D. RNA – ribonucleic acid 1. RNA Structure a] ribose sugar + phosphate + nitrogenous base but Uracil replaces Thymine (Almost always) b] single stranded molecule c] much shorter than DNA 5’P—sugar—P—sugar—P—sugar—P—sugar—P—sugar—3’ l l l l l A C G C U

2. features unlike DNA, RNA can survive in the cytoplasm if properly prepared Consider…..if a student loses their notes, they can always make another copy from the textbook. However, if they lose the textbook……they have problem.

3. types of RNA a. mRNA – messenger RNA - varies in length, but always much shorter than DNA - carries the coded message for protein building from the DNA to the ribosomes

b. tRNA – transfer RNA - very short, bases only - acts to transport the amino acids to the mRNA at the ribosomes

c. rRNA – ribosomal RNA - varies in length, but shorter than mRNA - binds the large and small subunits to form a functional ribosome

E. TRANSCRIPTION 1. Initiation a. RNA polymerase binds to a specific region of the DNA that is A-T rich and so easy to separate b. the DNA is unwound and the two strands are separated – the process of copying the information from a piece of DNA to make RNA [usually mRNA]

2. Elongation a. only the 3’ to 5’ strand is used  template strand b. the unused strand [5’ to 3’] is called the coding strand G C C T A A T C G T C A C T G C A A C T 3’—C G C A T T G C G T A A C G—5’ 5’—G C G T A A C G C A T T G C—3’ G A C G G A T T A G C A G T G A C G T T

c. free floating nucleotides A, U, C & G are H—bonded to their complimentary basesby RNA polymerase d.RNA polymerase moves along the DNA unwinding & separating as it goes while the DNA winds back up behind it e. the mRNA hangs free off the side of the DNA strand attached only at a few base pairs G C C T A A T C G T C A C T G C A A C T 3’—C G C A T T G C G T A A C G—5’ 5’—G C G T A A C G C A T T G C—3’ G A C G G A T T A G C A G T G A C G T T 5’ G C G U A A G C GG A U U A G C Coding strand Template strand RNA polymerase

3. Termination a.RNA polymerase encounters a sequence of bases at the end of the gene called a terminator sequence b. this results in RNA polymerase and the primary transcript being released from the DNA

Note: only a small piece of the total DNA is transcribed

4. Post-transcriptional modifications a. a 5’ CAP is added to the mRNA to protect it from cytoplasmic enzymes b. a poly-A tail of 200 or so adenines is added by poly-A- polymerase to the 3’ end INTRONEXON INTRON EXONINTRONEXON CAP poly-A tail

e. in eukaryotes spliceosomes remove all the non-coding regions [introns] and ligate the coding regions [exons] to form the mature mRNA transcript c. this results in the mRNA transcript being ready for release from the nucleus INTRONEXON INTRON EXONINTRONEXON CAP poly-A tail EXON CAP poly-A tail d. in prokaryotes, [bacteria] that is all of the processing

INTRONEXON INTRON EXONINTRONEXON INTRONEXON INTRON EXONINTRONEXON CAP poly-A tail EXON CAP poly-A tail primary transcript mRNA transcript mature mRNA transcript

categoryDNA replicationRNA transcription direction strands copied amount copied # of enzymes bonds broken bonds formed 3’  5’ leading & laggingtemplate only all of DNAsmall piece only total of 6only one hydrogen bonds & covalent bond hydrogen bonds & covalent bond 5. Comparing DNA replication with RNA transcription