Exam 2 Flashcards
What are the other names for the Pentose Phosphate Pathway
Hexose Monophosphate Pathway
Phosphoglycerate Pathway
Pentose Monophosphate Shunt
Where does the Pentose Phosphate Pathway Take place?
Cytoplasm
Functions of the Phosphate Pentose Pathway?
1) Synthesis NADPH
2) catabolism/synthesis of C5 (pentose) carbohydrates for nucleotide biosynthesis
3) catabolism/synthesis of C4 (tetrose) carbohydrates
4) Linking to Glycolysis
Glucose 6-Phosphate Dehydrogenase
Pentose Phosphate Pathway-Oxidation Phase
Glucose 6-Phosphate-> 6-Phosphoglucono-8-lactone
- NADP+ reduced to NADPH
- irreverisible
Regulated:
-inhibited by low concentration of NADP+
Lactonase
Pentose Phosphate Pathway-Oxidation Phase
6-Phosphoglucono-8-lactone-> 6-Phosphoglucate
-hydrolysis->ring opening-ketone
6-Phosphosphoglucate dehydrogenase
Pentose Phosphate Pathway-Oxidation Phase
6-Phosphoglucate-> Ribulose 5-Phosphate + CO2
- NADP+ reduced to NADPH
- Cleaves CO- to form 5C
Phosphopentose Isomerase
Pentose Phosphate Pathway
Calvin Cycle
Ribulose 5-Phosphate Ribose 5-Phosphate
Phosphopentose Epimerase
Pentose Phosphate Pathway
Calvin Cycle
Ribulose 5-Phosphate Xylulose 5-Phosphate
Transketolase
-def
Transfers COCH2OH (2C) of Ketose to Aldose producing a Ketose -coenzyme TPP
Transaldolase
-def
Transfers DHAP (3C) to aldose making a ketose
Similarities in Transketolase and Transaldolase mechanism
Both enzymes produce carbanions that are stabilized by resonance during catalysis
- Transaldolase-Lysine
- Transketolase- TPP
Why Does the pentose phosphate pathway adjust to cell needs?
For production of NADPH or different variations of carbohydrates
Pentose Phosphate Pathway: Situation 1
High Demand for Ribose 5-Phosphate (DNA synthesis) and low demands for NADPH
Do not use Oxidative Phase
Nonoxidative Phase through glycolysis to produce Fructose 6-P -> Ribose 5-Phosphate
G3P-> Ribose 5-Phosphate
Pentose Phosphate Pathway: Situation 2
Balanced Need for Ribose 5-Phosphate and NADPH
Oxidative Phase only
Glucose 6-P to Ribulose 5-P-> Ribose 5-P
NADPH and CO2 produced
Pentose Phosphate Pathway: Situation 3
More NADPH than Ribose 5-Phosphate required
Oxidative and Nonoxidative phase + Gluconeogenesis to reform Glucose 6-Phosphate
Pentose Phosphate Pathway: Situation 4
Both NADPH and ATP required
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
Glutathione
- Protects?
- Structure?
- Catalyzed?
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+
Source of Glucose
- Diet
- Glycogen Degradation
- Gluconeogenesis
What is the normal concentration of Glucose in Humans?
80-120 mg/100mL
Where is a ready supply of glucose found?
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
Where is glycogen stored in our cells?
Cytoplasm in liver and muscle cells
Debranching enzyme of Glycogen Catabolism
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
Liver Specific Glycogen Catabolism
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)
Glycogen Phosphorylase
-function
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
Glycogen Phosphorylase
-structure
Homodimer
1) N-terminal Domain
- Glycogen Binding Site
- catalytic site between the two domains
2) C-terminal Domain
Prosthetic Group-PLP-pyridoxal Phosphate
PLP
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)
Regulation of Glycogen Phosphorylase
-forms etc
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
Allosteric Regulation of Muscle Glycogen Phosphorylase
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
Allosteric regulation of Liver Glycogen Phosphorylase
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
Hormonal Regulation of Glycogen Phosphorylase
Glucagon (to a lesser extent epinephrine)
-in the liver stimulates glycogen catabolism
Epinephrine
-in the muscle stimulates glycogen catabolism
Epinephrine
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
Glucagon
Peptide Hormone
Secreted in alpha cells of pancreas
In liver, binds to glucagon receptor activating glycogen catabolism
Glycogen Catabolism: Signal Transduction Pathway
-Fasting or exercise
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
7TM receptor
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
G Protein
-structure
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
Adenylate Cyclase
Amplifies hormonal signal by synthesizing cAMP by using a LOT of ATP as substrate
Protein Kinase A
-structure
Heterotetramer-R2C2
1) Catalytic Subunit
- Phosphorylates target proteins when freed from R subunit
2) Regulatory Subunit
- each subunit contains 2 binding sites for cAMP
Phosphorylase Kinase
- structure
- fuction
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
A-(1-4) glucosidase
Lysosomal degradation of glycogen by degrading glycogen in vacuoles in cytoplasm
Hexokinase
Glycogen Synthesis
A-D-Glucose-> Glucose 6-P
-requires ATP-ADP
Phosphoglucomutase
Glycogen Synthesis and degradation
converts glucose 6-P Glucose 1-P
UDP-Glucose Pyrophosphorylase
Glycogen Synthesis
Glucose 1-P + UTP-> UDP-glucose +PPi
-PPi is hydrolyzed
Inorganic Pyrophosphatase
Glycogen Synthesis
Hydrolysis PPi-> 2Pi
-exergonic and provides energy for glycogen synthesis
Glycogen Synthase
Glycogen Synthesis
REGULATED
UDP-Glucose + Existing Glycogen with at least 4 residues converted to Glycogen (N+1) + UDP
-requires glycogenin
Nucleoside Diphosphate Kinase
Glycogen Synthesis
Regenerate UTP
UDP +ATP-> UTP + ADP
Glycogenin
Composed of Tyrosine residue that contains OH that serves as primer for synthesis of glycogen
Branching enzyme
Glycogen Synthesis
synthesizes a-1,6 branches every 8-10 residues
Protein Phosphatase I (PP1)
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
Fatty Acid Function
1) Fuel stored as triacylglycerol
2) Synthesis of Phospholipids and glycolipids (membranes)
3) Synthesis of hormones
4) Protein Modification
Fatty Acid Structure
Long Hydrocarbon chains with terminal Carboxylate group
-saturated/unsatured
Triacylglycerol Function
Energy Dense Energy Storage
-reduced and anhydrous
Triacylglycerol Structure
Uncharged esters of Fatty acids with glycerol group
Where is triacylglycerol stored?
