STRUKTUR DAN FUNGSI KROMOSOM Niken Satuti Nur Handayani Lab. Genetika Fakultas Biologi UGM.

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.