TranscriptionUsing DNA to make RNA

The “Big Picture” Goal•Use DNA to make protein

▫Step 1: Replicate the DNA▫Step 2: Transcribe DNA into RNA▫Step 3: Translate RNA into protein

•Today is all about step 2: TRANSCRIPTION

What Does it Mean to “Transcribe” something?

•The definition in English: to make a written copy of something

•The scientific definition: when RNA polymerase uses one strand of DNA as a template, from which nucleotides are assembled into a strand of RNA in the nucleus

•The “in our own words” definition: using DNA to make RNA

Things to Keep in Mind:•All of our traits come from our genes

•Genes are special segments of our DNA that code for 1000’s of very specific different proteins

•Human DNA is estimated to have 20,000-25,000 different genes!

Transcription•An enzyme called RNA polymerase finds

the beginning of a gene

Gene

DNA Molecule

RNA Polymerase

Transcription•RNA polymerase moves down the gene

and…▫Unwinds the DNA molecule into 2

temporarily separated strands▫“Reads” one of the strands of DNA and

pairs free floating nucleotides to it forming a new single strand of RNADirection of Movement

New single strand of RNA

Transcription•RNA polymerase reaches end of gene

▫RNA polymerase detaches▫New strand of RNA detaches from DNA

template

DNA Molecule

RNA Polymerase

Completed new strand of RNA

RNA•Stands for ribonucleic acid

•Single stranded

•Has a phosphate, ribose sugar, and base in each nucleotide

•Made from 4 different bases: ▫Guanine (G), cytosine (C), adenine (A),

uricil (U)

Practice:•If RNA polymerase were to find a gene,

move down the gene unwinding the double stranded DNA, read the template strands to be this:

A G G C T A T T G C A

what would the sequence of the new strand of RNA be?

Practice:•If RNA polymerase were to find a gene,

move down the gene unwinding the double stranded DNA, read the template strands to be this:

A G G C T A T T G C A

what would the sequence of the new strand of RNA be?

U C C G A U A A C G U

Similarities Between Replication and Transcription

•Both involve enzymes

•Both pair matching bases together

•Both occur in the nucleus

Differences BetweenReplication and TranscriptionReplication Transcription

• Copies ENTIRE strand of DNA

• Copies BOTH sides of DNA

• Adenine (A) matches with thymine (T)

• Final product: same thing you started with

• Copies only ONE gene of DNA

• Transcribes ONE side of DNA

• Adenine (A) matches with uracil (U)

• Final product: new single strand of RNA