Transcription andGene Expression - Mrs. Winegar's World - AP ...

Transcription andGene Expression - Mrs. Winegar's World - AP ...

Transcription and Gene Expression 2.7 & 7.2 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 Deduce the DNA base sequence for the mRNA strand Skills: 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 The promoter as an example of non-coding DNA with a function Application: Analyze changes in the DNA methylation patterns Skill:

I. Central Dogma of Biology A. First stated by Crick 1958 B. DNA is used to make RNA which is used to make proteins II. Transcription

A. Genes sections of DNA that code for proteins B. 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 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 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 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 we have pre-mRNA! Transcribe this sequence of DNA in to mRNA AT T G T C T C C AA G A G T T T C G AA G C G A C C

III. Post-transcription modification A. Sections of the pre-mRNA are removed 1. Spliceosomes composed of small nuclear RNAs (snurps) 2. Results in introns being removed, and exons being joined to form mature mRNA 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 (modification of central dogma) C. Poly A Tail on 3 end and 5 cap (GTP) prevent degradation of mRNA by exonucleases in the nucleus Discuss:

If a protein is coded for by a gene, how can a human have 25,000 genes but over 100,000 proteins? IV. Gene expression A. Methylation methyl groups (CH3) packed around genes

to block transcription 1. Example Barr bodies in females (1 X chromosome inactivated) B. Protein regulation 1. Transcription factors help RNA

polymerase bind to promoter 2. Transcription activators loop DNA to bring activator closer to promoter

3. Repressors/Silencers bind to DNA to block transcription C. 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

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