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MC Biochem 2 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What are the other names for the Pentose Phosphate Pathway

A

Hexose Monophosphate Pathway
Phosphoglycerate Pathway
Pentose Monophosphate Shunt

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2
Q

Where does the Pentose Phosphate Pathway Take place?

A

Cytoplasm

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3
Q

Functions of the Phosphate Pentose Pathway?

A

1) Synthesis NADPH
2) catabolism/synthesis of C5 (pentose) carbohydrates for nucleotide biosynthesis
3) catabolism/synthesis of C4 (tetrose) carbohydrates
4) Linking to Glycolysis

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4
Q

Glucose 6-Phosphate Dehydrogenase

A

Pentose Phosphate Pathway-Oxidation Phase

Glucose 6-Phosphate-> 6-Phosphoglucono-8-lactone

  • NADP+ reduced to NADPH
  • irreverisible

Regulated:
-inhibited by low concentration of NADP+

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5
Q

Lactonase

A

Pentose Phosphate Pathway-Oxidation Phase

6-Phosphoglucono-8-lactone-> 6-Phosphoglucate
-hydrolysis->ring opening-ketone

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6
Q

6-Phosphosphoglucate dehydrogenase

A

Pentose Phosphate Pathway-Oxidation Phase

6-Phosphoglucate-> Ribulose 5-Phosphate + CO2

  • NADP+ reduced to NADPH
  • Cleaves CO- to form 5C
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7
Q

Phosphopentose Isomerase

A

Pentose Phosphate Pathway
Calvin Cycle

Ribulose 5-Phosphate Ribose 5-Phosphate

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8
Q

Phosphopentose Epimerase

A

Pentose Phosphate Pathway
Calvin Cycle

Ribulose 5-Phosphate Xylulose 5-Phosphate

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9
Q

Transketolase

-def

A 
Transfers COCH2OH (2C) of Ketose to Aldose producing a Ketose
-coenzyme TPP
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10
Q

Transaldolase

-def

A

Transfers DHAP (3C) to aldose making a ketose

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11
Q

Similarities in Transketolase and Transaldolase mechanism

A

Both enzymes produce carbanions that are stabilized by resonance during catalysis

  • Transaldolase-Lysine
  • Transketolase- TPP
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12
Q

Why Does the pentose phosphate pathway adjust to cell needs?

A

For production of NADPH or different variations of carbohydrates

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13
Q

Pentose Phosphate Pathway: Situation 1

High Demand for Ribose 5-Phosphate (DNA synthesis) and low demands for NADPH

A

Do not use Oxidative Phase

Nonoxidative Phase through glycolysis to produce Fructose 6-P -> Ribose 5-Phosphate
G3P-> Ribose 5-Phosphate

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14
Q

Pentose Phosphate Pathway: Situation 2

Balanced Need for Ribose 5-Phosphate and NADPH

A

Oxidative Phase only
Glucose 6-P to Ribulose 5-P-> Ribose 5-P
NADPH and CO2 produced

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15
Q

Pentose Phosphate Pathway: Situation 3

More NADPH than Ribose 5-Phosphate required

A

Oxidative and Nonoxidative phase + Gluconeogenesis to reform Glucose 6-Phosphate

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16
Q

Pentose Phosphate Pathway: Situation 4

Both NADPH and ATP required

A

Oxidative Phase to produce Ribose 5-Phosphate which is converts to F6-P and G3P to enter glycolysis to Pyruvate then to Krebs to Produce ATP

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17
Q

Glutathione

  • Protects?
  • Structure?
  • Catalyzed?
A

Protects us from Reactive Oxygen Species (ROS)

Structure: Tripeptide of ECG w/free Sulfhydryl
** Peptide bond attached to Glutamate R Group

GSH->GSSG; GSH-reduced, GSSG-oxidized
catalyzed by glutathione reductase
-FAD prosthetic group
-NADPH to NADP+

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18
Q

Source of Glucose

A
  • Diet
  • Glycogen Degradation
  • Gluconeogenesis
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19
Q

What is the normal concentration of Glucose in Humans?

A

80-120 mg/100mL

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20
Q

Where is a ready supply of glucose found?

