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200 Cards in this Set

  • Front
  • Back
Enzymes are involved in many important physiological rxns that together promote ?
a homeostatic state.
In addition, enzymes are vital for the ....... which, in turn, is needed for....?
- regulated production of the cellular energy (ATP)

- such widespread events as muscle contraction, nerve cell function, and chemical signal transduction.
Cells use three distinct but linked metabolic pathways to transfer the energy released from the breakdown of fuel molecules to ATP. They are known as?
glycolysis, the Krebs cycle, and oxidative phosphorylation.
Glycolysis operates only on ..?
All the categories of nutrients – carbs, fats, and proteins – contribute to ATP production via...?
the Krebs cycle and oxidative phosphorylation.
_________ are the sites of the Krebs cycle and oxidative phosphorylation.
One important generalization to keep in mind is that glycolysis can occur ...... whereas both the Krebs cycle and oxidative phosphorylation require
- in either the presence or absent of oxygen

- oxygen.
Glycolysis is a pathway that partially catabolizes....?
carbs, primarily glucose.
Glycolysis consists of 10 enzymatic rxns that convert
a six-carbon molecule of glucose into two three-carbon molecules of pyruvate, (the ionized form of pyruvic acid).
The glycolysis rxns produce a net gain of _________ of ATP and ___________ of hydrogen, ____ transferred to NAD+ and ___ released as hydrogen ions
-two molecules

-four atoms

- two

- two
What is the rxn for Glycolysis?
Glucose + 2 ADP + 2Pi + 2 NAD+ ~~~~> 2 pyruvate + 2 ATP + 2 NADH + 2 (H+) + 2 H2O
These 10 Glycolysis rxns, none of which utilizes molecular oxygen, take place in ____ ________.
the cytosol
All the intermediates btwn glucose and the end product pyruvate contain ?
one or more ionized phosphrate groups.
Plasma membranes are impermeable to such highly ionized molecules, and thus these molecules?
remain trapped within the cell.
The early steps in glycolysis (rxn 1 & 3) each use, rather than produce, ........... , to form ___________ ________?
- one molecule of ATP

- phosphorylated intermediates.
Rxn 4 in glycolysis splits ........ , and rxn 5 converts
- a six-carbon intermediate into two three-carbon molecules

- one of these three-carbon molecules into the other.
At the end of rxn 5, we have ........... derived from this point on, two molecules of each intermediate are involved.
two molecules of 3-phosphoglyceraldehyde
The first formation of ATP in glycolysis occurs ...... when a .......?
- during rxn 7

- phosphate group is transferred to ADP to form ATP.
Since the two intermediates exist at this point, rxn 7 produces ...?
two molecules of ATP, one from each intermediate
In this rxn (#7)in glycolysis, the mechanism of forming ATP is known as ...........since
- substrate-level phosphorylation

-the phosphate group is transferred from a substrate molecule to ADP.
A similar substrate-level phosphorylation of ADP occurs during rxn 10 in glycolysis, where ....?
again two molecules of ATP are formed.
Thus rxn 7 & 10 in glycolysis generate a total number of .....
four molecules of ATP for every molecule of glucose entering the pathway.
There is a net gain, however, of only ...... of ATP are used in rxn 1 & 3 in glycolysis.
two molecules
The end product of glycolysis, _______ , can proceed in one of two directions, depending on ........., which, as we stressed earlier, is not utilized in any ....?
- pyruvate

- the availability of molecular oxygen

- of the glycolytic rxns themselves.
If oxygen is present (aerobic condition exist) pyruvate can enter....?
the Kreb cycle and be broken down into carbon dioxide.
In the absence of oxygen (anaerobic conditions), pyruvate is converted to ...?
lactate (the ionized form of lactic acid) by a single enzyme-mediated rxn.
In anaerobic conditions, two hydrogen atoms derived from ______ _______ are transferred to ...?
-(NADH+) + ( H+)

-each molecule of pyruvate to form lactate, and NAD+ is regenerated.

