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10/02/2016
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Mei Vita Cahya Ningsih, Ns.
KROMOSOM
Kromosom manusia 46 buah t.d 22 autosom dan 1 ps. Sex
kromosom
Satu bagian diturunkan dari ayah, satu bagian lain dari ibu
Pasangan yg homolog membawa informasi genetik yang
sesuai
Penurunan dilaksanakan melalui proses pembelahan
Terdapat dua macam pembelahan sel yaitu MITOSIS DAN
MEIOSIS
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Sel tubuh/somatik mempunyai
kromosom diploid
Sel gamet mempunyai kromosom
haploid
Sebelum mengalami pembelahan DNA
mengalami replikasi terlebih dahulu
Replikasi terjadi selama interfase
( S phase)
MORFOLOGI KROMOSOM
� Tiap kromosom t.d 2 kromatid yang
berkumpul di sentromer
�Sentromer berfungsi utk pegangan
fiber dari spindel pd waktu pembelahan
�Sentromer membagi kromosom menjadi
2 bagian p (lengan pendek) dan q
(lengan panjang)
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Berdasar letak sentromer, kromosom
dibedakan menjadi :
�Metasentris : letak sentromer di tengah, sehingga lengan kromosom hampir sama panjang
�Submetasentris : sentromer tidak ditengah, lengan kromosom tidak sama panjang, bila membengkok seperti huruf J
�Akrosentris : sentromer terletak di ujung sehingga membentuk satelit (13,14,15,21 dan 22)
Gambar Kromosom
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KLASIFIKASI KROMOSOM
Didasarkan pada besar dan letak
Sentromernya
� A : terbesar, metasentrik (1,2,3)
� B : submetasentrik besar, p ¼ lengan
q (4,5)
� C : submetasentrik, medium (6-12,X)
� D : akrosentrik, medium, satelit (13-15)
� E : metasentrik, medium (16) dan
submetasentrik kecil (17,18)
� F : metasentrik kecil (19,20)
� G : akrosentrik kecil, satelit (21,22)
dan akrosentrik tak bersatelit (Y)
Klasifikasi juga berdasar pada gambaran
kromosom waktu dilakukan pengecatan
1q24.3 = kromosom 1, lengan panjang,
regio 2, band 4 dan sub band 3
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Gambar Kromosom
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DNA and Protein
(Structure and
Functions)
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DNA carries the genetic information of a cell
and consists of thousands of genes. Each
gene serves as a recipe on how to build a
protein molecule.
Proteins perform important tasks for the cell
functions or serve as building blocks.
The flow of information from the genes
determines the protein composition and
thereby the functions of the cell.
DNA is the physical carrier of inheritance. It is like a giant book of information containing all the instructions for building and maintaining a living organism.
Replication followed by cell division is the answer to one of life's most interesting questions: How can the union of a single sperm and an egg become a five-trillion-cell baby, all containing the same DNA?
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The helix
makes a
complete
turn every
3.4 nm and
there are
about 10.5
base pairs
per turn.
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The building blocks of DNA are the 5-
carbon sugar deoxyribose linked
together by phosphodiester bonds
forming two strands of sugar-phosphate
backbones on the outside of the double
helix
The human genome contains 3x109 base
pairs of DNA divided into 23 chromosomes
which if linked together would form a thread
of 1 meter with a diameter of 2 nm.
This DNA codes for about 105 different
proteins. In fact only about 2-4 % of the total
coding capacity in the human DNA is used for
coding of different genes, the rest of it
probably has other more structural and
organizational functions.
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Chromatin
The DNA double helix in the cell is
packaged by special proteins called
histones to form a protein/DNA complex
called chromatin
The structural unit of chromatin is the
nucleosome.
It consists of a central protein complex,
the histone octamer, and two turns of
DNA, about 146 base pairs, which are
wrapped around the histone octamer
complex.
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There are four different types of core
histones which form the octamer
containing two copies each of H2A, H2B,
H3 and H4.
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There is a linker histone, H1, which contacts the exit/entry of the DNA strand on the nucleosome.
