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Biochem block 2 > Lecture7-PROTEIN&AMINOACIDNUTRITION&UREACYLCE > Flashcards

Lecture7-PROTEIN&AMINOACIDNUTRITION&UREACYLCE Flashcards

1
Q

Most energy in our body comes from

A

fatty acids

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2
Q

______ store more energy than _____ but they both release the same amount of energy (hey have the same metabolic energy-4kcal/g)

A

Proteins, carbohydrates

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3
Q

____ ____ are broken down into amino acids which are taken up by the cells for the synthesis of new proteins and other nitrogen containing compounds

A

dietary proteins

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4
Q

Although protein contains more energy than carbs, why is the metabolic energy the same?

A

The products of nitrogen metabolism are not completely oxidized (AKA nitrogen is not completely degraded)

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5
Q

Your ____ amino acids can be used to make your ________ amino acids

A

essential, nonessential

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6
Q

It is important to know that the pathways for biosynthesis of AA are divers but their common feature is that their carbon skeleton comes from intermediates of which pathways?

A

Citric acid cycle(TCA), glycolysis, pentose phosphate(PPP)

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7
Q

What are the major metabolic precursors that lead to the formation of amino acids and proteins. Organize them by the 3 pathways that make up the carbon skeleton

A

TCA: oxaloacetate, alpha-ketoglutarate
Glycolysis: PEP, pyruvate, 3-phosphoglycerate
PPP: erythrose-4-phosphate, ribose-5-phosphate

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8
Q

What are essential amino acids?

A

Amino acids must be supplied from diet
requires many synthesis steps
can be used to make nonessential amino acids if deficient

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9
Q

What are nonessential amino acids?

A

Do not require many synthesis steps

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10
Q

If you have too much methionine or phenylalanine what can these amino acids be turned into?

A

Methionine can turn into cysteine
Phenylalanine can turn into tyrosine

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11
Q

WHY IS ARGININE BOTH ESSENTIAL AND NONESSENTIAL?

A

We can make arginine naturally but the rate is not sufficient during growth and development phases so we acquire thought the diet

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12
Q

Excess dietary protein is treated as a source of energy with glycogenic amino acids being converted to

A

glucose

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13
Q

Excess dietary protein is treated as a source of energy with ketogenic amino acids being converted to

A

fatty acids and keto acids

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14
Q

In the fasting state, the breakdown of body protein is _____ and the resulting amino acids are utilized for glucose production and the synthesis of non-protein nitrogenous compounds and essential proteins.

A

enhanced

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15
Q

Marasmus

A

inadequate intake of both protein and energy in children 2 years and younger

SX: Losses of subcutaneous fat reserves and muscle mass

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16
Q

What can be observed with a child with marasmus?

A

normal hair, old man/wizened appearance, thin limbs with little muscle or fat, very underweight body

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17
Q

Kwashiokor

A

inadequate intake of protein in the presence of adequate energy (caloric) affecting children age 2-3

SX: easy, painless hair pluckability, pitting edema, skin breakdown, delayed wound healing

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18
Q

Why is redistribution of amino acids among proteins essential?

A

If for any reason the supply of protein in diet is insufficient, the need to synthesize specific proteins for vital physiological functions results in a redistribution of amino acids among proteins. Thus, deficiencies in certain proteins (reduction in synthesis) may be tolerated under certain conditions so that levels of critical proteins may be maintained.

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19
Q

Explain redistribution with hemoglobin

A

Hemoglobin is degraded to the extent of almost 1% a day as red blood cells die, and under normal conditions the degradation is balanced by re-synthesis.

In a deficiency of amino acids, relatively less hemoglobin is synthesized because a degree of anemia is more tolerable than a deficiency of certain other proteins.

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20
Q

What is nitrogen balance?

A

A comparison between the intake of nitrogen, mostly in the form of protein, and the excretion of nitrogen, mostly as undigested protein in the feces, and urea and ammonia in the urine.

