Question

Describe the process by which the information in a gene is transcribed and translated into a protein. Correctly use these words in your description (and highlight them as bold text in your submission):

• tRNA
• amino acid
• start codon
• transcription
• mRNA
• gene
• codon
• RNA polymerase
• ribosome
• translation
• anti-codon
• peptide bond
• stop codon

Answer 1

Transcription is a process in which DNA is transcribed into RNA.It is first step of gene expression. RNA polymerase is main transcription enzyme.RNA polymerase uses a ssDNA template to synthesize complemetary strand of RNA.When RNA polymerase binds to promoter region of template strand near beginning of gene,transcription begins.One strand of DNA acts as template strand while other acts as coding strand.Termination occurs when termination sequences are transcribed.

In eukaryotes,transcription factors bind first,helping RNA polymerase.Eukaryotes have TATA box which is recognized by the transcription factors and allows RNA polymerase to bind.Next is the process of elongation.During this,RNA polymerase walks along template strand and adds a complementary nucleotide to the 3' end of strand.Transcription terminates via rho termination in prokaryotes.

In eukaryotes,RNA molecules must be processed after transcription.They are spliced and introns (non coding segments) are removed and have a 5' cap and poly-A tail on their ends.

Translation is process of conversion of mRNA to polypeptide chain.The codons of mRNA are read by transfer RNA in 5' to 3' direction.Each tRNA has anticodon, a set of three nucleotides that binds to matching mRNA codon through base pairing.The other end of tRNA carries amino acid that's specified by the codon.Initiation of translation occurs by forming a initiation complex.It comprises of mRNA,ribosome and tRNA carrying amino acid usually methionine.

tRNA carrying methionine binds to small ribosomal unit.tRNA binds to 5' end of mRNA by recognizing GTPCap.Then they walk along in 3' to 5' direction until start codon.Further large subunit joins initiation complex.In prokaryotes Shine Dalgarno sequence is present before start codon.

Chain elongation-When met-tRNA occupies P site of of ribosome( peptide chain),another aminoacyl-tRNA occupies A site.It requires GTP.Enzyme peptidyl transferase forms a peptide bond between methionine and next amino acyl tRNA.In this manner peptide chain is built from N to C terminus.

Chain terminates when stop codon in mRNA enters A site.Ribosomal units dissociate and peptide chain is released in cytoplasm.