Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Fuel Metabolism > Protein and Nitrogen Metabolism > Flashcards

Protein and Nitrogen Metabolism Flashcards

1
Q

Protein Turnover

A
  • Protein turnover- proteins are constantly degraded; 75% recycled in synthesis and 25% catabolized and used for gluconeogenesis
  • Diff proteins have diff half-lives
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Nitrogen Balance (+ Pos and Neg Balances)

A
  • Nitrogen balance- nitrogen intake - nitrogen excretion
    • Pos balance - more input
      • Pregnancy, growth, lactation
      • Recovering from recent illness (after)-metabolic stress, injury
    • Neg Balance - more excretion
      • Inadequate dietary protein
      • During actual illness- metabolic stress, sepsis, trauma
      • Deficiency of an essential AA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the minimum dietary protein requirement for adults?

A
  • MIN dietary requirement - 56g/day for avg 70 kg adult

this is minimum needed to maintain nitrogen balance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Biological Value

A
  • Biological Value - depends on whether or not that protein has essential AAs and digestibility
  • Generally animal sources&raquo_space; plant sources
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is a mixed diet important for vegetarians?

A

Mixed diet ensures that you will get all essential AAs (whatever is missing from one ingredient will be in another)

Supplementation or complementation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Name the Essential AAs (+ 1 conditionally essential)

A
  • PVT TIM HALL
  • phenylalanine, valine, threonine
  • tryptophan, isoleucine, methionine
  • histidine, arginine**, leucine, lysine
  • **Arginine is “conditionally essential” because only needed as an infant/child then can make it on own
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the metabolic fate of dietary AAs? (6 options)

A
  • NOT STORED
  • Digested —> AA pool then…
replenish tissue proteins (turnover)
make non-essential AAs, 
used immediately as energy, 
makes specialized products (nucleotides, heme, cell signal molecules, pigments) 
leaves as nitrogenous waste
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does protein malnutrition lead to edema?

A
  • Dec protein intake —> dec albumin (hypoalbuminemia)

- Less albumin in blood means that fluid is not contained in blood vessels and leaks —> edema (swollen abdomen)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Proenzymes

Endopeptidases

Exopeptidases

A
  • precursors of proteolytic enzymes (inactivate); activated once in GI tract via limited proteolysis
  • proteolytic enzymes that hydrolyze/cleave protein in middle of polypeptide chain
  • proteolytic enzymes that hydrolyze/cleave protein @ ends (either C or N end)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Peptidases in Stomach, Pancreas and SI

A

Stomach- pepsinogen- inactive precursor of pepsin; secreted by chief cells; autocatalytic activation if low enough pH; once active it cleaves C term of proteins

Pancreas- zymogens (trypsin, chymotrypsin, elastase, CPA an CPB)

SI-oligopeptidases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 2 nonenzymatic components of gastric acid? What does each do?

A

HCl- secreted by parietal cells; dec pH to denature proteins and create low enough pH for activation of pepsinogen/ activity of pepsin

Gastrin- peptide hormone secreted by mucosal cells; gastrin works on parietal and chief cells to stimulate their release of above molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How are pancreatic proteases activated?

A

CASCADE

  • Trysinogen is activated —> trypsin (via enteropeptidase)
  • Trypsin then goes on to activate remaining zymogens (chymotrypsin, elastase, CPA and CPB)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the final products of protein digestion in the lumen of SI?

A

free AAs + di/tripeptides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are AAs transported in and out of SI cells?

A
  • Lumen side- depends on Na+ gradient (active transport)
  • Brush border side- Na+ indep (passive transport) ; AAs leave cell to enter portal circulation by moving down natural concentration gradient
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What 2 conditions are caused by long-term use of proton pump inhibitors?

A
  • Proton Pump Inhibitors - used for acid reflux/heartburn
  • Block parietal cells (HCl) which also release intrinsic factor which is needed to absorb B12)
  • B12 deficiency —> anemia OR peripheral sensory/motor neuronal deficiencies
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What 2 reactions remove amino groups from AAs?

A
  • 1- deamination
    • Prod free NH4+ directly
  • 2- transamination
    • transfer NH4+ to an acceptor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Glucogenic v Ketogenic AAs

A
  • Gluconeogenic - carbons contribute to glucose production (gluconeogenesis)
    • All but 2 AAs have this capacity
    • Make pyruvate, OAA, alpha-KG, succinyl CoA, fumarate
  • Ketogenic - carbons contribute to ketone formation
    • Only pure keotgenic AAs are lysine and leucine
    • Make acetyl CoA and acetoacetyl CoA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the 3 main alpha-keto acids that accept amino groups?