These hydrogens (derived from (NADH+) + ( H+) were originally transferred to ____ during rxn 6 of glycolsis so the coenzyme NAD+ shuttles hydrogen btwn....?
- NAD+

- the two rxns during anaerobic glycolysis.
The overall rxn for anaerobic glycolysis is
Glucose + 2 ADP + 2 Pi ~~~~~> 2 Lactate + 2 ATP + 2 H2O
Under aerobic conditions pyruvate is not converted to lactate but rather...?
enters the Krebs cycle.
Under aerobic conditions pyruvate is not converted to lactate but rather enters the Krebs cycle. Therefore, the mechanism for regenerating NAD+ from (NADH+) + ( H+) by forming lactate ....
does not occur.
Under aerobic conditions and pyruvate, The hydrogens of NADH are transferred to ....?
oxygen during oxidative phosphorylation, regeneration NAD+ and producing H2O.
In most cells, the amount of ATP glycolysis produces from one molecule of glucose is _____ ______ than the amount formed under aerobic conditions by the other two ATP-generating pathways ......?
- much smaller

- the Krebs cycle and oxidative phosphorylation.
In special cases, glycolysis supplies most, or even all, of a cell’s ____.
Certain types of skeletal muscles contain considerable amounts of glycolytic enzymes but _____ _________. During intense muscle activity, glycolysis provides ____________ and is associated with the production of .....
- few mitochondria

- most of the ATP in these cells

- of large amounts of lactate.
most cells do not have sufficient concentrations of _______ ________ or enough ________ to provide, by glycolysis alone, the high rates of ATP production necessary to meet their energy requirements.
- glycolytic enzymes

- glucose
Other Carbs, such as fructose and galactose, can also be catabolized by __________ since these carbs are converted into several of the intermediates that participate in the .....
- glycolysis

- early portion of the glycolytic pathway.
The Krebs cycle aka
aka: citric acid cycle or tricarboxylic acid
The Krebs cycle is the _______ of the three pathways involved in fuel catabolism and ATP production.
The Krebs cycle utilizes and it produces ....
-molecular fragments formed during carbs, protein, and fat breakdown

-carbon dioxide, hydrogen atoms (half of which are bound to coenzymes), and small amounts of ATP.

In the Krebs cycle, The enzymes for this pathway are located ....
-in the inner mitochondrial compartment, the matrix.
The primary molecule entering at the beginning of the Krebs cycle is
-acetyl coenzyme A (acetyl CoA).
Coenzyme A (CoA) is derived from ...... and functions primarily to ....
-the B vitamin pantothenic acid

- transfer acetyl groups, which contain two carbons, from one molecule to another.

These acetyl groups transfered by CoA come either from ..... or from .....
-pyruvate – the end product of aerobic glycolysis –

- the breakdown of fatty acids and some amino acids.
Pyruvate, upon entering mitochondria from the cortisol, is converted to ____ & _____.
- acetyl CoA

- CO2.

Note that this rxn in which pyruvate is converted to acetyl CoA and CO2 produces the first molecule of ___ formed thus far in the pathway of fuel catabolism, and that the rxn also transfers .....

-hydrogen atoms to NAD+.
The Krebs cycle begins with ....... to the four-carbon molecule, oxaloacetate, to form ....
- the transfer of the acetyl group of acetyl CoA

- the six-carbon molecule, citrate.
At the third step in the Krebs cycle, a molecule of ___ is produced, and again at the fourth step. Thus, two carbon atoms entered the cycle as part of the _____________ , and two carbons (although not the same ones) have left ....

-acetyl group attached to CoA

-in the form of CO2.
Note also that the oxygen that appears in the CO2 is not derived from molecular oxygen, but from ....
- the carboxyl groups of the Krebs cycle intermediates.
In the remainder of the Kreb cycle, the four-carbon molecules formed in rxn 4 is modified through a series of rxns to produce..... which then...
- the four-carbon molecule oxaloacetate

- becomes available to accept another acetyl group and repeat the cycle.
In addition to producing carbon dioxide, intermediates in the Krebs cycle generate ..... ...... , most of which are transferred to ...
- hydrogen atoms

- the coenzymes NAD+ and FAD to form NADH and FADH2.

This hydrogen transfer during the Krebs cycle to ____ occurs in each of the steps 3,4, and 8 and to ___ in rxn 6.
- NAD+


These hydrogens in the Kreb cycle will be transferred from the coenzymes, along with the free H+, to ..... in the next stage of fuel metabolism – .......?
- to oxygen

-oxidative phosphorylation.

Since oxidative phosphorylation is necessary for regeneration of the hydrogen-free form of these coenzymes, the Krebs cycle can operate only .....
- under aerobic conditions.


