7.2 Transcription and Gene Expression

GuidanceRNA polymerase adds the 5’ end of the free RNA nucleotide to the 3’ end of the growing mRNA molecule

Understandings- Transcription occurs in a 5’ to 3’ direction- Nucleosomes 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

Applications/Skills

- A: the promoter as an example of non-coding DNA with a function

- S: Analysis of changes in the DNA methylation patterns

http://dnamismatch.com/Test/wp-content/uploads/2013/07/Sense-and-antisense.gif

Transcription: Initiation • RNA polymerase binds to the DNA at the promoter and breaks the

hydrogen bonds between the nitrogenous bases, separating the strands

• A transcription bubble opens

Helicase

Transcription: Elongation

• RNA nucleotides are added (5’3’ direction)

http://geneed.nlm.nih.gov/images/transcription_sm.jpg

Transcription: Termination• Terminator signals for the

release of RNA polymerase

• Transcription stops• RNA detaches• This is the primary mRNA

transcript

mRNA Modification• Primary transcript has introns

removed (splicing)• Exons are put together to form

mature mRNA• These can be arranged in multiple

orders, increasing the number of possible proteins

• 5’ cap and poly-A tail are added to protect the mRNA in the cytoplasm

http://upload.wikimedia.org/wikipedia/commons/a/a6/Rna_splicing.JPG

Control of gene expression• Addition of methyl groups to

segments of DNA/chromosomes

• Transcription factors to help bind RNA polymerase

• Transcription activators that loop DNA between the activator and promoter

• Repressor proteins that prevent transcription of a segment of DNA

http://mcubed.umich.edu/sites/default/files/projects/Slide1_6.jpg

DNA Methylation

http://xarquon.jcu.cz/edu/zbb/prednasky/09nucleus/092function/images/activation3.jpg

Epigenetics

http://www.frontiersin.org/files/Articles/105911/fcell-02-00049-HTML/image_m/fcell-02-00049-g001.jpg