Biochemistry Final: Exam #3 Review Flashcards Preview

Biochemistry > Biochemistry Final: Exam #3 Review > Flashcards

Flashcards in Biochemistry Final: Exam #3 Review Deck (157):
1

What are the three sources of glutamate?

1) Diet (major)
2) Transamination of a-KG
3) Deamination of Glutamine

2

Transamination

Amino acid + a-KG--> Glutamate + a-ketoacid

- Amine group from amino acid is carried by B6(pyridoxal 5'-phosphate) to a-KG & swapped for carboxyl group
- Makes Glutamate & corresponding a-Ketoacid

3

Deamination of Glutamine

Glutamine--> Glutamate, via the enzyme "Glutaminase"

4

Why do we make glutamine?

Glutamine production in peripheral tissues in an important mechanism of ammonium ion removal

5

How do we make glutamine?

Glutamate--> Glutamine, via the enzyme "Glutamine Synthetase"

- Ammonium ion required (removes toxic substance too!)
- ATP hydrolyzed to ADP + Pi

6

Where does this glutamine go?

Enters the bloodstream and is absorbed by the:

- Kidneys
- Liver
- Gut

Here, the amide group is hydrolyzed by Glutaminase (Glutamine--> Glutamate), generating Glutamate & NH4+

7

What do the kidenys and liver do with ammonium ion (NH4) generated by the glutaminase reaction i.e. deamination of glutamate?

- Kidneys excrete NH4 directly
- Liver channels NH4 into the urea cycle
(Gut, NH4 serves as an important nutrient)

8

PLP

- Active form of pyridoxal phosphate
- Vitamin B6
- Cofactor that is required for aminotransferase reactions

9

ALT

Alanine + a-KG --> Pyruvate + Glutamate
Pyruvate + Glutamate--> a-KG + Alanine

- Alanine Aminotransferase (ALT)
- Requires Vitamin B6 (PLP)
- Connects muscle & liver metabolism
- Found primarily in the liver

10

Glucose-Alanine Cycle

- Muscle glycolysis produces pyruvate
- ALT converts pyruvate into alanine that is released into the blood
- Blood carries alanine to the liver
- In liver, ALT converts alanine back into pyruvate
- Pyruvate is used for gluconeogenesis

11

AST

1) Oxaloacetate + Glutamate --> a-KG + Aspartate
2) Aspartate + ATP + Glutamine--> Asparagine, via the enzyme "Asparagine Synthetase"

12

Clinical Significance of ALT vs. AST

Serum elevation of ALT is more specific for liver damage

13

Folate & THF

- Tetrahydrofolate (THF) Serves as an acceptor of 1-carbon groups (methylene)
- Derived from the vitamin, Folate

14

Most oxidized form of THF

N10-formyl THF

15

Most reduced from of THF

- N5-methyl THF
- Is NOT readily oxidized back to N10-formyl THF
- Thus, accumulates in the body

16

Which amino acid is the main donor of 1 carbon groups?

Serine

17

Serine Hydroxymethyl transferase

Serine + THF--> Glycine + N5, N10-methylene THF + H20

18

Phenylalanine Hydroxylase

Phenylalanine--> Tyrosine

- Requires oxygen, NADH, & the reduced cofactor tetrahydrobiopterin (THBtn) to oxidize the aromatic ring of phenylalanine

19

Dihydrobiopterin Reductase

Dihydrobiopterin (DHBtn, oxidized) -->Tetrahydrobiopterin (THBtn, reduced)

20

Phenylketonuira (PKU)

- Most common inborn error of metabolism
- Accumulation of phenylalanine that causes: severe intellectual disability, recurrent seizures, hypopigmentation, & eczematous skin rashes
- Caused by defect in phenylalanine hydroxylase OR DHBtn Reductase
- Must avoid nutrisweet/ aspartame

21

The overall rate of amino acid degradation is influenced by the activity of which enzyme? What inhibits this enzyme & what activates this enzyme?

Mitochondrial Glutamate Dehydrogenase

- Inhibited, high energy: GTP, ATP, NADH
- Activated, low energy: GDP, ADP, NAD+

22

Mitochondrial Glutamate Dehydrogenase

Glutamate + NAD+ + H20 --> a-KG + NADH + NH4+

23

Which amino acids can be converted into pyruvate? And what is pyruvate eventually used to make?