A

Liver Glycogen stored in glycogen granules provides glucose to blood for our cells

Skeletal Muscle remains in muscle cell and enters glycolysis to provide energy for muscle contraction

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21
Q

Where is glycogen stored in our cells?

A

Cytoplasm in liver and muscle cells

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22
Q

Debranching enzyme of Glycogen Catabolism

A

Bifunctional Enzyme

1) Oligo-a(1-4)-a(1-6) glucan transferase
- transfers 3-4 residues at branch to other chain
- Phosphorylyisis

2) Amylo-a(1-6) glucosidase
- releases free glucose from the final glucose residue at branch
- Hydrolysis

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23
Q

Liver Specific Glycogen Catabolism

A

Liver contains the enzyme Glucose 6-Phosphatase to maintain blood glucose levels

1) Glucose 1-P (cytosol)-> Glucose 6-P (cytosol)
- Phosphoglucomutase
2) Glucose 6-P -> G 6-P (lumen of ER)
- Glucose 6-P translocase
3) Glucose 6-P -> Glucose
- Glucose 6-Phosphatase (lumen)

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24
Q

Glycogen Phosphorylase

-function

A

Catalyzes the sequential removal of G 1-P from the nonreducing end of Glycogen until it reaches 4 residues from branch and requires debranching enzymes
-PHOSPHORYLYSIS-Phosphate attacks

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25
Q

Glycogen Phosphorylase

-structure

A

Homodimer

1) N-terminal Domain
- Glycogen Binding Site
- catalytic site between the two domains
2) C-terminal Domain

Prosthetic Group-PLP-pyridoxal Phosphate

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26
Q

PLP

A

Pyridoxal Phosphate
Prosthetic group for Glycogen Phosphorylase
-attached to Lys by Schiff Base

Fxn- Group transfer to or from amino acids
-proton acceptor/donor

Vit-Pyridoxine (Vit B6)

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27
Q

Regulation of Glycogen Phosphorylase

-forms etc

A

Allosteric: Tissue Specific

  • Liver
  • Muscle

Reversible Phosphorylation

  • a=phosphorylated
  • b=dephophorylated

Ca2+=muscles

Alternated between two forms:
Phosphorylase A:
-Active form
-may exist in either T or R state

Phosphorylase B:

  • Inactive form
  • may exist in either T or R state
  • phosphorylation of Ser to convert B->A

Tight (T) State

  • favors B
  • inactive form

Relaxed (R) state

  • favors A
  • active form

Liver and Muscle cells differ in response to inhibitors
because they are Isozymes -90% identical

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28
Q

Allosteric Regulation of Muscle Glycogen Phosphorylase

A

Release Glucose 6-Phosphate which enters glycolysis to produce ATP to power muscle contraction

  • resting muscles contain phophorylase B
  • Exercise stimulates conversation from B->A by phosphorylating Ser

Muscle Phosphorylase A:
Hormonal signals stimulates phosphorylation b->A by phosphorylase Kinase
-independent of [ATP][AMP][G6P]

Muscle Phosphorylase B:
Stimulated by: Low energy charge
-High concentration of AMP increases activity, AMP binds to nucleotide binding site release ATP for muscle contraction
-indirectly high concentration of Ca2+ increases activity

Inhibited by: high energy charge:

  • High concentration of ATP decreases activity, ATP competes with AMP for nucleotide binding site
  • increased concentration of G6P decreases activity
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29
Q

Allosteric regulation of Liver Glycogen Phosphorylase

A

Prefers Phosphorylase A form
Liver produces free glucose to the blood to maintain blood glucose levels

High glucose concentration in blood decreases activity
-no need to breakdown to glycogen to produce free glucose

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30
Q

Hormonal Regulation of Glycogen Phosphorylase

A

Glucagon (to a lesser extent epinephrine)
-in the liver stimulates glycogen catabolism

Epinephrine
-in the muscle stimulates glycogen catabolism

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31
Q

Epinephrine

A

Catecholamine derivative of tyrosine

Synthesized in adrenal medulla
-located in adrenal glands on top of kidneys

Stimulates glycogen catabolism in muscles ( and to a lesser extent in the liver)

  • In Muscle, epinephrine binds to B-adrenergic receptor
  • In Liver, epinephrine binds to B-Adrenergic receptor and A-adrenergic receptor
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32
Q

