1. 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. 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. 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

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

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

6. E. TRANSCRIPTION
– the process of copying the information from a piece of DNA to make RNA [usually mRNA]
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

7. 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

8. RNA polymerase Template strand Coding strand
5’ G C G U A A G
C GG A U U A G C
Template 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
Coding strand
c. free floating nucleotides A, U, C & G are H—bonded to their complimentary bases by RNA polymerase
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

9. 3. Termination
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

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

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

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

13. mature mRNA transcript
INTRON
EXON
primary transcript
INTRON
EXON
CAP
poly-A tail
mRNA transcript
EXON
CAP
poly-A tail
mature mRNA transcript

15. 5. Comparing DNA replication with RNA transcription
category DNA replication RNA transcription
direction
strands copied
amount copied
# of enzymes
bonds broken
bonds formed
3’  5’
3’  5’
leading & lagging
template only
all of DNA
small piece only
total of 6
only one
hydrogen bonds
hydrogen bonds
hydrogen bonds
& covalent bond
hydrogen bonds
& covalent bond

16. Textbook work to consolidate your knowledge
pg 249 Section 5.3 questions
# 8, 6, 2, 3, 11