Biochem- Protein

IAAO method is based on a few principles, including

(1) if a test amino acid is not provided, oxidation of the indicator amino acid will be maximal and protein synthesis will be minimal; (2) at an intake above the expected requirement of the test amino acid, oxidation of the indicator amino acid will diminish; and (3) at an intake that is the requirement for the test amino acid, oxidation of the indicator amino acid will be fairly constant.

hepatic catabolism and uses of aromatic, sulfur containing, branched chain, basic, and other amino acids

**know this

depending on the pH of the environment, the amino and carboxy groups can accept or donate H+, and thus the amino group may be represented as _____ and the carboxy group as _____

+NH3 COO-

Like other tissues, muscles preferentially catabolize some amino acids more than others; six amino acids.... appear to be catabolized to greater extents in the skeletal muscle than other tissues

- aspartate -asparagine -glutamate -leucine -isoleucine -valine

NITROGEN CONTAINING COMPOUNDS

READ

STRUCTURE AND ORGANIZATION

STRUCTURE AND ORGANIZATION

_____ simultaneously carry two substances into the cell

Symporters

Not all tripeptides, however, undergo additional digestion to produce free amino acids at the brush border of enterocytes. ____ and ______ peptides tend to be absorbed intact and hydrolyzed within the enterocyte.

Triglycine and proline-containing

neutral amino acids

alanine asparagine cysteine glutamine glycine isoleucine leucine methionine phenylalanine proline serine threonine tryptophan tyrosine valine

nonpolar neutral amino acids

alanine glycine isoleucine leucine methionine proline valine

Frequently (but not always), the first step in amino acid catabolism is the transfer or removal of an amino acid's ________group

amino

some amino acids enter cells via an ______ mechanism in which two substances move across the enterocyte membrane in opposite directions

antiport

amino acids with a net positive charge

arginine histidine lysine

amino acids with side chains containing basic groups

arginine lysine histidine

polar charged amino acids

arginine lysine histidine glutamate aspartate

the kidneys are considered to be the major site in the body for ... production

arginine, histidine, serine, and perhaps tyrosine

polar neutral amino acids

asparagine cysteine glutamine serine threonine

amino acids with a net negative charge

aspartic acid glutamic acid

amino acids with side chains containing acidic groups or their amides

aspartic acid glutamic acid asparagine glutamine

Insufficient amino acid concentrations also trigger (through unclear means) ______

autophagy

Polar charged amino acids include

both the dicarboxylic (aspartic acid and glutamic acid) and basic (lysine, arginine, histidine) amino acids

Structurally, amino acids have a

central carbon (C) at least one amino group (—NH2) at least one carboxy acid group (-COOH) side chain R group (makes every amino acid unique)

a third category exists:

conditionally or acquired indispensable amino acids -tyrosine -cysteine -proline -arginine -glutamine

The term alipathic is often used when discussing nonpolar amino acids; amino acids that are alipathic...

contain carbons and hydrogens in their side chains but no functional groups like hydroxyl groups.

A complete protein

contains all the indispensable amino acids in the approximate amounts needed by humans. Sources of complete proteins are mostly foods of animal origin such as milk, yogurt, cheese, eggs, meat, fish, and poultry.

amino acids with side chains containing sulfur atoms

cysteine methionine

amino acids formed posttranslationally

cystine hydroxyproline hydroxylysine 3-methylhistidine

________ reactions involve only the removal of an amino group from an amino acid, with no transfer of the amino group to another compound.

deamination

The hydrochloric acid content of the gastric juice results in a gastric pH less than 3 and enables _______

denaturation of the quaternary, tertiary, and secondary structures of protein

Polar charged amino acids functions

interact with aqueous environments, can form salt bridges, and can interact with electrolytes/minerals such as potassium, chloride, and phosphate

the aromatic amino acids are considered

relatively nonpolar

Small intestine: The chyme-nutrient mixture that is delivered into the duodenum further stimulates the release of regulatory hormones and peptides such as ____ and ____

secretin and cholecystokinin

Nitrogen losses are measured in the

urine (U), feces(F), and skin (S)

amino acids with no carboxy or amino groups in their side chain to generate an additional charge to the molecule.

zwitterion, or dipolar ion

Amino acids circulating in the plasma and found within cells arise from digestion and absorption of dietary (exogenous) protein as well as from the breakdown of existing body (endogenous) tissues. These endogenous amino acids intermingle with exogenous amino acids to form a "pool" totaling about ____g.