During oxidative phosphorylation, There is _____ ________ in the mitochondria that can remove the hydrogen from these coenzymes under anaerobic conditions.
- no pathway
The Krebs cycle directly produces only _____________ . This occurs during _____ in which inorganic phosphate is transferred to ....... to form
- one high-energy nucleotide triphosphate

- rxn 5

- guanosine diphosphate (GDP)

- guanosine triphosphate (GTP).
The Krebs cycle directly produces only .....
- one high-energy nucleotide triphosphate.
The hydrolysis of GTP, like that of ATP, can provide
- energy for some energy-requiring rxns.
In addition, the energy in GTP can be transferred to ATP by the rxn: ?
GTP +ADP <~~~~~> GDP + ATP.
To reiterate, the formation of ATP from GTP is the only mechanism by which ...
ATP is formed within the Krebs cycle.
the formation of ATP from GTP is the only mechanism by which ATP is formed within the Krebs cycle. Why, then, is the Krebs cycle so important?
Because the hydrogen atoms transferred to coenzymes during the cycle (plus the free hydrogen ions generated) are used in the next pathway, oxidative phosphorylation, to form large amounts of ATP.
The net result of the catabolism of one acetyl group from acetyl CoA by way of the Krebs cycle can be written:
Acetyl CoA + 3 (NAD+) + FAD + GDP + Pi + 2 H2O ~~~~> 2 CO2 + CoA + 3 NADH + 3 (H+) + FADH2 + GTP
Oxidative Phosphorylation provides the __________ , and most important, mechanisms by which .........

- energy derived from fuel molecules can be transferred to ATP.
The basic principle behind Oxidative Phosphorylation is simple:
- the energy transferred to ATP is derived from the energy released when hydrogen ions combine with molecular oxygen to form water.
The hydrogen in Oxidative Phosphorylation comes from ........ generated by the Krebs cycle, by ...
- the NADH + (H+) and FADH2 coenzymes

- the metabolism of fatty acids and to a much lesser extent, during aerobic glycolysis.
The net rxn for Oxidative Phosphorylation is:
- ½ O2 + NADH + H+ ~~~~~> H2O + (NAD+) + energy.
enzymes of the Krebs cycle are _________ enzymes in the mitochondrial matrix
- soluble
Unlike the enzymes of the Krebs cycle, which are soluble enzymes in the mitochondrial matrix, the proteins that mediate oxidative phosphorylation can be divided into two groups:
(1) those that mediate the series of rxn that cause the transfer of hydrogen ions to molecular oxygen

(2) those that couple the energy released by these rxns to the synthesis of ATP.
Most of the first group of proteins contain iron and copper cofactors and are known as .
cytochrome structure resembles ....... which binds ....
- the red iron-containing hemoglobin molecule,

- oxygen in red blood cells.
The cytochromes form the components of the ......, in which ......... .
-electron transport chain

-two electrons from the hydrogen atoms are initially transferred either from NADH + (H+) or FADH2 to one of the elements in this chain
These electrons, from the hydrogen atoms are initially transferred either from NADH + (H+) or FADH2, are then successively transferred to
-other compounds in the chain, often to or from an iron or copper ion, until the electrons are finally transferred to molecular oxygen, which combines with hydrogen (protons) to form water.
These hydrogen ions, like the electrons, come from free hydrogen ions and the hydrogen-bearing coenzymes, having been released early in the transport chain when ?
- the electrons from the hydrogen atoms were transferred to the cytochromes.

Importantly, in addition to transferring the coenzyme hydrogens to water, this process regenerates the hydrogen-free form of the coenzymes, which then becomes available to accept two more hydrogens from intermediates in the Krebs cycle, glycolysis, or fatty acid pathway.
the electron transport chain
the electron transport chain provides the aerobic mechanism for ....., whereas, the anaerobic mechanism, which applies only to glycolysis, is
-regenerating the hydrogen-free form of the co-enzyme

- coupled to the formation of lactate.
At each step along the electron transport chain, small amounts of energy are?
At each step along the electron transport chain, small amounts of energy are released. Because this energy is released in small steps, it can be linked to
the synthesis of several molecules of ATP in a controlled manner.
ATP is formed at three points along the electron transport chain. The mechanism by which this occurs is known as the
chemiosmotic hypothesis.
As electrons are transferred from one cytochrome to another along the electron transport chain, the energy released is used to ..... thus producing a source of
- move hydrogen ions (protons) from the matrix into the compartment btwn the inner and outer mitochondrial membranes

- potential energy in the form of a hydrogen-ion gradient across the membrane.
At three points along the electron transport chain, a protein complex forms a channel in the ......, allowing the hydrogen ions to flow back to the matrix side and in the process
- inner mitochondrial membrane

