Gene Structure-Prokaryotic vs Eukaryotic

Question 1

The size difference b/w prokaryotic and eukaryotic genomes is due to (2)

Answer 1

1. the presence of more genes in eukaryotes

2. significant differences in genes and genome structure

Question 2

Prokaryotic Genes (6)

Answer 2

• arranged in operons
• can be polycistronic
• mRNA is co-linear w/ DNA
• regulation of gene expression at the level of Tc initiation and control, mediated by trans-acting factors at cis-acting sites
• no post Tc modification of mRNA
• Tc and TL are coupled

Question 3

Eukaryotic Genes (6)

Answer 3

Post Tc processing after synthesis of pre-RNA

• addition of 7 methylguanosine cap to the 5’ end (serves to position the mRNA on the ribosome)
• removal of introns (splicing)
• poly A tail addition via poly A polymerase
• reg elements upstream and downstream of genes
• reg of gene expression is at the level of Tc initiation and control (trans/cis)
• transcripts exported from nucleus before TL

Question 4

Prokaryotic and Eukaryotic Ribosomal RNA genes

Answer 4

rRNA genes in prokaryotes and eukaryotes undergoing processing

• methylation and pseudouridine conversion
• cleavage generates tRNA, 5S, 17S, 25S
• nucleases generate 16S and 23S from 17S, 25S

Question 5

Eukaryotic genes can be very large-The human dystrophin gene

Answer 5

• encodes a protein involved in anchoring the internal cytoskeleton to the ECM
• mutations lead to Duchenne muscular dystrophy
• more than 99% removed by splicing