1. RNA and Transcription Lecture #19 Honors Biology Ms. Day

2. Gene expression DNA contains…
information in a specific sequence (order) of nucleotides along 2 DNA strands
Leads to specific traits
Gene expression includes two stages
Transcription: DNA  RNA
“transcribe” = to copy into another form
Translation: RNA  polypeptide
“translate” = to change into another language

3. THINK: Translation happens “LATER”

4. What are the characteristics of RNA?
Ribose Nucleic Acid
Single stranded
Made of sugars (called ribose), phosphate groups and nitrogen bases
Backbone= alternating ribose sugar/phosphates held together by PHOSPHODIESTER BONDS
Made of RNA nucleotides
Contains bases:
(A) Adenine
(G)Guanine
(C) Cytosine
(U) Uracil (replaces Thymine)

8. Brings message from DNA (DNA instructions) to ribosome to make protein
Type of RNA
Function Job
Picture
mRNA
(messenger RNA)
Brings message from DNA (DNA instructions) to ribosome to make protein
tRNA
(transfer RNA)
Transfers/moves amino acids to ribosomes
rRNA
(ribosomal RNA)
Makes up ribosomes along with proteins

9. The Ribosome Part of cell where translation (protein synthesis) occurs
Where proteins are actually made

10. Basic Principles of Transcription and Translation
Transcription (uses mRNA)
the synthesis of RNA from DNA
Produces messenger RNA (mRNA)
Occurs in the nucleus of eukaryotes and nucleid region of prokaryotes
Translation (uses mRNA, tRNA, rRNA)
actual synthesis of a polypeptide
mRNA  polypeptide  protein
Occurs on ribosomes

11. Transcription & Translation
DNA
mRNA
Ribosome
Polypeptide

12. How is Protein Made?
Cells are controlled by a cellular chain of command
DNA RNA protein
Called the “Central dogma of biology”
What are proteins made out of?
Amino acids
There are 20 different amino acids
building blocks of proteins
All living things use the same 20 amino acids to make proteins!!!

13. The Genetic Code
It’s a table used that TRANSLATES RNA nucleotides (or mRNA “words”) into one of the 20 amino acids
3 letter mRNA “word” = 1 amino acid
There are 4 different RNA “letters” that can be used to make “words”  A, U, C, and G

14. Codons: Triplets of Bases
nonoverlapping base triplet is a codon
3 letter mRNA “words” = codon
FOUND ONLY ON mRNA
Codons must be read in the correct order
For specified polypeptide to be produced
Always read in the 5’  3’ direction

15. THE GENETIC CODE 64 CODONS TOTAL

16. During transcription, a gene determines the sequence of bases along length of mRNA.
Figure 17.4
DNA
molecule
Gene 1
Gene 2
Gene 3
DNA strand
(template)
TRANSCRIPTION
mRNA
Protein
TRANSLATION
Amino acid A C G T U
Trp
Phe
Gly
Ser
Codon 3 5

17. mRNA is made by RNA polymerase breaks DNA strands apart
Transcription
DNA  RNA
mRNA is made by RNA polymerase
breaks DNA strands apart
breaks H bonds btw bases
hooks together RNA nucleotides

18. Transcription
Follows same DNA base-pairing rules, except in RNA, uracil substitutes for thymine
A = U (T on DNA = A in RNA)
C = G

19. Synthesis of an RNA Transcript
Initiation
DNA strands unwind
RNA polymerase binds DNA
Elongation
RNA polymerase makes mRNA by reading DNA’s message
Termination
mRNA transcript (mRNA) is released
RNA polymerase detaches from the DNA

20. Transcription Animation
Another good animation