Gene Expression Honors Biology

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.

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

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 )

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)

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

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

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

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

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

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

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