A

alanine + alpha-KG pyruvate + glutamate

aspartate + alpha-KG OAA + glutamate

glutamate + NADP+ —> alpha-KG + NADPH + NH4+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What 2 major reactions prevent accumulation of ammonia in peripheral tissues?

A
  • ALT: alanine + alpha-KG pyruvate + glutamate
  • AST: aspartate + alpha-KG OAA + glutamate

both reversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What role does Vit B6 have in AA metabolism?

A

Vit B6 is precursor for pyridoxal-P (transaminase coenzmye) so required in order to transamination to work

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Effects of isoniazid and penicillamine

A
  • Isoniazid- used for tuberculosis; “suicide substrate” that covalently binds pyridoxal so that it cannot by phosphorylated by pyridoxal kinase
  • Penicillamine- used to treat Willson’s disease; inactivates pyridoxal (amine of drug reacts w/ aldehyde of pyridoxal)

**Both treated w/ extra pyridoxine to normalize transaminase activity levels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the general route by which AA nitrogen in muscle gets incorporated into glutamate or aspartate in liver?

A

1-Nitrogen waste in muscle is converted to glutamate
2- Glutamate + pyruvate —> alanine (via ALT)
3- Alanine transferred to liver in blood (good because non-toxic unlike NH4+)
4- Alanine converted back to glutamate in liver (via ALT)
5- glutamate can also react w/ OAA —> alpha-KG + aspartate (via AST)

**both glutamate and aspartate can be converted to urea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why do alanine and glutamine make up more than 50% of AAs released from muscle?

A

B/c these are by-products of branched chain AA transamination (which occurs primarily in muscle by BCAT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the major metabolic fuel for the small intestine? What by-products are produced?

A

uses glutamine (from diet as well as muscle)

glutamine —> citrulline + alanine —> released into circulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

BCAA catabolism reactions and location

A

Leucine, isoleucine, valine

transaminated via BCAT (mainly in muscle mito)
BCAA –> alpha keto acid

carboxylated via BCKA DH (in muscle, kidney, liver and brain MITO)
alpha keto acid –> CoA derivative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

BCKA DH v pyruvate and alpha KG DH

A
  • All 3 unit enzymes w/ identical E3
  • Like pyruvate DH regulated by own kinase/phosphatase that modify E1
  • All in mito
  • Similar structure and mechanism
  • All require 5 coenzymes (thiamine pyrophosphate, lipoid acid, CoASH, NAD+, FAD)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How is propionyl CoA used?

A
  • Propionyl CoA —> D-methylmalonyl CoA —> L-methymalonyl CoA —> succinyl CoA —> TCA Cycle
    • Propionyl CoA carboxylase requires biotin
    • Methymalonyl CoA mutase requires it B12
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are the symptoms of propionyl CoA utilization problems?

A

Back up of propionyl CoA or methylmalonyl CoA –> side reaction w/ carnitine –> acyl carnitine which is then excreted (SO CARNITINE DEF)

Hypoglycemia b/c that propionyl CoA is not being made into succinyl CoA –> TCA cycle for eventual gluconeogenesis

Hyperammonia b/c buildup –> dec ATP and metabolic stress on enzymes of urea cycle (ammonia not converted to urea as efficiently)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What defect causes maple syrup urine disease?

A

deficiency or defect in BCKA DH complex

30
Q

How to treat propionic or methylmalonic acidemia?

A

Restricted protein intake (so no extra BCAA)

Some methylmalonic acidemia can be treated w/ Vit B12 supplements if it is an acquired acidemia from Vit B12 deficiency BUT not if it is a genetic defect w/ the enzyme itself

31
Q

Regulation of BCAA Metabolism

A
  • Allosterics - inhibited by acyl CoA and NADH
  • Covalent - BCAK DH is deactivated when phosphorylated
    • Even though this is a catabolic rxn (BCAA are being broken down), it contributes to the overall anabolic state (fed state) of the body b/c BCAAs are essential AAs so when the body is fed it can afford to break them down while when the body is fasted/starved it wants to conserve these essential AAs so it halts this step of metabolism
    • So…fits w/ insulin —> more BCKA made —> inhibits the kinase —> no longer phosphrylates/deactivates BCKA DH
32
Q

Name 3 Carriers of 1-Carbon Units + Oxidation States of Carbons They Carry

A
  • Folic acid - active form is THF
    • Oxidation states -
      • Methyl (most reduced)
      • Methylene
      • Formyl
      • Formimino
      • Methenyl (most oxidized)
  • SAM- carries methyl groups (most reduced)
  • Biotin - transfers CO2 groups
33
Q

3 synthetic pathways that require 1-carbon units

A
  • Making epinephrine from norepinephrine
  • Synthesis of carnitine
  • Synthesis of creatine (**greatest use of SAM)
34
Q

What is the role of SAM in metabolism?

