1. Transcription and Gene Expression
2.7 & 7.2

2. Essential Idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.
2.7
DNA replication, transcription and translation
Understandings:
Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase
Skills:
Deduce the DNA base sequence for the mRNA strand

3. Essential Idea: Information stored as a code in DNA is copied onto mRNA.
7.2
Transcription and Gene Expression
Understandings:
Transcription occurs in a 5’ to 3’ direction
Nucleosome help to regulate transcription in eukaryotes
Eukaryotic cells modify mRNA after transcription
Splicing of mRNA increases the number of different proteins an organism can produce
Gene expression is regulated by proteins that bind to specific base sequences in DNA
The environment of a cell and of an organism has an impact on gene expression
Application:
The promoter as an example of non-coding DNA with a function
Skill:
Analyze changes in the DNA methylation patterns

4. I. Central Dogma of Biology
First stated by Crick – 1953
DNA is used to make RNA which is used to make proteins

5. II. Transcription Genes – sections of DNA that code for proteins
Only 1 strand is transcribed
1. Sense strand – NOT transcribed - carries same sequence as resulting mRNA (but with Ts instead of Us)
2. Anti-sense strand – Transcribed - complimentary to sense strand and to mRNA

6. C. 3 segments of the gene 1. Promoter – short sequence of bases that is not transcribed, but indicates where transcription should start a. RNA Polymerase – unzips DNA and attaches at promoter, creating a transcription bubble

7. 2. Transcription unit – section of the DNA that codes for RNA a
2. Transcription unit – section of the DNA that codes for RNA a. Free-floating RNA nucleotides pair up with complimentary DNA b. New nucleotides always add on to the 3’ end (build 5’ 3’) c. RNA Polymerase bonds RNA nucleotides together

8. 3. Terminator – sequence of nucleotides that cause the mRNA to detach from the DNA
a. In eukaryotes, transcription goes past the terminator for a while and then detaches – now have pre-mRNA

9. III. Post-transcription modification
Sections of the pre-mRNA are removed
Spliceosomes – composed of small nuclear RNAs (snurps)
Results in introns being removed, and exons being joined to form mature mRNA

10. B. Alternative Splicing - different pieces may be introns at different times, and exons may be rearranged - means 1 gene can code for more than one protein

11. IV. Gene expression
A. Methylation – methyl groups (CH3) packed around genes to block transcription 1. Example – Barr bodies in females (1 X chromosome inactivated)

12. Protein regulation
1. Transcription factors – help RNA polymerase bind to promoter
2. Transcription activators – loop DNA to bring activator closer to promoter

13. 3. Repressors/Silencers – bind to DNA to block transcription

14. Environmental factors can enhance or suppress gene expression
1. Pollutants – stimulate expression of genes that cause asthma
2. Fur color in Himalayan rabbits
3. Hydrangea color and soil pH