UNIT 4b-Gene Expression

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Genes are pieces of DNA that code for specific traits according to the sequence of the nitrogenous bases. The majority of genes are expressed as the proteins they encode.SO it works like this: The recipe for each of the genetic traits/proteins is carried in the sequence of the bases on the DNA strand. The DNA is precious to the cell and cannot be tied up to for the amount of time necessary for the protein synthesis process....

1) TRANSCRIPTION: messenger RNA (mRNA) comes into the nucleus. The DNA strand unzips and a strand of complimentary mRNA forms along the template DNA.

The process occurs in two steps:
  • Transcription = DNA RNA
Step 1: DNA unwinds/"unzips" as the Hydrogen Bonds Break.
Step 2: The free nucleotides of the RNA (aided by RNA Polymerase) pair with complementary DNA bases (URACIL is the base that pairs with ADENINE as there is no THYMINE in RNA). Just as the DNA created in replication, complementary mRNA is created from the 5' → 3'
Step 3: mRNA (messenger RNA) sugar-phosphate backbone forms. (Aided by RNA Polymerase.)
Step 4: Hydrogen bonds of the untwisted RNA+DNA "ladder" break, then the mRNA leaves the nucleus through the small nuclear pores.
This mRNA then goes to the cytoplasm to continue on to protein synthesis or TRANSLATION.

2) TRANSLATION: mRNA moves out of the nucleus and to the cytoplasm to the ribosomes (remember- the protein factories of the cell) to create amino acid chains from the recipe sequence on the mRNA.

  • Translation = RNA protein



Put these steps in order as they occur in the entire process of gene expression:

a) RNA polymerase travels along the DNA gene bases transcribing the code to mRNA
b) tRNA "clovers" move in to match their anticodon to the mRNA codons and bring with them specific amino acids associated with their anticodon
c) mRNA breaks off of the DNA and leaves the nucleus
d) the protein is finished and the gene is expression is complete
e) DNA unzips at a specific gene location
f) mRNA enters the ribosome
g) amino acids are linked in a long strand

Transcribe and Translate a GENE!!!



Questions to ponder:
1) What is eugenics?
2) Do we own our DNA?
3) Does your view of eugenics change if the traits being selected are with respect to disease rather than cosmetics?
4) Summarize these three court cases:

5) What is your reaction to this link and the information provided?