This question is about mechanisms of gene regulation in eukaryotes. a) List four

Question

This question is about mechanisms of gene regulation in eukaryotes. a) List four gene regulation mechanisms present only in eukaryotes and not prokaryotes. b) Select one of the eukaryotic mechanisms from part (a) and describe it in detail. Include diagrams if appropriate. c) List two RNA modifications present in eukaryotes. Describe in detail the function of one of these RNA modifications in a living cell. d) Describe the function of two different DNA and/or histone modifications present in eukaryotes.

Explanation / Answer

a) In eukaryotes, the expression of genes can be controlled at various stages. This process involved many steps which can be regulated.

1. Chromatin accessibility : The structure of chromatin is regulated. If chromatin is open or relaxed, the gene is more available for transcription.

2. Transcription : Transcription factor proteins bind to specific DNA sequences in a gene and promote or repress the transcription into an RNA.

3. RNA Processing : Splicing, capping, and addition of a poly-A tail to an RNA molecule can be regulated and therefore it can exit from the nucleus. Different mRNAs may be made from the same pre-mRNA by alternative splicing.

4. Translation : Translation of mRNA can be increased our decreased by regulators. miRNAs sometimes block translation of their target RNAs rather than they being chopped off.

b) The expression of eukaryotic genes is controlled at the level of initiation of transcription. It is controlled by proteins that bind to cis-acting regulatory sequences that control the transcription of adjacent genes and modulate the activity of RNA polymerase. The packaging of DNA into chromatin and its modification by methylation imparts more levels of complexity to the control of eukaryotic gene expression.

c) 1. Addition of 5'Cap and poly-A tail : A group is attached at the beginning (5' end) of a pre-mRNA which is called a cap and another group is attached at the end (3' end) which is called a tail. Both the cap and the tail protect the transcript and help it from getting exported from the nucleus and translated on the ribosomes.

2. RNA Splicing : Specific parts of pre-mRNA called introns are recognized and removed by a protein-and-RNA complex called the spliceosome. The regions of RNA that code for protein are called exons.

Splicing can be regulated so that different mRNAs can contain or lack exons in a process called alternative splicing which allows no more than one protein to be produced from a gene and is important as a regulatory step in determining which functional proteins are produced from gene expression.

d) DNA methylation and histone methylation work together during replication to ensure that specific methylation patterns are passed on to progeny cells.

Covalent modification of carbohydrate residues of membrane proteins takes place which are abubdant on the surface of eukaryotic cells. A carbonyl group is generated after cleavage of these carbohydrates which undergo a chemoselective oxime ligation with aminooxybiotin to produce biotinylated proteins. These are targeted by DNA oligonucleotides. This method is good for DNA coupling to cell surfaces because of its high labeling efficacy, specificity, and low impact on cell viability.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.