Chapter 8.4: Differences in Gene Expression Between Prokaryotes and Eukaryotes

Question 1

What is the difference between eukaryotes and prokaryotes in terms of promoters?

Answer 1

Prokaryotes: Promoters are not wound up in chromatin

Eukaryotes: Transcription initiation requires promoters to be cleared of chromatin to allow access to RNA polymerase

Question 2

What is the difference between eukaryotes and prokaryotes in terms of exons and introns?

Answer 2

Prokaryotes: Genes are not divided into exons and introns

Eukaryotes: The DNA of a gene consists of exons separated by introns; the exons are defined by posttranscriptional splicing, which deletes the introns.

Question 3

What is the difference between eukaryotes and prokaryotes in terms of coupling?

Answer 3

• In Eukaryotes, the Nuclear Membrane Prevents the Coupling of Transcription and Translation
o In prokaryotes, coupling is possible because transcription extends mRNAs in the same 5’ to 3’ direction as the ribosome moves along the mRNA

Question 4

What is the difference between eukaryotes and prokaryotes in terms of RNA polymerase?

Answer 4

Prokaryotes: One RNA polymerase consisting of five subunits

Eukaryotes: Several kinds of RNA polymerase, each containing 10 or more subunits; different polymerases transcribe different genes

Question 5

What is the difference between eukaryotes and prokaryotes in terms of translation initiation?

Answer 5

o In prokaryotes, translation begins at a ribosome binding site on the mRNA
o In eukaryotes, the small ribosomal subunit first binds to the methylated cap at the 5’ end of the mature mRNA and then migrates through the 5’ UTR to the initiation site

Question 6

What is the difference between eukaryotes and prokaryotes in terms of primary transcripts?

Answer 6

Prokaryotes: Primary transcripts are the actual mRNAs; they have a triphosphate start at the 5’ end and no tail at the 3’ end

Eukaryotes: Primary transcripts undergo processing to produce mature mRNAs that have a methylated cap at the 5’ end and a poly-A tail at the 3’ end

Question 7

What is the difference between eukaryotes and prokaryotes in terms of initiator tRNA?

Answer 7

Prokaryotes: Unique initiator tRNA carries formylmethionine

Eukaryotes: Initiator tRNA carries methionine

Question 8

What is the difference between eukaryotes and prokaryotes in terms of mRNA start sites?

Answer 8

Prokaryotes: mRNAs have multiple ribosome binding sites (RBSs) and can thus direct the synthesis of several different polypeptides

Eukaryotes: mRNAs have only one start site and can thus direct the synthesis of only one kind of polypeptide

Question 9

What is the difference between eukaryotes and prokaryotes in terms of ribosomal subunit binding?

Answer 9

Prokaryotes: Small ribosomal subunit immediately binds to the mRNA’s ribosome binding site

Eukaryotes: Small ribosomal subunti binds first to the methylated cap at the 5’ end of the mature mRNA and then scans the mRNA to find the ribosome binding site

Question 10

Define polycistronic

Answer 10

they contain the information of several genes each of which can be translated independently starting at its own ribosome binding site

Question 11

What is the difference between eukaryotes and prokaryotes in terms of transcription initiation?

Answer 11

Prokaryotes: DNA sequences needed for transcription initiation are located close to the promoter

Eukaryotes: Enhancer sequences far from the promoter are often needed for transcription initiation

Question 12

Define monocistronic

Answer 12

contains the information for translating only a single kind of peptide