Glucagon

A

Peptide Hormone

Secreted in alpha cells of pancreas

In liver, binds to glucagon receptor activating glycogen catabolism

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33
Q

Glycogen Catabolism: Signal Transduction Pathway

-Fasting or exercise

A

1) Epinephrine or Glucagon binds to 7TM Receptor which activates the G protein
2) G protein stimulates Adenylate Cyclase which synthesize cAMP
3) cAMP activates Protein Kinase A by binding to the regulatory subunit and the catalytic subunit is freed from R subunit which phosphorylates Phosphorylase Kinase turning it on and Phosphorylates Glycogen Synthase converting it to A->B form Turning OFF
4) Phosphorylase Kinase phosphorylates the ser residue on Glycogen phosphorylase converting B->A

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34
Q

7TM receptor

A

seven-transmembrane helix receptor
-7 membrane spanning alpha helixes

50% of therapeutic drugs targets these classes of cells
-ex: B-adrenergic

Binding of Hormone stimulates HUNDREDS Of G proteins

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35
Q

G Protein

-structure

A

Heterotrimeric protein bind Guanyl nucleotides

Heterotrimer:

1) alpha subunit=nucleotide binding subunit
- inactive=GDP
- active=GTP
2) B/Y subunit- exchanges GDP for GTP on alpha subunit

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36
Q

Adenylate Cyclase

A

Amplifies hormonal signal by synthesizing cAMP by using a LOT of ATP as substrate

37
Q

Protein Kinase A

-structure

A

Heterotetramer-R2C2

1) Catalytic Subunit
- Phosphorylates target proteins when freed from R subunit
2) Regulatory Subunit
- each subunit contains 2 binding sites for cAMP

38
Q

Phosphorylase Kinase

  • structure
  • fuction
A

Function:
-Phosphorylates Ser of glycogen Phosphorylase converting B->A
Duel Control
-ser Phosphorylation of Glycogen Phosphorylase
-Ca2+

Structure:
ABDYx4
1) Y subunit=catalytic subunit
2) ABD=regulatory subunit
-D subunit-contains 4 Ca2+ binding sites, serving as Calcium sensor. Activates Many Pathways
-B subunit-target for phosphorylation by PKA

39
Q

A-(1-4) glucosidase

A

Lysosomal degradation of glycogen by degrading glycogen in vacuoles in cytoplasm

40
Q

Hexokinase

A

Glycogen Synthesis

A-D-Glucose-> Glucose 6-P
-requires ATP-ADP

41
Q

Phosphoglucomutase

A

Glycogen Synthesis and degradation

converts glucose 6-P Glucose 1-P

42
Q

UDP-Glucose Pyrophosphorylase

A

Glycogen Synthesis

Glucose 1-P + UTP-> UDP-glucose +PPi
-PPi is hydrolyzed

43
Q

Inorganic Pyrophosphatase

A

Glycogen Synthesis

Hydrolysis PPi-> 2Pi
-exergonic and provides energy for glycogen synthesis

44
Q

Glycogen Synthase

A

Glycogen Synthesis

REGULATED

UDP-Glucose + Existing Glycogen with at least 4 residues converted to Glycogen (N+1) + UDP
-requires glycogenin

45
Q

Nucleoside Diphosphate Kinase

A

Glycogen Synthesis

Regenerate UTP
UDP +ATP-> UTP + ADP

46
Q

Glycogenin

A

Composed of Tyrosine residue that contains OH that serves as primer for synthesis of glycogen

47
Q

Branching enzyme

A

Glycogen Synthesis

synthesizes a-1,6 branches every 8-10 residues

48
Q

Protein Phosphatase I (PP1)

A

Dephophorylates
-Thr of Glycogen Synthase Converting it from B->A Turing it ON and stimulating Glycogen SYNTHESIS

-Ser of Glycogen Phosphorylase converting it from A->B TURING IT OFF and inhibiting Glycogen CATABOLISM

49
Q

Fatty Acid Function

A

1) Fuel stored as triacylglycerol
2) Synthesis of Phospholipids and glycolipids (membranes)
3) Synthesis of hormones
4) Protein Modification

50
Q

Fatty Acid Structure

A

Long Hydrocarbon chains with terminal Carboxylate group

-saturated/unsatured

51
Q

Triacylglycerol Function

A

Energy Dense Energy Storage

-reduced and anhydrous

52
Q

Triacylglycerol Structure

A

Uncharged esters of Fatty acids with glycerol group

53
Q

Where is triacylglycerol stored?

