion: breakdown of complex molecules to their component building blocks
- conversion of building blocks to acetyl-CoA (or other simple intermediates)
- metabolism of acetyl-CoA to CO2 and formation of ATP
complex molecules and building blocks involved in catabolism
- proteins –> amino acids –> acetyl-CoA
- carbohydrates –> monosaccharides –> acetyl-CoA
- lipids –> fatty acids, glycerol –> acetyl-CoA
- alcohol –> acetyl-CoA
only energy in ATP can be used directly to:
- synthesize new compounds
- contract muscles
- conduct nerve impulses
- pump ions across membranes (ex. active transport/the sodium-potassium pump)
ATP structure
made of adenine and ribose together which is adenosine bound to 3 phosphate groups
in ATP the bonds that connect the phosphate groups contain
energy
how is the energy released from the bonds in ATP
hydrolysis
someone who is about to do a high intensity exercise
- in 3 to 5 seconds use up the ATP
- have to continually produce ATP
- when we can’t keep up with the demands of ATP during exercise, activity levels decrease
ATP is the cell’s direct
energy source
in order to provide a constant supply of energy
the body must continually produce ATP
adenosine diphosphate (ADP)
formed when one phosphate molecule is removed from ATP
regenerating ATP from ADP requires a source of
phosphate
sources of phosphate:
- inorganic phosphate produced from initial breakdown of ATP
- inorganic phosphate in creating phosphate (phosphocreatine or PCr)
creatine phosphate (PCr) is stored in the
muscles
when do we have higher levels of creatine phosphate
at rest
how long does this system last during exercise
creatine phosphate lasts for about 15 seconds during exercise depending on effort and intensity (10-20 seconds)
both sources of phosphate provide enough ATP to sustain a
sprint for up to 10 seconds
creatine phosphate
high energy compound formed in muscle cells when creatine combines with phosphate
how does creatine phosphate make ATP
a phosphate molecule is released to form ATP
as creatine phosphate levels dwindle
the body switches to anaerobic and aerobic metabolism to make ATP
anaerobic metabolism
- no oxygen
- produces less ATP per minute
- only provides 1-1.5 minutes of maximal activity
aerobic metabolism
- with oxygen
- produces more ATP per minute
- is able to produce ATP indefinitely
- when demand for ATP is greater than the rate of metabolism, the activity slows down
during high intensity, short duration activities like sprinting and heavyweight lifting, what type of metabolism do we use
anaerobic metabolism
during low intensity, long duration activites like hiking, what type of metabolism do we use
aerobic metabolism
ATP synthesis involves
the exchange of ions in the form of hydrogen ions from energy-yielding compounds
oxidation reduction reactions are used
- when electrons are transferred eventually to oxygen
- to form water and release energy used to produce ATP
in oxidation reduction reactions, oxygen is
not used in every step
a substance is oxidized when it
loses one or more electrons or hydrogens
a substance is reduced when it
gains one or more electrons or hydrogens
what controls oxidation reduction reactions
enzymes
example of oxidation reduction reaction during glycolysis
glucose is oxidized, producing NADH and ATP
niacin is also called
B3
riboflavin is also called
B2
niacin and riboflavin are
key electron carriers
niacin and riboflavin help transfer hydrogens from energy-yielding compounds to
oxygen in metabolic pathways
niacin functions as a coenzyme
nicotinamide adenine dinucleotide (NAD)
oxidized form of niacin
NAD+ found in cells
reduced form of niacin
NADH found in cells
oxidized form of riboflavin
FAD
reduced form of riboflavin
FADH2
what is the first step in forming ATP from glucose
glycolysis
glucose metabolism is an essential energy source for all cells and particularly the
brain and red blood cells
where does glycolysis take place
the cytosol of the cells
glycolysis is a 10 step
anaerobic (no oxygen) catabolic (breaks down) pathway
in glycolysis we start with
a six carbon glucose, 2 ATP, 2 NAD+
in glycolysis we end with
2 three carbon pyruvates, 4 ATP, 2 NADH
glucose is transformed to pyruvate
- begins with one 6 carbon glucose molecule