-150

mTORC1 signal activation occurs within about ___minutes of meal consumption, and maximum protein synthesis occurs at about ___ hours after eating and then declines

-30 -1-1 1⁄2

Glutamine uptake by the kidneys has been estimated at __ g per day but uptake increases dramatically with __, whereas glutamine uptake by the intestine, liver, and other organs diminishes. Especially in acidotic conditions, glutamine and then glutamate are deamidated and deaminated, respectively, in the kidneys, resulting in two _____.

-7-10 -acidosis -ammonias

endogenous proteins typically total ____ g or more per day, and are digested and provide amino acids that are available for ______

-70 -absorption

two examples of aminotransferases are ____ and ____, which are among the body's most active and involve three key amino acids and α-keto acids— these reactions are ________, and because glutamate and α-ketoglutarate readily transfer and/or accept amino groups, these compounds play central roles in amino acid metabolism

-ALT and AST -alanine and its α-keto acid pyruvate glutamate and its α-keto acid α-ketoglutarate and aspartate and its α-keto acid oxaloacetate -reversible

Several peptidases are produced by enterocytes, including those in the ileum, enabling peptide digestion and amino acid absorption to occur in the distal small intestine. Some of these intestinal peptidases include the following:

-Aminopeptidases, which vary in specificity, cleave amino acids from the amino/(N)-terminal end of oligopeptides. -Dipeptidyl aminopeptidases, some of which are magnesium dependent, hydrolyze dipeptides. -Tripeptidases, which are specific for selected amino acids, hydrolyze tripeptides to yield a dipeptide and a free amino acid.

Glutamine serves several roles in the intestines.

-It is degraded extensively by intestinal cells, providing a primary source of energy. -It has also been shown to have trophic (growth) effects, stimulating gastrointestinal mucosa cell proliferation. -Consequently, glutamine helps to prevent both atrophy of gut mucosa and bacterial translocation. -In addition, glutamine has been shown to enhance the synthesis of heat shock proteins. -It is also needed in large quantities along with threonine for the synthesis of mucins found in gastrointestinal tract mucus secretions.

The transport of the H+ into the enterocyte results in an intra-cellular acidification. The H ions are pumped back out into the lumen in exchange for ____ ions. A _____ allows for Na+ extrusion at the basolateral membrane to maintain the gradient.

-Na+ -Na+/K+-ATPase

The transport system designated ___ appears to transport all di-and tripeptides. This transport of peptides across the brush border membrane using this system is associated with the comovement of protons (H+) and thus ____ of the brush border membrane.

-PEPT1 -depolarization

Many amino acids are catabolized within the brain and nervous system to generate biogenic amines. These biogenic amines also may function as neurotransmitters. Some of these amino acids and the amines they produce include:

-Tryptophan, which is used to synthesize serotonin. Serotonin functions as an excitatory neurotransmitter (biogenic amine) in the central nervous system and in circulation as a potent vasoconstrictor and stimulator of smooth muscle contraction. Serotonin affects sleep, mood, and appetite, as well as memory and learning (e.g., cognitive functions). ● Tyrosine, which is used in sympathetic neurons to make catechol derivatives, collectively called catecholamines (dopamine, norepinephrine, and epinephrine). In the brain and neurons, the catecholamines function as neurotransmitters. Dopamine affects a variety of behaviors as well as coordination of movement. Norepinephrine plays roles in alertness and sleep. Epinephrine is found in low concentrations in the brain; however, in circulation, it functions as a hormone with major (primarily catabolic) effects on nutrient metabolism. ● Histidine, which is decarboxylated to generate histamine. The neurotransmitter histamine mediates attention and alertness, among other possible roles.

