Cell Compartmentalization

Question 1

What are organelles?

Answer 1

Discrete structures in cells that are adapted to perform one or more vital functions
* Are efficient since they are specialized for a limited range of functions - good at some things, does not have to be good at everything
* In some cases, a single membrane or a double membrane encloses the fluid contents of an organelle
* In other cases the organelle is a solid structure, composed of proteins or RNA, and it is not membrane-bound

Question 2

Which organelles have no membrane?

Answer 2

Proteosomes
Ribosomes
Centrioles
Microtubules
Nucleoli

Question 3

Which organelles have a single membrane?

Answer 3

Vesicles and vacuoles
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatus
Lysosomes

Question 4

Which organelles have a double membrane?

Answer 4

Mitochondria
Amyloplasts
Nuclei
Chloroplasts
Chromoplasts

Question 5

What are not considered to be organelles?

Answer 5

• Cells walls are outside the plasma membrane and are extracellular structures
• Cytoskeletons consist of narrow protein filaments spread through much of the cell so are not discrete enough to be an organelle
• Cytoplasm is not a discrete structure as it includes many different structures and performs many functions

Question 6

Advantages of eukaryotic cells being compartmentalized?

Answer 6

Efficiency of metabolism - Enzymes and substrates for a particular process can be localized and much more concentrated.
Toxic/damaging substances can be isolated - Substances harmful to the cell can be contained within the membrane of an organelle. (e.g., digestive enzymes in lysosomes)
Localized conditions - pH and other factors can be kept at optimal levels. Ideal conditions for a particular process can be maintained in certain areas of the cell.
Numbers and locations of organelles can be changed - Organelles with their contents can be moved around within the cell and changed dependent on the requirements of the cell.

Question 7

Properties of the nucleus?

Answer 7

Contains genetic information in the form of chromosomes (DNA and associated histone proteins)
- Uncoiled chromosomes are referred to as chromatin - they stain a dark colour and are concentrated at the edges of the nucleus
- The nucleolus is a small, dense region inside the nucleus where proteins and ribosomal

RNA join to form the subunits of ribosomes.
mRNA is transcribed in the nucleus (prior to use in protein synthesis in the cytoplasm) mRNA leaves the nucleus via the pores
(DNA is too large to move through the pores)

Question 8

The Advantage of Separating the Nucleus and the Cytoplasm

Answer 8

Keeping the chromosomes inside the nucleus keeps the chromosomes (genetic material) safe
In prokaryotes (no nucleus), the DNA and ribosomes come together in the cytoplasm and protein synthesis can occur immediately
In eukaryotes, the separation allows for the mRNA to be modified in the nucleus before exiting into the cytoplasm for the next process in protein synthesis to begin