Question

Name five common characteristics of protein-coding genes and the regions surrounding them.

Why is prediction of eukaryotic genes more complex than prediction of prokaryotic genes?

Answer 1

The Structure of both eukaryotic and prokaryotic genes involved several nested sequence elements. Each element has a specific function in multi-step process of gene expression. The sequence and lengths of these elements are vary, but the same general functions are present in most genes.

1.DNA is a double stranded molecule typically only one of the strand encodes information that tth RNA polymerase reads to produce protein coding mRNA

2. The protein coding strand runs in the 5' to 3' direction

3. Regulatory sequences are located at the extremities of genes, these sequence regions can either be next to the pramote.

4. The pramoter is located at the 5' end of the gene and is composed of a core pramoter sequence and proximal pramoter sequence. The core pramoter marks the start site for transcription by binding RNA polymerase and other proteins necessary for copying DNA to RNA. The proximal pramoter region binds transcription factor that modify the affinity of the core pramoter of RNA polymerase.

5. Genes may be regulated by multiple enhancer and Silencer sequences that further modify the activity of pramoters by binding activator (or) represssor proteins. Enhancers silencers may be distantly located from the gene, many thousands of basepairs away.

6. The binding of different transcription factors, there fore regulates the rate of transcription initiation at different times and in different cells.

7. Regulatory elements can overlap one another with a section of DNA able to interact with many competing activators and repressors as well as RNA polymerase.

COMPLEXITY OF EUKARYOTIC GENES :

The genes of most eukaryotes are longer and more complex than those of prokaryotes.

The genome of most eukaryotic cells contain not only functional genes but also large amounts of DNA sequence that do not code for proteins. The coding regions are called exons, non-coding regions are called intros. The pressence of large amount of non-coding sequence is a general property of the genomes of complex eukaryotes.

Another factor contributing to the large size of eukaryotic genome is that some genes are repeated many times, where as prokaryotic genes are represented only once in that genome, many eukaryotic genes are present in multiple copies called gene families.

Repetitive DNA sequences : Eukaryotic genome consist of highly repeated non-coding DNA sequences. These sequences some times present in hundreds of thousands of copies per genome. From the above reasons the eukaryotic genome is complex than the prokaryotic genome.