- ends with two 3 carbon pyruvate molecules
- generate hydrogen ions
- NAD+ is reduced to form NADH (picks up hydrogen ions)
- NADH carrier hydrogen ions and electrons to the ETC
what happens to pyruvate under anaerobic conditions (no oxygen)
pyruvate gets converted to lactate
for the start of glycolysis
only glucose can start this process, so fructose would have to be converted first
pyruvate to lactate under anaerobic conditions
- metabolic conversion occurs in any cell in the body, including muscle
- during anaerobic metabolism, pyruvate is reduced to lactate to prevent a buildup of excess hydrogen ions
- lactate diffuses out of the cell and enters the liver
once in the liver, how does lactate get converted to glucose
via the Cori Cycle
the Cori Cycle helps maintain maintain energy supply during anaerobic conditions and recycles lactate
minimizing acidosis in muscles
acidosis
a condition in which there is too much acid in the body’s fluids (the body’s acid-base balance is disrupted)
during high intensity exercise, muscle cells rely on anaerobic respiration for ATP production
- causes lactate to build and NAD+ regeneration
- lactate is transferred to the liver where it is converted back to glucose via the Cori Cycle
overview process of the Cori Cycle (from book)
- glucose is converted to pyruvate during glycolysis. If there is not enough oxygen, pyruvate is converted to lactate and is released from the muscle into the blood
- lactate travels through the blood to the liver
- lactate is taken up by the liver and converted to pyruvate and then into glucose through gluconeogenesis
- some glucose can be stored as glycogen through glycogenesis or sent back into the blood to be taken up by the muscle (causing a regeneration of NAD+)
gluconeogenesis
- making glucose out of non-CHO sources
- amino acids, lactate, and glycerol can be used
during gluconeogenesis, this processes uses ATP and ends up
with ADP
how many amino acids are considered glucogenic
18 out of 20 amino acids
glucogenic amino acids can be
transformed into pyruvate and other TCA cycle intermediates that enter gluconeogenesis and produce glucose
pyruvate is the entry point into metabolism for how many of these 18 glucogenic amino acids
for 6 of these 18 amino acids
the 6 amino acids that pyruvate is their entry point into metabolism are
alanine, serine, glycine, threonine, tryptophan, and cysteine
if CHOs are low, we can utilize amino acids to go through the process of glycolysis
being a major source of blood glucose (not under standard conditions in the body)
the other 12 glucogenic amino acids enter at
points along the TCA cycle
glucogenic amino acids are
converted to pyruvate anaerobically and them transformed into glucose through gluconeogenesis, which can then be used to produce energy
ketogenic amino acids are
aerobically converted to CoA, which can either be transformed into fatty acids and stored as a triglyceride in adipose tissue or energy for the TCA cycle
some amino acids can enter the TCA cycle
directly
ketogenic amino acids + oxygen =
Acetyl CoA
triglyceride structure
glycerol backbone and 3 fatty acids
glycerol to pyruvate
only the glycerol portion of the triglyceride is glucogenic and can be used to make glucose
compared with glucose, amino acids, and fatty acids, glycerol produces
very little energy
transition reaction
synthesis of Acetyl-CoA from pyruvate
what happens to all energy producing nutrients before entering the TCA cycle
all energy producing nutrients are transformed to acetyl CoA before entering the TCA cycle
transition reaction occurs in the
presence of oxygen (aerobic)
beta oxidation
adding coenzyme A (CoA)
transition reaction process
- 2 molecules of pyruvate cross the mitochondrial membrane and enter the mitochondria
- a carbon molecule is removed and coenzyme A is added (beta oxidation)
acetyl CoA can enter 2 pathways
- the TCA cycle (if ATP is limited)
- converted to fatty acid and stored as fat (ample ATP)
before fatty acids can be used for energy, what must happen
fatty acids are hydrolyzed from triglycerides by lipolysis
lipolysis
a metabolic process that breaks down triglycerides into glycerol and free fatty acids
what catalyzes the reaction of triglycerides to fatty acids via lipolysis
