1. Introduction to Central Dogma a.k.a. Gene Expression
Chapter 17
17.1
Pgs
Objective: I can describe the process of gene expression by decoding DNA and noting what polypeptide protein is made.

2. Central Dogma (of Molecular Biology) Path of information:
Genes are made of DNA – how do traits come from them? (How does info turn into traits?)
Central Dogma (of Molecular Biology)
Path of information:
DNA  RNA  Protein
Transcription Translation
A.K.A.
Gene Expression
Protein Synthesis
Decipher DNA code to make proteins (traits)
RNA processing (splicing)

3. Evidence for Central Dogma/Gene Expression
Must read on own
Study of Metabolic Defects
Archibald Garrod
Bread Mold: Neurospora
Beadle and Tatum
Current hypothesis
One Gene-One Polypeptide hypothesis
Some proteins made of more than 1 polypeptide
Sometimes RNA made is good enough (no need protein)…

4. Review of Ribonucleic Acid (RNA)
Same as DNA… except for 3 things
1) Single-Strand (DNA is double-strand)
2) Ribose sugar (DNA has deoxyribose)
3) Does not have Thymine (T)
Has Uracil (U) to replace Thymine
For RNA: A pairs with U
3 types of RNA
mRNA (messenger)
tRNA (transfer)
rRNA (ribosomal)
1 less oxygen atom

5. Transcription (Step 1) Overview
more details later…
Enzyme: RNA Polymerase  binds to promoter
Reads DNA (certain spot, certain side/strand) and constructs mRNA from it (builds 5’ to 3’)
Still utilizes complementarity…but differently
Replication Transcription
DNA  DNA DNA  mRNA
C  G C  G
G  C G  C
T  A T  A
A  T A  U

6. Summary of Overview of Transcription
Occurs in the nucleus
Transcribes info from DNA to mRNA – why?
DNA is protected (trapped) in nucleus
Allows info to leave, with original copy unharmed/unchanged
Animations

7. Translation (Step 2) Overview
mRNA leaves nucleus  goes to ribosome
tRNA matches up to mRNA (complementarity)
Replication Transcription Translation
DNA  DNA DNA  mRNA mRNA  tRNA
C  G C  G C  G
G  C G  C G  C
T  A T  A U  A
A  T A  U A  U
Note:
tRNA is NOT a thread-like strand, like DNA and mRNA (more details later…)
MANY tRNA molecules match to one mRNA

8. Summary of Overview of Translation
Each tRNA will bring one amino acid
According to order of mRNA, will polymerize amino acids into
protein
Animations

9. Summary Overview of Central Dogma
Must know in 2 ways:
Molecular Details Coding Instructions

10. tRNA = anticodon (complementary to codon)
Coding Labels
Because every 3 nitro. bases  1 amino acid…
DNA = triplet
mRNA = codon (code)
tRNA = anticodon (complementary to codon)
When reading genetic code, easiest to read from mRNA (full strand traveling in cell)
Codon table use mRNA to determine amino acid  protein
Pg. 330

11. Codons – How many are there?
64 different codons (64 different ways to combine 4 bases in sets of 3  43)
20 different amino acids (like 26 letters)
Most amino acids have more than one codon
Different combinations/sequence of amino acids will create different proteins
Special start codon: AUG  Methionine
At beginning of gene (signal + amino acid)
Stop codons: UAA, UGA, UAG
At end of gene (JUST a signal)
Does not make an amino acid!!!
Says protein is finished

12. Practice Protein Synthesis
Random DNA sequence:
AAT-GGG-ATA-AAA-GTT
(how many bases? 15 how many triplets? 5)
1st step = transcription (DNA mRNA)
UUA-CCC-UAU-UUU-CAA (how many codons? 5)
2nd step = translation (mRNA  tRNA)
AAU-GGG-AUA-AAA-GUU (# of anti-codons = 5)
Amino acid sequence (read off mRNA in table)
Leucine-Proline-Tyrosine-Phe-Glu (# of a.a. = 5)
Do you have to go to tRNA to get a.a.?
Not if just deciphering code (in reality, yes!)