A

Synthesis of creatine

Coordinated between kidney enzyme (AGAT) and liver enzyme (GAMT)

35
Q

What 2 reactions are important in making nonessential AAs? Examples?

A
  • Transamination -transfer amino group to alpha-keto acid
    • Ex) alanine + alpha-KG —> glutamate + pyruvate
  • Amidation -formation of amide bond
    • Ex) Glutamate + NH4+ + ATP —> glutamine + ADP + P
    • Ex) Aspartate + glutamine (N source) + ATP —> asparagine + glutamate + ADP + P
36
Q

Which glycolysis and TCA molecule are precursors for non-essential AAs?

A
  • Phosphoglycerate —> serine —> glycine
  • Pyruvate —> alanine
  • Alpha-ketogluterate —> glutamate —> proline, arginine, glutamine
  • OAA —> aspartate —> asparagine
37
Q

Which 2 non-essential AAs are made from essential AAs?

A
  • Phenylalanine —> tyrosine

- Methionine —> cysteine

38
Q

Classic PKU
Atypical PKU
Maternal PKU

A
  • Classic- deficiency in phenylalanine hydroxylase (auto recessive)
  • Atypical - deficiency in enzymes needed for biopterin biosynthesis or regeneration of BH4 (source of reducing power)
  • Maternal PKU - damage to fetus from mom’s phenylketones
39
Q

What are the consequences of folic acid deficiency?

A

in pregnancy can lead to spina bifida

40
Q

Which 2 reactions require Vit B12?

A
  • B12 deficiency —> cannot recycle methionine —> folate trapped in 5-CH3-THF form —> secondary folate deficiency (cannot be used in this form)
  • B12 also required for methylmaolonyl CoA —> succinyl CoA
41
Q

Endogenous Arginine Synthesis

A
  • First 2 enzymes of urea cycle in SI - make citrulline —> blood —> kidney
  • Next 2 enzymes of urea cycle in kidney - make arginine

***So citruline levels in plasma are indicative of function SI mass

42
Q

Deficiency in which enzyme leads to black urine?

A
  • *Alkaptonuria**
  • deficiency in homogentisic acid oxidase (catalyzes third step in tyrosine catabolism)
  • Urine has high levels of homogentisic acid which readily oxidizes and turns urine black
43
Q

Metabolic Functions of Glutamine (in which tissues?)

A
  • Precursor form of nitrogen (esp for purine and pyrimidine synthesis) - All tissues
  • Non-toxic transporter of ammonium ions from extrahepatic tissues to liver where it is converted to urea
  • Major fuel for enterocytes and macrophages and lymphocytes - Gut and immune system
  • Maintains acid-base balance - can be made into bicarb during metabolic acidosis - In kidney
44
Q

How, where and why is glutamine synthesized?

A
  • Made via detox in extrahepatic tissues
    • Glutamate + NH4+ + ATP –> Glutamine + ADP
      • Glutamine synthetase (GS)
  • To get rid of NH4+ (toxic)
  • Cytosol of all tissues but esp brain (NH4+ is toxic) AND muscle (high protein turnover)
45
Q

How do different liver cells lead to efficient detox?

A
  • Periportal Hepatocytes - enriched in glutaminase (glutamine –> NH4+) and CPS-1 (NH4+ –> carbamoyl phosphate)
    • Glutaminase inc the conc of ammonium in this cell in order for CPS-1 to work (has a high Km - so need high conc of NH4+)
  • Perivenous Hepatocytes - enriched in glutamine synthestase (NH4+ –> glutamine)
    • Has low Km for ammonium so that the ammonia ions that are not used in urea cycle are easily converted to glutamine and trapped in perivenous cells
46
Q

Where does urea get its carbon, oxygen and nitrogen?

A
  • Nitrogen- ammonium ions (from blood and action of glutaminase and glutamate DH) and aspartate (AA pool or transamination of OAA)
  • Carbon and oxygen- bicarbonate (reacts w/ NH3 to make the carbomyl phosphate)
47
Q

Relationship b/n ureagenesis and gluconeogenesis

A

Urea cycle produces fumarate which then enters TCA cycle and adds net carbons to it –> produce more malate–> OAA –> gluconeogenesis

48
Q

What is the energy cost to make 1 urea molecule?

