M&c Lectures 68 - 75

Front 1

What is gained from the Pentose Phosphate Pathway?

Back 1

A) Production of NADPH - needed for synthesis of cholesterol, fatty acids, steroids, detoxification reactions by the cytochrome P450 system.
B) Production of ribose - needed to produce the nucleotides for RNA and DNA synthesis; for NAD, FAD, CoASH
C) To reduce oxidative stress: PPP makes NADPH which is used to regenerate glutathione, fatty acid synthesis, and more!

Front 2

Pentose Phosphate Pathway overview

Back 2

Glucose -> Glucose-6-P -> G-3-P ->->-> pyruvate

Glucose-6-P + NADP+ -> Ribulose-5-P + NADPH

Ribulose-5-P <-> Xyulose-5-P <-> Ribose-5-P

Xyulose + Ribose-6-P <-> F-6-P + G-3-P

Front 3

Substrates for synthesizing glucose

Back 3

The primary substrates for synthesizing glucose are lactate, pyruvate, glucogenic amino acids (all except lysine, lucine) and to a lesser extent, glycerol from breakdown of triglycerides.

Front 4

Basic runthrough of pentose phosphate shunt?

Back 4

1. G-6-P oxidized by NADP+, G6PDH to produce 6-phosphogluconic acid + NADPH
2. 6-phosphogluconic acid undergoes oxidative decarboxylation via 6-PGADH/NADP+ to make Ribulose-5-P + CO2 + NADPH
3. Ribulose-5-P -> Ribose-5-P via phosphopentose isomerase (PPI).
4. rearrangement reactions take 3 ribulose-5P (15C total) to make 2 F-6-Ps plus one glyceraldehyde-3-P (15C total).

Front 5

How does the RBC get rid of H2O2?

Back 5

RBCs get rid of hydrogen peroxide via:
1. The heme enzyme catalase
2. Glutathione peroxidase: GSH --> GSSH

Front 6

How does pyruvate become PEP?

Back 6

Pyruvate is converted to PEP by 2 gluconeogenic enzymes needed to bypass the irreversible pyruvate kinase reaction:
a) pyruvate carboxylase: pyruvate + ATP + CO2 -> OAA + ADP +Pi
THIS USES BIOTIN

b) PEPCK: OAA -> PEP + CO2 +GDP

Front 7

What are pyruvate carboxylase and PEPCK involved in besides gluconeogenesis?

Back 7

They are also replenishing reaction for the TCA cycle

Front 8

Enzymes of gluconeogenesis:

Back 8

1. pyruvate carboxylase
2. PEPCK
3. fructose biphosphatase
4. glucose-6-phosphatase

Front 9

How and when is lipase activated/inactivated in adipose tissue?

Back 9

The
hormone-sensitive lipase in adipose tissue is activated by glucagon, epinephrine or norepinephrine via cAMP-dependent PKA phosphorylation (in the fed state, insulin inhibits this lipase via dephosphorylation)

Front 10

Give an overview of beta oxidation

Back 10

1. Fatty acid activated to fatty acyl-CoA by Acyl CoA synthase

2. Long chained fatty acyl-CoA converted into long chain fatty acyl carnitine (acyl carnitine transferase 1), transported into mito and converted back to fatty acyl CoA (acyl carnitine transferase 2).

3. Acyl CoA undergoes 4 enzyme catalyzed reactinoos that produce one NADH, one FADH2, and one Acetyl CoA. The shortened (-2C) fatty acyl CoA repeats this step.

Front 11

How are odd-chained fatty acids processed? What happens to the products?

Back 11

Same way as even chained, except last product is a 3C propionyl CoA, which is made into succinyl CoA via B12.
Succinyl CoA can enter heme synthesis or go into the TCA to OAA, glucose.

Front 12

Why can't acetyl CoA build up?

Back 12

We cannot pile up acetyl CoA because you would deplete CoASH (all tied up as acetyl CoA) and therefore could not continue fatty acid oxidation.

