Pg. 721-727.docx

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11 Apr 2012
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Pg. 721-727
Peroxisomes
Peroxisomes: can be used to break down harmful chemicals
Differ from chloroplast and mitochondria
Lack their own genome
It contains oxidative enzymes such as catalase and urate catalase
Peroxisomes are major sites of oxygen utilization
Peroxisomes use Molecular Oxygen and Hydrogen Peroxide to Perform Oxidation
Reaction
Catalase can break down hydrogen peroxide into water and oxygen
This reaction can occur in liver cells
Peroxisomes are important in plants; one type is present in leaves: helps
with photorespiration; the other type is present in germinating seeds: helps
young plant grow
A Short Signal Sequence Directs the Import of Proteins into Peroxisomes
Peroxins: 23 distinct proteins participate in importing the proteins
Human disease called zellwegger syndrome: defect in peroxisomes
The Endoplasmic Reticulum
Endoplasmic reticulum (ER): labyrinth like branching tubules
ER lumen: space between the ER and the nuclear membrane
The ER is Structurally and Functionally Diverse
ER contains co-translational process: import of proteins; ribosomes are
attached translating the proteins; rough ER
Mitochondrion, chloroplast, nuclei and peroxisome contain post-translational
process: to import proteins; proteins are already translated
Smooth ER: do not contain any ribosomes
Bud off the golgi apparatus
Liver cell has an abundance of smooth ER
ER is also important for transferring Ca2+ into the cytosol
There is a Ca2+ pump that releases Ca2+ to the cytosol
Signal Sequences Were First Discovered in Proteins Imported into the Rough ER
Two types of proteins were transmembrane proteins: only partly located in
the ER and water soluble proteins: fully located in the ER
ER signal sequence: initiates translocation