cytoplasm of adipose cells for mobilization to bloodstream
muscle cells for generation of ATP
Dietary Triacylglycerols are digested by:
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
Triacylglycerol Lipase
- function
- Glycerol fat (Mechanism)
- Fatty Acid Fate (NO MECHANISM
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
Fatty Acid Degradation: Signal Transduction pathway
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
Preparation of Fatty Acids for B-Oxidation
- Activation
- Transportation
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
Acyl CoA Dehydrogenase
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)
Enoyl CoA Hydratase
Fatty Acid Catabolism
2) Hydration
trans Enoyl CoA + H2O-> L-3-hydroxyacyl CoA
-stereospecific hydration
L-3-hydroxyacyl CoA dehydrogenase
Fatty Acid Catabolism
3) 2nd oxidation
L-3-hydroxyacyl CoA-> 3-Ketoacyl CoA
-OH on C3 oxidized to Ketone
B-Ketothiolase
Fatty Acid Catabolism
3-Ketoacyl CoA-> Acetyl CoA + Acyl CoA(-2C)
-CoA cleaves at 3C
Beta Oxidation of Unsaturated Fatty Acids
-enzymes
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
Beta Oxidation of Unsaturated Fatty Acids
- results in?
- mechanism
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)
Vitamin B12
- Used In?
- Structure
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
What two enzymes in Mammals use Vit B12
Cobalamin
1) Methylmalonyl CoA Mutase
2) Methionine Synthase or homocysteine methyltransferase
Propionyl CoA Carboxylase
Carboxylation: for Unsatured Fatty acids result in
Propionyl CoA-> L/D-3-methylmalonyl CoA
-requires Biotin and ATP
Methylmalonyl CoA Mutase
Requires B12
Isomerization of:
L/D-3-methylmalonyl CoA-> Succinyl CoA
-exchanges H and O=C-CoA via Homolytic cleavage reaction forming CH2 radical
Fatty Acid Oxidation in Peroxisomes
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
What happens to the excess Acetyl CoA from Fatty Acid Oxidation?
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
Ketone Bodies
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
Acetoacetate is reconverted
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
Where does synthesis of Fatty Acids Occur?
Cytoplasm
Where does degradation of Fattty Acids Occur
Matrix of Mitochondria
Synthesis vs Degradation of Fatty Acids:
-Intermediates are linked to?
Synthesis- ACP=acyl Carrier protein
Degradation=CoA=Coenzyme A
Acetyl CoA Carboxylase
Carboxylation with HCO- of Acetyl CoA to Malonyl CoA
- commited step of Fatty Acid Synthesis REGULATED
- requires ATP
- Biotin=prosthetic group
Biotin
-What enzymes use?
Prosthetic group
-attached to E amino group of Lysine
Pyruvate Carboxylase, Acetyl CoA Carboxylase,
Propionyl CoA Carboxylase
Acetyl CoA transacylase
exchange ACP for CoA to from Acetyl ACP
Malonyl CoA transacylase
exchange ACP for CoA to form Malonyl ACP
ACP
Acyl Carrier Protein
- 77 amino acid
- acyl group attaches to Ser R group
Acyl-Malonlyl ACP condensing enzyme
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
B-Ketoacyl ACP reductase
Second Step of Fatty Acid Synthesis Elongation Phase
Reduction
Acetoacetyl ACP-> D-3-hydroxybutyryl ACP
-NADPH oxidized to NADP+
3-hydroxyacyl ACP dehydratase
3Rd step of Fatty Acid Synthesis Elongation Phase
Dehydration
D-3-hydroxylbutyryl ACP-> Crotonyl ACP
Enoyl ACP reductase
Final Step of Fatty Acid Synthesis Elongation Phase
Reduction
Crotonyl ACP-> Butyryl ACP
-NADPH oxidized to NADP+
Fatty Acid Synthase
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
How are acetyl groups transported to the cytoplasm for Fatty Acid Synthesis?
-Mechanism
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
The NADPH required for Fatty acid synthesis if from:
Pentose Phosphate Pathway
-Phosphoglucate Dehydrogenase
Fatty Acid Synthesis
-Malate-> pyruvate by NADP+ linked Malate enzyme
Control of Fatty Acid Synthesis
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
Hormonal Control of Fatty Acid Synthesis
Acetyl CoA Carboxylase
1) Insulin activates Protein Phosphatase 2A which dephosphorylates Turing enzyme ON
Glucagon/epinephrine maintains carboxylase in phosphorylated state (OFF)
