STRUKTUR DAN FUNGSI KROMOSOM
Niken Satuti Nur HandayaniLab. Genetika
Fakultas Biologi UGM
Genetics: From Genes to Genomes
Second EditionHartwell ● Hood ● Goldberg ● Reynolds ● Silver ● Veres
The bacterial genome is composed of one circular chromosome
4-5 Mb long Condenses by
supercoiling and looping into a densely packed nucleoid body
Chromosomes replicate inside cell and cell divides by binary fission
Fig. 14.4 b
Genetics: From Genes to Genomes
Second Edition
Hartwell ● Hood ● Goldberg ● Reynolds ● Silver ● Veres
The Eukaryotic Chromosome
An Organelle for Packaging and managing DNA
Each chromosome packages a single long molecule of DNA
Chemical and Physical analysis Studies examine stretching and recoiling find
longer pieces recoil more slowly than shorter pieces
Pulse field electrophoresis Separates large pieces of DNA – number and sizes
correspond to number and sizes expected if each chromosome contains a single piece of DNA
Protein components of DNA
Histone proteins abound the chromatin of all eukaryotic cells Histones – small proteins with basic, positively charged amino
acids lysine and arginine Bind to and neutralize negatively charged DNA Make up half of all chromatin protein by weight Five types: H1, H2A, H2B, H3, and H4 Core histones make up nucleosome: H2A, H2B, H3, and H4 DNA and histone synthesis regulation correlate timing so both
are synthesized together High level of similarity of histones among diverse organisms
Protein components of DNA
Nonhistone proteins are a heterogeneous group Half of proteins in chromatin are nonhistone Large variety of nonhistone proteins – 200 – 2,000,000 in
diploid genomes Large variety of functions
Scaffold – backbone of chromosome DNA replications – e.g., DNA polymerases Chromosome segregation – e.g., motor proteins of kinetichores Transcriptional regulation – largest group regulates transcription
during gene expression Occur in different amounts in different tissues because of
variety of function
The nucleosome:
the fundamental unit of chromosomal packaging arises from DNAs association with histones
Chromatin fibers with beads having diameter of about 100 A and strings having diameter of 20 A
The nucleosome:
the fundamental unit of chromosomal packaging arises from DNAs association with histones
Bead is a nucleosome with about 160 bp of DNA wrapped twice around a core of 8 histones
40 bp of DNA link together nucleosomes
The nucleosome:
the fundamental unit of chromosomal packaging arises from DNAs association with histones
X-ray diffraction analysis DNA does not coil smoothly Base sequences dictate
preferred nucleosome positions along DNA
Spacing and structure affect genetic function
The nucleosome:
the fundamental unit of chromosomal packaging arises from DNAs association with histones
Spacing of nucleosomes affects gene expression Regions between nucleosomes available for interactions
with proteins involved in expression, regulation, and further compaction
Determines how and whether certain proteins interact with specific sequences
Packaging into nucleosomes condenses DNA sevenfold 2 meters of DNA shortens to less than 0.25 meters
Models of higher level compaction seek to explain extreme compaction of chromosomes at mitosis
Formation of 300 A fiber through supercoiling
Models of higher level compaction seek to explain extreme compaction of chromosomes at mitosis
Radial loop-scaffold model for higher levels of compaction Each loop contains
60-100 kb of DNA tethered by nonhistone scaffold proteins
Radial loop-scaffold model continued
Experimental support for radial loop-scaffold model
Electron micrograph shows long DNA loops emanating from the protein scaffold
A closer look at karyotypes:
fully compacted metaphase chromosomes have unique, reproducible banding patterns
Banding patterns are highly reproducible
Not known what they represent
A closer look at karyotypes: fully compacted metaphase chromosomes have unique, reproducible banding patterns.
Banding patterns help locate genes
A closer look at karyotypes: fully compacted metaphase chromosomes have unique, reproducible banding patterns
Banding patterns can be used to analyze chromosomal differences between species
Can also be used to reveal cause of genetic disease e.g., Downs syndrome – 3
copies of chromosome 21
Centromere structure and function
Fig. 12.11 a
Kromosom Eukaryotik dan Prokaryotik
1. AUTOSOM : kromosom yang tidak ada hubungannya dengan penentuan jenis kelamin
2. KROMOSOM KELAMIN (sex chromosome) : kromosom yang ada hubungannya dengan penentuan jenis kelamin
Chromosome structure
HISTONES are proteins with a high proportion ofPositively charged amino acids (lysine and arginin),Which enable them to bind firmly to the negativelyCharged DNA doble helix.
There are 5 types of histone molecules: H1, H2A, H2B, H3, and H4.Except for H1, they occur in exactly equal numbers.In less condensed chromatin fibers, it becomes apparentthat DNA between nucleosomes is bound to H1 histones.
DNA in metaphase chromosomes must be shortened10,000-fold by very efficient packing. This occurs in discrete units, the NUCLEOSOMES,Consisting of DNA and histones.
Chromosome
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or arms.
The short arm of the chromosome is labeled the p arm. The long arm of the chromosome is labeled the q arm.
Long arm
Short arm
The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
Characteristic shapes of chromosomes
BENTUK KROMOSOM
1. TELOSENTRIS : sentromer terletak di terminal (bagian ujung kromosom)
2. AKROSENTRIS/SUB
TELOSENTRIS : sentromer terletak di sub terminal (mendekati ujung kromosom)
3. SUB METASENTRIS : sentromer terletak di sub median (mendekati bagian tengah)
4. METASENTRIS : sentromer terletak di median (bagian tengah)
Ada empat bentuk kromosom berdasarkan letak sentromer:
1 2 3 4
Bentuk kromosom Nilai Indeks Sentromer (NIS)
p x 100 p + q
p = panjang lengan pendek kromosomq = panjang lengan panjang kromosomp+q = panjang absolut kromosom
Nilai Indeks Sentromer
Posisi Sentromer
Bentuk Kromosom Simbol Kromosom
Rata-rata
NIS
Median Metasentris m 38 -50
Sub Median Sub Metasentris sm 26 - 37
Sub Terminal Akrosentris /
Sub Telosentris
st 13 - 25
Terminal Telosentris t 0 - 12
Nilai Indeks Sentromer
Karyotype
A display of the paired homologues chromosomes from a cell
Allows determination of:
sex of an individual,
abnormal chromosome number,
other chromosome abnormalities,
etc.
How many chromosomes do people have?Banding pattern during metaphase
Banding pattern during prophase
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. The 22 autosomes are numbered by size. The other two chromosomes, X and Y, are the sex chromosomes.