A

uses 3 ATP but one ATP is further broken down to AMP so uses equivalent of 4 high energy phosphate bonds

49
Q

Short term and long term regulation of urea cycle

A
  • Short-term
    • CPS-1 is regulated step
    • Allosterically activated by NAG (high acetyl Coa-high energy + glutamate –> NAG in mito)
  • Long-term
    • Level of urea cycle enzyme transcription changes w/ level of dietary protein intake
    • Inc in high protein diet or starvation (because protein broken down then)
    • Dec in low protein diet
50
Q

How would you detect a CPS-I deficiency?

A

low citrulline but no high urinary orotate b/c carbamoyl phosphate not made

51
Q

How would you detect a OTCase deficiency?

A

high AAs, low citrulline, high urinary orotate (side reaction of carbomyl phosphate–> pyrimidine synthesis)

52
Q

How would you detect a ASS deficiency?

A

build up of citrulline and no argininosuccinate in blood

53
Q

How would you detect a ASL deficiency?

A

build up of arginosuccinate in blood

54
Q

Why are urea cycle disorders treated w/ benzoate and phenylacetate?

A
  • Sodium benzoate- makes benzyl CoA which reacts w/ glycine (N) –> hippuric acid –> excreted in urine
  • Sodium phenylacetate- makes phenylacetate Coa which reacts w/ glutamine (2N) –> phenylacetylglutamine –> excreted in urine

**phenyl more effective b/c gets rid of 2N

55
Q

4 major end products of nitrogen metabolism

A
  • Urea -urea cycle in liver
  • Creatinine -derived from spontaneous cyclization of creatine or creatine phosphate
  • Ammonium Ion -from glutamine –> glutamate –> alpha-ketogluterate
  • Uric Acid - from purine catabolism
56
Q

What 2 reactions are required for renal ammoniagenesis?

A
  • Glutamine –> glutamate (via glutaminase)
  • Glutamate –> alpha-KG (via glutamate DH)

**prod 2 NH3

57
Q

How is ammoniagenesis related to H+ excretion?

A

Gluatamine –> glutamate also produces 2 molecules of bicarb (acts as buffer)

58
Q

What metabolic abnormality would lead to increase in renal ammoniagenesis?

A

If acidosis …you do not want to use that many cations so inc ammoniagenesis so that you now use more NH3/NH4+ buffer instead

59
Q

How does increased renal ammoniagenesis lead to increase in renal gluconeogenesis?

A

b/c alpha-KG produced in ammoniagenesis–> TCA cycle –> inc OAA –> gluconeogenesis

60
Q

Creatine synthesis v creatinine synthesis

A
  • Creatine - made by enzymatic reaction (using SAM); also requires ATP
  • Creatinine- made by spontaneous, non-enzymatic reaction (creatine or creatine phosphate spontaneously cyclizes)
61
Q

How are purines catabolized? What is the end product?

A
  • Remove phosphate –> nucleoside
  • Remove ribose –> purine base alone
  • Oxidize w/ xanthine oxidase –> xanthine
  • Oxidize again w/ xanthine oxidase –> uric acid (end product)
62
Q

What 3 enzyme defects can lead to inc uric acid production?

A
  • Def in HGPRT (cannot recycle purines)
  • Abnormally high activity of PRPP Synthetase (inc purine synthesis)
  • Gluc-6-P def
63
Q

Why is allopurinol used to treat gout?

A
  • inhibits xanthione oxidase so less uric acid produced and build up of hypoxanthine which will be recycled back to purines via HGPRT
64
Q

What are the digestion products of polynucleotides?

A

purines, pyrimidines, ribose, deoxyribose, phosphate

65
Q

Purine synthesis v pyrimidine synthesis

A
  • Purines - (PRPP then make ring on ribose molecule)

- Pyrimdines - (make ring then add to PRPP- make ring before on ribose molecule)

66
Q

What metabolites give nitrogen and carbon to purines?

A
  • Carbon from… glutamine, glycine, THF and CO2

- Nitrogen from glutamine, aspartate

67
Q

What metabolites give nitrogen and carbon to pyrimidines?

A
  • Carbon- aspartate and CO2

- Nitrogen- glutamine, aspartate

68
Q

What is the primary regulatory mechanism to control nucleotide metabolism?

A
  • Allosterics
    • Act by availability of substrates
    • Inhib by end products
69
Q

What makes certain cells more sensitive to inhibition of nucleotide metabolism?

A

rapidly proliferating cells more sensitive (autoimmune diseases, cancers, ectopic pregnancy, immunosuppression in transplant, anti-tumor)

70
Q

Name 5 enzymes in nucleotide metabolism that are targeted by therapeutics

A
  • PPAT (PRPP –> IMP)
  • Enzymes that convert IMP –> ATP and GTP
  • HIV reverse transcriptase
  • Viral DNA polymerases
  • Thymidylate synthase that converts dUMP –> dTMP

Fuel Metabolism (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions