LecTop2: Bacterial Cell structure & function

Question 1

Why does Pace say that Prokaryote is an outdated term?

Answer 1

Because PRO - means Pre…

But PROkaryotes are NOT precursors to more complicated organisms (Eukaryotes).

Question 2

What method was used to construct the current version of the Universal Phylogenetic Tree?
-Why are Viruses not included in this phylogenetic tree?

Answer 2

Genetic assessment using the 16s rRNA.

• By sequencing the 16s rRNA it was found that Archaea are actually more closely related to Eukaryotes than Prokaryotes.
• Viruses are not included in the tree because they do not have 16s rRNA, in fact they don’t have any rRNA b/c they can’t carry out transcription and only have either DNA or RNA but NEVER both.

Question 3

Eukaryotes (E) vs. Prokaryotes (P): For each topic, describe in E and P.

1. Organelles
2. Nuclear Membrane
3. Membrane Composition
4. Sterols
5. Ribosomes
6. Cell Wall
7. Chromosome
8. RNA life span
9. Presence of Introns
10. Division time

Answer 3

1. E=Organelles Present; P=No true Organelles
2. E=Nucleat Membrane present; P=No nuclear membrane
3. E=Complex; P=Simple phospholipids
4. E=Have sterols & can synthesize; P=No sterols and can’t synthesize.
5. E=80s Ribosome; P=70s Ribosome
6. E=Cell wall not present; P=Peptidoglycan cell wall present
7. E=Multiple, Diploid Chromosomes; P=Single, Circular, Haploid Chromosome.
8. E=Relatively long; P=Relatively short
9. E=Has introns in DNA; P=Colinear transcription, everything in the DNA is transcribed and translated
10. E=Relatively long; P=Relatively short

Question 4

What is an important Eubacteria that is an exception to the two rules that prokaryotes do not have sterols and do have peptidoglycan cell walls? Why do these traits make this Eubacteria so important?

Answer 4

Microplasmas = exception to the absence of sterols and presence of cell wall rules.

• Can’t make sterols but pick up from env’t and incorporate into membrane.
• Important b/c allows them through certain pores allowing them to traverse membranes.
• Microplasmas are important for dentistry because they makes sterilization very difficult and are associated with certain Pneumonia like diseases.

Question 5

What is endosymbiosis? What is a common example?

Answer 5

The process by which two symbiotes eventually form a single, as one absorbs and incorporates the other. The incorporated symbiote is no longer able to live independently.
-Formation of Mitochondria in Eukaryotic cells is thought to have occurred through endosymbiosis. Evidence that suggests this includes the fact that mitochondria, and thus eukaryotes, have 70s ribosomes (note: this is an exception to the rule discussed previously).

Question 6

Name 5 distinguishing characteristics of viruses from Prokaryotes.

Answer 6

1. Contains either DNA or RNA, never both
2. Usually lipids are absent. May contain lipid coat but no true lipid proteins
3. No energy metabolism
4. No transcription or translation
5. Cannot replicate autonomously