Lysosomes Recycle Protein Building Blocks

Biological Strategy

Humans

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Catalyze Chemical Breakdown

Life depends upon the building up and breaking down of biological molecules. Catalysts, in the form of proteins or RNA, play an important role by dramatically increasing the rate of a chemical transformation––without being consumed in the reaction. The regulatory role that catalysts play in complex biochemical cascades is one reason so many simultaneous chemical transformations can occur inside living cells in water at ambient conditions. For example, consider the 10-enzyme catalytic breakdown and transformation of glucose to pyruvate in the glycolysis metabolic pathway.

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Chemically Break Down Polymers

The vast majority of biochemical assembly and breakdown processes–even by the most complex organisms–occur within cells. In fact, cells are able to perform hundreds, even thousands of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). For example, one of the biochemical pathways that break down proteins into their constituent amino acids is the protease enzyme-catalyzed processes that occur within the confined space of the lysosome–a membrane bound organelle in eukaryotic cells.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Lysosomes in human cells recycle amino acid building blocks by capturing and breaking down malfunctioning proteins.

Lysosomes are organelles within the cell that prevent the accumulation of malfunctioning proteins by continuously breaking them down into their constituent amino acids which are, in turn, used to build new proteins. This process involves enzymes and increases the efficiency of cells in two ways: (1) by eliminating the need for complex waste management systems and (2) by providing the cells with new building blocks that don’t need to be “purchased” externally.

Lysosomes: In the cell, a waste protein (A) is taken up by a lysosome (B). In a process called proteolysis, the waste protein is broken down into the useful building block amino acids (C). Artist: Emily Harrington. Copyright: All rights reserved.

Last Updated September 19, 2016

References

“The other main degradation system is the lysosome, which contains multiple proteases [enzymes] and accounts for ~20% of protein turnover in cells. Lysosomes mainly degrade organelles and membrane proteins. Cytoplasmic proteins can also be degraded through autophagy, a process in which organelles and bulk cytoplasm are enveloped in double membranes and then delivered to lysosomes.” (Bingol and Sheng 2011: 22)

Journal article

Deconstruction for Reconstruction: The Role of Proteolysis in Neural Plasticity and Disease

Neuron | 13/01/2011 | Baris Bingol, Morgan Sheng

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