- transfer energy to the formation of ATP from ADP and Pi.
FADH + (H+) enters the electron transport chain at....
a point beyond the first site of ATP generation.
The process where FADH + (H+) enters the electron transport chain is not perfectly stoichiometric, however, and thus the transfer of electrons to oxygen produces....
- approx. 2.5 & 1.5 molecules of ATP for each molecule of NADH + (H+) and FADH2, respectively.
How much ATP is formed at points along the electron transport chain.
most ATP formed in the body is produced during oxidative phosphorylation as a result of ?
processing hydrogen atoms that originated largely from the Krebs cycle during the breakdown of Carbs, fats, and proteins.
The mitochondria, where the.... occur, are thus considered the powerhouses of the cell.
oxidative phosphorylation and the Krebs cycle reactions
most of the oxygen we breathe is ________ within these organelles, and most of the carbon dioxide we exhale is ___________ within them as well.

The formation of ATP by oxidative phosphorylation involves the transfer of ...?
electrons and hydrogen to molecular oxygen.
Several highly reactive transient oxygen derivatives can also be formed during this process. What are these derivatives?
- hydrogen peroxide and the free radicals superoxide anion

- hydroxyl radical.
Although most of the electrons transferred along the electron transport chain go into the formation of water, small amounts can combine with oxygen to form...?
reactive oxygen species.
reactive oxygen species can react with and damage?
proteins, membrane phospholipids, and nucleic acids.
Such damage caused by reactive oxygen species has been implicated in....
the aging process and in inflammatory reactions to tissue injury
Some cells use reactive oxygen species to kill?
invading bacteria
Reactive oxygen molecules are also formed by _________ & ___________.
- the action of ionizing radiation on oxygen

- by rxns of oxygen with heavy metals such as iron.
Cells contain ......... for removing these reactive oxygen species and thus providing....
- several enzymatic mechanisms

- protection from their damaging effects.
The three classes of fuel molecules ..... enters the ATP-generating pathways.
carbs, fats, and proteins –
These anabolic pathways (ATP-generating pathways) are also used to synthesize.....
molecules that have functions other than the storage and the release of energy.
With the addition of a few enzymes, the pathway for fat synthesis is also used for?
synthesis of the phospholipids found in membranes.
What is the major pathways of carbohydrates catabolism:
- the breakdown of glucose to pyruvate or lactate by way of the glycolytic pathway, and the metabolism of pyruvate to carbon dioxide and water by way of the Krebs cycle and oxidative phosphorylation.
The amount of energy released during the catabolism of glucose to carbon dioxide and water is?
686 kcal/mol of glucose
The amount of energy released during the catabolism of glucose to carbon dioxide and water is 686 kcal/mol of? glucose. What is the rxn?
C6 H12 O6 ~~~> 6 H2O + CO2 + 686 kcal/mol
About 40 percent of energy released during the catabolism of glucose to carbon dioxide and water is transferred to?
- ATP.
A net gain of ____ ATP molecules occurs by substrate-level phosphorylation during glycolysis, and ...... are formed during the Krebs cycle from GTP, one from each of the...
- two

- two more

- two molecules of pyruvate entering the cycle.
The majority of ATP molecules glucose catabolism produces ~ ___ ATP per molecule ~ form during oxidative phosphorylation from....
- 34

- the hydrogens generated at various steps during glucose breakdown.
Since, in the absence of oxygen, only two molecules of ATP can form from ....... to lactate, the evolution of aerobic metabolic pathways greatly increased the amount...
- the breakdown of glucose

- of energy available to a cell from glucose catabolism.
Although only two molecules of ATP are formed per molecule of glucose under anaerobic conditions, large amounts of ATP can still be supplied by....
the glycolytic pathway if large amounts of glucose are broken down to lactate.
amounts of ATP can still be supplied by the glycolytic pathway if large amounts of glucose are broken down to lactate. This is not an efficient utilization of fuel energy, but it does...
permit continued ATP production under anaerobic conditions, such as occur during intense exercise.
A small amount of glucose can be stored in the body to provide the reserve supply for use when..
glucose is not being absorbed into the blood from the intestinal tract.
Glucose is stored by the ...., mostly in
- polysaccharide glycogen

- skeletal muscles and the liver.
Glycogen is synthesized from _________.
The enzymes for both glycogen synthesis and glycogen breakdown are located in
the cytosol.
The first step in glycogen synthesis, .........., that forms ........., is the same as the first step of..
the transfer of phosphate from a molecule of ATP to glucose,

