1. RNA & Gene Expression

2. 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

3. 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

4. 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)

5. 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

6. 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

7. Transcription
NUCLEUS
mRNA leaves nucleus

8. 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

9. 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

10. Translation C A G U G C U G C U U U A C Ribosome codon codon codon

11. Translation G U C U G C A G Ribosome codon codon codon C U U A U G G A

12. Translation G U C U G C A G Ribosome codon codon codon A U G G A A G U

13. Translation G U C U G Ribosome codon codon A U G G A A G U C G A C U G

14. Translation A C U
Ribosome
codon A U G G A A G U C G A C U G A C G G

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

16. Translation