Transcript DNA, Genes & Genomes

DNA, Genes
& Genomes
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.
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.
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.
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.
Prokaryotic Genomes
-Single
Chromosome
- Loop of DNA
- Limited genome
- Still, E. coli
has 4.6 Million
base pairs with
almost 5000
genes!
Prokaryotic Genomes
How to fit all of those genes
into a single DNA loop?
Overlap them:
One gene starts
before the
ending of the
previous one.
Prokaryotic Genomes
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.
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.
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:
Eukaryotic Genomes
Largest Human
Chromosome:
Chromosome #1, with
250 Million base
pairs!
Smallest Human
Chromosome:
Chromosome #23, Y
with 50 Million
b.p.
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
Eukaryotic Genomes
Supercoiling compacts the DNA
more:
Tension builds, & nucleosomes
twist together more tightly,
compactly.
*
Eukaryotic Genomes
You’ve seen supercoiling before:
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
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’.