chromosome packaging with reference to coiling, m irfan
TRANSCRIPT
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
1/39
Muhammad Irfan
M.Phil Zoology
1
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
2/39
Prokaryotes
Prokaryotes dont have nucleus, so not packtheir DNA as chromatin
Their seem some organization to their DNA
This suggest that prokaryotes have proteinsthat act like histones
2
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
3/39
Bacterial Chromosome Structure
Prokaryotic cells (bacteria) contain theirchromosome as circular DNA
Usually the entire genome is a single circle butoften there are extra circles called plasmids
The DNA is packed by DNA-binding proteins(HU and H)
The bacterial DNA is packed in loops and this
bundled DNA is called the nucleoid It concentrates the DNA in part of the cell
The DNA does form loops back and forth to aprotein core, attached to the cell wall
3
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
4/39
Life, the Science ofBiology, by Purves, Orians, & Heller, 5th ed., 1997
4
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
5/39
5
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
6/39
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
7/39
Why Coiling of DNA is Important inEukaryotes?
The haploid human genome containsapproximately 3 billion base pairs of DNApackaged into 23 chromosomes
Most cells in the body (except forreproductive cells) are diploid with 23 pairsof chromosomes
That makes a total of 6 billion base pairs ofDNA per cell
7
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
8/39
Cont..
Because each base pair is around 0.34nanometers long (10-9) each diploid celltherefore contains about 2 meters of DNA
(6 ft long)It is estimated that the human body contains
about 50 trillion cells
Which works out to 50 x 2 = 100 trillionmeters of DNA per human
8
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
9/39
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
10/39
There are certain proteins that compact
chromosomal DNA into the microscopic space ofthe eukaryotic nucleus
These proteins are called histones
The resulting DNA-histones complex is calledchromatin
Within the nucleus histones provide the energy
(mainly in the form of electrostatic interactions)to fold DNA
Chromatin can be packaged into a much smaller
volume than DNA
Answer!
10
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
11/39
Charge on Histones
nar.oxfordjournals.org biog1105-1106.org/demos
Charge on DNA
Electrostatic Interaction
11
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
12/39
Structure of Chromatin
NucleosomeThe basic repeating structural and
functional unit of chromatin is the
nucleosome which contains 9 histoneproteins
The observation by electron microscopistssuggests that chromatin appeared similarto beads on a string provided an earlyclue that nucleosomes exist
12
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
13/39
molecularstation.com 13
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
14/39
http://origins.swau.edu/papers/complexity/trilo/eng/histone.jpg
14
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
15/39
Electronic micrograph observations
Beads on a string, the 10nm fiber.
15
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
16/39
X-ray diffraction experiments
Studies show thatchromatin has a repeating
pattern with an interval ofapproximately 100
This repeat is different
from the repeatingpattern of DNA itself
dnaftb.org16
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
17/39
Comparison between X-Ray DiffractionPattern of DNA and Chromatin
17
sunclipse.orgdnaftb.org
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
18/39
Life, the Science ofBiology, byPurves, Orians, & Heller, 5th
ed., 1997 18
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
19/39
Experiments using nucleases
Digest chromatin with ratliver nuclease at lowconcentration
Electrophoresis of the
digested chromatin materialA regular pattern of bands on
the gel approx. every 200 bp
Histones distributed evenlyon DNA
Histone core protect DNAfrom nuclease digestion
dnaftb.org
19
Experiments using nucleases
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
20/39
Histone
A protein around which DNA is wrapped andformed into structural components callednucleosomes
Histones are the chief protein components ofchromatin
It is the spool (cylinder of histones) aroundwhich DNA is wrapped
DNA wraps around 8 histone (core)molecules
20
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
21/39
Structure of HistonesHistone proteins
5 main typesH2A
H2B
H3H4
H1attached to the nucleosomeand involved in furthercompaction of the DNA(conversion of 10 nm chromatin
to 30 nm chromatin)21
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
22/39
A possible nucleosome structure
Peter J. Russell, iGenetics: Copyright Pearson Education, Inc., publishing as
Benjamin Cummings. 22
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
23/39
H1 Protein
H1 is called a"linker" histonebecause it bindsthe DNA betweennucleosomes
H1 is thought tohelp in organizing
and compactingthe DNA inchromosomes
Linker DNA
Linker DNA isdouble- strandedDNA between twonucleosome
Linker DNAconnects histone H1
to another histoneH1 sits on thenucleosome core
23
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
24/39
L
ife, the Science ofB
iology, by Purves, Orians,& Heller, 5th ed., 199724
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
25/39
Structure of Chromatin
Histone proteinsAbundant
Histone protein sequence is highlyconserved among eukaryotesconserved
functionProvide the first level of packaging for the
chromosome
DNA is wound around histone proteins toproduce nucleosomes
25
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
26/39
- Core DNA = 146 bp
- Linker DNA = 8-114 bp (usually 55bp)
- DNA turns around histone octamer.
Life, the Science ofBiology, byPurves, Orians, & Heller, 5th ed.,
1997 26
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
27/39
10 nm chromatin is produced in the first level of packaging.
Peter J. Russell, iGenetics: Copyright Pearson Education, Inc., publishing as
Benjamin Cummings.
Nucleosomes connected together by linker DNA and H1 histone to produce
the beads-on-a-string extended form of chromatin
27
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
28/39
DNA is further compacted when the DNAnucleosomes associate with one anotherto produce 30 nm chromatin which is
called solenoidH1 plays a role in compaction (if H1 is
absent then chromatin cannot beconverted from 10 to 30 nm)
Cont..
28
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
29/39
29
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
30/39
Packaging of nucleosomes into the 30-nm chromatin fiber
Peter J. Russell, iGenetics: Copyright Pearson Education, Inc., publishing as
Benjamin Cummings.
30 nm
30
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
31/39
Eukaryotic chromosomal organization
Compaction continues by forming loopeddomains from the 30 nm chromatin whichseems to compact the DNA to 300 nmchromatin
Human chromosomes contain about 2000looped domains
30 nm chromatin is looped and attached to a
nonhistone protein scaffolding
31
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
32/39
Model for the organization of 30-nm chromatin fiber into looped domains thatare anchored to a nonhistone protein chromosome scaffold
Peter J. Russell, iGenetics: Copyright Pearson Education, Inc., publishing as
Benjamin Cummings.
300 nm
32
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
33/39
Eukaryotic chromosomal organization
Nonhistone proteins
Other proteins that are associated with thechromosomes
May have role in compaction or be involved inother functions requiring interaction with theDNA
Many are acidic and negatively charged bind tothe histones
33
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
34/39
The many different orders of chromatin packing that give rise to the highly condensed metaphase chromosome
Peter J. Russell, iGenetics: Copyright
Pearson Education, Inc., publishing asBenjamin Cummings.34
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
35/39
35
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
36/39
DNA compaction
Level of DNA compaction changesthroughout the cell cycle most compact
during M-Phase least compact during S-Phase
2 types of chromatin related to the level of
gene expressionEuchromatindefined originally as areas
that stained lightly
Heterochromatindefined originally asareas that stained darkly
36
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
37/39
Euchromatin
Found in regions ofchromosome wherethere are many genes
Unfolded structure
Functions in the activetranscription of DNAto mRNA
Usually areas wheregene expression isoccurring
molecularstation.com37
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
38/39
Heterochromatin
Found in regions of achromosome wherethere are few to no
geneschromosomal regions
that are condensedthroughout the cell
cycle
molecularstation.com 38
-
8/6/2019 Chromosome Packaging With Reference to Coiling, M Irfan
39/39
Thank You!
39