- glucose 6-phosphate

- glycolysis.
In the first step in glycogen synthesis, glucose 6-phosphate can either be...
broken down to pyruvate or used to form glycogen.
____ _________ are used to synthesize and break down glycogen.
Different enzymes
The existence of two pathways containing enzymes that are subject to both covalent and allosteric modulation provides a mechanism for...
regulating the flow btwn glucose and glycogen.
When an excess of glucose is available to the liver or muscle cells, the enzymes in the glycogen synthesis pathway are _________, and the enzyme that breaks down glycogen is...
- activated

- stimultaneously inhibited.
When an excess of glucose is available to the liver or muscle cells, the enzymes in the glycogen synthesis pathway are activated, and the enzyme that breaks down glycogen is simultaneously inhibited.

This combination leads to...
the net storage of glucose in the form of glycogen.
When less glucose is available, the reverse combination of enzyme stimulation and inhibition ______ and ensues.
- occurs

- net breakdown of glycogen to glucose 6-phosphate (known as glycogenolysis)
Two paths are available to this glucose 6-phosphate:
(1) In most cells, including skeletal muscle, it enters the glycolytic pathway where it is catabolized to provide the energy for ATP formation

(2) in liver (and kidney) cells, glucose 6-phosphate can be converted to free glucose by removal of the phosphate group, and the glucose is then able to pass out of the cell into the blood to fuel other cells.
In addition to being formed in the liver from the breakdown of glycogen, glucose can be synthesized in ......... from intermediates derived from?
- the liver and kidneys

- the catabolism of glyderol (sugar alcohol) and some amino acids.
This process of generating new molecules of glucose from non-carb precursors is known as ....
The major substrate in gluconeogenesis is ..... formed from ..... during protein breakdown.
- pyruvate

- lactate and from several amino acids
glycerol derived from the hydrolysis of triglycerides can be converted into...
glucose via a pathway that does not involve pyruvate.
The pathway for gluconeogenesis in the liver and kidneys makes use of many but not all of .......because most of these rxns are...
- the enzymes used in glycolysis

- reversible
rxns 1,3, & 10 of the pathway for gluconeogenesis are ..... and ........ to form glucose from pyruvate.
irreversible and additional enzymes are required
In gluconeogenesis, Pyruvate is converted to _________ by a series of mitochondrial rxns in which ...... to form the four carbon Krebs-cycle intermediate oxaloacetate out of the mitochondria and its conversion to .........

Phosphoenolpyruvate then reverses the steps of glycolysis back to the level of rxn __ , in which can be converted to.....
- phosphoenolpyruvate

- CO2 is added to pyruvate

- phosphoenolpyruvate in the cytosol.

- 3

- glucose in the liver and kidneys or stored as glycogen.
Since energy in the form of heat and ATP generation is released during the glycolytic breakdown of glucose to pyruvate, energy must be.......
- added to reverse this pathway.
A total of _____ ATP are consumed in the rxns of gluconeogenesis per molecule of glucose formed.
- six
Many of the same enzymes are used in glycolysis and gluconeogenesis, so the questions arise:

What controls the direction of the rxns in these pathways?

What conditions determine whether glucose is broken down to pyruvate or whether pyruvate is converted into glucose?
The answer lie in the concentrations of glucose or pyruvate in a cell and in the control the enzyme exert in the irreversible steps in the pathway, a control carried out via various hormones that alter the concentrations and activities of these key enzymes.
Fat metabolism~Fat catabolism

Triglyceride (fat) constists of ..... linked to ______.
- three fatty acids linked to glycerol.
Fat metabolism~Fat catabolism

Fat accounts for approx. __ percent of the energy stored in the body.
- 80
Fat metabolism~Fat catabolism

Under resting conditions, approx. half the energy used by muscle, liver, and the kidneys is derived from
- the catabolism of fatty acids.
Fat metabolism~Fat catabolism

Although most cells store small amounts of fat, the preponderance of the body’s fat is stored in specialized cells known as
- adipocytes
Fat metabolism~Fat catabolism

Almost the entire cytoplasm of each of adipose cells is filled with _____.
a single large fat droplet.
Fat metabolism~Fat catabolism

Clusters of adipocytes form .........., most of which is in deposits underlying the skin.
adipose tissue
Fat metabolism~Fat catabolism

The function of adipocytes is to ...... and then, when food is not being absorbed from the intestinal tract, adipocytes release ....... to provide ........
- synthesize and store triglycerides during periods of food uptake

- fatty acids and glycerol into the blood for uptake and use by other cells

- the energy needed for ATP formation.
Fat metabolism~Fat catabolism

Pathway for fatty acid catabolism is achieved by ?
enzymes present in the mitochondrial matrix.
Fat metabolism~Fat catabolism

The breakdown of a fatty acid is initiated by
linking a molecule of coenzyme A to the carboxyl end of the fatty acid.

