3.5 & 7.3

DNA Transcription

IB Biology

Types of RNA:rRNA: ribosomal RNA

Major component of ribosomestRNA: transfer RNA

Carries amino acids to mRNA An interpreter in translation

mRNA: messenger RNA Encodes genetic info from DNA and convey it to

the ribosomes, where the info is translated into amino acid sequences

TranscriptionThe process by which RNA is made from a DNA templatePurpose: to read the DNA, one gene at a time. RNA polymerase starts transcription at promoters and end at terminatorsComplimentary RNA strand is formedRNA is assembled in the 5’ 3’ directionBubbles open- instead of unzipping

DNA “words”…DNA gives instructions.The instructions are written in a language where words are ALWAYS three base pairs long.

Ex: AAT,CCG,GCA,TTC, etc.Each is called a triplet.

Triplets on DNA make Codons on mRNA

Codon- genetic code made of one triplet of bases.Codons are found on mRNA (messenger RNA)

Formation of mRNA

Creates a “mirror image” of the triplets found on DNA (except TU)mRNA then travels out of the nucleus and toward a ribosome.The formation of RNA is called transcription

New Enzyme- RNA Polymerase

Links together the growing chain of RNA nucleotides during transcription

Uses DNA as template

Similar to DNA polymerase but only facilitates a reaction on one side of the strand

New Players:Promoter- place on gene where RNA polymerase initially attaches.Terminator- place on gene where transcription ends.

New…the “Middle” Step

Transcription - beginningMiddle = mRNA processingTranslation - end

RNA processing

Post-transcriptional

Introns- non-coding sequences are removed

Exons- coding sequences are spliced together

IB Terms: Sense vs. Antisense strands

Sense strand - the “other” strand, not transcribed.

Antisense strand - the one mRNA attaches to, and is complimentary to.

mRNA is similar to the sense strand, except TU.

The code is universalThe same codons are found in all living organisms.