A

cytoplasm of adipose cells for mobilization to bloodstream

muscle cells for generation of ATP

54
Q

Dietary Triacylglycerols are digested by:

A

1) In the Intestinal Lumen Triacylglycerol are incorporated into micelles with bile salts.
2) Pancreases lipases which remove 2 FA from glycerol to form monoacylglycerol
3) the monoacylglycerol and FA’s are absorbed into the mucosal cells

55
Q

Triacylglycerol Lipase

  • function
  • Glycerol fat (Mechanism)
  • Fatty Acid Fate (NO MECHANISM
A

Released fatty acids from triacylglycerol stored in adipose tissue due to hormonal control (Glucagon/epinephrine) stimulating Signal Transduction pathway

Glycerol enters the blood and carried to the liver enters glycolysis/gluconeogensis

1) Glycerol-> L-Glycerol 3-Phosphate by Glycerol Kinase at the expense of ATP
2) Glycerol 3-Phosphate-> DHAP + G3P by Glycerol 3-Phospahte dehydrogenase at expense of NAD+ to NADH

Fatty Acids enter the blood attached to albumin and are transported to tissue containing mt (Liver) to undergo beta oxidation (FATTY acid catabolism

56
Q

Fatty Acid Degradation: Signal Transduction pathway

A

1) Hormone binds to 7TM receptor which stimulates G protein
2) G protein binds to and activates Adenylate Cyclase which synthesizes cAMP
3) cAMP binds to and activates Protein Kinase A
4) PKA phorphorylates Triacylglycerol Lipase turning it ON releasing Fatty acids into the blood

57
Q

Preparation of Fatty Acids for B-Oxidation

  • Activation
  • Transportation
A

Activation: by attachment of CoA via Thioester bond
In the cytoplasm of the Outer mitochondrial membrane
1) FA + ATP-> Acyl Adenylate + ADP
-catalyzed by Acyl Adenylase
-hydrolysis of PPi drives the reaction
2) Acyl Adenylase + SH-COA-> Acyl CoA + AMP
-Acyl CoA Synthetase

Transportation: to matrix of mitochondria

1) Acyl CoA + Carnitine-> Acyl Carnitine + CoA
- via Carnitine Transacylase I located in inter membrane space of mt
- Acyl group transfers from CoA of S to OH of carnitine
2) Carnitine Translocase located in innermitochondrial membrane
- transfers Acyl Carnitine from intermembrane space to matrix of mt
3) Acyl Carnitine (matrix) + SH-CoA-> Acyl CoA + Carnitine
- via Carnitine Transacylase II located in matrix

58
Q

Acyl CoA Dehydrogenase

A

Fatty Acid Degradation

1) Oxidation Reaction
Acyl CoA -> trans Enoyl CoA
-forms Double bond between C2 and C3
-FAD reduced to FADH2 and is linked to ETC

Acyl CoA Dehydrogenase has 3 forms:
Long- (12-18C)
Medium (4-14C)
Short (4-6C)

59
Q

Enoyl CoA Hydratase

A

Fatty Acid Catabolism

2) Hydration
trans Enoyl CoA + H2O-> L-3-hydroxyacyl CoA
-stereospecific hydration

60
Q

L-3-hydroxyacyl CoA dehydrogenase

A

Fatty Acid Catabolism

3) 2nd oxidation
L-3-hydroxyacyl CoA-> 3-Ketoacyl CoA
-OH on C3 oxidized to Ketone

61
Q

B-Ketothiolase

A

Fatty Acid Catabolism
3-Ketoacyl CoA-> Acetyl CoA + Acyl CoA(-2C)
-CoA cleaves at 3C

62
Q

Beta Oxidation of Unsaturated Fatty Acids

-enzymes

A

Depend on location of Double Bond
-NOT a substrate for Acyl CoA Dehydrogenase
1) Odd number carbon double bond
-Isomerization
cis D3 Enoyl CoA Isomerization which transfers Double bond to even number carbon

