1. Gene Expression
Honors Biology

2. Objectives
Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.
Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.

3. Gene expression: what What is gene expression?
The process of using DNA code to make protein

4. Gene expression: When When does gene expression occur? All the time!
Example: during development (Hox genes and body plan)
Example: in your cells NOW (such as hormones )

5. Gene expression: Who Who goes through gene expression? All cells
Able to turn on/turn off
Cell type dependent
Muscle cells turn on the genes for what they need (like making actin), turn off the genes for what they don’t (like making lactase)
Cellular need dependent
Turn genes on/off depending on cell’s needs at the time (such as food molecules present needing digestion)
Environmental conditions
Soil pH and hydrangeas (the more acidic the pH, the bluer the flower)

6. Gene Activation Human genes cannot all be active at the same time
If they were, all the cells in our bodies would look the same and have the same function(s)
For specialization to occur, some genes or gene products must be active while others are turned off or inactive

7. Gene expression: Where
Where in the cell does gene expression occur?
Cell structures and their function:
Nucleus
Store DNA
Ribosome
Make protein
Rough endoplasmic reticulum
Ribosomes attach
Vesicles
Transport proteins around cell
Golgi body
Modify/complete protein
Cell membrane
Control entry/exit of materials
Vacuoles
Store materials

8. Gene Expression: Why Why do organisms express genes?
Proteins carry out the essential functions of life through systems of specialized cells

9. Gene expression: How How are genes expressed? 2 steps: Transcription
In nucleus
mRNA is made from DNA
Translation
In cytoplasm
Protein is made from mRNA

10. Transcription
DNA section with desired gene is unzipped by RNA polymerase
RNA polymerase adds complementary nucleotides, mRNA strand is made
When a stop sequence is reached, mRNA separates from DNA and DNA is re-zipped
mRNA leaves the nucleus

11. Translation mRNA finds a ribosome
Ribosome scans mRNA for the start codon (AUG)
tRNA with the corresponding anti-codon carries in amino acid
Ribosome shifts down, reads the next codon
Next tRNA moves into place
Amino acids bond together
Repeats until a stop codon is reached and protein is released

12. How does the cell determine what amino acid goes with the mRNA’s codon?
Codon Table
CODON = AUG
Start in the center and work your way out A U G
Amino acid is methionine
Try finding the amino acid for the codon ‘CUA’
LEUCINE