Biochemistry Review Lecture 2--Metabolism

Front 1

Glycosidic bonds of carbohydrates are broken by:

Back 1

1. Salivary amylase in the mouth
2. Pancreatic alpha amylase in the pancreas

3. alpha glucosidases, sucrase and lactases in the gut breakdown the remaining di/poly saccharides into individual glucose molecules.

Front 2

Transport of glucose

Back 2

Into gut epithelial cells is facilitated by Na+/Glc symport.

GLUT transporters then shuttle glucose into the blood, erythrocytes (GLUT1), liver/b-cell/kidney (GLUT2), brain (GLUT3), muscle/fat (GLUT4), and small intestine (GLUT 5).

Front 3

Summarize chemical rx. of glycolysis:

Back 3

glucose + (2NAD+) + 2ADP + 2Pi --> 2 Pyruvate (3C) + 2NADH + 2(H+) + 2ATP + 2H2O

Stage 1: Glucose--> 2-Triose Phosphate

Stage 2: 2-Triose-phosphate--> 2 Pyruvate

Pyruvate + NADH --> (NAD+) + Lactate (ENZYME=Lactate Dehydrogenase)

Pyruvate-->Acetyl CoA (PDH Complex)

Front 4

Beri Beri

Back 4

Thiamin deficiency. If you're missing thiamin, then the PDH complex isn't going to do well.

So tissues that have a lot of aerobic metabolism (brain and heart) are not going to do very well.

The brain and heart are two of the first things to get harmed by beri beri.

Front 5

Tx. for kids with lactic acid/pyruvate acidemias?

Back 5

1. Thiamin
2. Lipoic acid.

Kids have mutations in PDH complex and affects binding of lipoate/TPP. High doses of these compounds can override the defect in the binding by providing more substrate for the enzyme.

This can override the mutational effect.

Front 6

PDH complex

Back 6

Pyruvate from glycolysis hops onto the PDH complex via Thyiamine pyrophosphate. Forming hydroxyethyl TPP (E1.)

The ethyl group is picked up from hydroxylethyl TPP by oxidized lipolysine in E2. It is oxidized lipolysine that carries the two carbons for delivery to CoA-SH (which picks up the two carbons, releasing Acetyl CoA from the PDH complex. This leaves a remnant "reduced" lipolysine.

Finally, FAD from E3 restores the oxidized (bridged structure via an oxidation) lipolysine. In doing so it is reduced to FADH2 and reoxidized to FAD via NAD+ (which becomes NADH + (H+) via the restoration of FAD, which can then generate more oxidized lipolysine.

The FAD that oxidizes lipolysine as well as the NAD that restores FAD from FADH2 is all located in E3 of PDH complex.

Front 7

In regards to the TCA cycle, what are the metabolically important reactants, products, etc. from the cycle?

Back 7

Acetyl CoA produced from the PDH complex combines with 4(c) oxaloacetate to form 6 carbon citrate.

During the course of the reactions, 2 decarboxylations give off 2 mol CO2 and 2 mol NADH respectively.

Then the energy given off from the release of CoA-SH releases a GTP (ATP).

Two subsequent dehydrogenation reactions (succinate-->fumarate (malate-->oxaloacetate) give off FADH2 and NADH respectively.

NADH and FADH2 feed electrons into the e transport chain (complex I and II). etc.

Front 8

In the TCA cycle, what enzymes are responsible for the production of the 3 mol NADH, FADH2, GTP, and 2 mol CO2?

Back 8

The first 2 decarboxylation reactions that produce the first 2 mol of NADH are (and release CO2):

1. isocitrate dehydrogenase
2. alpha-ketoglutarate dehydrogenase complex

GTP formation occurs due to

3. succinyl CoA synthetase

FADH2 occurs owing to dehydrogenation of succinate.

4. Succinate dehydrogenase

The 3rd molecule of NADH is produced via dehydrogenation of malate, and is

5. malate dehydrogenase

Front 9

In the TCA cycle, what is the end product of the isocitrate dehydrogenase reaction?

Back 9

Alpha-keto glutarate

Front 10

In the TCA cycle, what is the end product of the alpha-keto glutarate dehydrogenase reaction?

Back 10

Succinyl CoA

Front 11

What is the product of the succinate dehydrogenase reaction?

Back 11

Malate

Front 12

Regulation of the TCA cycle?

Back 12

The PDH complex (Pyruvate-->Acetyl CoA) is positively regulated by AMP, CoA, NAD+ and Ca+, but negatively regulated by ATP, acetyl CoA, NADH, and fatty acids.

Citrate (6C) synthase is postively regulated by ADP, but negatively regulated by APT, NADH, acetyl CoA.

Isocitrate dehydrogenase is postively regulated by: Ca2+ and ADP but negatively regulated by ATP.

Aplha-ketoglutarate dehydrogenase is positively regulated by Ca2+ and negatively regulated by succinyl Coa and NADH.

Front 13

Rate limiting enzymes in glycolysis

Back 13

Glycolysis is regulated at 3 steps.

1. Glucose-->Glucose 6-P is catalyzed by hexokinase and glucokinase. Hexokinase is saturated quickly and glucokinase is saturated slowly, so glucokinase deficiency leads to problems in retaining glucose in the liver, etc.

2. Phosphofructokinase 1 is the principal regulatory enzyme of glycolysis. It makes the first commited metabolite of glycolysis, fructose 1,6 and ADP bisphosphate.

This rx. is negatively regulated by ATP and citrate, but positively regulated by AMP, ADP, and fructose 2,6 bisphosphate.

The enzyme has a tetramer and allosteric sites that bind APT, AMP and ADP (one site) and has site for citrate and fructose 2,6 bisphosphate.

This is highly regulated pathway and commits one to glycolysis.

3. Pyruvate kinase is deativated by cAMP and PKA and is the 2nd major regulatory enzyme in glycolysis. It catalyzes the rx. PEP-->Pyruvate, and generates ATP! It actually is the first net ATP gain during glycolysis that occurs, so this is a very important reaction.

It is negatively inhibited by alanine, acetyl CoA, and fatty acids,. It is positively regulated by fructose 1,6,-bp

Front 14

Insulin activates what enzyme that regulates glycolysis?

Back 14

glucokinase

Front 15

Regulation of the PDH complex

Back 15

1. Phosphtase (Ca2+ binds the phosphatase to the E1 complex when we need to bind and reactivate the enzyme.)

2. The kinase phosphorylates E1, inhibiting the complex.

High levels of acetyl CoA, NADh and ATp will activate the kinase and inhibit the complex (fatty acids too).

The PDH complex is positively regulated by AMP, CoA, NAD+, and Ca2+

Front 16

Glycogen synthesis

Back 16

Glycogenin (a protein primer for amylose chain with intrinsic glucosyl transferase activity) gets the ball rolling and then glycogen synthase can come in and put alpha-1,4 linkages on. (Magnesium cofactor)

Branching enzyme allows for the compact storage of glycogen and makes the branched alpha-1,6 linkages.

Front 17

Glycogen breakdown

Back 17

Free phosphate (not ATP!!) is used to by glycogen phosphorylase to catalyze (break alpha 1,4 bonds) breakage of glycosidic bond to give glucose 1-P.

Glucose 1-P must be isomerized to Glucose 6-P .

In muscle cells glucose 1-P is turned into glucose 6-P where it can be kept intracellularly and used for its own substantial glycolytic needs.

In the liver, glucose-6-phosphatase can break glycogen into free glucose and release it into the circulation where it can be used as "free glucose"