2) Even number Double Bond
-Reductase and Isomerization
2,4-dienoyl CoA Reductase-uses NADH to reduce DB
cis D3 Enoyl CoA Isomerization

63
Q

Beta Oxidation of Unsaturated Fatty Acids

  • results in?
  • mechanism
A

Propionyl CoA=metabolic dead end so rearranged to enter Krebs cycle (Succinyl CoA)

1) Propionyl CoA (3C) -> D/L-metylmalonyl CoA
- Carboxylation via Pripionyl CoA Carboxylase
- coenzyme group-Biotin
2) D/L-methylmalonyl CoA (4C)-> Succinyl CoA
- Isomerization via methylmalonyl CoA mutase
- coenzyme-vit B12(calbalamin)

64
Q

Vitamin B12

  • Used In?
  • Structure
A 
Structure:
Corrin ring with central Cobalt atom:
Cobalt forms 6 coordinate bonds to:
-4 to N of pyrrole
-1 to 5' deoxyadenosyl unit
-1 to dimethylbenzimidazole units (usual) or cyan, methyl, or other ligands

Used In?

  • Intramolecular reaction
  • Methylation
    1) Synthesis of Methionine
    2) Reduction of ribonucleotides to deoxyribonucleotides
65
Q

What two enzymes in Mammals use Vit B12

A

Cobalamin

1) Methylmalonyl CoA Mutase
2) Methionine Synthase or homocysteine methyltransferase

66
Q

Propionyl CoA Carboxylase

A

Carboxylation: for Unsatured Fatty acids result in
Propionyl CoA-> L/D-3-methylmalonyl CoA
-requires Biotin and ATP

67
Q

Methylmalonyl CoA Mutase

A

Requires B12

Isomerization of:
L/D-3-methylmalonyl CoA-> Succinyl CoA
-exchanges H and O=C-CoA via Homolytic cleavage reaction forming CH2 radical

68
Q

Fatty Acid Oxidation in Peroxisomes

A

Peroxisomes contain isozymes of mitochondrial enzymes and can oxidize Long Fatty Acid chains to Octanoyl CoA
-electrons are transferred to O2 yielding H2O2 which a ROS and is detoxified by catalase

69
Q

What happens to the excess Acetyl CoA from Fatty Acid Oxidation?

A

Acetyl CoA enters Krebs cycle if fat and carbohydrate degradation are balanced

1) to enter Krebs cycle Acetyl CoA must combine with OAA
- OAA concentration is dependent on carbohydrate oxidation
- during fasting or in a diabetic person the OAA is bled off and is converted to Pyruvate to synthesize glucose in gluconeogenesis. During Gluconeogenesis the rate of Krebs cycle slows down

HUMANS LACK THE ABILITY TO SYNTHESIZE GLUCOSE FROM ACETYL COA

70
Q

Ketone Bodies

A

Synthesized in the liver during fasting or in diabetic persons from the Acetyl CoA from B-oxidation
-Acetoacetate, D-3-hydroxybutyrate, and Acetone

Ketone bodies are normal energy source for certain tissues during a fast or diabetes
-Acetoacetate for heart muscle and Renal cortex and travel to these cells and regenerate 2 Acetyl CoA-> Krebs

High Levels of Ketone Bodies is life threatening because they are moderately strong acids leading to acidosis which impairs tissue function

71
Q

Acetoacetate is reconverted

A

In renal Cortex and Heat muscle cells during a fast or diabetes are used as energy source by going though Krebs cycle

1) Acetoacetate-> AcetoAcetyl CoA
- CoA Transferase; liver lacks this CoA transferase enzyme
- Succinyl CoA to Succinate
2) AcetoAcetyl CoA + CoA-> 2 Acetyl CoA
- Thiolase

72
Q

Where does synthesis of Fatty Acids Occur?

A

Cytoplasm

73
Q

Where does degradation of Fattty Acids Occur

A

Matrix of Mitochondria

74
Q

Synthesis vs Degradation of Fatty Acids:

-Intermediates are linked to?

