RNA & Gene Expression

Gene Expression Making sense of the code and doing what it says! Even though the DNA in all of the cells of one organism are the same, they all don’t perform the same functions Certain cells only “express” certain genes For example Eye cells don’t express genes that relate to digestion Liver cells don’t express genes that relate to reproduction Genes are expressed by way of proteins

Making a Protein Proteins are built according to instructions coded in DNA But, DNA does not directly make proteins RNA takes information from DNA to the ribosomes where the proteins are made Why? Proteins are made in two steps Transcription (DNA  RNA) Translation (RNA  Proteins) Why? The cytoplasm is too dangerous of an environment for the precious DNA

DNA vs. RNA DNA is composed of two strands of nucleotides; RNA is composed of one strand DNA and RNA have different types of sugars (deoxyribose vs. ribose) DNA has the bases A,T,C,G; RNA has the bases A,U,C,G (Thymine is replaced by Uracil)

Types of RNA Messenger RNA (mRNA): Carries instructions from DNA to the ribosome Transfer RNA (tRNA): Translates the instructions into protein building blocks (amino acids) Ribosomal RNA (rRNA): What ribosomes are made up of

Transcription A process where information coded on a specific region of DNA (a gene) is transcribed (copied) into mRNA Occurs in nucleus Steps in transcription: A certain segment of DNA strand unwinds and separates Complementary nucleotides are added (Adenine pairs with Uracil instead of Thymine) DNA strand joins back together and “re-winds” mRNA then travels out of nucleus to ribosome

Transcription NUCLEUS mRNA leaves nucleus

Three-Letter “Words” Every three nucleotide bases in mRNA is called a codon Each codon is matched to 1 of 20 amino acids The amino acids will later link up to form proteins A G U C codon mRNA strand

Translation Translation uses the codons on the mRNA strand to link amino acids together to make proteins at the ribosome Amino Acid tRNA C tRNA’s anti-codon joins to mRNA’s codon A U anti-codon codon codon codon Ribosome codon codon codon A U G G A A G U C G A C U G A C G G

Translation C A G U G C U G C U U U A C Ribosome codon codon codon

Translation G U C U G C A G Ribosome codon codon codon C U U A U G G A

Translation G U C U G C A G Ribosome codon codon codon A U G G A A G U

Translation G U C U G Ribosome codon codon A U G G A A G U C G A C U G

Translation A C U Ribosome codon A U G G A A G U C G A C U G A C G G

Translation Protein! codon A U G G A A G U C G A C U G A C G G

Translation

http://www.youtube.com/watch?v=4PKjF7OumYo