GENE EXPRESSION
Honors
Biology
GENE EXPRESSION: WHAT
 What is gene expression?
 The process of using DNA
code to make protein
GENE EXPRESSION: WHEN
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


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 of f
 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 of f 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
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:
1. Transcription


In nucleus
mRNA is made from DNA
2. Translation


In cytoplasm
Protein is made from mRNA
TRANSCRIPTION
1. DNA section with desired gene is
unzipped by RNA polymerase
2. RNA polymerase adds
complementary nucleotides, mRNA
strand is made
3. When a stop sequence is reached,
mRNA separates from DNA and DNA
is re-zipped
4. mRNA leaves the nucleus
TRANSLATION
1. mRNA finds a ribosome
2. Ribosome scans mRNA for
the start codon (AUG)
3. tRNA with the corresponding
anti-codon carries in amino
acid
4. Ribosome shifts down, reads
the next codon
5. Next tRNA moves into place
6. Amino acids bond together
7. 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
CRASH COURSE
 https://www.khanacademy.org/partner -content/crashcourse1/partner-topic-crash-course-bio-ecology/crash-coursebiology/v/crash-course-biology -111