1. Gene Expression How a gene goes from being “just DNA” to showing up as a trait

2. RNA Ribonucleic acid is similar to DNA in many ways: Nucleotides polymer RNA is also different from DNA: Ribose (instead of deoxyribose) No thymine (instead it has uracil) RNA is a single-strand

3. Codons DNA (and RNA) codes for specific amino acids. There are 20 amino acids, but only four nitrogen bases in each nucleic acid. How can we work the code? Sequences of THREE nitrogen bases will code for an amino acid. These triplets are called “CODONS”.

4. Transcription The DNA “code” is transcribed (copied) as a messenger RNA molecule (mRNA) during transcription. DNA is unwound at one transcription bubble. RNA polymerase adds RNA nucleotides to one side of the DNA molecule, starting at a promoter region or ‘start’ codon. Base pairing is the same except RNA doesn’t have thymine. Uracil takes its place. When it reaches a ‘stop’ codon, mRNA is released and the DNA rewinds. http://www.youtube.com/watch?v=vJSmZ3DsntU

6. Read everything, but copy what’s in black – I’ll put the chart back up for you to complete (or use page 186 in your book) Write the sequence of amino acids that would result from the following sequence: AUGGCAUUUCGAAUG Write out a sequence of nucleotides on a mRNA strand that would code for: Threonine – alanine – glycine – lysine

7. Mutations Chromosomalmutations involve large portions, or even entire chromosomes.

8. Point Mutations occur at just one point in the DNA Substitutions Insertions & Deletions are often referred to as “frameshift” mutations

9. TranslationUsing the information on mRNA to complete a polypeptide Introns are spliced out, mRNA leaves the nucleus and ends up at a ribosome. Ribosomes have 2 subunits. They are made partially of protein, but also contain RNA, called ribosomal RNA (rRNA)

10. rRNA Many types… Complex…. May fold back on itself (bonding with complementary bases)

11. mRNA actually goes through a ribosome

12. Transfer RNA (tRNA) brings the correct amino acid to the ribosome to create a chain of amino acids in the prescribed sequence. tRNA has two important ends: Anticodon, which is a complementary sequence to the mRNA codon End that attaches to an amino acid

14. The ribosome acts as an enzyme and catalyzes the linking of the amino acids together into a polypeptide. -------------------------- There are regions of prokaryotic DNA that allow RNA polymerase access to the gene. These are called “operators”. There are proteins that act as “repressors” when bound to the DNA. Molecules that can remove a repressor are called “inducers”. http://www.youtube.com/watch?v=5bLEDd-PSTQ

15. Example of an inducer: lac operon (page 190-191) When lactose is present around some bacteria, it acts as an inducer. It binds to the repressor so that it falls off the operator. This means transcription can occur. Transcription, followed by translation, will produce the enzyme to break down lactose. When lactose is absent, the repressor binds to the operator so that the genes can’t be transcribed.

16. Enhancers Enhancers are proteins in eukaryotic DNA that increase transcription. Example (pg 193): Steroid hormones like estrogen and testosterone are lipids that bind to enhancer proteins in the nuclear membrane. This binding will stimulate RNA polymerase to transcribe certain genes.

17. Other factors affect eukaryotic gene expression… Eukaryotic DNA is a double helix. Transcription occurs in areas where it has uncoiled, which will change and are different in different types of cells. Gene expression can be regulated at many spots in the process – before or after transcription.