For an amino acid to be considered ketogenic, the catabolism of the amino acid must generate ______ or ________, which are used for the formation of ketone bodies

-acetyl-CoA or acetoacetate

Because of the presence of an additional carboxy group in the side chain, the ______ amino acids exhibit a net negative charge at pH 7; these forms of the amino acids are called _______ and ______. Dicarboxylic amino acids or proteins with a high content of dicarboxylic amino acids migrate _____ the anode if placed in an electric field. In contrast, because of the presence of an additional amino group in the side chain, the ___ amino acids exhibit a net positive charge at pH 7. These amino acids or proteins rich in them will migrate _____ the cathode if placed in an electrical field.

-acidic (aspartic acid and glutamic acid) -aspartate and glutamate -toward -basic (lysine, arginine, histidine) -toward

The brain has a high capacity for the ____ transport of amino acids. In fact, the brain has transport systems for neutral, basic, and acidic amino acids

-active

Transamination reactions are catalyzed by enzymes called _________. These enzymes typically require vitamin _____ in its coenzyme form, __________.

-aminotransferases/transaminases -B6 -pyridoxal phosphate (PLP)

Glutamine has several major roles in the body, one of which is in _____ transport.

-ammonia

Glycine utilization by the kidneys under acidotic conditions is similar to glutamine utilization; glycine is degraded, forming ____ and____

-ammonia and carbon dioxide.

The sodium-dependent N system is especially prominent in the periportal cells of the liver and functions as an ____ to take up ____ and _____ in exchange for H+. The process occurs in reverse in the perivenous hepatic cells; _____ is released in exchange for H+

-antiporter -glutamine and sodium -glutamine

For amino acids to enter the blood and be used by other body tissues, the amino acids must be transported across the ______ membrane of the enterocyte and into interstitial fluid, where they enter the blood through capillaries of the villi for transport into the portal vein leading to the liver. The carriers found in the enterocyte's basolateral membrane are generally sodium ______ and similar to those found in other cell membranes

-basolateral (serosal) -independent

Glutamate is formed in muscle and other cells from the transamination of the _____ with _____ to form branched-chain _____ and _____, respectively

-branched-chain amino acids with α-ketoglutarate -α-keto acids and glutamate

Muscle, as well as the heart, kidneys, diaphragm, adipose tissue, and other organs (except, for the most part, the liver), possesses _______, located in both the cytosol and mitochondria and responsible for the transamination of all three branched-chain amino acids.

-branched-chain aminotransferases

Further catabolism of the branched-chain α-keto acids occurs by decarboxylation in an irreversible reaction catalyzed by the ________ complex. This enzyme complex operates in a fashion similar to the pyruvate dehydrogenase complex (see Chapter 3) in that it requires ____in its coenzyme form TDP, ____ as NADH, and ___ and ____ from pantothenic acid.

-branched-chain α-keto acid dehydrogenase (BCKAD) -thiamin -niacin -Mg2+ and CoA

Because 3-methylhistidine cannot be reused for protein synthesis following protein degradation and is excreted in the urine, its urinary excretion can be measured and serves as an indicator of muscle _____.

-breakdown

The proteasomal system accounts for the majority of proteolysis in skeletal muscle. However, in muscle and perhaps other tissues (including neurons and the brain), another group of proteases, called _____, also may initially participate.

-calpains

These exopeptidases attack peptide bonds at the ______ of polypeptides to release ...

-carboxy (C)-terminal end (A-neutral a.a, B- basic a.a) -free amino acids

functional elements

-catalyst -messengers -structural elements -buffers -fluid balancers -immunoprotectors -transporters -acute-phase responders -others

Enteropeptidase (an endopeptidase formerly known as enterokinase), which is secreted from the enterocyte in response to ____ and ____, converts trypsinogen to trypsin. Once trypsin is formed, it can convert other trypsinogen molecules and other zymogens to their respective active _____

-cholecystokinin and secretin -proteases

Urinary creatinine excretion is used to assess muscle mass because creatinine is the degradation product of ____, which constitutes a fairly standard proportion of muscle

-creatine

While muscle proteolysis generates amino acids that are released into the plasma for circulation to and use by other tissues, changes in plasma amino acid concentrations do not reflect changes in muscle mass. Instead, two previously mentioned compounds, ____ and ____, are used as indicators of existing muscle ____ and muscle _____, respectively

-creatinine and 3-methylhistidine -mass -degradation

Endogenous proteins presented to the digestive tract represent another source of amino acids and nitrogen. Endogenous proteins include:

-desquamated mucosal cells -digestive enzymes and glycoproteins.

