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Module: BIOM - 1006

Lecturer: Dr Sherwood

Date: 19/10/16

The Golgi Apparatus, Mitochondria, Lysosomes and Peroxisomes
o

The Golgi apparatus, discovered by Camillo Golgi in 1897, is present in each eukaryotic cell
 It is a collection of flattened discs/stacks that make up two main large networks:
 The cis Golgi network (CGN)
 The CGN is a collection of flattened, membrane-bound discs known as cisternae
(singular: cisterna)
...
This is how the
proteins are modified
 For example, an oligosaccharide chain could be added
 The trans Golgi network (TGN) is at the end of the Golgi stacks and is where proteins
bud off from the Golgi all together
 The proteins can then either be destined for the plasma membrane or for a
lysosome
o They can be sent to the plasma membrane:
 When being sent to the plasma membrane, the proteins are packaged
and bud off in vesicles to accumulate around the membrane and
wait for an extracellular signal to cause them to fuse with the
membrane
 This is known as constitutive secretion as they are sent
automatically
 Regulated secretion is for when proteins are made and then stored
for later release
 These proteins have special surface properties that cause
them to aggregate together under the ionic conditions
(acidic and high Ca2+) that are prevalent in the TGN
...
They were not termed mitochondria until 1898
 Mitochondria are the powerhouse of the cell and are responsible for the synthesis of ATP
 Adenosine-triphosphate
 They range from ~0
...
05 to 0
...
2 cytosol
 The constant pH is kept by actively pumping H+ ions into the cell
 The leftovers of molecules that have been broken down will be transported into the cytosol and
either used by the cell or excreted, leftovers include, among other things:
 Amino acids
 Sugars
 Nucleotides
 The following are some EM images of a lysosome:

o

Finally, peroxisomes, discovered in 1967 by Christian de Duve, are responsible primarily for the
oxidation of toxic molecules
 They range from 0
...
5m in dimeter
 They are also bound by a single membrane which makes them very weak
 They contain more enzymes (50+) than lysosomes and also contain marker enzymes such as
catalase
 This degrades hydrogen peroxide (H2O2) into water and oxygen
 One function of peroxisomes is the β-oxidation of long and very long fatty acids (C20+)
 These long fatty acids cannot be broken down in the mitochondria for use in generating
acetyl-CoA
 These long fatty acids produce H2O2
 Peroxisomes are also responsible for some bile acid synthesis and the breakdown of uric acid
and some amino acids
 The following images are some EM’s of peroxisomes (very similar
to lysosomes):



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