Transcription NotesTranscription Notes

TranscriptionTranscription

• Information in Information in DNA DNA is used to make is used to make proteinsproteins (specifically in the (specifically in the basesbases – – A, T, G or C)A, T, G or C)

• DNA is found in the DNA is found in the nucleusnucleus• Proteins are made in the Proteins are made in the ribosomesribosomes• DNA is DNA is double-strandeddouble-stranded and is too and is too

big big to leave the nucleusto leave the nucleus

How does the information on How does the information on DNA get to the ribosomes?DNA get to the ribosomes?

• This is where RNA comes in:This is where RNA comes in:• RNA = RNA = Ribonucleic acidRibonucleic acid• RNA is RNA is single-strandedsingle-stranded, so it is , so it is

smaller and can fit out of the smaller and can fit out of the nucleusnucleus

• DNA’s information is copied onto DNA’s information is copied onto mRNAmRNA (messenger RNA) and mRNA (messenger RNA) and mRNA takes the message to the takes the message to the ribosomeribosome to make to make proteinsproteins

Definition of TranscriptionDefinition of Transcription

• The process of The process of copyingcopying DNA DNA onto onto mRNAmRNA in order to get the in order to get the information from the information from the nucleusnucleus to to the the ribosomesribosomes to make proteins to make proteins

Picture of TranscriptionPicture of Transcription

Ribosomes

Cell MembraneNucleus

mRNADNA

RNA VS. DNARNA VS. DNA

• SingleSingle – Stranded – Stranded

• Sugar – Sugar – RiboseRibose

• 4 Bases:4 Bases:– Adenine (A)Adenine (A)– Guanine (G)Guanine (G)– Cytosine (C)Cytosine (C)– Uracil (U)Uracil (U)

DoubleDouble – Stranded – Stranded

Sugar – Sugar – DeoxyriboseDeoxyribose

4 Bases:4 Bases:Adenine (A)Adenine (A)

Guanine (G)Guanine (G)

Cytosine (C)Cytosine (C)

Thymine (T)Thymine (T)

How is information copied How is information copied onto mRNA?onto mRNA?

• This process is similar to This process is similar to replicationreplication

• RNA Complementary Base Pairs RNA Complementary Base Pairs are a little are a little differentdifferent than than DNADNA Base PairsBase Pairs– G – CG – C– A – A – UU (instead of (instead of TT))

Steps of TranscriptionSteps of Transcription

• Step 1:Step 1: • DNA must DNA must unwindunwind and and unzipunzip. . • The weak The weak HydrogenHydrogen bonds that bonds that

hold the hold the DNADNA strand together in strand together in the middle are broken by an the middle are broken by an enzymeenzyme..

Steps of TranscriptionSteps of Transcription

• Step 1 (Picture):Step 1 (Picture):

A - TA - T

T - AT - A

C - G Enzyme unzipsC - G Enzyme unzips

G CG C DNA at the DNA at the

A TA T WEAK WEAK

G C hydrogen bondsG C hydrogen bonds

G CG C

Steps of TranscriptionSteps of Transcription

• Step #2:Step #2:• The DNA strand pulls apart and The DNA strand pulls apart and

free free RNARNA nucleotides (that are nucleotides (that are floating around in the floating around in the nucleusnucleus) ) begin to pair up with their begin to pair up with their complementary nucleotide on complementary nucleotide on ONEONE side of the DNA strand with the side of the DNA strand with the help of an help of an enzymeenzyme..

Steps of TranscriptionSteps of Transcription

• Step #2 (Picture):Step #2 (Picture): A A AA - T - T Free RNAFree RNA T T UU - A - A nucleotidesnucleotides C C CC - G - G floating infloating in G G GG - C - C the nucleusthe nucleus A A AA - T - T G CG C G CG C DNA DNA mRNAmRNA DNA DNA

U

G

GU

A

A

C

Steps of TranscriptionSteps of Transcription

• Step #3:Step #3:• After copying the desired section of After copying the desired section of

DNADNA, the mRNA , the mRNA separates separates from the from the DNADNA strand strand

• The mRNA (which is The mRNA (which is single-single-strandedstranded) now leaves the ) now leaves the nucleusnucleus and goes to the and goes to the ribosomesribosomes to make to make proteinsproteins

Steps of TranscriptionSteps of Transcription

• Step #3: (Picture)Step #3: (Picture) A A

U U C mRNA single-strandedC mRNA single-stranded

GG AA G G GG

Steps of TranscriptionSteps of Transcription

• Step #4:Step #4:• The The originaloriginal DNA zips back DNA zips back

togethertogether and stays in the and stays in the nucleusnucleus

Steps of TranscriptionSteps of Transcription

• Step #4 (Picture):Step #4 (Picture): A - T A - T T – A T – A

C – C – G Original DNA strandG Original DNA strandG – C G – C A - TA - T

G – CG – C G - CG - C

Transcription AnimationsTranscription Animations

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

Transcription Simulation

Make sure Biological Make sure Biological Simulations CD is in the driveSimulations CD is in the drive