- Glycine
- Serine
- Cysteine
- Alanine

- OAA

24

Glycine, through several steps, can eventually be converted into pyruvate. How is glycine also related to the formation of kidney stones?

Glycine--> Serine --> Pyruvate = one possible path
Glycine--> Glyoxalate--> Oxalate= second possible path

- Oxalate is a metabolic end product that is excreted in the urine
- Oxalate also has a high affinity for Ca++, and can precipitate as kidney stones

25

Besides via pyruvate, two other amino acids can be shunted to make OAA. Which?

- Asparagine
- Aspartate

Asparagine--> Asparate, via enzyme "asparaginase"
Aspartate--> OAA, via AST

26

Which amino acid can be used to make a-KG?

Glutamine

Glutamine--> Glutamate, via enzyme "Glutaminase"
Glutamate--> a-KG, via Aminotransferases & Glutamate Dehydrogenase

Therefore, amino acids that can make glutamate, can also be used to make a-KG

27

Which amino acids can make glutamate?

- Proline
- Histidine
- Arginine

28

Glycine Encephalopathy

- Nonketotic hyperglycemia that presents soon after birth with symptoms of: lethargy, lack of muscle tone, & muscle twitching
- Caused by defects in glycine cleavage system

29

What amino acids can make propoionyl-CoA?

- Threonine
- Methionine
- Valine
- Isoleucine

30

What is propionyl-CoA eventually made into, and enzymes & cofactors are needed for that transformation?

Succinyl-CoA

1) Carboxylase= Propionyl-CoA--> D-methylmalonyl-CoA, requires Biotin
2) Racemase= D-methylmalonyl-CoA--> L-methylmalonyl-CoA
3) Mutase= L-methylmalonyl-CoA--> Succinyl-CoA, requires Vitamin B12

31

What is the clinical significance of defects in Carboxylase/ Biotin, Racemase, or Mutase/ B12?

- Carboxylase/ Biotin= Propionic Acidemia
- Racemase= D-methylmalonyl-CoA Aciduria
- Mutase/ B12= Methylmalonic Aciduria

32

What is the only direct source of B12?

Bacteria

33

What protein is needed to absorb B12?

- Intrinsic Factor
- Produced by parietal cells of the stomach

34

Once in the body, what protein transports B12?

Transcolbalamin

35

Where do you store B12?

Liver

36

Pernicious Anemia

- Anemia caused by a lack of intrinsic factor (protein that is needed to absorb B12 from the diet)
- Autoimmune disorder w/ antibodies against parietal cells of the stomach that produce intrinsic factor

37

Megaloblastic Anemia

- Megaloblastic cells reach a large size because they are unable to complete cell division due to deficient DNA replication
- N5- methyl-THF is the most reduced form of THF
- More oxidized forms of THF are required in the enzymatic reactions that generate purines (A, G) & thymidine for DNA synthesis
- Vitamin B12 is required for the only reaction that converts N5-methyl-THF back to THF

38

What is the only reaction in mammals that converts N5 methyl-THF back to THF?

Homocytsine--> Methionine, catalyzed by the enzyme "methionine synthase"

39

How does B12 deficiency lead to mental confusion & loss of sensation?

- Demyelination
- Though that methionine/ methionine synthase reaction (homocytsine-->methionine & requires B12 cofactor) is somehow involved

40

B12 Deficiency & Atherosclerosis

- Homocysteine builds up in B12 deficiency (methionine synthase reaction impaired)
- Thought that homocysteine damages arteries, oxidizes LDL, & interferes with blood clotting

41

BCAA Catabolism steps

1) BCAA--> Branched chain a-ketoacid, via "branched chain aminotransferase"
2) Branched chain a-ketoacid--> branched chain acyl-CoA via decarboxylation by BCKDH
3) Remainder proceeds like B-oxidation

42

BCKDH

Branched chain a-ketoacid dehydrogenase complex

43

Maple Syrup Urine Disease

- Accumulation of branched chain a-ketoacids in the urine, which gives the urine a characteristic maple syrup odor
- When untreated, can cause: poor feeding, vomiting, slow or irregular breathing, ketoacidosis, hypoglycemia, & neurological dysfunction
- Caused by a defect in BCKDH
- Treatment is a diet low in BCAAs

