Amino Acid Metabolism I

Question 1

How many amino acids do we have

Answer 1

20

Question 2

unneeded or damaged proteins are marked for destruction by the covalent attachment of chains of a small protein called _____. and then degraded by a large, ATP-dependent complex called the ______

Answer 2

Ubiquitin, proteasome

Question 3

What is the primary use of amino acids provided through degradation or digestion

Answer 3

building blocks for the synthesis of proteins and other nitrogenous compounds such as nucleotide bases

Question 4

Amino acids in excess of those needed for biosynthesis can neither be ____ or _____.

Answer 4

stored, excreted

Question 5

Surplus amino acids are used as

Answer 5

metabolic fuel ( the alpha-amino group is removed, and the resulting carbon skeleton is converted into a major metabolic intermediate)

Question 6

most amino groups harvested from surplus amino acids are converted into ____ through the ____. And their carbon skeletons are transformed into

Answer 6

urea through the urea cycle. Acetyl CoA, Acetoacetyl CoA, pyruvate, or one of the intermediates of the TCA cycle

Question 7

Coenzyme that forms Schiff-base intermediates, that allow alpha amino groups to be shuttled between amino acids and ketoacids

Answer 7

pyridoxal phosphate

Question 8

Protein digestion begins in the

Answer 8

stomach

Question 9

Primary proteolytic enzyme of the stomach

Answer 9

pepsin

Question 10

In the small intestine the low pH of the food as well as the polypeptide products for pepsin digestion stimulate the release of

Answer 10

Sodium bicarbonate and a variety of proteolytic enzymes are released from the pancreas

Question 11

Pancreatic enzymes are secreted as _______. Name them

Answer 11

-Zymogens

Tyrpsinogen, chymotrypsinogen, proelastase, and procarboxypeptidase

Question 12

What is the proteolytic enzyme on the plasma membrane of intestinal cells.

Answer 12

Aminopeptidase N

Question 13

Aminopeptidases digest proteins form the ____ end

Answer 13

amino-terminal end

Question 14

____ amino acids, as well as ___ and ____, are transported into the intestinal cells

Answer 14

Single amino acids, as well as Di and Tripeptides

Question 15

At least ____ different amino acid transporters exist, each specific to a different group of amino acids. They transport amino acids into the intestinal cells

Answer 15

7

Question 16

Amino acids in the intestinal cells are transported into the blood by a number of _______ antiporters for use by other tissues

Answer 16

Na+-amino acid

Question 17

Protein digestion is primarily a result of the activity of enzymes secreted by the ____

Answer 17

pancreas

Question 18

The half-lives of proteins range over ____ orders of magnitude

Answer 18

several (from minutes to days)

Question 19

A small (76 amino acids) protein present in all eukaryotic cells, is a tag that marks proteins for destruction

Answer 19

Ubiquitin (Ub)

Question 20

The first step in amino acid degradation is the

Answer 20

removal of nitrogen

Question 21

what is the major site of amino acid degradation in mammals

Answer 21

the liver (although muscles readily degrade the branched chain amino acids)

Question 22

______ catalyze the transfer of an alpha-amino group form an alpha amino acid to an alpha ketoacid

Answer 22

aminotransferases (also called transaminases)

Question 23

Aminotransferases (also called transaminases) generally funnel alpha amino groups form a variety of amino acids to ______ for conversion into NH4+

Answer 23

alpha-ketoglutarate

Question 24

The nitrogen atom in glutamate is converted into fee ammonium ion (NH4+) by oxidative deamination, a reaction catalyzed by

Answer 24

glutamate dehydrogenase

Question 25

Glutamate dehydrogenase is unusual because it can utilize either ____ or _____

Answer 25

NAD+ or NADP+

Question 26

glutamate dehydrogenase is allosterically inhibited by ____ and stimulated by ___

Answer 26

inhibited by GTP, stimulated by ADP

Question 27

What is negative nitrogen balance? and when can it be seen

Answer 27

more nitrogen out than in. Commonly seen in Cancers because you are degrading proteins unnaturally fast

Question 28

What is positive nitrogen balance? and when is it commonly seen

Answer 28

Postive nitrogen balance is seen in athletes, pregnancy, and newborns

Question 29

all aminotransferases contain the prosthetic group _____, which is derived form ______

Answer 29

pyridoxyl phosphate (PLP), which is derived form pyridoxine (vitamin B6)

Question 30

The production of Ammonia from amino acids has how many steps and what are they

Answer 30

• 2
• Step 1: Transamination: transfer of an alpha amino group form an alpha amino acid to an alpha-ketoacid
• Step 2: oxidative Deamination: Nitrogen atom in glutamate is converted into free ammonium ion

Question 31

muscles lacks the enzymes of the ____ cycle

Answer 31

urea

Question 32

Enzyme that catalyzes the coupling of free NH3 with HCO3 to make Carbamoyl phosphate

Answer 32

Carbamoyl phosphate synthetase I

Question 33

What is the committed step in the urea cycle

Answer 33

the coupling of free NH3 with HCO3- to make Carbamoyl phosphate (catalyzed by carbamoyl phosphatase syntheses I)

Question 34

Carbamoyl phosphate synthetase I requires how many ATP

Answer 34

2

Question 35

Enzyme that catalyzes the transfer of Carbamoyl group (from carbamoyl phosphate) to Ornithine to form Citrulline

Answer 35

Ornithine transcarbamoylase

Question 36

Enzyme that Catalyzes the condensation of Citrulline with Aspartate to form Argininosuccinate

Answer 36

Argininosuccinate synthetase

Question 37

Enzyme that cleaves Argininosuccinate into Arginine and Fumarate

Answer 37

Argininosuccinase (Argininosuccinate lyase)

Question 38

In the urea cycle the aspartate carbon skeleton is conserved in the production of

Answer 38

fumarate

Question 39

Catalyzes Arginine hydrolysis to urea and ornithine

Answer 39

Arginase

Question 40

Carbamoyl group has a high transfer potential because of its

Answer 40

anhydride linkage