A

Synthesis- ACP=acyl Carrier protein

Degradation=CoA=Coenzyme A

75
Q

Acetyl CoA Carboxylase

A

Carboxylation with HCO- of Acetyl CoA to Malonyl CoA

  • commited step of Fatty Acid Synthesis REGULATED
  • requires ATP
  • Biotin=prosthetic group
76
Q

Biotin

-What enzymes use?

A

Prosthetic group
-attached to E amino group of Lysine

Pyruvate Carboxylase, Acetyl CoA Carboxylase,
Propionyl CoA Carboxylase

77
Q

Acetyl CoA transacylase

A

exchange ACP for CoA to from Acetyl ACP

78
Q

Malonyl CoA transacylase

A

exchange ACP for CoA to form Malonyl ACP

79
Q

ACP

A

Acyl Carrier Protein

  • 77 amino acid
  • acyl group attaches to Ser R group
80
Q

Acyl-Malonlyl ACP condensing enzyme

A

First step of Fatty acid Synthesis Elongation phase:
Condensation/Decarboxylation

Acetyl ACP + Malonyl ACP->Acetoacetyl ACP

  • loss of ACP and CO2
  • provides energy by decreasing free energy
81
Q

B-Ketoacyl ACP reductase

A

Second Step of Fatty Acid Synthesis Elongation Phase

Reduction
Acetoacetyl ACP-> D-3-hydroxybutyryl ACP
-NADPH oxidized to NADP+

82
Q

3-hydroxyacyl ACP dehydratase

A

3Rd step of Fatty Acid Synthesis Elongation Phase

Dehydration
D-3-hydroxylbutyryl ACP-> Crotonyl ACP

83
Q

Enoyl ACP reductase

A

Final Step of Fatty Acid Synthesis Elongation Phase

Reduction
Crotonyl ACP-> Butyryl ACP
-NADPH oxidized to NADP+

84
Q

Fatty Acid Synthase

A

All enzymes in Fatty Acid synthesis are found

Dimer- 3 domains with 7 enzymes
Acetyl CoA Carboxylase

Domain 1-substrate transfer and condensation
AT-Acetyl CoA transacylase
MT- Malonlyl CoA transacylase
CE- Acyl-malonyl CoA condensing enzyme

Domain 2- reduction/dehydration
KR-B-Ketoacyl Reductase
DH-D-3-hydroxylacyl reductase
ER-Enoyl ACP reductase

Domain 3- release of 16 C fatty acid-Palmitate
TE-ThioEsterase

85
Q

How are acetyl groups transported to the cytoplasm for Fatty Acid Synthesis?
-Mechanism

A

Acetyl CoA can’t cross Inner Mt membrane

When Acetyl CoA and OAA concentration are High, citrate is synthesized and travels to cytoplasm of Cell

1) Citrate-> OAA + Acetyl CoA
- ATP Citrate Lipase in cytoplasm
- acetyl CoA enter FAtty acid synthesis
2) OAA reduced to Malate
- Malate dehydrogenase
- NADH to NAD+ which is used in glycolysis and fermentation
3) Malate oxidized to Pyruvate
- NADP+ linked Malate enzyme
- NADP+ reduced to NADPH

86
Q

The NADPH required for Fatty acid synthesis if from:

A

Pentose Phosphate Pathway
-Phosphoglucate Dehydrogenase

Fatty Acid Synthesis
-Malate-> pyruvate by NADP+ linked Malate enzyme

87
Q

Control of Fatty Acid Synthesis

A

Acetyl CoA Carboxylase

Maximum Acitivity

  • High concentration of carbs represented by Citrate
  • High Energy Charge

TURNED ON:

  • Dephosphorylated by Protein Phosphatase 2A
  • Allosterically by Citrate which faciliates polymerization of dimers of Acetyl CoA carboxylase

TURNED OFF:

  • Phosphorylation by AMP dependent Protein Kinase which is stimulated by AMP and inhibited by ATP
  • Allosterically by Palmitoyl CoA
88
Q

Hormonal Control of Fatty Acid Synthesis

A

Acetyl CoA Carboxylase

1) Insulin activates Protein Phosphatase 2A which dephosphorylates Turing enzyme ON

Glucagon/epinephrine maintains carboxylase in phosphorylated state (OFF)

MC Biochem 2 (31 decks)

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