gene expression. what is gene expression? expression can be defined as: –shown –manifested...
TRANSCRIPT
Gene Expression
What is Gene Expression?
Expression can be defined as:– Shown
– Manifested– Articulated
We can determine a person’s genes by what is shown or seen in their body.
What is Gene Expression?
Genes contain the specific information for our body
They are instructions for making proteins Proteins make us:
– look the way we do – function the way we do– develop and grow the way we do– behave the way we do– think the way we do
What is Gene Expression?
All cells within an organism have the same DNA, but not all genes are expressed. – Example: a neuron (nerve cell) will express
genes necessary for nerve function. Therefore, some genes are active (or
expressed) in some cells and some genes are inactivated
How are genes expressed? With the help of RNA
Making Proteins
Step One = Transcription
Step Two = Translation
Transcription
1. Initiation: DNA section with desired gene (the yellow strand) is unzipped by RNA polymerase (the green triangle)
2. Elongation: RNA polymerase adds complementary nucleotides, mRNA strand is made (torquoise strand)
3. Termination: when a stop sequence is reached, mRNA separates from DNA and DNA is re-zipped
RNA Processing Before leaving the
nucleus:– 1. Introns are
removed or spliced - “junk DNA”
– 2. Exons (“expressed”) are put back together
– 3. mRNA leaves the nucleus
See page 204 (fig. 8.26) in your text for more info
Codon
3 letter sequence on mRNA
Carries code for amino acid from DNA
Anti-codon
3 letter sequence on tRNA
Complimentary to mRNA codon
1. Initiation: Ribosome finds the first codon of the gene on mRNA (It’s ‘AUG’ for every gene!)
2. Elongation: ribosome shifts down to next codon; tRNA brings in next amino acid, repeats
3. Termination: ribosome reaches a “stop” codon, protein is released
Translation
Animations
Transcription Translation
How does the cell determine what amino acid goes with the mRNA’s codon?
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
Decoder Chart #1 –
REVIEWMAKE SURE YOU KNOW THE FOLLOWING! What gene expression means 4 Differences between DNA and RNA 3 Types of RNA and their functions Codon and Anticodon How mRNA is processed Steps of Transcription Steps of Translation How to use the ‘decoder chart’(s)