44

Tyrosinemia- II

- Rare disorder characterized by keratitism, photophobia, & painful skin lesions on the palms or the hands/ soles of the feet, as well as intellectual disability
- Caused by a tyrosine aminotransferase defect

45

Alkaptonuria

- Black urine
- Caused by a defect in homogentisate oxidase
- build-up of homogentisate turns black when oxidized by exposure to air

46

Tyrosinemia- I

- Potentially fatal disease that causes liver failure, kidney dysfunction, & neurological impairment
- Diagnosis is based on succinylacetone in the urine
- Maleylacetoacetate & fumarylacetoacetate accumulate and are eventually converted to succinylacetone
- Succinylacetone inhibits heme synthesis

47

What is the rate-limiting step of urea synthesis? What is the required allosteric activator of this enzyme?

- Mitochondrial carbamoyl phosphate synthatase I
- N-acetylglutamate

48

N- acetylglutamate is produced by what enzyme? What activates this enzyme?

N-acetylglutamate Synthetase produces N-acetylglutamate (required cofactor of Mitochondrial carbamoly phosphate synthatase I), which is activated by arginine

49

What are high levels of arginine indicative of?

High levels of peripheral ammonium

50

Urea Cycle Mnemonic

- Ordinarily= Ornithine
- Careless= Carbamoyl Phosphate
- Crappers= Citrulline
- Are= Aspartate
- Also= Arginosuccinate
- Frivolous= Fumarate
- About= Arginine
- Urination= Urea

51

Ornithine Transcarbamylase

- Ornithine + Carbamoyl Phosphate--> Citrulline
- Mitochondria-->Cytoplasm

52

Arginosuccinate Synthetase

- Citrulline + Aspartate--> Arginosuccinate
- Cytoplasm

53

Argininosuccinase

- Arginosuccinate--> Fumarate + Arginine
- Cytoplasm

54

Arginase

- Arginine--> Urea + Ornithine
- Cytoplasm

55

urea-TCA bicycle

- Fumarate links the urea cycle to the TCA cycle
- Oxaloacetate in the TCA cycle, which is converted to Aspartate completes the bicycle

56

Where do the two amino groups in urea come from?

1) carbamoyl phosphate
2) aspartate

57

What is the only organ that can perform the entire urea cycle?

Liver

58

Hyperammonemia

Caused by defects in the urea cycle

- Early cycle defects are the worst (Carbamoyl Phosphate Synthetase I & Ornithine Transcarbamoylase)

59

In addition to urea cycle defects, what else can cause hyperammonemia?

- Urea cycle is carried about by the liver
- Liver disease (alcoholic cirrhosis) causes hyperammonemia
- Ammonia is a potent neurotoxin & can cause lethargy (AMS) & convulsions
- Why? causes swelling of astrocytes/ brain

60

Creatine Kinase

Phosphorylates creatine to creatine phosphate

61

What is creatine phosphate used for?

- Energy reserve
- Creating phosphate is able to donate high phosphate to ADP, making ATP

62

A percentage of creatine phosphate spontaneously converts to what? Why is this important?

- Creatinine
- Indication of kidney function

63

The amount of creatinine excreted per day is proportional to _____?

Muscle mass

64

What amino acids are the thyroid hormones derived from?

Tyrosine

65

Thyroid Peroxidase

Iodinates thyroid hormones (T3 & T4)

66

What amino acid is used to synthesize melanin?

Tyrosine

67

What enzyme is needed to synthesize melanin from tyrosine?

- Tyrosinase
- Tyrosine-->DOPA-->Dopaquinione

68

Oculocutaneous Albinism Type I

- Albinism
- Caused by a defect in the TYR gene, which leads to a tyrosinase defect
- Tyrosinase is the enzyme that converts Tyrosine-->DOPA-->Dopaquinone, which is further metabolized to melanin

69

Melatonin & Serotonin are derived from what amino acid?

Tryptophan

70

Which amino acid is converted to niacin? What enzyme catalyzes the first step of the reaction?

- Tryptophan
- IDO

71

Why is IDO important?

