W3: 3.1 Organelles

Question 1

What are the advantages of having organelles?

Answer 1

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

Question 2

What fraction of a typical cell is occupied by membrane bound organelles?

Answer 2

half of the cell volume.

Cell: nucleus + cytoplasm

Cytoplasm: cytosol + organelles

Question 3

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?

Answer 3

High lysosomes to aid in neutralization and digestion. Some levels of Smooth ER since SER is responsible for detoxification.

Question 4

Which organelles have double membranes and what does this indicate with regard to their origins?

Answer 4

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

Question 5

What organelle has a three membranes? and what is the origin of each?

Answer 5

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)

Question 6

What is one way to analyze composition of an organelle system?

Answer 6

Centrifugation strategy

Question 7

Why are organelles important?

Answer 7

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

Question 8

explain how centrifugation organizes organelles?

Answer 8

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

Question 9

If you have a small organelle does the speed of the centrifugation need to be slow or fast? What about large organelles? Why?

Answer 9

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.

Question 10

Abundance of organelles in a system is consistent with what of the cell?

Answer 10

The function of the cell

Question 11

How did the endosomal membrane develop?

Answer 11

As an invationation of the plasma membrane which wrapped around the DNA of cells to form the nucleus.

Question 12

Why is the nucleus surrounded by a double membrane?

Answer 12

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.)

Question 13

How are RER and SER formed?

Answer 13

From endosomal membrane.

side pockets of the original invaginating membrane

Question 14

Which organelles are “linked” and collectively called endosomal organelles?

Answer 14

Endoplasmic reticulum and other organelles that are biologically continuous w/the outside face of the plasma membrane

Question 15

What is the theory of endosymbiosis?

Answer 15

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

Question 16

Why does mitochondria have a double membrane system?

Answer 16

when mitochondria was engulfed by predatory cel it retained its original cell membrane and the membrane produced by the predatory cell

Question 17

Why does mitochondria have what is called an almost third type of membrane?

Answer 17

mitochondria has a double membrane system. The inner mitochondrial membrane has become highly folded and specialized aka it almost a third type of membrane

Question 18

Which organelles were thought to form from an ancient endosymbiosis relationship?

Answer 18

chloroplast, mitochondria

Question 19

What is the third membrane of chloroplast called? Why does choroplst have a third membrane and how did it develop?

Answer 19

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.

Question 20

Which organelles are double/triple membrane ?

Answer 20

nucleus, mitochondria, chloroplast

Question 21

Which organelles have single membranes? Why are they single?

Answer 21

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

Question 22

Which organelles are endosomal?

Answer 22

RER, SER, Golgi stacks, Secretory vesicles, lysosomes, vacuoles in plants

Question 23

Explain the movement of proteins

Answer 23

RER to
golgi apparatus to
secretory vesicles to
fuse back w/plasma membrane

Question 24

What are the three mechanisms of protein movement?

Answer 24

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

Question 25

Movement of proteins in and out of the nucleus is an example of what type of mechanism?

Answer 25

Gated transport

Question 26

Explain vesicular transport. What happens to the orientation of the membrane of each compartment during vesicle fusion?

Answer 26

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

Question 27

What happens to the contents of a membrane system that fuses with another?

Answer 27

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

Question 28

The ER and other organelles is biologically continuous with what?

Answer 28

the outside face of the plasma membrane even though there’s no longer a physical connection between them

Question 29

What is meant by equivalent spaces?

Answer 29

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.

Question 30

Electron microscopy allows us to see what?

Answer 30

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

Question 31

What does vesicular transport involve?

Answer 31

the creation of small, membrane-bound packages of material by one membrane system and fusion with another

Question 32

Do all organelle systems have the same inner and outer faces in their bilayers?

Answer 32

no, all the organelle systems have bilayers with distinct inner and outer faces.

Question 33

Which organelles are said to have equivalent spaces? Why?

Answer 33

• 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.