Trypsin and chymotrypsin are both _____. Trypsin is specific for peptide bonds at the carboxy end of ____ amino acids. Excess trypsin also acts by ____ feedback to inhibit _______ synthesis by pancreatic cells, thereby regulating pancreatic zymogen secretion. Chymotrypsin is specific for peptide bonds at the carboxy end of _____amino acids and for peptide bonds adjacent to ___, ___, and ____

-endopeptidases -basic -negative -trypsinogen -aromatic -methionine, asparagine, and histidine.

Whereas the cells of the gastrointestinal tract as well as the immune system (such as lymphocytes, monocytes, and macrophages) rely on glutamine catabolism for ____ production, glutamine in the liver and kidneys is utilized differently.

-energy

the complete oxidation of amino acids generates .... Amino acids are used for ____production when the diet is inadequate in energy

-energy, along with water, CO2 /HCO3-, and ammonia/ammonium ions -energy

The activation of trypsinogen by ______ is important since the formation of trypsin facilitates activation of other zymogens. Yet, while trypsinogen activation is important in the intestine, extensive damage would occur should trypsinogen become active within the pancreas. To prevent this, the pancreas produces a compound called ____ ____.

-enteropeptidase -trypsin inhibitor

The degradative processes are stimulated by _____ and _______ release and by the higher glucagon-to-insulin ratio in the blood. This higher glucagon-to-insulin ratio diminishes insulin's ability to inhibit protein ____ and diminishes the overall rate of protein _____.

-epinephrine -cortisol -degradation -synthesis

Leucine appears to be preferentially oxidized during _____ situations

-fasting

Leucine is oxidized in a manner similar to ___ ___, and its oxidation results in the production of 1 mol of _____ and 1 mol of ____. Complete oxidation of leucine generates more ATP molecules on a molar basis than complete oxidation of _____.

-fatty acids -acetyl-CoA -acetoacetate -glucose

Major sources of ammonia and/or ammonium ions in the body include:

-formation in the body from chemical reactions such as deamination -generation by the deamidation of the amide groups from glutamine and asparagine -ingestion and absorption from foods (e.g, cheeses, processed meats) -generation by the bacterial lysis of urea and amino acids in the gastrointestinal tract and subsequent absorption into the body.

the digestive process is influenced to some extent by the ___ ____ ____ end products, which can sometimes inhibit the activity of brush border peptidases (a process called end product inhibition) to diminish digestion.

-free amino acid

Glutamine synthetase can also use ammonia or an ammonium ion for the amidation of glutamate's ___ ____ group to form glutamine in an _____-dependent reaction that also requires magnesium or manganese

-gamma carboxy -ATP

autophagy in liver cells is enhanced by ____ and suppressed by ___, ___, and ____; In addition, in liver cells, cellular uptake and accumulation of three amino acids—leucine, phenylalanine, and tyrosine—as well as increases in cell volume associated with the sodium-dependent cellular uptake of alanine, glutamine, and proline ____ autophagy.

-glucagon -insulin, amino acids, and mTORC1 -inhibit

The conversion of amino acids to glucose is accelerated by a high blood _____ ratio and by high blood _______concentrations

-glucagon-to-insulin -cortisol

Glutamate dehydrogenase readily uses an ammonia or ammonium ion and α-ketoglutarate to make the amino acid _____ -the glutamate generated in this reversible reaction can then release the ammonia or ammonium ion for the synthesis of either ______ or _________

-glutamate -urea or a dispensable amino acid

Within the liver, alanine undergoes transamination back to pyruvate, which is then used to remake glucose. The ____ that is generated with transamination can undergo deamination to provide _____ for urea synthesis.

