biological chemistry metabolism

8/13/2019 Biological Chemistry Metabolism

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Adenosine 5’-triphosphate(ATP)



Metabolic Pathways

Metabolism: the sum total of all reactions that take place in aliving cell or organism

Metabolic pathway: sequence of enzymatic reactions in which the product of one reaction is the substrate for the

next



Metabolism Metabolism is generally divided into 2 parts:

Catabolism: larger compounds are broken into smallercompounds; this process usually generates energy (ATPis generated)

Anabolism: larger compounds are synthesized fromsmaller ones; this process usually requires energy (ATPis hydrolyzed)

Compounds that are used, directly or indirectly, to releaseenergy (also called activated carrier molecules) are centralto metabolism and include: ATP, GTP, NAD+, NADP+, FAD,acetyl-CoA



Metabolism: the Usual Suspects



Metabolism: the Usual Suspects II



The Eukaryotic Cell



Catabolism

Most catabolic pathways occur in a sausage-shapedorganelle enclosed by 2 separate membranes called themitochondrion: citric acid cycle, electron transport chain, fattyacid oxidation, amino acid catabolism, oxidativephosphorylation

Only glycolysis takes place in the cytoplasm of the cell



Catabolism I: Digestion

When food is ingested the first stage of catabolism is todigest it, or to break the large biopolymers into theirrespective monomer units

This occurs primarily in the stomach and intestinesthrough both hydrolytic and enzymatic processes



ΔG and Coupled Reactions

Recall for a reaction to be spontaneous ΔG< 0 Coupled reactions: nonspontaneous reactions (ΔG>0) can

be made to occur if coupled with a spontaneous reaction sothat the total ΔG (both steps) < 0

Fructose 6-phosphate + Pi fructose 1,6-bisphosphate + H2OΔG= 3.9 kcal

ATP + H2O ADP + Pi ΔG= -7.3 kcal

•Is the conversion of F-6-P into F-1,6-bP spontaneous ornonspontaneous in absence of ATP?

• Write the net coupled reaction and calculate the net ΔG for the

overall reaction.



Multiple Paths for Pyruvate I

In yeast, pyruvate undergoes alcoholic fermentation is firstsplit into acetaldehyde and CO2, followed by the reductionof acetaldehyde to ethanol

The reduction of acetaldehyde occurs with concomitant

oxidation of NADH to produce NAD+ to go back intoglycolysis



Multiple Paths for Pyruvate III

In humans, when oxygen is sufficient (aerobic conditions)pyruvate is converted into acetyl-CoA, ready for the firststep in the CAC

This occurs in the mitochondria where CAC will begin



Gluconeogenesis

Gluconeogenesis: a linear anabolic pathway in whichglucose is synthesized from noncarbohydrate sources i.e.glycerol, lactate, and amino acids

This cycle goes into effect during periods of fasting or early

starvation when diet glucose and glycogen have beendepleted

This cycle is necessary for the protection of brain cells whose sole source of energy is glucose

This cycle converts small non-carbohydrate molecules intoglucose in a cycle resembling the reverse of glycolysis



Occurs primarily in the liverand to some extent in thekidneys



Glycogen Metabolism

Glycogen is a highly branched homopolymer of glucose[α(14) and α(16)] that is an immediately available formof glucose between meals and during activity

The main glycogen stores are in the liver and skeletalmuscle

Glycogenolysis Glycogenesis



Glycogenolysis Reaction

n residues



Glycogenesis Reaction



Covalent Modification

Many enzymes including those involved in glycogenmetabolism are controlled through reversiblephosphorylation

Glycogen synthesis is closely coordinated with itsdegradation, thus when glycogen phosphorylase is on,glycogen synthase is off and vice versa

Phosphorylase b phosphorylase a(usually inactive) (active)



Citric Acid Cycle

Glycolysis yields 2 ATP, 2 NADH, and 2 pyruvate

Pyruvate can be converted into acetyl-CoA and be furthercatabolized by the Citric Acid Cycle

CAC is a circular cycle that takes place in the mitochondriaand yields: 3 NADH, 1 FADH2, and 1 GTP

Net Reaction:

Acetyl-CoA + 3 NAD+

+ FAD + GDP + Pi 2CO2 + CoA + 3 NADH + FADH2 + GTP ΔG= -11 kcal



From 1 Glucose…

For a total of: 4 ATP, 10 NADH, 2 FADH2

El t T t Ch i d O id ti



Electron Transport Chain and Oxidative

Phosphorylation: Aerobic Respiration The ETC is a group of proteins embedded in the inner

mitochondrial membrane ETC/OP use the electrons from NADH and FADH2 to

ultimately generate the majority of the ATP in an organism

On Average:1 NADH= 2.5 ATP1 FADH2= 1.5 ATP



Shuttle Systems

The 2 NADH generated

by glycolysis in the

cytoplasm cannot enter

ETC directly b/c theycannot cross the inner

mitochondrial

Membrane

They must enterindirectly through 1 of 2

shuttle systems



Lipid Metabolism Triglycerides are concentrated stores of metabolic energy

When hydrolyzed, triglycerides form 3 fatty acids and 1molecule of glycerol

glycerol

Dihydroyacetoneglycolysis



Fatty Acid Catabolism

β-oxidation

A Spiral Cycle

Each turn of the cycle produces: 1 NADH, 1 FADH2, and acetyl-CoA



Problem1. Beginning with hexanoic acid, how many passes

through the oxidation spiral will take place?2. From your answer to part a, what is the net change in

NADH, FADH2, acetyl-CoA, and ATP, when onlyactivation and the passes through the oxidation spiral

are considered?3. From the answer to the previous questions, what will be

the total yield of ATP once all of the acetyl-CoA hasmoved through the citric acid cycle and all of thereduced coenzymes produced (including those from thecitric acid cycle) have been used for electron transportand oxidative phosphorylation?

4. How does the total yield of ATP obtainable from onehexanoic acid molecule compare with that from one

glucose molecule?



Ketone Bodies

During fasting or uncontrolled diabetes, acetyl-CoA buildsup b/c there is limited oxaloacetate for it to condense within the step 1 of the citric acid cycle (oxaloacetate will beused in gluconeogenesis to synthesize glucose)

Excess acetyl-CoA is therefore used to generate 3compounds known as ketone bodies: acetoacetate, 3-hydroxybutyrate, and acetone

Acetoacetate is a major fuel source in some cells (heart and

renal cortex) and under starvation conditions, brain cellsderive 75% of their energy from it



Congratulations…The End!

biological chemistry metabolism

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