/
AI Flashcards
Save to my account
Sign up
AI Flashcards
Amino Acid Metabolism and Nitrogen Balance
Study
1
Question
True or False: Protein digestion begins in the stomach when gastrin stimulates secretion of hydrochloric acid (HCl) and pepsinogen, and pepsin hydrolyzes about 10% of peptide bonds.
Page 4
Answer
True. Gastrin stimulates HCl and pepsinogen release; HCl denatures proteins and converts pepsinogen to pepsin, which hydrolyzes roughly 10% of peptide bonds in dietary proteins.
2
Question
Describe the two main effects of gastric HCl on proteins during stomach digestion (one sentence each).
Page 4
Answer
1) HCl denatures protein tertiary structure, making peptide bonds accessible. 2) HCl activates pepsinogen to pepsin, which hydrolyzes peptide bonds.
3
Question
Multiple choice: Which enzyme is activated in the stomach to begin protein hydrolysis? A) Trypsin B) Pepsin C) Aminotransferase D) Arginase
Page 4
Answer
B) Pepsin. Pepsin is activated from pepsinogen by HCl in the stomach and starts protein hydrolysis.
4
Question
Define nitrogen balance and give the physiological meaning of a positive nitrogen balance.
Page 4
Answer
Nitrogen balance is the state where nitrogen intake as protein equals nitrogen excretion. A positive nitrogen balance means intake exceeds output, indicating net tissue synthesis (e.g., growth, pregnancy, recovery).
5
Question
What does a negative nitrogen balance indicate clinically?
Page 4
Answer
A negative nitrogen balance indicates degradation exceeds synthesis, resulting in tissue wasting; seen in starvation, severe illness, or protein-poor diets.
6
Question
List the three primary sources that make up the body's 'amino acid pool'.
Page 4
Answer
1) Digestion of dietary protein 2) Protein turnover (continuous degradation and resynthesis of body proteins) 3) Biosynthesis of non-essential amino acids in the liver
7
Question
True or False: The amino acid pool only comes from dietary protein.
Page 4
Answer
False. The amino acid pool comes from dietary digestion, protein turnover, and biosynthesis of non-essential amino acids in the liver.
8
Question
Describe, in two steps, how an amino group is removed from an amino acid for disposal.
Page 4
Answer
Step 1: Transamination – the amino group is transferred from the amino acid to an $oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{oldsymbol{}}}}}}}}}}$-keto acid (usually $oldsymbol{ ext{α-ketoglutarate}}$) forming glutamate. Step 2: Oxidative deamination – glutamate is oxidatively deaminated to regenerate $oldsymbol{ ext{α-ketoglutarate}}$, releasing the amino group as a free ammonium ion $oldsymbol{ ext{NH}_4^+}$ which enters the urea cycle.
9
Question
What is the primary purpose of the urea cycle?
Page 4
Answer
The urea cycle converts toxic ammonium ions ($ ext{NH}_4^+$) into non-toxic urea for excretion, thereby removing nitrogen generated from amino acid catabolism.
10
Question
Identify the two primary nitrogen-carrying 'fuel' molecules that supply nitrogen into the urea cycle.
Page 4
Answer
1) Carbamoyl phosphate (derived from $ ext{NH}_4^+$, CO$_2$, and ATP) 2) Aspartate (an amino acid that donates the second nitrogen)
11
Question
Enumerate the four stages of the urea cycle (one phrase per stage).
Page 7
Answer
1) Carbamoyl group transfer: carbamoyl phosphate transfers its carbamoyl group to ornithine to form citrulline (mitochondria). 2) Citrulline-aspartate condensation: citrulline condenses with aspartate to form argininosuccinate (requires ATP). 3) Argininosuccinate cleavage: argininosuccinate is cleaved into arginine and fumarate. 4) Hydrolysis of urea: arginine is hydrolyzed by arginase to produce urea and regenerate ornithine.
12
Question
Which cellular compartments are involved in the urea cycle?
Page 7
Answer
Both the mitochondrial matrix and the cytosol are involved; early steps (carbamoyl phosphate formation and ornithine carbamoyltransfer) occur in mitochondria, later steps occur in the cytosol.
13
Question
What enzyme catalyzes the conversion of glutamate to $ ext{α-ketoglutarate}$ and $ ext{NH}_4^+$ in oxidative deamination?
Page 7
Answer
Glutamate dehydrogenase catalyzes the oxidative deamination of glutamate to $ ext{α-ketoglutarate}$ and ammonium ion ($ ext{NH}_4^+$).