-glutamate -ammonia

kidney's role include

-glutamine catabolism for acid-base balance -glycine catabolism for acid-base balance -serine synthesis from glycine -arginine and glycine use to form guanidinoacetate for creatine synthesis -glutathione catabolism -arginine synthesis from citrulline -tyrosine synthesis from phenylalanine -histidine generation from carnosine degradation.

Several amino acids act directly as neurotransmitters, including:

-glycine, which acts primarily in the spinal cord as an inhibitory neurotransmitter -taurine, which is thought to function as an inhibitory neurotransmitter -aspartate, which is derived chiefly from glutamate through aspartate aminotransferase activity common in neural tissue, and is thought to act as an excitatory neurotransmitter in the central nervous system -glutamate, which acts primarily in the brain and spinal cord as an excitatory neurotransmitter. Glutamate also can be decarboxylated in a vitamin B6-(PLP)-dependent reaction to produce the neurotransmitter γ-amino butyric acid (GABA) (Figures 6.37 and 6.38). GABA functions in the brain as an inhibitory neurotransmitter

AST is found in higher concentrations in the ____than in the ____, ____, and ______. In contrast, ALT is found in higher concentrations in the ___ than in the ____but is also found in moderate amounts in the ______ and small amounts in ________

-heart -liver, muscle, and other tissues -liver -heart -kidneys -other tissues

In addition to phenylalanine degradation, carnosine is oxidized by the kidneys, releasing ____ for use by other body tissues.

-histidine

Stomach: the digestion of protein begins in the stomach with the action of ____, which is found in gastric juice.

-hydrochloric acid (HCl)

Within the small intestine, these zymogens are chemically altered to be converted into their respective active enzymes capable of protein ______.

-hydrolysis

Pepsin functions as an endopeptidase (meaning that it ...) at a pH < ~3.5. Specifically, pepsin attacks peptide bonds adjacent to the ____ end of a relatively wide variety of amino acids (i.e., pepsin has low specificity), including ...

-hydrolyzes interior peptide bonds within proteins or polypeptides -carboxy -leucine; methionine; the aromatic amino acids (phenylalanine, tyrosine, and tryptophan); and the dicarboxylic amino acids (glutamate and aspartate).

The neurosecretory cells of the ___ are foremost in the secretion of the neuropeptides.

-hypothalamus

Renal glutaminase activity and ammonia excretion ____with acidosis and _____with alkalosis

-increase -decrease

In the absorptive state (or with alkalosis), liver glutaminase activity _____, yielding ammonia for the urea cycle. In an acidotic state, the use of glutamine for the urea cycle _____, and the liver releases glutamine into the blood for transport to and uptake by the kidneys for use in acid-base balance.

-increases -diminishes

The liver is the main site for the catabolism of the ____ amino acids, with the exception of the _________ amino acids, which tend to be utilized to a greater extent by muscle and other organs such as the heart.

-indispensable -branched-chain

The oxidation of several amino acids, including.. yields acetyl-CoA, which can be metabolized to produce ____

-isoleucine, leucine, lysine, tryptophan, and threonine -cholesterol

The total amount of the essential amino acids found in the pool is ____ than that of the nonessential amino acids. The essential amino acids found in greatest concentrations are ____ and _____. Of the nonessential amino acids, those found in greatest concentrations are ____, ____, ____, _____.

-less -lysine and threonine -alanine, glutamate, aspartate, and glutamine

the urea cycle functions in the ____ and is extremely important for the removal of ______ from the body

-liver -ammonia (and ammonium ions)

The enzymes carrying out the deamination reactions are generally _____,____, or ____ and produce...

-lyases, dehydratases, or dehydrogenases -an α-keto acid and ammonia or an ammonium ion.

Two techniques—____ and _____—are commonly used to assess the adequacy of protein and amino acid intakes.

-nitrogen balance and indicator amino acid oxidation

secretin and cholecystokinin are carried by the blood to the ______, where selected pancreatic cells are stimulated to secrete zymogens and pancreatic juice containing bicarbonate, electrolytes, and water.

-pancreas

Hydrochloric acid does, however, begin ____ activation from _____, which is secreted as a zymogen (inactive enzyme) by gastric chief cells.

