LIPID METABOLISM

INTRODUCTION

• Biological world contains 4 major families of small organic molecules- sugars , fatty acids, nucleotides, amino acids
• They form 4 types of macromolecules- polysaccharide carbohydrates, lipids, nuclei acids, proteins
• These macromolecules are the most abundant carbon containing molecules.

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INTRODUCTION

LIPIDS

• Fat or lipids are fatty acids ester of alcohol and related substances which are insoluble in water , but get dissolved in non – polar organic compounds-
• Like chloroform
• Acetone
• Ether
• Benzene

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METABOLISM

Metabolism is the sum total of catabolic and anabolic reactions occurring at any time in a cell

LIPID METABOLISM

• Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown or storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membrane.

FATTY ACIDS

• They are organic acids having carboxylic group (-COOH) and a short or long hydrocarbon chain which is generally unbranched .
• The carboxyl group is hydrophilic while the hydrocarbon chain is lipophilic.

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TYPES OF FATTY ACID

SATURATED FATTY ACID

UNSATURATED FATTY ACID

BIOSYNTHESIS OF FATTY ACIDS

• Fatty acid are synthesized by an extra mitochondrial system.
• Fatty acid synthesis occurs in many tissue including liver, kidney, brain, lung, mammary gland and adipose tissue.
• Acetyl-CoA is the intermediate substrate and free palmitate is the end product.

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OXIDATION OF FATTY ACIDS

• Enzyme lipase brings about the hydrolysis of fats into glycerol and fatty acids
• Fats + H₂O −─────→ Glycerol + Fatty acid
• Fatty acids can undergo α-oxidation or β-oxidation and Ѡ oxidation.

α-oxidation

By this process, the long chain of fatty acid is gradually broken down until it is reduced to 12 C-atoms. Fatty acids with less than 13-C atoms are not affected by this process. One complete α-oxidation results in the elimination of one carbon atom in the form of CO₂ from the—COOH group of the fatty acid, while α-C-atom i.e., C atom no. 2 (which is adjacent to — COOH) is oxidised (α-oxidation).

α-oxidation

• ALPHA-OXIDATION is a process in which fatty acids are shortened by one carbon atom. The alpha-oxidation sequence of 3-methyl-branched fatty acids starts with an activation to the corresponding CoA-ester. Subsequently this acyl-CoA-ester undergoes a 2-hydroxylation by the peroxisomal phytanoyl-CoA hydroxylase 

α-oxidation

β-oxidation

• Demonstrated by Knop in 1904
• Takes place inside glyoxysomes, mitochondria and peroxisome
• Β-Oxidation occurs in 4 steps
• Oxidation
• Hydration
• Dehydrogenation
• Acetyl transfer

β-oxidation

OMEGA(Ѡ) OXIDATION

• Cellular site: Endoplasmic reticulum.
• Oxidation occur at (Ѡ-oxidation)carbon- the carbon most distant from the carboxyl group.
• Substrate: Medium and long chain fatty acid.
• Importance: It is a minor pathway but become active when β-oxidation is defective.
• The product formed are di-carboxylic acid.

STORAGE AND MOBILIZATION OF FATTY ACIDS

• Fats and oils are mainly found in the triacyl-glycerols or triglycerides in which fatty acid molecules are linked by ester bonds to 3- hydoxal groups of glycerols .
• For examples:

Peanut oil is about 9% palmitic acid, 59% oleic acid, 21% linoleic acid.

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STORAGE AND MOBILIZATION OF FATTY ACIDS IN PLANTS

• In some fat storing seeds e.g. Castor bean, bacteria and fungi, lipids are converted into sucrose and other carbohydrates.
• Some of the carbon atoms of fatty acids are also diverted toward amino acids during this conversion.
• The lipids are converted into sugars and then translocated to growing axis like Root and shoot apex.

Mobilization of fat in plants

MOBILIZATION IN ANIMALS

• In the times stress when the body requires energy , fatty acids are released from adipose cells and mobilized for use.
• The process begins when levels of glucagon and adrenaline in the blood increase and those hormones binds to specific receptor on the surface of adipose cells.

MOBILIZATION IN ANIMALS

KETOGENESIS

• Acetyl CoA derived from fatty acid oxidation enter the citric cycle only if carbohydrated metabolism is properly balanced.
• When fatty acid oxidation produced more acetyl CoA then can be combined with OAA to form citrate, then the extra Acetyl CoA is converted to Acetyl CoA and ketone body including acetone. Ketogenesis (synthesis of ketone body) takes place primarily in the liver.

KETOGENESIS

FUNCTIONS OF LIPIDS

• MEMBRANE

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• IMMUNITY

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• INDUSTRY

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• SIGNALLING

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• ENERGY