Transcription and Translation Haileybury Astana IB Biology

Transcription and translation

Types of RNA Messenger RNA is synthesised in the nucleus during transcription and carries the genetic code to the rough endoplasmic reticulum where translation occurs. Transfer RNA attached to an amino acid. tRNA transfers specific amino acids to a polypeptide chain during the ribosomal site of protein synthesis during translation. Ribosomal RNA consisting of small and large subunits. rRNA translates mRNA into amino acid peptide sequences known as proteins.

The synthesis of RNA on a DNA template Transcription The synthesis of RNA on a DNA template

Messenger RNA Carries the genetic information from the nucleus to the site of protein synthesis (RER) Three bases form a codon Each codon is TRANSLATED into an amino acid

Transcription DNA acts as a template (antisense strand) Synthesis of a mRNA molecule occurs in a 5’-3’ direction according to complimentary base pairing with the antisense strand. The mRNA molecule has the same sequence as the sense strand except thymine is replaced by uracil. The process is catalysed by RNA polymerase. Introns are removed from the mRNA before it passes through the nuclear pores to the cytoplasm. Copy figure 30.12 on page 494 of Biology – A Functional Approach by MBV Roberts

Sense and antisense strands The SENSE strand is the coding strand. Its nucleotide sequence is the same as the mRNA except thymine is replaced by uracil. The ANTISENSE strand is the template strand. The sense strand may not be the same for all genes! 3’ – 5’ direction

Transcription Explain the process of transcription leading to the formation of mRNA.(8)

Explain the process of transcription leading to the formation of mRNA

unwinding the DNA strands; binding RNA nucleotides; Transcription is the synthesis of a mRNA molecule from a DNA template/gene; RNA polymerase; unwinding the DNA strands; binding RNA nucleotides; to the antisense strand of DNA; mRNA assembled in a 3’-5’ direction; using complementary pairing/A-U and C-G; mRNA detaches from the template and DNA rewinds; RNA polymerase detaches from the DNA; many RNA polymerases can follow each other; mRNA leaves the nucleus via nuclear pores. 8 max

The Genetic Code (codons)

The Genetic Code (codons)

TRANSLATION

Question: complete the sequences.... Sense DNA 5’ .... A T G C 3’ Anti-sense Polypeptide Anti-codons tRNA Codons ‘ mRNA

Question: complete the sequences.... Sense DNA 5’ .... A T G C 3’ Anti-sense Ser Met Ala Try Thr Polypeptide Anti-codons A G U tRNA Codons 5‘ A U G C 3‘ mRNA