-pepsin -pepsinogen

Peptides found in the blood can be hydrolyzed by ____ or ____ in the plasma or at the cell membrane (especially in the liver, kidneys, and muscle). Intracellular hydrolysis of the peptide, if absorbed intact, may also occur in the cytosol or in various organelles. Peptide transport into renal tubular cells is influenced by the ___ ____ of the amino acid at the amino (N-) and the carboxy (C-) terminals. Peptides containing either basic or acidic amino acids at either the N-or C-terminal have ____ affinity for transport than peptides with neutral side chains at these positions.

-peptidases or proteases -net charge -lower

Denaturants such as hydrochloric acid break apart hydrogen and electrostatic bonds to unfold or uncoil the protein; however, ______ bonds are not affected by the hydrochloric acid.

-peptide

Protein digestion yields two main end products:

-peptides (principally dipeptides and tripeptides) -free amino acids.

Amino acids that are excitatory stimulate receptors on post-synaptic membranes; this stimulation in turn ____ the nerve impulse. In contrast, amino acids that are inhibitory ____ the postsynaptic neuron from propagating nerve impulses

-propagates -retard

the degradation of proteins yields amino acids that are mostly reused by body tissues. Proteins are degraded within cells primarily by the action of ____, which are compartmentalized in the cytosol in ____ and _____.

-proteases -lysosomes and proteasomes

A dispensable amino acid may become indispensable if, for example, there are... Similarly, if an organ does not function properly then...

-rate limitations to its synthesis such as may occur if precursor availability is limited -amino acid metabolism may not proceed normally.

the digestive enzymes and glycoproteins are derived from ... The digestive tract's mucosal cells contain a variety of proteins (such as apoproteins, structural proteins, and cytosolic enzymes) that when sloughed into the gastrointestinal (GI) tract are ____.

-secretions of the salivary glands, stomach, intestine, liver, and pancreas. -degraded

Under healthy (nonacidotic) conditions, glycine is used by the kidneys (proximal tubule) for the synthesis of the amino acid ____. The kidneys also use glycine along with arginine for the synthesis of _____; this compound then travels to the liver, where it is used to generate ______.

-serine -guanidinoacetate -creatine

those categorized as nonpolar or hydrophobic (water fearing): Hydrophobicity tends to increase as the length of the ___ ____ increases.

-side chain

Some of the uses of amino acids in enterocytes include:

-structural proteins -nucleotides -apoproteins necessary for lipoprotein (chylomicron) formation -new digestive enzymes -hormones -nitrogen-containing compounds.

the distinctive characteristics of the side chains of the amino acids that make up a polypeptide bestow on a protein its ____ and influence its ____ role in the body. These same distinctive characteristics determine whether certain amino acids can be ____ in the body or must be _____.

-structure -functional -synthesized -ingested

mTOR is thought to "sense" the amino acid supply (along with information provided independently by insulin and leucine, among other factors) and to serve as a signal transduction pathway to promote protein ____ and overall _____

-synthesis -anabolism

Elastase, once activated by _____, functions as an ____to hydrolyze bonds adjacent to _____amino acids, including those in elastin. Elastin is a component of ....

-trypsin -endopeptidase -aliphatic -connective tissues and is found especially in meats.

Procarboxypeptidases are also converted to carboxy-peptidases by ____ and function as ______.

-trypsin -exopeptidases

Zymogens secreted by the pancreas into the intestine and further responsible for protein and polypeptide digestion include:

-trypsinogen -chymotrypsinogen -procarboxypeptidases A and B -proelastase

Hydrogen (H) bonds are ... Electrostatic attractions, also called ionic attractions or salt bonds...

-weak electrical attractions that can occur between hydrogen atoms and negatively charged atoms such as oxygen or nitrogen. -occur between oppositely charged side chains of amino acids

"fast proteins," which include .... better stimulates muscle protein and whole-body protein synthesis than slow proteins both at rest and following _____ exercise.

-whey protein, soy protein, amino acid mixtures, and protein hydrolysates -resistance

Some amino acid transporters, such as ___, are passive and function as uniporters; they bind to one amino acid and transport it into the cell with its concentration gradient

-y+

Carboxypeptidases are _____dependent, specifically requiring it at the enzyme's active site. Carboxypeptidase A hydrolyzes peptides with C-terminal ____ or ____ neutral amino acids. Carboxypeptidase B cleaves ____amino acids from the C-terminal end to generate free basic amino acids as end products.

