Transcription: DNA  mRNA

Remember… DNA is the genetic code and is found in the nucleus. The genetic code is used to make proteins, which you are made of. But…proteins are made on the ribosomes.

Remember… nucleus DNA

So how does the code get from the nucleus to the ribosomes? RNA

Structure of RNA RNA differs from DNA in 3 ways: RNA is a single strand. RNA has the sugar ribose. RNA has the nitrogen base uracil instead of thymine.

Structure of RNA Single strand

3 Types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)

mRNA mRNA delivers the instructions for making a protein from the nucleus to a ribosome in the cytoplasm.

Transcription DNA cannot leave the nucleus. However, its code can be copied by mRNA and taken out of the nucleus.

Transcription First, the enzyme RNA polymerase binds to DNA and separates the DNA strands.

Transcription Then, a strand of mRNA is transcribed (copied) using one DNA strand as a template.

Transcription To copy the code, RNA nucleotides are added using the base pairing rules for DNA, except that in RNA, uracil pairs with adenine. (G – C, A – U)

Practice Transcribing Let’s practice transcribing a strand of DNA: DNA: G T C A G A T A C mRNA:________________ C A G U C U A U G

Transcription Animation http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

RNA Processing The sequences that code for proteins are called exons because they are “expressed” in the synthesis of proteins. The introns do not code for proteins and are cut out of the mRNA sequence before it leaves the nucleus. The remaining exons are spliced together.

After Transcription The single strand of mRNA leaves the nucleus and enters the cytoplasm. It will then travel to a ribosome where its code will be translated into a protein.

After Transcription

Transcription & Translation In the nucleus In the cytoplasm (ribosome)