- IDO is overexpressed by tumors, which decreases their tryptophan concentration
- This depletion of tryptophan blocks proliferation of T-cells that would normally destroy the tumor
- Thus, IDO has become an anti-cancer drug target

72

Pellagra

- 4 D's: Dermatitis, Diarrhea, Dementia, Death
- Caused by a Niacin deficiency OR lack of tryptophan

73

What amino acid is GABA derived from? What cofactor is required for this reaction?

- Glutamate
- PLP (Vitamin B6)

74

Histamine is derived from which amino acid?

Histidine

75

Glutathione

Intracellular reducing agent

76

What type of bond makes glutathione stable?

Gamma Glutmyl Linkage

77

Rate determining enzyme of Glycolysis

- Phosphofructokinase- 1

78

Rate determining enzyme of Gluconeogenesis

- Fructose 1,6-bisphosphatase

79

Rate determining enzyme of TCA Cycle

- Isocitrate Dehydrogenase

80

Rate determining enzyme of Glycogenesis

- Glycogen Synthase

81

Rate determining enzyme of PPP

- Glucose 6-phosphate Dehydrogenase

82

Rate determining enzyme of de novo pyrimidine synthesis

- Carbamoyl Phosphate Synthetase II

83

Rate determining enzyme of de novo purine synthesis

- PRPP amidotransferase

84

Rate determining enzyme of the Urea Cycle

- Carbamoyl Phosphate Synthetase I

85

Rate determining enzyme of Fatty Acid Synthesis

- Acetyl-CoA Carboxylase

86

Rate determining enzyme of Fatty Acid Oxidation

- Carnitine Acyltransferase I

87

Rate determining enzyme of Ketogenesis

- HMG-CoA Synthase

88

Rate determining enzyme of Cholesterol Synthesis

- HMG-CoA Reductase

89

Rate determining enzyme of Glycogenolysis

- Glycogen Phosphorylase

90

Energy Source: Fatty Acid

- Beta-oxidation requires O2; therefore, cannot use for anaerobic activity
- Cannot cross BBB
- Acetyl-CoA cannot be converted to glucose

91

Energy Source: Glucose

- Can be used for anaerobic activity (Lactate will be produced)
- Can get to the brain

92

Energy Source: Amino Acids

- Cannot be stored
- Some can be converted to glucose for energy

93

RBC: fuel preference & special considerations

- Glucose
- produces lactate

94

Skeletal Muscle: fuel preference & special considerations

- Fat
- Can also use glucose & ketones
- Can store glycogen
- Can break down into amino acids for energy

95

Heart: fuel preference & special considerations

- Fat
- Cannot function anaerobically
- Stores little energy

96

Brain: fuel preference & special considerations

- Glucose
- Can use ketones in starvation

97

Adipose: fuel preference & special considerations

- N/A
- Converts glucose to TAGs for storage
- Breaks down TAGs in times of need

98

Liver: fuel preference & special considerations

- ALL
- Stores glycogen
- Well-fed, can export fats in lipoproteins
- Fasting, can turn amino acids & FA into glucose & ketones

99

Well-Fed

- Insulin secretion
- Nutrients must be removed from circulation & put into storage
- Glucose is stored directly in liver & muscles
- Excess glucose is converted to VLDL for storage in adipose tissue
- Amino acids are used for protein synthesis

100

Early Fast

- Blood glucose concentration falls & alpha cells of the pancreas secrete glucagon
- Objective is to mobilize nutrients stored in the well fed state
- Glucose is released from glycogen stores
- Fatty acids and glycerol are released from adipose tissue
- Ketone bodies are produced from fatty acids by the liver
- Amino acids from protein breakdown are released from muscles
- Urea cycle enzymes are induced to cope with rise in ammonia

101

Late Fast

- Corticosteroids cause the body to develop an adaptive metabolism
- Basal metabolic rate drops & tissues consume less energy
- CNS begins to increase use of ketone bodies
- Liver glycogen is depleted
- Kidney begins to aid liver in synthesis of ketones
- Breakdown of muscle protein slows down due to the reduced demand for glucose

102

Refeeding Syndrome: what are the major concerns when refeeding a starved patient?

1) Lack of digestive enzymes--patient will not be able to breakdown dietary carbohydrates & fats, which will lead to diarrhea
2) Intracellular phosphate stores are depleted--& the reintroduction of carbohydrates induces glycolysis, which consumes large amounts of phosphate (ATP)
- leads to life threatening hypophosphatemia

103

What are the three effects of ineffective glucose removal?