This initial step is accompanied by the breakdown of ATP to AMP and two Pi.
Fat metabolism~Fat catabolism

The breakdown of a fatty acid is initiated by linking a molecule of coenzyme A to the carboxyl end of the fatty acid. This initial step is accompanied by?
the breakdown of ATP to AMP and two Pi.
Fat metabolism~Fat catabolism:

The co-enzyme A derivative of the fatty acid then proceeds through a series of rxns, collectively known as beta oxidation, which split off ....
a molecule of acetyl coenzyme A from the end of the fatty acid and transfer two pairs of hydrogen atoms to coenzymes (one pair to FAD and the other to NAD+).
Fat metabolism~Fat catabolism:

During beta oxidation, The hydrogen atoms from the coenzymes then enter the oxidative phosphorylation pathway to?
form ATP.
Fat metabolism~Fat catabolism:

When an acetyl coenzyme A is split from the end of a fatty acid, another coenzyme A is ?
added (ATP is not required for this step) and the sequence is repeated.
Fat metabolism~Fat catabolism:

Each passage through beta oxidation sequence shortens the fatty acid chain by ....... until ........
two carbon atoms all the carbon atoms have transferred to coenzyme A molecules.
Fat metabolism~Fat catabolism:

As we saw, coenzyme A molecules transferred by beta oxidation sequence then lead to production ...... via ......
of CO2 and ATP via the Krebs cycle and oxidative phosphorylation
Fat metabolism~Fat catabolism:

How much ATP is formed as a result of the total catabolism of a fatty acid?
Most fatty acids in the body contain 14 to 22 carbons, 1 and 18 being most common.
Fat metabolism~Fat catabolism:

The catabolism of one 18-carbon saturated fatty acid yields ??? ATP molecules.
Fat metabolism~Fat catabolism:

The catabolism of one glucose molecule yields a maximum of ?? ATP molecules.
Fat metabolism~Fat catabolism:

Thus, taking into account the difference in molecular weight of the fatty acid and glucose, the amount of ATP formed from the catabolism of a gram of fat is about ..... greater than the amount of ATP produced by catabolizing 1 gram of carbohydrate.
2 ½ times
Fat metabolism~Fat catabolism:

If an average person stored most of his or her fuel as carbohydrate rather than body fat, body weight would have to approx. ??% greater in order to store the same amount of usable energy, and the person would consume more.....
- 30%

- energy moving this extra weight around.
Fat metabolism~Fat catabolism:

a major step in fuel economy occurred when ....
animals evolved the ability to store fuel as fat.
Fat metabolism - Fat Synthesis

The synthesis of fatty acids occurs by rxns...
that are almost the reverse of those that degrade them.
Fat metabolism - Fat Synthesis

the enzymes in the synthetic pathway are in ___ ______ , whereas the enzymes catalyzing fatty acid breakdown are in ?
- the cytosol

- the mitochondria
Fat metabolism - Fat Synthesis

Fatty acid synthesis begins with ....., which transfers its ...... to form .....
- cytoplasmic acetyl coenzyme A

- acetyl group to another molecule of acetyl coenzyme A

- a four-carbon chain.
Fat metabolism - Fat Synthesis

By repetition of this process, long-chain fatty acids are built up two carbons at a time. This accounts for the fact that all the fatty acids synthesized in the body contain .......
an even number of carbon atoms
Fat metabolism - Fat Synthesis

Once the fatty acids are formed, triglycerides can be synthesized by ....
linking fatty acids to each of the three hydroxyl groups in glycerol, more specifically, to a phosphorylated form of glycerol called alpha-glycerol phosphate.
Fat metabolism - Fat Synthesis

The synthesis of triglyceride is carried out by ______ associated with the membranes of the
- enzymes

- smooth endoplasmic reticulum.
Fat metabolism - Fat Synthesis

Compare the molecules produced by glucose catabolism with those required for synthesis of both fatty acids and alpha-glycerol phosphate. (3)
First, acetyl coenzyme A, the starting material for fatty acid synthesis, can be formed from pyruvate, the end product of glycolysis.

