most cells have several Golgi • the cis (entry) Glogi is closest to the ER • the trans (exit) Golgi is closest to the plasma membrane • medial cisternae are in between the entry and exit Golgi • transport vesicles move proteins between the sacs of the Golgi
Organelles • Golgi cont. – there are different enzymes in the entry, medial, and exit cisternae – these areas will then be responsible for modifying, sorting, and packaging different proteins for various destinations
Transport vesicle from rough ER (a) Details Entry or cis face Medial cisterna Transfer vesicle Exit or trans face Secretory vesicle
Organelles • Lysosomes – vesicles that form from the Golgi – contain as many as 60 digestive enzymes and hydrolytic enzymes – work best at acidic pH • lysosomes have active pumps that keep H+ ions inside the vesicles – keeps lysosomes at pH of 5 (cytosol is ~ pH 7) – also contain transporters in the membrane that move the products of digestion into the cytosol • glucose, amino acids, fatty acids
Organelles • Lysosomes cont. – recycle worn-out cell structures • can engulf an organelle, digest it, and release components for reuse • this process is known as autophagy – autophagy involved with: • cellular differentiation, control of growth, tissue remodeling, adaptation to adverse environments, cell defense – the enzymes in the lysosome may also destroy the entire cell if the vesicle is compromised • this is called autolysis • occurs in injured and dead tissues
(a) Lysosome Digestive enzymes
Organelles • Peroxisomes – similar in structure to lysosomes but smaller – contain oxidases • enzymes that oxidize (remove hydrogen atoms or lose electrons) organic substances – substances can be oxidized as part of normal metabolism • amino acids and fatty acids – they can also be oxidized to detoxify • alcohol – abundant in the liver – byproduct of oxidation is hydrogen peroxide (H 2 O 2 ) • toxic compound associated with free radicals • convert to water
Organelles • Proteasomes – sometimes cytosolic proteins need to be disposed of • if they are damaged, unneeded, faulty – barrel-shaped structures – cells will have many thousands of these – contain proteases • the amino acids can be recycled to make new proteins
Organelles • Mitochondria – generate most of the ATP the cell uses – “powerhouses” of the cell – some cells have a few hundred while others have a few thousand • muscles, liver, kidneys have thousands – exercise can increase number of mitochondria – consist of outer and inner membranes with a small fluid-filled space between them • similar in structure to the plasma membrane • inner membrane has folds called cristae – the central cavity is called the matrix
(a) Details Outer mitochondrial membrane Inner mitochondrial membrane Mitochondrial matrix Mitochondrial cristae Ribosome Enzymes
Organelles • Mitochondria cont.
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- Fall '19