1) No glucose storage-->tissue starvation
2) Damage to blood vessels
3) Osmotic pressure increases--> tissue dehydration & HTN

104

What are the three chronic morbidities of DM?

1) Retinopathy
2) Nephropathy
3) Neuropathy

105

Four processes that are regulated by insulin

1) Increase GLUT4 transporters (uptake of glucose)
2) Increase in glucose utilization (glycolysis, glycogen synthesis, FA synthesis, & protein synthesis)
3) Downregulate gluconeogenesis
4) Downregulate FA mobilization

106

What happens when tissue don't respond to insulin?

1) Fasting hypoglycemia
2) Hyperlipidemia
3) Uninhibited gluconeogenesis

107

What are the three causes of tissue damage in DM?

1) Spontaneous glycation
2) Formation of sorbitol (uses NADPH)
3) Loss of antioxidant protection (from NADPH usage)

108

What enzymes are involved in heme synthesis?

ALA synthase- Succinyl CoA + Glycine--> ALA
PBG Synthase- ALA + ALA --> PBG
UPG Synthase III- PBG x4--> UPG
Ferrochelatase- Insertion of Fe

*begins & ends in the mitochondria

109

Porphyrias

Diseases of heme synthesis

110

What is the committed step of heme synthesis?

ALA Synthase

- Inhibited by heme in a classical feedback loop

111

Why do drugs & alcohol induce heme synthesis?

- Alcohol induces the microsomal ethanol oxidizing system (MEOS), a cytochrome p450 containing enzyme
- Synthesis of cytochrome p450 enzymes consumes heme
- Consuming heme relieves inhibition of ALA synthase

112

Acute Intermittent Prophyria

- Caused by a deficiency of PBG Deaminase
- Urine turns a dark red color
- Neurological symptoms

113

Porphyria Cutanea Tarda

- Caused by a deficiency of uroporphyrinogen decarboxylase (UROD)
- Porphyrins absorb UV & visible light, which can lead to generation of ROS & blistering of the skin
- Urine will fluoresce pink under UV light

114

Which enzymes of heme synthesis are inhibited by lead?

- PBG Synthase
- Ferrochelatase

Causes an accumulation of ALA

115

What is the breakdown product of heme? How is it excreted?

- Bilibrubin, which is produced by the spleen

1) Binds to albumin to be transported by the circulation to the liver
2) Bilirubin-UDP glucuronyltransferase (UGT) adds glucuronic acid to bilirubin to make it more water soluble (conjugated)
3) Broken down by gut bacteria into urobilins
4) Urobilins are excreted in feces or reabsorbed and excreted in urine

116

Prehepatic (Hemolytic) Jaundice

- Hemolysis of RBCs overwhelm's the liver's capacity to conjugate bilirubin
- Normal amounts in feces & urine
- Unconjugated bilirubin found in other tissues

117

Hepatocellular Jaundice

- Liver is unable to conjugate bilirubin
- Feces & urine turn pale
- Unconjugated bilirubin is found in other tissues

118

Cholestatic Jaundice

- Blockage of the bile duct
- Liver is able to conjugate bilirubin, but unable to excrete it into feces
- Conjugated bilirubin is thus excreted via kidneys
- Urine is dark orange color
- Feces are pale

119

What is the committed step of de novo nucleotide synthesis?

- Conversion of Ribose 5-phosphate to PRPP by PRPP synthase
- PRPP is required for BOTH purines & pyrimidines

120

What is the committed step of de novo purine synthesis?

PRPP--> PRA, via the enzyme "amidophophoribosyltransferase"

121

What is the first purine to be produced?

IMP

- Amino acids donate carbon & nitrogen
- CO2 provides carbon & oxygen
- N10-THF is a 1-carbon donor
- ATP is required for several steps

122

What is IMP the precursor for?

AMP & GMP

123

What enzyme is necessary to make AMP from IMP?

Adenylosuccinate synthase

- Note that it is inhibited by its product, AMP

124

What enzyme is necessary for GMP synthesis?

IMP dehydrogenase

- Note that it is inhibited by its product, GMP
- GMP is made via Xanthosine 5' monophosphate

125

How do all nucleotides become phosphorylated?