Second, the other ingredients required for fatty acid synthesis – hydrogen-bound coenzymes and ATP – are produced during carbohydrate catabolism.

Third, alpha-glycerol phosphate can be formed from a glucose intermediate.
Fat metabolism - Fat Synthesis

It should not be surprising, therefore, that much of the carbohydrate in food is converted into .... and stored in shortly after its absorption from the GI tract.
- fat

- adipose tissue
Fat metabolism - Fat Synthesis

It is very important to note that fatty acid, or more specifically the acetyl coenzyme A derived from fatty acid breakdown, cannot be used to synthesis new molecules of glucose.


(2 reasons)
First, because the rxn in which pyruvate is broken down to acetyl coenzyme A and carbon dioxide is irreversible, acetyl coenzyme A cannot be converted to pyruvate, a molecule that could lead to the production of glucose.

Second, the equivalents of the two carbon atoms in acetyl coenzyme A are converted into two molecules of carbon dioxide during their passage through the Krebs cycle before reaching oxaloacetate, another takeoff point for glucose synthesis, and therefore they cannot be used to synthesize net amounts of oxaloacetate.
Fat metabolism - Fat Synthesis

glucose can readily be converted into fat, but...
the fatty acid portion of fat cannot be converted to glucose.
Protein & A.A metabolism

In contrast to the complexities of protein synthesis, protein catabolism requires only a few enzymes, termed ________, to break the peptide bonds btwn amino acids (a process called ___________).
- proteases

- proteolysis
Protein & A.A metabolism

Some of these proteases split off .........., whereas others ........
- one amino acid at a time from the ends of the protein chain,

- break peptide bonds btwn specific amino acids within the chain, forming peptides rather than free amino acids.

Protein & A.A metabolism

Amino acids can be catabolized to ......... , and they can also provide ......
- provide energy for ATP synthesis

- intermediates for the synthesis of a number of molecules other than proteins.

Protein & A.A metabolism

Since there are 20 different amino acids, a large number of intermediates can ......
- be formed, and there are many pathways for processing them


Protein & A.A metabolism

A few basic types of A.A. rxns common to most of these pathways can provide an overview of ..
- amino acid catabolism.
Protein & A.A metabolism

Unlike most carbohydrates and fats, amino acids contain ........ in addition to carbon, hydrogen, and oxygen atoms.
- nitrogen atoms (in their amino group)
Protein & A.A metabolism

Once the nitrogen-containing amino group is removed from A.A, the remainder of most amino acids can be ...
- metabolized to intermediates capable of entering either the glycolytic pathway or the Krebs cycle.
Protein & A.A metabolism

The two types of rxns by which the amino group is removed is by ?
-oxidative deamination and transamination of amino acids.
Protein & A.A metabolism

In the first rxn, oxidative deamination, the amino group gives rise to ...... and is replaced by....
- a molecule of ammonia (HN3)

- an oxygen atom derived from water to form a keto acid (a categorical name rather than the name of a specific molecule)

Protein & A.A metabolism

In the second rxn by which the amino group is removed is called transamination and involves ..........
- the transfer of the amino group from an amino acid to a keto acid.


Protein & A.A metabolism

Note that the keto acid the amino acid group is transferred to becomes
- an amino acid
Protein & A.A metabolism

Cells can also use the nitrogen derived from amino groups to synthesize ........ such as .....
-other important nitrogen-containing nolecules, the purine and pyrimidine bases found in nucleic acids.
Protein & A.A metabolism

The keto acids formed in oxidative deamination and transamination are intermediates either in ... or .....
- the Krebs cycle (alpha-ketoglutaric acid)

- glycolytic pathway (pyruvate acid).
Protein & A.A metabolism

Once formed in oxidative deamination and transamination , these keto acids can be metabolized to produce .... or .....
- carbon dioxide and form ATP,

- they can be used as intermediates in the synthetic pathway leading to the formation of glucose.
Protein & A.A metabolism

As a third alternative, these keto acids can be used to
synthesize fatty acids after their conversion to acetyl coenzyme A by way of pyruvic acid.
Protein & A.A metabolism

amino acids can be used as a .......... , and some can be converted into .........
- source of energy

- carbohydrate and fat.
Protein & A.A metabolism

The ammonia that oxidative deamination produces is highly toxic to cells.....

