Structure of RNASingle strand of

nucleotides bonded into a chain

– Each nucleotide contains • Ribose, sugar

• Phosphate

• Nitrogen base: adenine, guanine, cytosine or uracil

• Adenine pairs with Uracil/ Cytosine pairs with Guanine

RNA Types

• Messenger RNA- carries the code for making proteins

• Ribosomal RNA- combine with a ribosome • Transfer RNA- brings the amino acid to the

ribosome

TRANSCRIPTIONTRANSCRIPTION• When DNA gives RNA the code • RNA polymerase enzyme unzips DNA at Promoters• RNA nucleotides join the DNA complimentary bases• mRNA nucleotides bond and leave the nucleus

• http://www.pbs.org/wgbh/aso/tryit/dna/shockwave-nojs.html

Transcription Cont.

• Editing RNA sections called introns are spliced out leaving sections called exons

• Exons splice together and leave the nucleus

RNADNA

RNApolymerase

 TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

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TRANSLATION

• Process of assembling proteins from the information encoded in RNA

• mRNA leaves the nucleus and goes to the ribosome– the codon ( 3 bases in sequence on the mRNA)

• tRNA, transfer RNA leaves the nucleus and picks up an amino acid– the anticodon is the compliment to the codon on

mRNA

Messenger RNA

Messenger RNA is transcribed in the nucleus.

Transfer RNA

The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

 TranslationSection 12-3

mRNA

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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

 Translation (continued)Section 12-3

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START & STOP SIGNALS

• To start the protein synthesis the codon AUG must be present

• To stop the protein synthesis there’s a stop codon UAA, UGA, UUC

Practice Use your book page 338

DNA mRNA tRNA Amino Acid

CAT

UGC

GTC

UAA

start

Practice Answers

DNA mRNA tRNA Amino Acid

CAT GUA CAU valine

TGC ACG UGC Threonine

GTC CAG GUC glutamine

ATT UAA AUU STOP

TAC AUG UAC start