14
Question
Multiple choice: Which coenzymes can glutamate dehydrogenase use? A) NAD+ B) NADP+ C) NAD+ or NADP+ D) FAD
Page 7
Answer
C) NAD+ or NADP+. Glutamate dehydrogenase can use either NAD+ or NADP+ as a coenzyme.
15
Question
Explain why accumulation of ammonium ion ($ ext{NH}_4^+$) is toxic at the cellular level.
Page 7
Answer
Elevated $ ext{NH}_4^+$ depletes $ ext{α-ketoglutarate}$ by driving transamination and related reactions, impairing the citric acid cycle, reducing cellular ATP production, and causing central nervous system problems.
16
Question
Define transamination in one sentence.
Page 7
Answer
Transamination is a biochemical reaction where the amino group of an $ ext{α}$-amino acid is transferred to an $ ext{α}$-keto acid, creating a new amino acid and a new keto acid.
17
Question
What is the primary biochemical function of transamination reactions in nitrogen management?
Page 7
Answer
Transamination funnels amino groups from many different amino acids into a limited number of molecules (primarily glutamate and aspartate) for further processing and nitrogen disposal.
18
Question
Which two α-keto acids are the most common acceptors in transamination and are also citric acid cycle intermediates?
Page 7
Answer
The most common acceptors are $ ext{α-ketoglutarate}$ and oxaloacetate (both citric acid cycle intermediates).
19
Question
Identify the class of enzymes that catalyze transamination reactions and the required coenzyme.
Page 7
Answer
Enzymes called aminotransferases (or transaminases) catalyze transamination reactions, and they require the coenzyme pyridoxal phosphate (PLP), a derivative of Vitamin B6.
20
Question
True or False: Pyridoxal phosphate (PLP) is derived from Vitamin B6 and is required for all transamination reactions.
Page 7
Answer
True. PLP (the coenzyme form of Vitamin B6) is required for aminotransferase-catalyzed transamination reactions.
21
Question
Explain oxidative deamination in one sentence.
Page 7
Answer
Oxidative deamination is a catabolic reaction that converts an $ ext{α}$-amino acid (primarily glutamate) into the corresponding $ ext{α}$-keto acid, releasing the amine group as free ammonium ion ($ ext{NH}_4^+$).
22
Question
Where in the body do transamination and oxidative deamination primarily occur?
Page 7
Answer
These processes occur primarily in the liver (and oxidative deamination also occurs in the kidneys); the liver is the main site for converting amino acid nitrogen to urea.
23
Question
True or False: All amino acids are directly deaminated without first undergoing transamination.
Page 7
Answer
False. Most amino acids undergo transamination to transfer their amino group to acceptor keto acids (e.g., $ ext{α-ketoglutarate$) and are not directly deaminated.
24
Question
What happens to the carbon skeleton of amino acids after the amino group is removed?
Page 7
Answer
The carbon skeletons enter central metabolic pathways (e.g., glycolysis, citric acid cycle) as intermediates, where they can be oxidized for energy or used in gluconeogenesis or lipogenesis.
25
Question
Define a glucogenic amino acid in terms of its degradation products.
Page 4
Answer
A glucogenic amino acid degrades to products (such as pyruvate or TCA cycle intermediates like $ ext{α-ketoglutarate}$ or oxaloacetate) that can be used to produce glucose via gluconeogenesis.
26
Question
Define a ketogenic amino acid in terms of its degradation products.
Page 4
Answer
A ketogenic amino acid degrades to acetyl-CoA or acetoacetyl-CoA, which can be used to synthesize fatty acids or ketone bodies but cannot be used to produce net glucose.
27
Question
Give one example of why knowing whether an amino acid is glucogenic or ketogenic matters clinically in starvation.
Page 4
Answer
During prolonged starvation the body relies on gluconeogenesis for brain glucose; glucogenic amino acids can be converted to glucose, whereas ketogenic amino acids cannot, so glucogenic amino acids are more important for maintaining blood glucose.
28
Question
During hemoglobin catabolism, what happens to the globin protein portion?
Page 2
Answer
The globin protein is hydrolyzed into amino acids, which return to the amino acid pool for reuse in protein synthesis or metabolism.
29
Question
What is the fate of the iron atom released during hemoglobin breakdown?
Page 2
Answer
The iron atom is salvaged and stored in the protein ferritin for reuse in new hemoglobin synthesis or other iron-requiring processes.
30
Question
How is the heme (non-protein tetrapyrrole) group processed during hemoglobin catabolism?
Page 2
Answer
The heme group is not reused intact; it is degraded into a series of bile pigments (e.g., biliverdin, bilirubin) that are ultimately excreted in feces or urine after further transformations.