CFB 19: Amino Acids (Biochemistry)

T/F: There are storage forms of amino acids/proteins.

False

The carbons of excess amino acids from dietary protein are converted to what?

Fat or carbohydrate or CO2

What is positive vs. negative nitrogen balance?

Positive: gaining protein in body
Negative: losing protein from body

What is another name for amino acid metabolism?

Nitrogen metabolism

Where is the amino acid pool maintained?

Blood

The amount of urea in urine is proportional to what?

Dietary protein

Under conditions of constant weight (nitrogen balance), only the ____ level changes as a result of changed protein intake.

Urea

Where are acid and pepsinogen secreted?

Glands of the stomach

What does acid denature?

Proteins

What does pepsin produce?

Peptides

What does the pancreas secrete?

Bicarbonate and zymogens

Activated enzymes in the first part of the small intestine digest ________.

Peptides

What are the enzymes in the duodenum?

Trypsin
Chymotrypsin
Elastase
Carboxypeptidase

What is the final stage of dietary protein digestion?

Enzymes of intestinal lumen and villi produce mostly amino acids for absorption

Where does intracellular (body) protein degradation occur?

26S proteasome (mini stomach)

What enzymes add ubiquitin to target proteins?

E3

Poly-ubiquitinated proteins are ________.

Degraded

Abundant aminoopeptidases inside most cells degrade the short peptides to what?

Amino acids

Essential amino acids are obtained from what?

Degradation of body protein or the diet

What supplies AAs?

Amino acid pool of blood

Pepsin in the stomach is active at what pH?

1.5

Where are trypsin, chymotrypsin, and elastase located?

Lumen of small intestine

What do carboxypeptidase and aminopeptidases produce?

Amino acids

Intracellular proteins are tagged by _________ and degraded by what?

Ubiquitin; proteosome

Body protein is degraded with insufficient or incomplete _______ _______.

Dietary protein

The carbons of excess amino acids are used, the ________ is waste.

Nitrogen

Nitrogen is removed in 3 steps:

Transfer to a common carrier
Ammonia is regenerated in liver
Ammonia is incorporated into urea

What is the essential first step in the catabolism of amino acids?

Amino acids transfer their nitrogen via amino transfer reactions to a common carrier

All ____________ utilize α-ketoglutarate as the acceptor for the amino group or glutamate as the donor.

Transaminases

Aspartate amino transferase does...

Aspartate + α-ketoglutarate → oxaloacetate + glutamate

Alanine amino acid transferase does...

Alanine + α-ketoglutarate → pyruvate + glutamate

Removal of nitrogens occurs via ______.

Ammonia (ammonium ion)

What catalyzes the release of ammonia from glutamate?

Glutamate dehydrogenase

The ammonia is secreted in the form of ____ through the ____ cycle.

Urea

What does glutaminase do?

Converts glutamine to glutamate

What is the sum of the reactions catalyzed by transaminases and glutamate dehydrogenase?

Where is urea synthesized?

Liver

Two atoms of ________ are needed for the synthesis of one molecule of urea.

Nitrogen

Where does nitrogen enter the urea cycle?

At two points, one as carbamoyl phosphate synthesized from free ammonia, the other as the amino group of aspartate

What is the key regulatory step of the urea cycle?

The first irreversible reaction, catalyzed by CPSI

What is the first regulatory step of the urea cycle controlled primarily by?

Cofactor N-acetylglutamate (NAG)

Where is the NAG cofactor formed?

Only in mitochondria

What is NAG synthesized from?

Acetyl-CoA and glutamate (stimulated by arginine)

Feed the excess nitrogen into which AA?

Glutamate

Where is NH4+ made?

Mitochondria of liver cells

Where is NH4+ incorporated?

Carbamoyl phosphate (and eventually, urea)

What combines with carbamoyl phosphate in the mitochondria?

Ornithine

What catalyzes ornithine + carbamoyl phosphate?

Ornithine transcarbamoylase

Whta edoes ornithine + carbamoyl phosphate exit as?

Citrulline

Production of carbamoyl phosphate is controlled by ___.

NAG

What activates NAG?

Arginine

What does arginine produce?

Urea

What catalyzes arginine to urea?

Arginase

What are the two fates of the amino acids?

Glycogenic or ketogenic

T/F: You can get blood glucose from lysine and leucine.

False

T/F: In mitochondria, almost all AAs are degraded into TCA cycle compounds.

True

Breakdown of _______ begins like other branched-chain AAs, then diverges to...

Leucine; acetyl-CoA

Why would someone's urine smell of maple syrup/burnt sugar?

Some individuals lack the ketoacid dehydrogenase and build up the keto acids

Which amino acids are involved in maple syrup urine disease?

I L V

Where are reduced NADH and FADH found?

Mitochondria

When amino acids are broken down, their carbons form either ________ or ___ _____ intermediates.

Pyruvate or TCA cycle intermediates

If these intermediates can form OAA, you can make _______.

Glucose

What do branched chain amino acids form?

Branched chain keto acids

Which compounds are involved in the synthesis of catecholamines (dopamine)?

Tetrahydrobiopterin (in hydroxylase reaction)
PLP (in decarboxylase reaction)

What converts Dopa to Dopamine?

DOPA decarboxylase (PLP)

Epinephrine is made from ________.

Dopamine

What is the intermediate between dopamine and epinephrine?

Norepinephrine

Melanin is synthesized from ________.

Tyrosine

What do patients with Albinism lack?

Tyrosinase (leading to a lack of melanin pigments in skin and eyes)

Depending on the tissue, what 3 compounds can tyrosien form?

Dopamine
Epinephrine (adrenalin)
Melanin

The synthesis of glycine, serine, cysteine, methionine, and other molecules requires _-carbon transfers.

1

What group does Biotin and PLP transfer?

CO2

What group does cofactor SAM transfer?

Methyl

Tetrahydrofolate derives from dietary _______.

Folate

T/F: Folates can carry out essential methylation reactions.

True

Where are folates found?

Green leafy vegetables

Folate is required for synthesis of what?

Nucleic acid

T/F: All forms of folate interconvert.

False; the methyl form does not

What are these forms of THF known as?

One-carbon pool

What can be made from glycine using the methylene form?

Serine
This reaction is reversible

What is the methyl donor?

S-adenosyl-methionine (SAM)

THF (tetrahydrofolate) comes in different forms.

True

Using Methylene THF/THF, _______ can be interconverted with ______.

Glycine, serine

SAM is used in making what?

Epinephrine (from norepinephrine)

Oxaloacetate is the TCA cycle entry point for the breakdown of which amino acids?

Asparagine and aspartate

Conversion of glycine to serine requires which of the following enzymatic processes?

One carbon addition from N5,N10-methylene tetrahydrofolate

What is the glycolysis/TCA cycle intermediate that is transaminated to form glutamate?

α-ketoglutarate

Which precursors does mitochondrial carbamoyl phosphate synthase use?

NH4+, ATP, and CO2

One of the nitrogens for urea biosynthesis comes from aspartate. Aspartate is regenerated by the transamination of which TCA cycle intermediate?

Oxaloacetate

Which enzyme functions best at low pH (around 1.5)?

Pepsin

Body protein that is degraded is tagged with what molecule and is degraded by which cellular structure?

Ubiquitin, proteosome

An individual is on a diet that is deficient in leucine. They will lose muscle mass because leucine is...

An essential amino acid

An individual who is deficient in ornithine transcarbamoylase will most likely present with low levels of urea, and low levels of what other compound?

Citrulline

Which one of the following enzymes or compounds is not directly in the pathway from tyrosine to epinephrine?

Melanin