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Remember . . . . . .

DNA = genetic informationDNA = genetic information

DNA replication = unzipping of DNA replication = unzipping of double helix and creating a new double helix and creating a new strand of DNA!strand of DNA!

Picture this . . . . . Picture this . . . . . You are a cell!!You are a cell!!

You want to make a You want to make a protein, what do you protein, what do you

do???do???You have to getYou have to get

DNA DNA RNA RNA protein proteinProtein synthesis!!Protein synthesis!!

RNA carries DNA’s RNA carries DNA’s instructions.instructions.

• Central dogmaCentral dogma = info. flows in = info. flows in 1 direction, 1 direction, from DNA to from DNA to RNA to protein!RNA to protein!

8.4 KEY CONCEPT Transcription converts a gene into a single-stranded RNA molecule.

It includes 3 processes: It includes 3 processes: – ReplicationReplication– TranscriptionTranscription– TranslationTranslation

• RNA = RNA = Ribonucleic acidRibonucleic acid• RNA = link btwRNA = link btw DNA & proteins!DNA & proteins!

replication

transcription

translation

Oh Man!!!Oh Man!!! DNA can’t leave the DNA can’t leave the

nucleus!!!nucleus!!!• Which organelle makes Which organelle makes

proteins????proteins????• RIBOSOMES!RIBOSOMES!• DNA’s code must be carried DNA’s code must be carried

from the nucleus to the from the nucleus to the cytoplasm!!!cytoplasm!!!

• RNA does the job!RNA does the job!

Let’s compare DNA & Let’s compare DNA & RNA!!RNA!!

Deoxyribose Deoxyribose sugarsugar

A, C, T, GA, C, T, G

Double Double strandedstranded

Ribose sugarRibose sugar

A, C, Uracil, GA, C, Uracil, G

Single strandedSingle stranded

TranscriptionTranscription• Process by which a portion of DNA Process by which a portion of DNA

(a “gene”) is copied into a (a “gene”) is copied into a complementary strand of complementary strand of RNARNA. . – The DNA code is transferred out The DNA code is transferred out

of the nucleus of the nucleus ribosomesribosomes

RNA polymerase recognizes start site of gene & UNWINDS DNA!!

RNA pol. reads template & makes complimentary strand!!

RNA strand hangs free & detaches once transcribed!!!

DNA molecule

Nucleotides

New RNA strand

RNA polymerase

Transcription is catalyzed (started) byTranscription is catalyzed (started) by RNA RNA polymerase.polymerase.

– RNA polymerase and other proteins RNA polymerase and other proteins form a transcription complex.form a transcription complex.

– The transcription complex recognizes The transcription complex recognizes the start of a gene and unwinds a the start of a gene and unwinds a segment of it.segment of it.

start site

nucleotides

transcription complex

– RNA polymerase bonds nucleotides together.

– DNA helix winds again as the gene is transcribed.

– Nucleotides pair with one strand of the DNA.Nucleotides pair with one strand of the DNA.

DNA

RNA polymerase moves along the DNA

– The RNA strand detaches from the DNA once the gene is transcribed.

RNA

Transcription makes 3 types of Transcription makes 3 types of RNA:RNA:

– carries the message that carries the message that will be translated to form a will be translated to form a protein.protein.

– forms part of ribosomes forms part of ribosomes (where proteins are made)(where proteins are made)

– takes amino acids from the takes amino acids from the cytoplasm to a ribosome.cytoplasm to a ribosome.

Ribosomal Ribosomal RNA RNA (rRNA)(rRNA)

Transfer Transfer RNA (tRNA)RNA (tRNA)

The transcription process is similar to The transcription process is similar to replication....HOW?? replication....HOW??

• Transcription & replication both involve Transcription & replication both involve – complex enzymes & complex enzymes & – complementary base pairing.complementary base pairing.

• BUT...have different end results:BUT...have different end results:– Replication copiesReplication copies

all the DNA;all the DNA;transcription copiestranscription copiesa a genegene..

– Replication makesReplication makesoneone copy; copy;transcription cantranscription canmake make manymany copies. copies.

growing RNA strandsgrowing RNA strands

DNADNA

oneonegenegene