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21
Q

Explain digestion and absoption of proteins in the GI tract, specifically in the stomach

A
  1. When food enters the stomach it triggers the release of gastrin from the gastric mucosa.
  2. This in turn, signals the release of acid from the parietal cells.
  3. As a result, stomach pH drops to ~ pH 2, activating the autocatalytic conversion of pepsinogen (secreted by the chief cells) to pepsin (pH drops, protein denatures)
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22
Q

Proteins are broken down by hydrolysis of peptide bonds, the enzymes involved are termed…

A

peptidases

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23
Q

What are the two examples of peptidases and specify what they do.

A

Endopeptidases - cleave internal peptide bonds.

Exopeptidases - cleave off one amino acid at a time from either the C- or N-terminal of the polypeptide.
—–Carboxypeptidases (cleave at c term)
—–Aminopeptidases (cleave at n term)

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24
Q

Depending on the source of the peptidases, protein digestion can be divided into what three phases?

A

gastric, pancreatic and intestinal phases.

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25
Q

Upon the action of the endo and both exopeptidases, what occurs?

A

Proteins are hydrolyzed to di and tripeptides (smaller peptides) and free amino acids. These are absorbed into the intestinal cells by specific transporters. Free amino acids are then released into the blood for use by other tissues.

26
Q

______ ______ are the final class of biomolecules whose oxidation contributes significantly to the generation of energy

A

amino acids

27
Q

What are the two major classes of amino acids involved in oxidative degradation?

A

glucogenic and ketogenic

28
Q

What are glucogenic amino acids?

A

The amino acids that give rise to the net synthesis of glucose

29
Q

For glucogenic amino acids what are the catabolic products that form upon degradation of amino acids?

A

pyruvate, oxaloacatate, alpha-ketoglutarate, succinyl-CoA, fumarate

30
Q

What are ketogenic amino acids?

A

The amino acids that give rise to the net synthesis of ketone bodies

31
Q

For ketogenic amino acids what are the catabolic products that form upon degradation of amino acids?

A

acetoacetate
acetyl-CoA

32
Q

Which two amino acids are SOLELY ketogenic, and which one is the MAJOR ketogenic amino acid

A

Leucine and lysine, LEUCINE is the major ketogenic aa

33
Q

In humans, amino acids undergo oxidative degradation (OD) in three different metabolic circumstances. What are they

A
  1. Excess dietary proteins (some amino acids released during proteins breakdown undergo OD if they are not needed for new protein synthesis)
  2. When amino acids can’t be stored (high protein in diet, aa can’t be stored but it used for protein synthesis)
  3. Fuel source during starvation and/or diabetes (carbohydrates are either unavailable or cannot be properly used, so proteins are called to be used as fuel)
34
Q

Most amino acids are metabolized in the liver. What happens to excess ammonia generated in the extra-hepatic tissues?

A

It is transported to the liver for conversion to the appropriate excreted form

35
Q

What is transamination?

A

The transfer of the amino grp to a keto acid acceptor which requires pyridoxal 5’ phosphate (PLP)

36
Q

Tranaminators can also be called what

A

aminotransferases

37
Q

Three keypoints things Gloria wants us to know about transamination

A

In order for reaction to occur we need PLP to function WITH Aminotransferase, without PLP, rxn will not occur

Transamination includes the transfer of an amino group from the amino acid to keto group

Transamination rxn is reversible

38
Q

Key points for Glutamate Dehydrogenase Reaction

A

Location: Liver. mitochondria
Requires: PLP and NAD

  1. Complex enzyme (multiple subunits functioning like pyruvate dehydrogenase)
  2. Regulated by ADP (positive) and GTP (negative) relative to Glu to a-KG conversion.
  3. In liver, primary function in mitochondria is to produce NH4+ for the urea cycle.
  4. In extra-hepatic tissue, excess NH4+ can be removed to form glutamate.
  5. The enzyme can use either NADP+ or NAD+ as a cofactor.R
39
Q

Key points for Glutamine Synthetase reaction

A

Location: Extra-hepatic tissues (outside liver)
Requires: PLP and ATP

  1. The role of glutamine synthetase is to convert ammonia (which is extremely toxic) to glutamine for transport from extra-hepatic tissues to the liver or kidneys.
  2. Glutamine is the major transport form of ammonia; it is present in blood in much higher concentrations than other amino acids.
40
Q

Key points for Glutaminase

A

Location: mitochondria
Requires: PLP

In the liver, and to some extent in the kidneys and intestine, glutaminase converts glutamine back to glutamate, releasing free NH4+.

