1Importance of Packaging DNA
- Compact DNA to fit in cells
- Protect DNA
--When naked, can get destroyed easily and are unstable
- Provides organization that is easily accessible
--Contributes to recombination and diversity
2Overall Comparison of Gene Densities of Different Organisms
More complex
- larger genome
- smaller gene density
3Comparison of Gene Density for Different Organisms
Humans have
- more sequences for gene regulation
- more introns and non-coding regions than many other organisms
4Vital Stats for the Human Genome
- DNA length
- Number of Genes
- Percentage of DNA sequence in exons
- Pseudogenes
- Fun Fact
3.2 billion (haploid)
25,000
1.5 %
20,000
More than half the genome has no known function; may be junk DNA
5Pseudogenes
a nucleotide sequence of DNA that closely resembles a functional gene but is not expressed
6Psuedogenes arise...
from integration of reverse-transcribed messenger RNAs
7When reverse transcriptase is present in a cell...
messenger RNA (mRNA) molecules can be copied into double-stranded DNA
8In rare instances, these DNA molecules can...
integrate into the genome creating pseudogenes
9Psuedogenes do not have....
introns and gene regulation/expression elements
10Three Unique Sequence Elements (for maintenance and replication)
Telomere
Replication Origin
Centromere
11Telomere
protect the ends; ensure that the end can be completely replicated
12Replication origin
where replication starts
13Centromere
allows binding to kinetochore from spindle; necessary for distributing specialized DNA sequences to duplicated chromosomes for daughter cells
14Nucleosomes
basic unit of eukaryotic chromosome structure
15- proteins that pack DNA
- highly conserved among species
16H2A, H2B, H3, and H4
- responsible for folding DNA into nucleosomes.
(Core Histones)
17H1
bound to the DNA where the double helix enters and leaves the nucleosome core. (Linker Histone)
18H2A and H2B are monomers to come together...
to make a dimer
19H3 and H4 are monomers that come together..
make a tetramer
20two H3-H4 dimers come together...
to make an H3-H4 tetramer (wrapped in DNA)
21Two H2A-H2B dimers and one H3-H4 tetramer make
a histone octamer
22Site of Contact between the Histones and the DNA
Contact occurs in the minor groove
○ Lots of hydrogen bonds and ionic bonds
○ Other proteins will bind the major groove
23Nucleosomes prefer to bind bended DNA
AT rich region bends towards minor groove side
GC rich base pairs bend toward the major groove
24Alternating sequences of AT rich and GC rich with...
periodicity of 5 bp will act as preferred nucleosome binding sites
25the Chromatin Remodeling Complex:
Hydrolyze ATP and use that energy to change the structure of nucleosomes
26what are some mechanisms that ensure the dynamics of chromatin structure?
- Chromatin Remodeling Complex
- Reversible Modification of Histones
27Prominent Covalent Modifications found on Histone
Acetylation: adding lysine group
Methylation: replacing the proton with a methyl group
Phosphorylation: Adds phosphate group
28Acetylation
- Neutralizes the positive charge of lysine
- Weakens DNA and histone interactions because DNA is negatively charged
29Methylation
- Preserves positive charge of lysine
- This cannot be acetylated
- Can create a new binding site for other proteins to dock
- Initiates protein-protein interactions
30Phosphorylation
- Adds negative charge
- Weakens DNA and histone interactions because DNA is negatively charged