hormone sensitive lipase
before fatty acids can cross into the mitochondria, they
must be activated
where are fatty acids activated and then sent
fatty acids are activated in the cytosol and then go to the mitochondria
how does the fatty acid become activated
the addition of coenzyme A to the carboxylic end of the fatty acid chain activates the fatty acid
fatty acids are oxidized for energy (breakdown of the process from the book)
- triglycerides from the diet and adipose tissue undergo lipolysis to yield free fatty acids and glycerol. Hormone sensitive lipase stimulates the reaction
- glycerol is first converted to DHAP before it can enter anaerobic glycolysis to be converted to pyruvate. The first step requires ATP which results in ADP
- during beta oxidation, a molecule of CoA is attached to the end of a fatty acid. The 2 end carbons plus CoA are then cleaved off and converted to Acetyl CoA, reducing NAD+ to NADH+H+ and FAD to FADH2
- this aerobic process repeats itself until all the fatty acids have been converted to acetyl CoA
- the acetyl CoA formed enters the TCA cycle
inside the mitochondria, fatty acids are
disassembled by beta oxidation
beta oxidation steps
- 2 carbons at the end of the fatty acid are removed and joined with CoA to form Acetyl CoA
- this process continues until all carbon molecules are converted
- hydrogen and electrons are released as each pair of carbons is cleaved off
need CHOs to go through the process of
beta oxidation
fatty acids are
ketogenic (they can be used to form ketone bodies)
when _______ are low, acetyl CoA increases which is then converted to ketone bodies
CHOs
glucogenic amino acids
can be converted into glucose through gluconeogenesis
ketogenic amino acids
can be converted into ketone bodies or fatty acids (create acetyl CoA)
amino acids that are both ketogenic and glucogenic
are transformed to acetyl CoA before they enter the energy pathway
the tricarboxylic acid (TCA) cycle releases
high energy electrons and hydrogen ions
the TCA cycle is also called the
citric acid or Krebs cycle
what is the third stage for the oxidation of acetyl CoA
the TCA cycle
steps for the oxidation of acetyl CoA
glycolysis –> transition process –> TCA cycle
where does the TCA cycle take place
location is in the mitochondria
process of the TCA cycle
- these macronutrients enter the cycle as acetyl CoA, where most of the energy in the original molecule is now trapped
- this stored energy is freed during the TCA cycle and is transferred to 2 coenzyme hydrogen ion carriers to be released in the ETC
- stored energy is being released
key factors of the TCA cycle
- coenzyme hydrogen carriers
- NADH+H+
coenzymes and electron carriers are key in the
production of ATP
for every FAD how many ATP can we make
1.5 ATP
for every NAD+ how many ATP can we make
2.5 ATP
the ETC and oxidative phosphorylation produces the majority of
ATP
the ETC is comprised of
a series of protein complexes located in the inner mitochondrial membrane
the ETC makes
90% of the ATP used by the body for energy, growth, and maintenance
electrons are transferred from one protein complex to another, resulting in the formation of
ATP and water
protein complexes are called
flavoproteins
flavoproteins contain
riboflavin and cytochromes
cytochromes contain
iron and copper
although vitamins and minerals don’t provide energy, they are essential for
energy production (riboflavin, iron, and copper)
process of the ETC (from the book)
- hydrogen ions and high energy electrons are delivered to the inner mitochondrial membrane from the TCA cycle by NADH+H+ and FADH2
- as the electrons are passed down the ETC, hydrogen ions cross the mitochondrial membrane
- hydrogen ions are forced back across the membrane through the ATP synthase complex to produce ATP and water during oxidative phosphorylation
absorptive state of the body is the
feed state
absorptive state of the body is a period
within 4 hours following a meal in which anabolic (building) processes exceed catabolic (breakdown) processes
what happens to glucose in the absorptive state
build glycogen from glucose
postabsorptive state of the body is a period
of time usually more than 4 hours after eating where catabolic processes exceed anabolic processes
