Ribosomes, Golgi complexes, lysosomes, and endoplasmic reticulum are similar organelles {microsome}|.
Nucleated cells have cytoplasm membrane-tube networks {endoplasmic reticulum}| (ER), extending from cell nucleus. Endoplasmic reticulum can have attached ribosomes {rough endoplasmic reticulum} or no attached ribosomes {smooth endoplasmic reticulum}. Neurons, unlike other cells, have much rough endoplasmic reticulum. ER adds sugars to proteins.
All cells, except mature sperm cells and red blood cells, have tubular-membrane networks {Golgi complex}| that store cell products, such as plant-cell cellulose, before secretion. Golgi complexes are near cell nucleus. Golgi complex adds sugars to proteins.
Free-floating or rough-endoplasmic-reticulum RNA-protein complexes {ribosome}| synthesize cellular proteins.
Cells have membrane-surrounded regions {lysosome}| containing enzymes {lysozyme} that can catabolize {autophagy, lysosome} large molecules, such as membranes and poorly folded, denatured, foreign, damaged, or used proteins, and remove sugars from proteins. Ubiquitin recognizes and binds to such proteins, marking them for later break down. Autophagosomes fuse with lysosomes.
Double-layer membranes {phagophore} can form in cytoplasm. Phagophores increase if nutrients, growth factors, and/or oxygen have low concentration.
process
Phagophore membranes close around damaged cell molecules and make spheres {autophagosome}. Autophagosome formation needs apg8 protein, similar to ubiquitin, which undergoes phosphoglycerolipidation with phosphatidylethanolamine to integrate into membrane. Ubiquitin recognizes and binds damaged proteins, marking them for later break down.
lysosomes
After autophagosome formation, membrane proteins leave, and autophagosomes fuse with cell lysosomes. Lysosomes contain lysozyme, which removes sugars from proteins and catabolizes {autophagy, autophagosome} large molecules, such as membranes and poorly folded, denatured, foreign, damaged, or used proteins.
Structures {proteosome}| break peptide bonds using ubiquitin.
Cell organelles {processing body} {P-body} can store used mRNAs and break them down using RNAses, such as Dhh1p. They affect RNA interference using Argonaute protein.
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Date Modified: 2022.0225