Sequential action of nucleoside 5'-monophosphate kinases & nucleoside 5' diphosphate kinases

126

What is the end product of purine metabolism?

Uric acid

- AMP--> Hypoxanthine--> Xanthine
- GMP--> Guanine--> Xanthine

- Xanthine--> Uric acid, via Xanthine Oxidase

127

What diseases can result from purine breakdown?

1) Hyperuricemia
2) Gout
3) Kidney Stones

128

How does allopurinol treat gout?

Inhibits xanthine oxidase

- Xanthine--> Uric Acid via Xanthin Oxidase

129

What enzymes are involved in the production of pyrimidines?

1) CAD
-Carbamoyl phosphate synthetase II (regulated step)
- Aspartate transcarbamoylase
- Dihydrooratase
2) UMP Synthase

130

Orotic Aciduria

- Caused by a defect in UMP Synthase

131

How is CTP formed?

CTP Synthase

- Activated by UTP
- Inhibited by CTP

132

How are deoxyribonucleotides synthesized?

Ribonucleotide Reductase

- In this process Thioredoxin becomes oxidized
- For catalysis to continue, Thioredoxin must be reduced by thioredoxin reductase
- Uses NADPH

133

SCID

- Adenosine Deaminase Deficiency
- dATP build-up inhibits ribonucleotide reductase
- Immune cell proliferation is inhibited & patient cannot amount appropriate immune response

134

How is dTMP formed?

dUMP--> dTMP, via the enzyme Thymidylate Synthase

- requires N5, N10 THF
- Need B12

135

5- Fluorouracil

- Undergoes same pathways as uracil
- Eventually will become FdUMP instead of dUMP
- FdUMP is a irreversible inhibitor of thymidylate synthase i.e. it prevents the formation of dTMP

136

What enzymes are involved in the salvage of purines?

- HGPRTase
- APRTase

137

What enzyme is involved in the salvage of pryimadines?

Pyrimidine phosphoribozyltransferase

138

Which pyrimidine is not salvaged?

Cytosine

139

Hyponatermia

Overhydration

140

Hypernatremia

Dehydration

141

Hypokalemia

Potassium loss

142

Hyperkalemia

Renal insufficiency

143

Hypocalcemia

Hormonal problem

144

Hypercalcemia

Hormonal problem or bone disease

145

High Phosphate

Bone disease or failed clearance

146

Low Phosphate

Beware of glucose metabolism (glucose is phosphorylated immediately upon entering the cell)

147

Albumin

- Carrier protein
- Maintenance of osmotic pressure
- Low, leads to edema

148

Globulins

Immune system function

149

C-Reactive Protein

Secreted by the liver in response to acute injury

150

What enzymes are released from cardiomyocytes in response to MI?

- Myoglobin, very quickly but not heart specific
- Creatine Kinase, quickly
- AST
- Troponins, quickly & most sensitive marker!!!!!
- LDH, days after

151

How would you distinguish between liver & bone disease in a patient with elevated alkaline phosphatase?

- Check bilirubin levels (Liver)

152

What is a reactive oxygen species? What radicals are found in human cells?

Reactive intermediates of oxygen metabolism

- Singlet Oxygen- O
- Superoxide anion- O2- (1 electron transfer)
- Hydrogen Peroxide- H2O2 ( 2 electron transfer)
- Hydroxyl Radical- HO ( 3 electron transfer & most reactive!)

153

Hemochromatosis

- Iron overload
- Accumulation of iron causes cirrhosis of the liver, damage to the pancreas (diabetes), & damage to the heart

154

What enzymes are protective against ROS?

- Superoxide dismutase (superoxide anion)
- Catalase & Glutathione Peroxidase (hydrogen peroxide)

155

Which vitamins act as antioxidants?

- Vitamin C
- Vitamin E ( most protective of membranes)
- Vitamin A (singlet oxygen & membranes)

156

How do ROS damage membranes?

1) HO takes an electron from PUFA & forms a lipid radical
2) Lipid radicals react with O2 to form lipid peroxide
3) Lipid peroxides react with PUFAs & continue the cycle of damage OR reactive with self to form malondialdehyde

157

Malondialdehyde

Mutagenic reaction with purines