in the postabsorptive state, energy needs are met by
the breakdown of stores (body starts to break down some glycogen into glucose)
what happens to blood sugar in the postabsorptive state
blood sugar starts to dip
the absorptive state and postabsorptive state are both regulated by
hormones
red blood cells and the central nervous system use glucose for energy but
cannot store glucose
liver and muscle convert excess glucose into
glycogen
liver glycogen
- important to maintain blood glucose homeostasis
- only glucose from liver glycogen can enter the bloodstream
- depleted 12-18 hours after eating (will be shorted if someone isn’t eating CHOs because they don’t have those CHO stores)
muscle glycogen
used by muscle for energy
excess CHOs and amino acids are stored as
triglycerides
excess glucose that is not stored as glycogen is converted into
triglycerides
how much energy is spent to convert glucose into triglycerides
25% of energy (the body is taking a lot of energy to do this conversion)
protein promotes the most
satiety
with a diet really high in protein
going to pull back in amount of carbs and fats
excess amino acids not used by the body are converted to
triglycerides
amino acids undergo
deamination and remaining carbons are converted to acetyl CoA and then into fatty acids
fatty acids are stored as triglycerides
excess kcals in any form will be stored as a triglyceride via lipogenesis
lipogenesis
a metabolic process that converts CHOs and other substrates into fatty acids, which are then stored as fats
how much energy is spent to convert fatty acids to triglycerides
5% of energy
dietary fat is easier to store as a triglyceride than dietary CHO or protein
- most Americans decrease in carb intake and increase in fat intake
- people consume more fat (bumps up total caloric intake since fat is 9 kcals/g)
glucagon promotes
lipolysis
insulin promotes
fatty acid synthesis and inhibits lipolysis
glucagon increases
blood sugar levels
insulin decreases
blood sugar levels
lipolysis can cause
obesity induced Type 2 diabetes
during the postabsorptive state
metabolism favors energy production
how does the body meet energy needs 4 or more hours after eating
meets energy needs from stored energy
energy stores are depleted during
fasting
between meals and overnight
energy is from glycogen and fatty acids
after 18 hours the body adapts
- proteins, glycerol, pyruvate, and lactate are used to make glucose
- lipolysis is increased (the breakdown of fat)
prolonged fasting
ketone bodies provide energy to the brain
severe fasting or starvation
- fat reserves are depleted
- muscle tissue is broke down to provide energy
ketogenesis
the formation of ketone bodies
ketogenesis generates energy during
prolonged fasting
ketogenesis occurs
with the buildup of acetyl CoA then converts acetyl CoA into ketone bodies
ketogenesis peaks
after an individual has fasted or consumed a limited-carbohydrate dies for 3 days
as the fast continues the brain uses ketones for fuel
30% of fuel is from ketones, with 70% from blood glucose
ketoacidosis
the excess accumulation of ketone bodies
ketoacidosis occurs with
untreated Type 1 diabetes when glucose levels are very high
ketoacidosis can lead to
impaired heart activity, coma, and even death
metabolism of ATP: glucose
- yields glucose
- doesn’t yield amino acids for body proteins
- yields fat for adipose tissue stores
- high energy cost of conversion to adipose tissue stores
metabolism of ATP: fatty acids
- doesn’t yield glucose
- doesn’t yield amino acids for body proteins
- yields fat for adipose tissue stores
- minimal energy cost of conversion to adipose tissue stores
metabolism of ATP: glycerol
- yields glucose, but not a major pathway
- doesn’t yield amino acids for body proteins
- yields fat for adipose tissue stores
- high energy cost of conversion to adipose tissue stores
metabolism of ATP: amino acids
- yields glucose
- yields amino acids for body proteins
- yields fat for adipose tissue stores, but is inefficient
- high energy cost of conversion to adipose tissue stores
metabolism of ATP: alcohol
- doesn’t yield glucose
- doesn’t yield amino acids for body proteins
- yields fat for adipose tissue stores
- high energy cost of conversion to adipose tissue store
