6.10.3 Prokaryotes vs. Eukaryotes: Protein-Making Machinery

Question 1

Prokaryotes and eukaryotes have many physiological differences that lead to differences in protein synthesis. These differences include:

Answer 1

· the presence or absence of a nucleus
· chromosomal differences
· promoter recognition
· method of transcription termination
· ribosome size
· location of transcription and translation
· protein targeting

Question 2

note

Answer 2

• Eukaryotic cells have a double-membrane nucleus that
  encloses chromosomes, and they have membrane-bound organelles.
• Prokaryotes do not have a nucleus or membrane-bound organelles. Instead, prokaryotic cells have a region called the nucleoid, where the chromosome is found.
• The DNA of eukaryotic cells is organized into rod-like
  chromosomes. The DNA of a prokaryotic cell is organized into a single circular chromosome. In general, prokaryotes have less DNA than eukaryotes.
• RNA polymerase depends on transcription factors to
  recognize the promoter. Prokaryotic RNA polymerase
  recognizes the promoter without the aid of transcription
  factors.
• In eukaryotes, transcription proceeds through the stop
  sequence and ends about 10 to 35 nucleotides later. As seen in the diagram on the left, the mRNA that results from eukaryotic transcription extends past the termination signal, an AU-rich region. In prokaryotes, transcription stops at the end of the stop sequence.
• Eukaryotic cells perform both transcription and RNA
  processing in the nucleus. Translation takes place in the
  cytoplasm of the cell.
• Prokaryotic cells, on the other hand, have no nucleus. They perform transcription and translation in the cytosol of the cell. In addition, prokaryotes do not undergo any RNA processing.
• A signal peptide on eukaryotic proteins targets the protein to the ER. A receptor on the ER recognizes the signal. The diagram on the left shows the insertion of a protein (from right to left) into the ER of a eukaryotic cell.
• Because prokaryotes have no membrane-bound organelles, they have no complicated system for targeting proteins into organelles.

Question 3

Translation of eukaryotic mRNA occurs in the __________, while translation of prokaryotic mRNA occurs in the __________.

Answer 3

• cytoplasm, cytoplasm

Question 4

Which of the following is not a part of prokaryotic gene transcription?

Answer 4

• Excision of introns from transcribed RNA

Question 5

Place the following steps in the correct order for eukaryotic transcription and translation.

i. RNA processing
ii. DNA transcription
iii. transport of RNA from nucleus to cytoplasm
iv. formation of ribosome / RNA complex

Answer 5

• ii, i, iii, iv

Question 6

In prokaryotic cells, transcription ends at the terminator sequence, and translation can occur simultaneously with transcription. In eukaryotic cells, which of the following occur after reaching the terminator sequence, and prior to the beginning of translation?

i. addition of a 5′ methylated cap
ii. addition of a 3′ poly A tail
iii. continuation of transcription for 10–35 nucleotides
iv. excision of introns

Answer 6

• i, ii, iii, iv

Question 7

In eukaryotic transcription, the TATA box serves as a __________ where ___________ bind.

Answer 7

• promoter sequence, transcription factors