1. DNA, Genes & Genomes

2. DNA Recap:
All life forms rely on nucleic acids (DNA & RNA) for passing on their genetic information.
DNA is a complex polymer of repeating nucleotides
Each nucleotide = Deoxyribose Sugar + Phosphate + Nitrogenous Base.

3. Structure & coding:
The bases are paired across the double helix of DNA.
It is the order of these base pairs that makes up the genetic code.

4. DNA, Genes & Genomes
A gene is a section of DNA coding for one protein.
Its place on a chromosome is called its gene locus.
All of the genes a species has is called its genome.

5. Haploid or Diploid? Haploid organisms have single copies of each gene.
Diploid organisms have duplicate copies of each gene.
Prokaryotes are haploid; they reproduce asexually.
Eukaryotes have diploid somatic cells, but haploid gametes, for sexual reproduction.

6. Prokaryotic Genomes Single Chromosome Loop of DNA Limited genome
Still, E. coli has 4.6 Million base pairs with almost 5000 genes!

7. Prokaryotic Genomes Overlap them:
How to fit all of those genes into a single DNA loop?
Overlap them:
One gene starts before the ending of the previous one.

8. Prokaryotic Genomes

9. Prokaryotic Genomes
How to deal with the ‘sameness’ of being haploid & asexual?
Absorb as much foreign DNA as you can:
Plasmids confer new traits to a prokaryote, & come from various sources.

10. Prokaryotic Genomes Conjugation helps spread plasmids.
This is as close to sexual reproduction bacteria will come:
Like sexual reproduction, it introduces variety into a genome.

11. Eukaryotic Genomes Significantly larger
Human Genome = 3 Billion base pairs, with only 20 – 25 thousand genes.
All of this fits on 23 chromosomes
Diploid number: n = 46

12. Eukaryotic Genomes Largest Human Chromosome:
Chromosome #1, with 250 Million base pairs!
Smallest Human Chromosome:
Chromosome #23, Y with 50 Million b.p.

13. Eukaryotic Genomes
How to pack all of those genes into as few chromosomes as possible?
Smart packing:
DNA wraps around histone proteins, like thread around a spool.
This is called a
nucleosome

14. Eukaryotic Genomes * Supercoiling compacts the DNA more:
Tension builds, & nucleosomes twist together more tightly, compactly. *

15. Eukaryotic Genomes
You’ve seen supercoiling before:

16. Genomes are like libraries
All of the information needed to form an organism & keep it alive are in its genome:
Bacteriophage Phi (virus) has only 10 genes. Your mitochondria have 37!
Chlamydia has 936, Plague has 4000.
A fruit fly has 14000, your dog has 19000… but Rice has 37000!

17. Genome Complexity
General Rule: Prokaryotes have fewer genes than Eukaryotes.
The number of genes a Eukaryote has does reflect its complexity, but not in any sense of being ‘better’. It just ‘is’.