W3: 3.1 Organelles Flashcards
What are the advantages of having organelles?
1) Cells can compartmentalize biochemical reactions:
2) rxn’s are confined to a smaller volume;
higher enzymes con’t.
3) Rxn’s can be controlled by only permitting certain molecules to be in an organelle (transport control),
4) dangerous rxn’s are confined to a smaller area.
5) Organelles allow cells to perform specialized tasks: The amount of organelle membrane in a cell can predict the major function of that cell
What fraction of a typical cell is occupied by membrane bound organelles?
half of the cell volume.
Cell: nucleus + cytoplasm
Cytoplasm: cytosol + organelles
Based on the function of organelles, would you expect a B cell (which produces antibodies to have many or few of the following: lysosomes, peroxisomes, smooth ER rough, ER?
High lysosomes to aid in neutralization and digestion. Some levels of Smooth ER since SER is responsible for detoxification.
Which organelles have double membranes and what does this indicate with regard to their origins?
Nucleus, mitochondria, and chloroplast.
This indicates that they were produced from an endosymbiosis relationship: a predatory cell may have engulfed another one that was capable of conducting specialized actions. Instead of destroying the engulfed cell the two formed some sort of mutually beneficial or symbiotic relationship
What organelle has a three membranes? and what is the origin of each?
Chloroplast. The first two membranes resulted from ancient endosymbiotic relationship.
The inner membrane that was part of the engulfed organism progressively invaginated
the invagination of the inner membrane appears to have become complete resulting in the formation of a Thylakoid membrane (the third membrane)
What is one way to analyze composition of an organelle system?
Centrifugation strategy
Why are organelles important?
They compartmentalize biological processes: allows the cell to optimize the events inside the organelle and make them highly efficient.
- concentrate enzyme catalyst and substrates together
- control processes by restricting the contents of an organelle system
- perform rxn’s that would damage other parts of the cell if they weren’t contained.
Allow cells to become specialized for the performance of specific functions.
-generation of each organelle system is highly regulated and this regulatory ability allows for specialization
explain how centrifugation organizes organelles?
makes a homogenate of cells by spinning at different speeds.
-centrifuge homogenate at progressively higher speeds. Removing the pelleted components at the end of each stage of centrifugation
If you have a small organelle does the speed of the centrifugation need to be slow or fast? What about large organelles? Why?
For small organelles the speed of centrifugation must be fast in order to isolate the small organelles
-for large organelles the speed can be slower than smaller since the larger organelles will separate from the homogenate at slower speeds.
Abundance of organelles in a system is consistent with what of the cell?
The function of the cell
How did the endosomal membrane develop?
As an invationation of the plasma membrane which wrapped around the DNA of cells to form the nucleus.
Why is the nucleus surrounded by a double membrane?
When the endosomal membrane system wrapped around the nucleus it did so w/o breaking the plasma membrane and so the resulting membrane system, which surrounds the nucleus is a double membrane system (two separate lipid bilayers w/a space between them.)
How are RER and SER formed?
From endosomal membrane.
side pockets of the original invaginating membrane
Which organelles are “linked” and collectively called endosomal organelles?
Endoplasmic reticulum and other organelles that are biologically continuous w/the outside face of the plasma membrane
What is the theory of endosymbiosis?
It’s believed that a prokaryotic organism may have engulfed another one that is capable of conducting specialized forms of respiration such as oxidative respiration. Instead of destroying the engulfed cell, the two formed some sort of mutually beneficial or symbiotic relationship
Why does mitochondria have a double membrane system?
when mitochondria was engulfed by predatory cel it retained its original cell membrane and the membrane produced by the predatory cell
Why does mitochondria have what is called an almost third type of membrane?
mitochondria has a double membrane system. The inner mitochondrial membrane has become highly folded and specialized aka it almost a third type of membrane
Which organelles were thought to form from an ancient endosymbiosis relationship?
chloroplast, mitochondria
What is the third membrane of chloroplast called? Why does choroplst have a third membrane and how did it develop?
Thylakoid membrane
-the inner membrane of chloroplast when it was engulfed by predatory cell progressively invaginated (just like mitochondria’s) the invagination of the inner membrane appears to have eventually become complete resulting in the formation of the third membrane system.
Which organelles are double/triple membrane ?
nucleus, mitochondria, chloroplast
Which organelles have single membranes? Why are they single?
Thought to have arisen as out-pockets of the other membrane systems and are surrounded by only a single lipid bilayer
- Endosomal organelles
- RER
- SER
- Golgi stacks
- Secretory vesicles
- lysosomes
- vacuoles in plants
- peroxisomes
- glyoxysomes in plants
Which organelles are endosomal?
RER, SER, Golgi stacks, Secretory vesicles, lysosomes, vacuoles in plants
Explain the movement of proteins
RER to
golgi apparatus to
secretory vesicles to
fuse back w/plasma membrane
What are the three mechanisms of protein movement?
Gated transport: movement of proteins from one cell compartment to another through a regulated hole or pore of some kind (e.g movement of proteins in an out of the NUCLEUS is an example of this)
Transmembrane transport: movement of a molecule through a membrane or across it
Vesicular transport: is the process where small membrane bound packages are pinched off of one membrane system and then fuse with another
Movement of proteins in and out of the nucleus is an example of what type of mechanism?
Gated transport
Explain vesicular transport. What happens to the orientation of the membrane of each compartment during vesicle fusion?
The creation of small membrane bound packages of material by one membrane system and fusion w/another
The orientation of the bilayer and the direction of insertion of transmembrane proteins are preserved during vesicle fusion
What happens to the contents of a membrane system that fuses with another?
The contents of the internal space is transferred along w/lipids in the fusing membrane and any membrane associated proteins.
MEMBRANES AND PROTEINS TRAVEL TOGETHER
The ER and other organelles is biologically continuous with what?
the outside face of the plasma membrane even though there’s no longer a physical connection between them
What is meant by equivalent spaces?
Organelles that transfer proteins in a vesicle to another target cell is said to have equivalent spaces. Lumen of donor=lumen of target. The relationship among the components of the donor organelle and the target organelle are the same before and after the fusion event. AKA membrane systems can be said to be equivalent.
Electron microscopy allows us to see what?
1) study organelle morphology
2) analyze composition and function of the organelle system
3) evaluate the prevalence of organelle systems in different cells under different experimental conditions
What does vesicular transport involve?
the creation of small, membrane-bound packages of material by one membrane system and fusion with another
Do all organelle systems have the same inner and outer faces in their bilayers?
no, all the organelle systems have bilayers with distinct inner and outer faces.
Which organelles are said to have equivalent spaces? Why?
- perinuclear space
- ER lumen
- Golgi lumen,
- Endosomal lumen
- extracellular space
any organelle that transfers materials via vesicular transport is said to have equivalent spaces b/c their membranes have to fuse together and material found in one can be found in others.