Fortunately, it passes through .....
- if allowed to accumulate

- cell membranes and enters the blood, which carries it to the liver.
Protein & A.A metabolism

The liver contains enzymes that can link ................ to form urea.
two molecules of ammonia with carbon dioxide
Protein & A.A metabolism

Thus, urea, which is relatively nontoxic, is ............. of protein catabolism.
the major nitrogenous waste product
Protein & A.A metabolism

Urea enters the blood from and is excreted by .....
- from the liver

- the kidneys into the urine.
Protein & A.A metabolism

In amino acid synthesis, the keto acids pyruvate acid and alpha-ketoglutaric acid can be derived from ......... ; they can be transaminated to form the amino acids ...
- breakdown of glucose

- glutamate and alanine.
Protein & A.A metabolism

Glucose can be used to produce ......., provided ........for transamination.
- certain amino acids

- other amino acids are available in the diet to supply amino acids
Protein & A.A metabolism

However, only __ of the 20 amino acids can be formed by Glucose producing certain A.A. because .....
- 11

- 9 of the specific keto acids cannot be synthesized from other intermediates.
Protein & A.A metabolism

Since only 9 of the 20 amino acids can be formed by Glucose producing certain A.A. because 9 of the specific keto acids cannot be synthesized. We have to obtain the 9 amino acids corresponding to these keto acids from ...... and they are thus know as ?
- the food we eat

- the essential amino acids.
Protein & A.A metabolism

The amino acid pools, which consist of the body’s total free amino acids, are derived from ?
(1) ingested protein, which is degraded to amino acids during digestion in the intestinal track

(2) the synthesis of nonessential amino acids from the keto acids derived from carbs and fats

(3) the continuous breakdown of body proteins. .
Protein & A.A metabolism

These A.A pools are the source of amino acids for the synthesis of ... as well as for conversion to carbs and fat
body protein and a host of specialized amino acid derivatives,
Protein & A.A metabolism

The body loses a very small quantity of amino acids and protein via..
the urine, skin, hair, fingernails, and in women, the menstrual fluid.
Protein & A.A metabolism

The major route for the loss of amino acids is not their excretion but rather ....., with the eventual excretion of the ...
- their deamination

- nitrogen atoms as urea in the urine.
Protein & A.A metabolism

The terms negative nitrogen balance and positive nitrogen balance refer to whether there is....
a net loss or gain, respectively, of amino acids in the body over any period of time
Fat metabolism - Fat Synthesis

If any of the essential amino acids are missing from the diet,........ always results.
a negative nitrogen balance – that is, loss greater than gain –
Fat metabolism - Fat Synthesis

The proteins that require a missing essential amino acid cannot ..... , and the other amino acids that would have been incorporated into these proteins are....
- be synthesized

- metabolized.
Fat metabolism - Fat Synthesis

The proteins that require a missing essential amino acid cannot be synthesized, and the other amino acids that would have been incorporated into these proteins are metabolized. This explains why a dietary requirement for protein....
cannot be specified without regard to the amino acid composition of that protein.
Fat metabolism - Fat Synthesis

Protein is graded in terms of....
how closely its relative proportions of essential amino acids approx. those in the average body protein.
Fat metabolism - Fat Synthesis

The highest quality proteins are found in ..... whereas, the quality to most plant proteins ......
- animal products,

- is lower.
Fat metabolism - Fat Synthesis

it is quite possible to obtain adequate quantities of all essential amino acids from a mixture of ..... alone
plant proteins
Fat metabolism - Fat Synthesis

All three classes of molecules can enter the .... through some intermediate, and thus all three can be used as a source of energy for ......
- Krebs cycle

- the synthesis of ATP.
Fat metabolism - Fat Synthesis

Glucose can be converted into ___ or into some amino acids by the way of ......
- fat

- common intermediates such as pyruvate, oxoloacetate, and acetyl coenzyme A.
Fat metabolism - Fat Synthesis

Glucose can be converted into fat or into some amino acids by the way of common intermediates.

Similarly, some amino acids cannot be converted into ...
glucose and fat.
Fat metabolism - Fat Synthesis

Fatty acids cannot be converted into ______ because of ......... but the glycerol portion of triglycerides can be converted into glucose.
- glucose

- the irreversibility of the reaction converting pyruvate to acetyl coenzyme A,
Fat metabolism - Fat Synthesis

Fatty acids can be used to synthesize portions of ..... used to form ...
- the keto acids

- some amino acids.
Fat metabolism - Fat Synthesis

Metabolism is a highly integrated process in which ..... if necessary, to provide
- all classes of molecules can be used

- the raw materials required to synthesize most but not all members of other classes.