gene expression. what is gene expression? expression can be defined as: –shown –manifested...

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)