This document summarizes key aspects of DNA transcription. It describes the three main types of RNA - rRNA, tRNA, and mRNA. Transcription is the process by which RNA is made from a DNA template in order to convey genetic information from DNA to ribosomes for protein synthesis. During transcription, RNA polymerase binds to promoter regions and synthesizes a complementary RNA strand in the 5' to 3' direction until reaching a terminator region. The RNA codons formed during transcription correspond to DNA triplets. RNA processing occurs after transcription and involves splicing out introns and joining exons to form mature mRNA.

1. 3.5 & 7.3DNA Transcription IB Biology

2. Types of RNA: rRNA: ribosomal RNA Major component of ribosomes tRNA: 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

3. Transcription The process by which RNA is made from a DNA template Purpose: to read the DNA, one gene at a time. RNA polymerase starts transcription at promoters and end at terminators Complimentary RNA strand is formed RNA is assembled in the 5’ 3’ direction Bubbles open- instead of unzipping

4. 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.

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

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

7. 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

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

9. New…the “Middle” Step Transcription - beginning Middle = mRNA processing Translation - end

10. RNA processing Post-transcriptional Introns- non-coding sequences are removed Exons- coding sequences are spliced together

11. 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 TU.

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