BIOLOGY 2B03 Chapter Notes - Chapter 4: Catalase, Peroxisome, Primary And Secondary Antibodies
17 Jun 2018
School
Department
Course
Professor
BIOLOGY 2B03 - Module 4 Lecture I
Structure and Function of Peroxisome
Small oval-shaped organelle in the cell
● Bound by a single membrane
● Responsible for oxidative and synthetic functions in the cell
● Does not have its own genetic information
● Able to reproduce by fission
○ Very similar process that we see in bacterial cells
● In animal cells: responsible for cholesterol synthesis
● In nerve cells: synthesize plasmalogen for cell membranes
○ A Membrane component that increases the insulating capacity of the
membrane
● In the liver cells: the peroxisome is the site of oxidation of toxins
○ Such as alcohol
● In plant cells: required for the conversion of fatty acids into carbohydrates
○ Particularly important in seeds
● In cells: responsible for the catalysis of fatty acids
TEM Image of Peroxisomes
● Each have a single bi-lipid membrane
● Inside the peroxisome: dense region; contains protein
aggregates
○ Composed almost exclusively of one protein;
catalase
Fatty Acid Metabolism as an Energy Source
Major function of peroxisome: breakdown of very long chain
fatty acids through beta-oxidation to medium chain fatty
acids
● Which are subsequently shuttled to mitochondria
Fatty Acids
● Yields the most ATP on nan energy per gram basis
● The oxidation of fatty acids in the peroxisome is required for eventual release of
metabolic energy
○ True for both plants and animals
○ Hydrogen Peroxide: by-product of this, very toxic to the cell
By-Products of Fatty Acid Metabolism Are Toxic
Catalase Enzyme: that is able to convert to toxic hydrogen peroxide to non-toxic
oxygen and water molecules
find more resources at oneclass.com
find more resources at oneclass.com
● The abundance of catalase makes it useful marker for the visualization of
peroxisomes in the cell
Catalase is Used to Identify Peroxisomes
(Fluorescent microscopic image of a catalase in the cell)
● Catalase Antibody: recognized by a red-fluorescent
(secondary antibody)
● Each individual dot: peroxisome
● There are functional peroxisomes
● The peroxisomes are not static;
○ They move around, changing shape, and
undergoing both fission and fusion
Advantage to using fluorescence over TEM: we look at
living cells
Peroxisome Biogenesis Requires Protein Synthesis
Peroxisome Synthesis
● Occurs in cytosol then transported to the peroxisome
● PMP70: peroxisomal membrane proteins
○ Targeted to precursor membranes first to create peroxisomal ghost
● Once membrane proteins are present
○ They are used to transport peroxisomal matrix proteins; such as catalase
● New peroxisome are formed by fission
○ In this way a growing and dividing cell can create more peroxisomes and
distribute them to each new cell
Luciferase Transport to Peroxisomes
Luciferase: an excellent protein model for deciphering the mechanism of peroxisomal
protein transport
● An enzyme; allows the bioluminescence
● Specifically found in the peroxisomes of the cells in the abdomen
Luciferase expressed in mammalian cells
● The luciferase went specifically to the peroxisomes of the mammalian cells
○ Told the researcher that the pathways for protein transport to the
peroxisome are conserved from fireflies to mammals
○ Both have the same mechanisms for peroxisomal protein transport
5 Rules for Protein Transport
A Signal sequence is on the targeted protein
1. A receptor for that signal sequence is on the target organelles
2. A translocation channel is required to get the protein across the membrane into
the organelles
3. There is requirement for energy at some step in the process
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Responsible for oxidative and synthetic functions in the cell. Does not have its own genetic information. Very similar process that we see in bacterial cells. In animal cells: responsible for cholesterol synthesis. In nerve cells: synthesize plasmalogen for cell membranes. A membrane component that increases the insulating capacity of the membrane. In the liver cells: the peroxisome is the site of oxidation of toxins. In plant cells: required for the conversion of fatty acids into carbohydrates. In cells: responsible for the catalysis of fatty acids. Inside the peroxisome: dense region; contains protein aggregates. Composed almost exclusively of one protein; catalase. Major function of peroxisome: breakdown of very long chain fatty acids through beta-oxidation to medium chain fatty acids. Yields the most atp on nan energy per gram basis. The oxidation of fatty acids in the peroxisome is required for eventual release of metabolic energy. Hydrogen peroxide: by-product of this, very toxic to the cell.