-zinc -aromatic or aliphatic (nonpolar) -basic

Transamination reactions involve the transfer of an amino group from one amino acid to an _____ acid (also referred to as an amino acid carbon skeleton). The carbon skeleton/α-keto acid that gains the amino group becomes an ____acid, and the amino acid that loses its amino group becomes an _____ acid.

-α-keto -amino -α-keto

The Estimated Average Requirement for protein for adults (men and women age 19 years and older) is

0.66 g of protein per kg of body weight, or 105 mg of nitrogen per kg of body weight per day

8 structural classifications of amino acids

1) with aliphatic/nonpolar side chains 2) with side chains containing hydroxylic (OH) groups 3) with side chains containing sulfur atoms 4) with side chains containing acidic groups or their amides 5) with side chains containing basic groups 6) with side chains containing aromatic ring 7) Imino acids 8) amino acids formed posttranslationally

after a meal, the liver takes up about ____ - _____% of amino acids from portal blood.

50-65

Ubiquitination is an ATP-dependent process by which proteins that are to be degraded are ligated to ubiquitin, a _____ polypeptide

76-amino acid (read)

ABSORPTION

ABSORPTION

with liver damage, higher than normal blood concentrations of ___ and ____ as well as other enzymes such as alkaline phosphatase and lactate dehydrogenase normally found in the liver are observed. With heart damage (as may occur with a heart attack), enzymes that are normally found in the heart, such as ______, "leak" out into the blood and serve as indicators of heart cell damage

AST and ALT AST

CATABOLISM

CATABOLISM

DIGESTION

DIGESTION

FUNCTIONAL ROLES

FUNCTIONAL ROLES

INTERORGAN FLOW OF AMINO ACIDS AND CATABOLISM

INTERORGAN FLOW OF AMINO ACIDS AND CATABOLISM

methionine and cysteine metabolism

Methionine also is metabolized by intestinal cells. Studies suggest that up to 52% of methionine intake is metabolized in the gut. Cysteine, generated from methionine or obtained directly from the diet, is used in the intestinal cells to make glutathione.

PROTEIN QUALITY AND NEEDS

PROTEIN QUALITY AND NEEDS

PROTEIN SYNTHESIS

PROTEIN SYNTHESIS

Incomplete proteins are

derived from plant foods such as legumes, nuts, seeds, vegetables, and cereals/grains. Most plant foods tend to have too little of one or more indispensable amino acids. The exceptions are soy protein, quinoa, and chia seeds, which are of plant origin but are complete proteins.

Amino acid absorption occurs along the entire small intestine, but most amino acids are absorbed in the ___ and ____

duodenum and jejunum

In times of excess energy and protein intakes coupled with adequate carbohydrate intake, the carbon skeleton of amino acids may be used to synthesize ___ ____

fatty acids

indicator amino acid oxidation (IAAO) technique involves

feeding test amino acids individually to a person in graded amounts in the presence of an indicator amino acid. The amounts of the test amino acid that are provided include quantities below, at, and above the expected requirement.

The production of glucose from a noncarbohydrate source such as amino acids is known as ______.

gluconeogenesis

The liver derives up to 50% of its energy (ATP) from amino acid oxidation; the energy generated may in turn be used for _______ or ______, among other needs, depending on the body's state of nutriture

gluconeogenesis or urea synthesis

the periportal hepatocytes catabolize most amino acids with the exception of ____ and _____, which are metabolized to a greater extent by perivenous hepatocytes.

glutamate and aspartate

Typically three enzymes: ___ ____ _____, assist in the removal of the ammonia/ammonium ions from body cells. These enzymes are found in high concentrations in the liver but are also found in other organs.

glutamate dehydrogenase glutamine synthetase carbamoyl phosphate synthetase I (as part of the urea cycle)

Some amino acids that are more commonly deaminated include: however, many of these same amino acids also can be transaminated

glutamate, histidine, serine, glycine, and threonine

amino acids with aliphatic/nonpolar side chains

glycine alanine valine leucine isoleucine

After amino acids are transported out of the enterocyte, they enter portal blood and are transported to tissues. Uptake of the amino acids into liver cells (hepatocytes), as well as cells of the kidneys and other organs, occurs by some carrier systems similar to those found in the ....

intestinal cell membranes.

metabolism of aspartate from the diet generally occurs within

intestinal cells. Aspartate most often undergoes transamination to generate oxaloacetate; aspartate's amino group in turn is used to synthesize ornithine.

