Molecular Evolution

Lecture 1. Origins of variation: gene structure

Why this course

• A Human Language Gene Changes the Sound of Mouse Squeaks

• Of Mice and Monologues

• The Origins of Lactase Persistence

II. What is DNA? A. DNA1. Composition: polymer of nucleotides:

1. Nitrogen base

2. Deoxyribose [ribose for RNA]

3. Phosphate

Types of nitrogen bases

DNA nucleotides are attached to each other 5’ to 3’

Bases can form hydrogen bonds with a complimentary antiparallel DNA strand

Specific pairing between the nitrogen bases

The complete DNA alphabet (fyi)Symbol Meaning Origin of designationG G GuanineA A AdenineT T ThymineC C CytosineR G or A puRineY T or C pYrimidineM A or C aMinoK G or T KetoS G or C Strong interaction (3 H bonds)W A or T Weak interaction (2 H bonds)H A or C or T not-G, H follows G in the alphabetB G or T or C not-A, B follows AV G or C or A not-T (not-U), V follows UD G or A or T not-C, D follows CN G or A or T or C aNy

Some features of DNA

• Purines pair with pyrimidines

(e.g. # purines = # pyrimides)

• The # of A = # of T; #G = # of C• (% G + C content of 2 species’ DNA will vary)

• GC-rich DNA is more stable than AT-rich (more hydrogen bonding)

• Two strands of the duplex lie antiparallel

DNA replication

leading strand 5’ to 3’ continuous replication

lagging strand discontinuous replication

http://upload.wikimedia.org/wikipedia/commons/a/ac/GeneticCode21.svg

The genetic code: redundancy compensating for mutation

Redundancy and the Wobble position

5’ 5’3’3’

Functional redundancy in the amino acid code

• http://www.russell.embl-heidelberg.de/aas/general.html

5’3’ 3’5’

Transcription

Translation

CCAA BB

gene Bgene Bgene Agene A gene Cgene C

5’

Transcription/translation Differences between prokaryotic and eukaryotic mRNAs

EukaryoticEukaryoticMonocistronic

Poly A tails

Transported from nucleus to cytoplasm

Half-life: minutes - hours

5’ methylated G cap

PolycistronicProkaryoticProkaryotic

No tails

Transcription/Translation coupled

Half-life: seconds - minutes

No cap

Transcription/Translation