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PRESENTATIONON PEROXISOMESMade By: Suman Shaikh 1st Year DPT(Subject: Physiology)

outline of the topic:

Introduction to PeroxisomesStructure of PeroxisomeFunctions of PeroxisomeDisorders related to Peroxisomes

PEROXISOMES (Introduction) What are Peroxisomes??Peroxisomes are membrane bound organelles, occurring in the cytoplasm of almost all eukaryotic cells. Also called Microbodies.

Their existence was first discovered by J. Rhodin in 1954.

using electron microscopy in kidney cells of mouse .4

PEROXISOMES (Introduction)

They are found in nearly all eukaryotic cells

Human cells may contain upto hundred peroxisomes depending on type of cell.

They are called Peroxisomes because they are the site of synthesis and degradation of Hydrogen Peroxide [H2O2], a highly reactive and toxic oxidizing agent.

PEROXISOMES (Introduction)

PEROXISOMES (continued) Peroxisomes contain Oxidase enzymes

they originate from Endoplasmic reticulum, Lysosomes contain hydrolase enzymes

lysosomes come from Golgi apparatus.

They are similar to Lysosomes, being filled with enzymes.Difference with lysosomes Similarity with lysosomes

An enzyme catalase(a type of oxidase) present in large quantity in peroxisomes.

Peroxisomes are replicated by fission. They are believed to be formed from self replication.

Their life span is 1 day. And they are self assembling.

PEROXISOMES (continued)

They are abundant in cells of liver and kidney, where they are required the most.

PEROXISOMES (continued)

liver

Structure of PeroxisomeThey are particles of about 100-500 nm in diameter.

A lipid bilayer membrane surrounds which regulates what enters and exits the peroxisome.

Inside a dense matrix.

Urate oxidase crystalline core.

There are at least 32 known peroxisomal proteins, called peroxins, which carry out peroxisomal function inside the organelle.

Structure of peroxisome (Continued)

Peroxisomes have the thickest membrane of all organalles.

It has a dense matrix that contain enzymes.

More than 30 different enzymes are present in peroxisomes.

Structure of Peroxisome (Continued)

Structure of Peroxisome (Continued)It has a crystalloid core in the center, which is present in some species e.g. liver cells of rat.

It is absent in human liver cells.

It contains urate oxidase enzyme which oxidizes uric acid.

Humans do have agenefor urate oxidase, but it is nonfunctional.

Crystalline Core

Histological Picture of Peroxisomes

Functions of PeroxisomesIn order to carry out their activities, peroxisomes use significant amounts of oxygen.They are involved in many different activities, such as :hydrogen peroxide degradation by Catalase. Mechanism : First several oxidases combine oxygen and hydrogen to form H2O2. Then this H2O2 id oxidized by catalase(another oxidase) into H2O and O2.

-oxidation of Very Long Chain Fatty Acids (VLCFA) provides the cell with a major source of metabolicenergy.

Functions of PeroxisomesDetoxification of alcohol and other toxic compounds.

Peroxisomes detoxify about half of the alcohol a person drinks daily.

Purine catabolism by urate oxidase(not in all animals)

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Functions of Peroxisomes

Biosynthesis of plasmogens, ether phospholipids, which are necessary for normal function of brain and lungs.

Synthesis of unsaturated fatty acids.

production of plasmalogens is critical to proper functioning of the nervous system since a lack of plasmalogens causes abnormalities in the myelination of nerve cells.

These are considered to be more health beneficial than saturated fats or trans fats.

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Participates in the synthesis ofbile acids ion liver cells.

Participates in the synthesis ofcholesterol

Participates in the synthesis of the lipids used to makemyelin.Functions of Peroxisomes

Peroxisomes are important for normal brain and lungs functioning. Absence of peroxisomes can lead to abnormalities, specially brain disorders.Functions of Peroxisomes

Peroxisomal Disorders In humans, peroxisomal disorders may result due to abnormal function of single enzyme, which are necessary for normal peroxisomal function.Problems with nervous system are commonly observed.

Other problems include: Skeletal and craniofacial dysmorphismLiver dysfunctionSensorineural hearing lossRetinopathy

We will discuss here two nervous problems.AdrenoleukodystrophyZellwegers syndrome.

Peroxisomal Disorders

It is a fatal inherited disorder that leads to extensive brain damage and adrenal gland failure.disorder results from a failure to metabolize Very long chain fatty acids(VLCFA) properly.

One result is deterioration of themyelin sheathsof neurons. The disorder occurs in young boys because the gene isX-linkedAdrenoleukodystrophy

Adrenoleukodystrophy

A single peroxisomal enzyme absenceDefect in a membrane protein that transports VLCFAsVLCFAs accumulate in the brain Adrenoleukodystrophy

also called cerebrohepatorenal syndrome, is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual.

It is caused by mutation of those genes that are responsible for encoding the proteins required to assemble enzymes in the peroxisomes.

Zellwegers syndrome

Zellwegers syndrome

Gene mutationOf Proteins involved in transport of enzymes to peroxisomesEmpty peroxisomesZellwegers syndromeEnzymes failed to be transported

Thank you for your attention