Download struktur dan fungsi kromosom

STRUKTUR DAN FUNGSI
KROMOSOM
Niken Satuti Nur Handayani
Lab. Genetika
Fakultas Biologi UGM
Genetics:
From Genes to Genomes
Second Edition
Hartwell ● 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 loopscaffold 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.
2.
AUTOSOM : kromosom yang tidak ada hubungannya dengan
penentuan jenis kelamin
KROMOSOM KELAMIN (sex chromosome) : kromosom yang ada
hubungannya dengan penentuan jenis kelamin
Chromosome structure
HISTONES are proteins with a high proportion of
Positively charged amino acids (lysine and arginin),
Which enable them to bind firmly to the negatively
Charged 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 apparent
that DNA between nucleosomes is bound to H1 histones.
DNA in metaphase chromosomes must be shortened
10,000-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.
Characteristic shapes of
chromosomes
Short arm
Long 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.
BENTUK KROMOSOM
Ada empat bentuk kromosom berdasarkan letak sentromer:
1.
2.
TELOSENTRIS : sentromer terletak
di terminal (bagian ujung
kromosom)
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)
1
2
3
4
Nilai Indeks Sentromer
Bentuk kromosom
Nilai Indeks Sentromer (NIS)
p
x 100
p+q
p = panjang lengan pendek kromosom
q = panjang lengan panjang kromosom
p+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
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.