Arginine is also used by

intestinal cells. Up to 40% of dietary arginine is oxidized in enterocytes, yielding citrulline and urea

Amino acids in an aqueous solution are ______

ionized

limiting amino acid

is used to describe the indispensable amino acid that is present in the lowest quantity in the food

The end products of gastric protein digestion include primarily These end products are emptied in an acidic chyme through the pyloric sphincter into the duodenum for further digestion.

large polypeptides, along with some oligopeptides (short chains of amino acid peptide bonded to each other) and free amino acids.

The ____ is thought to monitor the absorbed amino acids and to adjust the rate of their metabolism (including catabolism or breakdown of amino acids, and anabolism or use of amino acids for synthesis) according to the needs of the body.

liver

____ is a large protein kinase complex that functions as part of a signaling pathway, primarily stimulating and mediating the effects of insulin and leucine (and perhaps other molecules), on protein synthesis through different multiprotein complexes

mTOR

Amino acids with no net charge, also called neutral amino acids, do not ______ substantially if placed in an electric field

migrate

the Brunnerʹs glands of the small intestine release ____-rich secretions needed for digestion

mucus

Polar amino acids are generally found

on the surfaces of proteins. If not found on the surface, they are oriented inward and function at a protein's (such as an enzyme's) binding site.

read changes in body mass with age

p.231

read about evaluation of protein quality

p.233

relatively nonpolar amino acids

phenylalanine tryptophan tyrosine

amino acids with side chains containing aromatic ring

phenylalanine tyrosine tryptophan

essential amino acids

phenylalanine valine threonine methionine tryptophan histidine isoleucine leucine lysine

the neutral amino acids interact with water to different degrees and can be divided into ___, ____, ____ categories

polar, nonpolar, and relatively nonpolar

After amino acids are transported out of the enterocyte, they enter ___ ____ and are transported to tissues.

portal blood

imino acids

proline

Ingestion of foods providing slow proteins, however, is important as the lower and more prolonged plasma amino acid concentrations that result from ingestion of these proteins help reduce ___ ___.

protein breakdown

amino acids with side chains containing hydroxylic (OH) groups

serine threonine

Polarity depends on the ______

side chain or R group of the amino acid.

Proteasomal degradation also has been shown to increase during ...

starvation as well as in pathological conditions such as sepsis, cancer, and trauma.

Amino acids may be classified in a variety of ways, including by

structure net charge polarity essentiality.

the term essential or indispensable means

that the body cannot make the nutrient (in this case the amino acid), and that it must be supplied by the diet

Calpains are calcium-activated proteases and are designated indicative of the different levels of calcium needed for activation. In muscle the calpain proteases appear to work in sequence with the proteasomal system, whereby ...

the calpain proteases initiate the degradation of damaged/oxidized myofibrillar proteins. The released myofilaments are then ligated to ubiquitin for further degradation.

In the intestinal cell, glutamate arises directly from

the diet or from glutamine metabolism. It is often transaminated with pyruvate to form α-ketoglutarate and alanine

Following ingestion, exogenous proteins serve as sources of ...

the essential amino acids nonessential amino acids additional nitrogen needed to synthesize more nonessential amino acids nitrogen-containing compounds protein in the body. (98-68g per day)

Nitrogen-balance studies involve

the evaluation of dietary nitrogen intake and the measurement and summation of nitrogen losses from the body.

polarity

the tendency of an amino acid to interact with water at physiological pH

Zwitterions have no net electrical charge because

their side chains are not charged, and the one positive and one negative charge from the amino and carboxy groups, respectively, in their base structure cancel each other out.