Editing Lysosome (section)

== Function and structure ==
[[File:The Biological bulletin (19756543133).jpg|thumb|TEM views of various vesicular compartments. Lysosomes are denoted by "Ly". They are dyed dark due to their acidity; in the center of the top image, a Golgi Apparatus can be seen, distal from the cell membrane relative to the lysosome.]]
Lysosomes vary in shape and size depending on their state, what they are digesting, and the cell type they are in.<ref name=":0">{{Cite book |last1=Kühnel |first1=Wolfgang |title=Color atlas of cytology, histology, and microscopic anatomy |last2=Kühnel |first2=Wolfgang |date=2003 |publisher=Thieme |isbn=978-1-58890-175-0 |edition=4th |series=Thieme Flexibook Basic sciences |location=Stuttgart New York}}{{pn|date=April 2025}}</ref> Their shape can differ from spherical and ovoid to occasionally tubular.<ref name="Bouhamdani A Compendium of Information on the Lysosome">{{cite journal |last1=Bouhamdani |first1=Nadia |last2=Comeau |first2=Dominique |last3=Turcotte |first3=Sandra |title=A Compendium of Information on the Lysosome |journal=Frontiers in Cell and Developmental Biology |date=15 December 2021 |volume=9 |doi=10.3389/fcell.2021.798262 |doi-access=free |pmc=8714965 |pmid=34977038 }}</ref> The size of lysosomes ranges from 0.1-1.2 μm,<ref name=":0" /> with some tubular ones reaching up to 15 μm in phagocytes. Several hundred lysosomes can be found within a single cell. However, upon nutrient deprivation or induced autophagy, their numbers can drop below 50 in a cell.<ref name="Bouhamdani A Compendium of Information on the Lysosome"/>

Lysosomes contain a variety of enzymes that enable the cell to break down various biomolecules it engulfs, including [[Peptide|peptides]], [[Nucleic acid|nucleic acids]], [[Carbohydrate|carbohydrates]], and [[Lipid|lipids]]. The enzymes responsible for this hydrolysis require an acidic environment for optimal activity, with a pH ranging from ~4.5–5.0. The interior of the lysosome is acidic compared to the slightly basic cytosol (pH 7.2).<ref>{{cite journal |last1=Feng |first1=Xinghua |last2=Liu |first2=Siyu |last3=Xu |first3=Haoxing |title=Not just protons: Chloride also activates lysosomal acidic hydrolases |journal=Journal of Cell Biology |date=5 June 2023 |volume=222 |issue=6 |doi=10.1083/jcb.202305007 |pmc=10191866 |pmid=37191899 }}</ref>

The lysosomal membrane is a phospholipid bilayer with high carbohydrate content from heavily glycosylated membrane proteins. This forms a [[glycocalyx]] that protects the cell from the [[Degradative enzyme|degradative enzymes]] held within the lysosome. Lysosomal hydrolases are pH-sensitive and do not function properly in the alkaline environment of the cytosol, ensuring that molecules and organelles in the cytosol are not degraded if there is leakage of hydrolytic enzymes from the lysosome.

In addition to breaking down polymers, lysosomes are capable of killing and digesting microbes, cells, or cellular debris. Through cooperation with [[Phagosome|phagosomes]], lysosomes conduct [[autophagy]], clearing out damaged structures and forming simple compounds, which are then used as new building materials. Similarly, lysosomes break down virus particles or bacteria during phagocytosis in macrophages.<ref>{{cite news |last1=Brouillette |first1=Monique |title=Biology 101 Update: A Cell's Lysosomes Are More Than Garbage Disposals |url=https://www.scientificamerican.com/article/biology-101-update-a-cell-rsquo-s-lysosomes-are-more-than-garbage-disposals/ |work=Scientific American |date=1 December 2016 }}</ref>

Lysosomes also help detect pathogens through [[Toll-like receptor|toll-like receptors]] (TLRs), like TLR7 and TLR9. Microbes can be degraded into antigens, which are then loaded onto MHC molecules and presented to T-cells, a critical part of immune defense. Additionally, lysosomal enzymes can trigger lysosomal-mediated programmed cell death (LM-PCD) if released into the cytoplasm.

To maintain their acidic environment, lysosomes pump protons (H⁺ ions) from the cytosol into the lysosomal lumen via a proton pump in the lysosomal membrane. [[V-ATPase|Vacuolar-ATPases]] are responsible for the transport of protons, while the counter transport of chloride ions is performed by ClC-7 Cl⁻/H⁺ antiporter.<ref>{{cite journal |last1=Feng |first1=Xinghua |last2=Liu |first2=Siyu |last3=Xu |first3=Haoxing |title=Not just protons: Chloride also activates lysosomal acidic hydrolases |journal=Journal of Cell Biology |date=5 June 2023 |volume=222 |issue=6 |doi=10.1083/jcb.202305007 |pmc=10191866 |pmid=37191899 }}</ref> This mechanism helps maintain a steady acidic environment, as well as ionic homeostasis, within the lysosome.<ref>{{cite journal |last1=Mindell |first1=Joseph A. |title=Lysosomal Acidification Mechanisms |journal=Annual Review of Physiology |date=17 March 2012 |volume=74 |issue=1 |pages=69–86 |doi=10.1146/annurev-physiol-012110-142317 |pmid=22335796 }}</ref><ref>{{cite journal |last1=Ishida |first1=Yoichi |last2=Nayak |first2=Smita |last3=Mindell |first3=Joseph A. |last4=Grabe |first4=Michael |title=A model of lysosomal pH regulation |journal=Journal of General Physiology |date=June 2013 |volume=141 |issue=6 |pages=705–720 |doi=10.1085/jgp.201210930 |pmc=3664703 |pmid=23712550 }}</ref>

Lysosomes also help balance cellular metabolism by sensing nutrient availability. When nutrients are plentiful, they activate [[MTOR signaling pathway|mTOR signaling]] to support anabolic (biosynthetic) processes. During starvation, lysosomes degrade autophagic material, recycling components to maintain cell survival.