Genes – Coding and Flanking Genes are made up of different regions: –Coding region – part that contains information for producing the protein –Flanking regions – the regions before (upstream) and after (downstream) the coding region

Coding Regions Coding regions contains the information for producing the protein It is not a continuous piece of information but is interrupted by many non-coding sequences called introns The coding parts are called exons

Introns and Exons

Flanking Regions Upstream – has an important role in starting the process of protein production – has promoters to which hormones can attach Downstream – this region is about 20 base pairs long and regulates gene action by ending the transcription process

Flanking regions Coding Region Upstream Flanking Region Downstream Flanking Region

RNA There are 3 different types of RNA: Messenger RNA (mRNA) – copies and carries the genetic code from the DNA in the nucleus to the ribosomes Ribosomal RNA (rRNA) – makes up ribosomes which are responsible for assembling the proteins according to the instructions on mRNA Transfer RNA (tRNA) – molecules which carry the amino acids to the ribosomes where they are used to construct the protein

Protein Production 1. Transcription: DNA code on genes copied to mRNA template 2. mRNA is able to pass through nuclear pores and travel to ribosomes 3. Translation: Amino acids are carried to the ribosomes by tRNA where they are assembled into a polypeptide chain according to the mRNA sequence

A closer look

Transcription An enzyme – RNA polymerase attaches to a region of the DNA in the upstream region of the gene that codes for the protein to be produced DNA unravels and separates the two strands of DNA, exposing one template strand The base sequence of the DNA template acts as a guide for the building of a complementary copy of messenger RNA (mRNA)

Transcription RNA polymerase moves along the DNA template as the mRNA strand is formed The resulting mRNA strand is called pre- mRNA

Transcription 3’… A G T C C T A A G T A C G A T C …5’ 5’… U C A _ _ _ _ _ _ _ _ _ _ U A C …3’ If this represents the sequence of bases on the template DNA, what would the sequence of the mRNA strand be? DNA mRNA Remember: RNA compared with DNA is – single-stranded and contains uracil instead of thymine.

Modification Introns are excised from the pre-mRNA 5’ and 3’ ends added

Modification About 30% of human genes are able to form more than one protein due to alternative splicing of the pre- mRNA –some of the introns are kept; or –the order of exons is altered in the final mRNA copy

Translation The modified mRNA exits the nucleus via the nuclear pores Once in the cytoplasm, it is able to attach to the smaller subunit of the ribosome at the 5’ end The mRNA is made up of triplets of nucleotides called codons The codons code for a particular amino acid There are 22 amino acids in total Remember the ribosome itself is made up of ribosomal RNA (rRNA)

Codons

Codons

Translation The corresponding amino acid is brought to the codon on the mRNA at the ribosome by the transfer RNA molecules (tRNA) Transfer RNA

Translation The tRNA attach to the mRNA via the anticodon on the tRNA molecule The anticodon is a sequence of nucleotides which is complementary to the codon on the mRNA On the opposite end, the tRNA carries the amino acid for which the codon corresponds

Translation When two tRNA molecules are adjacent to each other, the larger subunit of the ribosome is able to form a peptide bond between the two amino acids that they carry, releasing the first of the tRNA molecules With each formation of a peptide bond, the mRNA moves along the ribosome and the next tRNA molecule joins This process continues until all of the amino acids coded for by the mRNA are attached to the polypeptide and the STOP codon is reached

Translation What do A, B, C, D, E, and F represent ?

Codons Using this table, write the amino acid sequence coded for by the following mRNA sequence: 5’ AUG ACU GGU UUC GCC GAU AAA GAG GUG AAA CCA… MET THR _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

In Summary FeatureDNARNA Sugar type in nucleotide Possible bases found in nucleotide Usual Structure Double- stranded helix Complete the following table

In Summary IngredientsJob Nuclear DNA mRNA rRNA tRNA RNA polymerase Amino acids Complete the following table