Lysosomes and peroxisomes

Lysosomes and Peroxisomes

Made by: Sara Hassan

Lysosomes• Lysosomes are membrane bound organelles that contain

digestive enzymes.

• They are found in eukaryotic cells primarily animal cells and

plant cells.

• The primary function of lysosomes is extracellular and

intracellular digestion at acidic pH.

• Lysosomes were discovered by De Duve a Belgian Cytologist

in 1955 who designated them as suicide bags.

• De Duve discovered lysosomes in a fraction that was

intermediate between mitochondria and microsomes.

Anatomy of Lysosomes

Lysosomal Membrane

• The lysosomal membrane contains highly glycosylated lysosomal

associated membrane proteins (LAMP) and lysosomal integral

membrane proteins (LIMP)

• LAMPs and LIMPs coating the inner membrane surface protect the

membrane against attack by enzymes retained within lysosomes.

• An ATP dependant proton pump in the membrane pumps H+ into

the lumen, creating an acidic pH necessary for lysosomal enzymes

to function.

Morphology of Lysosomes

• Lysosomes have the remarkable characteristic of pleomorphism

• i.e size and shape of the particle and irregularities of its inner structure.

• In a cell ,lysosomes are surrounded by smooth or coated vesicles.

Manufacturing Lysosomes• Lysosomes are manufactured by golgi

apparatus and budded out into the

cytoplasm with enzymes inside them.

• The lysosomal enzymes are made by

ribosomes and sent to E.R. where they

are tagged with mannose 6 phosphate

for being recognized by receptors of

their next destination- the Golgi

apparatus.

• The Golgi Apparatus bud off to form

lysosomes.

Types of LysosomesPrimary lysosomes (storage granules) are small saclike

structures enclosing enzymes synthesized by Ribosomes and

stored in E.R. and transferred to Golgi apparatus.

Heterophagosome(Digestive Vacuole) The materials

engulfed through phagocytosis are digested by enzymes of

primary lysosomes.

Residual Bodies are formed in case of incomplete digestion. In

amoeba they are removed by defecation otherwise they are

accumulated like pigment inclusions in nerve cells.

Autophagic Vacuole: A special scenario in normal

cells where a part of the cell ( mitochondrion or E.R) is in lysosome for digestion.

Secondary Lysosomes

• The Secondary lysosomes

contain materials engulfed by

phagocytosis or pinocytosis

fused with primary lysosomes.

These materials are subjected

to cellular digestion by the

primary lysosomes enzymes.

• Hence, a secondary vacuole

can also be designated as a

digestive vacuole.

Functions of Lysosomes:

Functions of Lysosomes

Heterophagy.

Autophagy.

Programmed cell

death. 

Autolysis.

Fertilization.

Autophagy• Autophagy is a

physiological process for

digestion of cells in the

body to maintain

homeostasis.

• It maintains homeostasis

by protein degradation and

turnover of the destroyed

organelles for new cell

formation.

Autolysis• Autolysis refers to the digestion

of parent cells by the lysosomes. 

• Autolysis occurs during

amphibian metamorphosis for

instance the autolysis of tadpole

tail cells.

  Fertilization

• During fertilization , the nuclear

acrosome of the sperm which is

considered a giant lysosome

secretes hyaluronidase enzyme on

the surface of egg cell. This

disperses the cells around the egg.

Secondly, protease is also

secreted to dissolve zona pelucida

making a channel for the sperm to

enter the egg.

Heterophagy

• Heterophagy is the process

of lysosomal digestion of

extracellular materials

entering the cell by the

process of phagocytosis,

pinocytosis and receptor

mediated endocytosis.

Programmed cell death

• Lysosomal membrane permeabilization (LMP) induces

controlled cell death as it ensures the translocation of

lysosomal enzymes into the cytoplasm.

• Cathepsins B, L and C are proteases implicated in cell

death they initiate the cascade leading to PCD.

Lysosomal Storage Diseases• LSDs are metabolic disorders where lysosmal enzyme fail to function properly.

As a consequence of which the substrate is accumulated.• When a lysosomal enzyme is deficient or malfunctioning, the substrate it targets

accumulates, interfering with normal cellular activity.• These diseases include Tay Sachs disease and Gauchers Disease.• Healthy Cell Cell with accumulated Substrate

Peroxisomes• Peroxisomes are single membrane bound organelles

found in the cytoplasm of eukaryotic cells• Peroxisomes originate from Golgi Apparatus.

• They were discovered by De Duve in 1965 in liver cells.

• Peroxisomes are the site of synthesis and degradation of Hydrogen Peroxide hence designated as peroxisomes.

• An enzyme catalase, a type of oxidase, is present in large quantity in peroxisomes.

• Peroxisomes self replicate through fission.

Anatomy of Peroxisomes

• Peroxisomes have a lipid bilayer membrane that controls what enters and exits them.

• Peroxisomes have a Urate oxidase crystalline core with 32 peroxins (peroxisomal proteins), that execute peroxisomal functions inside the organelle.

Functions of Peroxisomes• They are involved in many different activities like the

degradation of hydrogen peroxide by Catalase.• For this purpose peroxisomes need significant amount of

Oxygen.• Initially many oxidases bind with oxygen and hydrogen to

form Hydrogen peroxide.• In the next step Hydrogen Peroxide is oxidized by catalase

into water and oxygen.• Peroxidase detoxify alcohol from liver cells.• Peroxisomes execute the ß-oxidation of Long Chain

Fatty Acids - a major source of energy.

Peroxisomal Disorders

• Peroxisomal disorders in humans result due to abnormal function of an enzyme necessary for normal peroxisomal function.

• This may result in peroxisomal disorders like: 1.Liver dysfunction2.Retinopathy

References

• Chapter 10 Lysosomes, Endosomes, Coated vesicles and peroxisomes from cell and molecular biology by De Robertis.