41
Q

What is the glucose-alanine shuttle?

A

Within the muscle, amino acid degradation leads to the transfer of nitrogen to a-ketoglutarate and pyruvate.

The alanine formed travels to the liver, where the carbons of alanine are used for gluconeogenesis and the alanine nitrogen is used for urea biosynthesis.

42
Q

Where does the Urea cycle occur?

A

Mitochondria and cytosol of the liver.

43
Q

What is the rate limiting enzyme for the urea cycle?

A

Carbomyl phosphate synthetase I (CPS I)

44
Q

Explain the Urea cycle with this picture and note key points

A

Point of entry: oxaloactetate whihc leads to formation of aspartate. Alpha-ketoglutarate which leads to form glutamate

RLE: carbomyl phosphate synthetase
Urea cycle occurs In mitochondria and cytosol of the liver

Ornithine and Citruline can leave and enter the mitochondria/cytosol

45
Q

What is the relationship between TCA and Urea Cycle?

A

The urea cycle, the citric acid cycle, and the transamination of oxaloacetate are linked by fumarate and aspartate.

46
Q

What regulates carbomyl phosphate synthetase I?

A

N-acetylglutamate: allosteric activator of CPS I

47
Q

How does n-acetylglutamate lead to activation of CPS i?

A

High levels of transamination during amino acid breakdown lead to elevated glutamate with concommitant increases in the concentration of N-acetylglutamate

48
Q

_______ are important for energy metabolism, gluconeogenesis and as precursors for important biomolecules.

A

Amino acids

49
Q

_______supplies essential amino acids to replenish the amino acid pool.

A

Dietary protein

50
Q

The process of protein digestion involves the action of a number of different _______ and _______ with different specificity resulting in degradation to free amino acids and small peptides.

A

proteases, peptidases

51
Q

Catabolism of amino acids occurs primarily in the

A

liver

52
Q

The carbon skeletons of amino acids can be completely oxidized via the TCA cycle to supply energy or can be converted to ________or to _________

A

glucose (glycogenic) or to ketone bodies (ketogenic)

53
Q

The removal of the a-amino group, the first step in catabolism of most amino acids, is catalyzed by

A

aminotransferases (transaminases)

54
Q

________which utilize alanine and glutamine as carriers are important for the transport of excess nitrogen from the extra-hepatic tissues to the liver for conversion to urea.

A

Shuttle systems

55
Q

The_______occurs exclusively in the liver and results in conversion of ammonia to the non-toxic excretion product, urea.

A

The urea cycle

56
Q

Some of the ammonia generated is used in biosynthesis; the excess is

A

excreted

57
Q

Excess ammonia generated in extra-hepatic tissues is transported to the ______

A

liver for conversion to the appropriate excreted form.

58
Q

The conversion of ammonia and glutamate to glutamine, catalyzed by__________ is especially important for the removal of free ammonia in extra-hepatic tissue.

A

glutamine synthetase

59
Q

The amide nitrogen of glutamine is released as ammonia only within the liver mitochondria where the enzyme _______ converts glutamine to glutamate and NH4+.

A

glutaminase

60
Q

Glutamate is transported from the cytosol to the mitochondria where it undergoes oxidative deamination catalyzed by

A

glutamate dehydrogenase.

61
Q

The immediate precursors of the nitrogen atoms of urea are

A

ammonia and the amino acid aspartate.

62
Q

The mitochondrial enzyme ________ is the major site of regulation for the urea cycle. ________ is a required regulatory molecule.

A

carbamoyl phosphate synthetase-1, N-acetylglutamate (NAG)

Biochem block 2 (10 decks)

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