Front 13

Give an overview of ketogenesis

Back 13

1. 2 acetyl CoA --> acetoacetate
2. Acetoacetate can be converted into β-hydroxybutyrate which can become acetone spontaneously.
3. Transferase in certain tissues (heart, muscle, kidney cortex, and brain under starvation) converts acetoacetate into acetoacetyl-CoA

Front 14

how are very long chain fatty acids metabolized?

Back 14

Peroxisomal fatty acid oxidation!
NAD and O2 are electron acceptors, generating NADH, H2O2, and acetyl CoA until medium chained fatty acids are produced. H2O2 removed by peroxisomal catalase.
Acetyl CoA enters mito as acetyl carnitine.

Front 15

What is produced in FA synthesis, and what is its fate?

Back 15

Palmitate
1. stored in liver
2. transported as VLDL to adipose for storage
3. converted to longer chain FA (i.e. stearate) or desaturated (i.e. oleic)

Front 16

Give an overview of fatty acid synthesis

Back 16

1. Acetyl CoA (from CITRATE shuttle) is carboxylated via Acetyl CoA carboxylase/BIOTIN to make malonyl CoA
2. Acetyl CoA and Malonyl CoA go to Fatty Acyl Synthase Complex. Acetyl CoA binds SH of condensing protein, malonyl CoA binds acyl carrier protein (ACP).
3. The two condense to form CO2 and acetoacetyl-ACP.
4. Reduced and dehydrated via 2NADPH's.
5. Repeat: another malonyl CoA adds on...

Front 17

What is the net reaction of palmitate synthesis?

Back 17

8 acetyl CoA's + 7ATP + 14 NADPH --> 1 palmitate-CoA + 7 CoA + 7ADP + 14 NADP+

Front 18

Where does cholesterol synthesis occur?

Back 18

ER and cytosol

Front 19

Rate limiting step of cholesterol synthesis

Back 19

HMGCoA reductase: HMGCoA reduced by 2 NADPH's to produce mevalonate

This is a target of statins

Front 20

How is HMG CoA reductase regulated?

Back 20

-activated by insulin, inhibited by cholesterol and low energy
HMGCoA reductase is inactivated when phosphorylated by AMP-activated protein
kinase. This kinase is activated by AMP, a low energy signal (as was acetyl CoA carboxylase)
-also, cholesterol inhibits SREBP-1 nuclear translocation/HMGCoA transcription

Front 21

Describe reduction of molecular oxygen O2

Back 21

O2 --> O2*- --> H2O2 --> H2O + OH* --> 2H2O

O2 has 2 unpaired electrons. Huh.

Front 22

Haber-Weiss reaction

Back 22

O2*- + H2O2 --> O2 + H2O + OH*

Front 23

Fenton reaction

Back 23

H2O2 + Fe2+ --> OH* + OH- + Fe3+

Cu and many other metals can serve as single electron donors in the Fenton reaction

Front 24

NADPH Oxidase

Back 24

activates to assemble in neutrophils during respiratory burst: generates superoxide --> ROS

lack of NADPH --> chronic granulomatous disease; chronic infection

Front 25

Nitric oxide synthase

Back 25

Arginine + O2 --> Citrulline + NO

utilizes NADPH, O2

Front 26

Superoxide Dismutases

Back 26

2 Types:
1) CuZn SOD in cyto
2) Mn SOD in mito: needed for life

Front 27

Vitamin A, E, and C as antioxidants

Back 27

Vit A : (β carotene) most effective quencher of singlet oxygen

Vit E (lipid soluble) terminates lipid peroxidation

Vit C (water soluble) terminates cytosolic radicals

Front 28

Ischemic Reperfusion Injury, treatment

Back 28

Burst of Oxygen radicals from ETC and Xanthine dehydrogenase/oxidase
XDH normally catalyzes the reaction:
ATP, ADP, AMP --> hypoxanthine --> xanthine --> uric acid

Under ischemic conditions, XDH becomes Xanthine Oxidase, and uses O2 instead of NAD+ to oxidize hypoxanthine, generating large amounts of radicals.

Allopurinol given to inhibit XO.

Front 29

thiolase

Back 29

Cholesterol synthesis: makes Acetoacetyl CoA from 2 Acetyl CoA