The nucleosome together with histone H1 is called a chromatosome.
Chromatosomes are held together by the continuous DNA strand, thus forming linker DNA of 30-50 base pairs in length.
The Gene
A functional and inheritable element in
the genome is referred to as a gene and
usually codes for a protein.
In some cases genes also code for RNA
molecules that are not translated to
protein, e.g. ribosomal RNA.
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The gene regulatory segment, of which the proximal part is referred to as the promoter, usually consists of many different DNA segments defined by their particular base pair sequences
Each individual segment, usually involving about 6-12 base pairs of DNA, serves as a binding target for a DNA binding protein which functions as a transcription factor
Furthermore, the DNA binding capacity of
various transcription factors is usually
regulated via cellular signals through
extracellular hormones and receptor
pathways or via cell interactions with the
environment.
In this way a particular stimulus in the
surrounding of a cell will trigger the
binding of a set of transcription factors to
a certain set of genes,
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RNALike DNA, the RNA molecule, is built up
by nucleotides linked together in a chain.
There are some differences though :
� The RNA molecule is single stranded
� The four bases in the DNA nucleotides are
adenine, guanine, thymidine and cytosine. In
RNA thymidine is replaced by uracil.
� The sugar in DNA is deoxyribose. In RNA it is
ribose.
There are three major types
of RNA: 1) mRNA,
messenger-RNA, which
transfer the information about
the aminoacid sequence from
the DNA to the protein
synthesis. 2) rRNA,
ribosomal-RNA, which builds
up the ribosome together with
proteins. 3) tRNA, transfer-
RNA, which transfer
aminoacids to the ribosome
for protein synthesis.
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Transcription
After transcription has been initiated RNA
polymerase II, together with the necessary
transcription elongation factors, travels along
the DNA template and polymerizes
ribonucleotides into an RNA copy of the gene
The polymerase moves at a regular speed
(approximately 30 nucleotides per second)
and holds on to the DNA template efficiently,
even if the gene is very long
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RNA ProcessingThe primary transcription product of a gene is therefore called a precursor of mRNA, pre-mRNA.
Both ends of the pre-mRNA are modified. An additional nucleotide, a 7-methylguanosine is added to the 5'-end to form a cap-structure. This process is called capping (1). The 3'-end of the pre-mRNA is cleaved and polyadenylated (4). The pre-mRNA is cut at a specific site and 150-200 adenylate residues are added to the 3'-end to form a poly(A)-tail. The third major modification is splicing (3).
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Translation
Translation is the actual synthesis of a protein
under the direction of mRNA
the ribosome, provides the basic machinery for
the translation process. The major role of the
ribosome is to catalyse coupling of amino acids
into protein according to the sequence specified
by the mRNA.
The amino acids are brought to the ribosome by
tRNA (transfer RNA) molecules.
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Initiation
formation of the initiation complex
between mRNA, charged tRNA and
the ribosome
translation begins at a specific
codon, the initiation codon (AUG)
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the growing polypeptide chain is attached to an amino acid in the P site
the next codon to be read is present beneath the A site
the tRNA bearing the next amino acid to be inserted enters the A site
ELONGATION
a peptide bond is formed between
the new amino acid and the growing
chain, transfering the chain to the
tRNA in the A site
the ribosome moves down one
codon moving the peptide-tRNA to
the P site and the cycle repeats
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Termination
translation of a particular protein
ends when the ribosome encounters
one of three termination codons
(UAG, UAA or UGA)
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REPLIKASI
A. Cara kerja Polimerase DNA
� Sebelum pembelahan salinan
genom (Replikasi)
� Dikatalis oleh Polimerase DNA
� Enzym ini memerlukan DNA untai
tunggal Untai Cetakan
(matrix strand)
� Substrat Polimerase DNA :
dATP,dGTP, dCTP, dTTp
B. Replikasi pada E. coli
• Dimulai pada titik awal mula replikasi dan
dilanjutkan ke kedua arah garpu replikasi
• Setiap garpu memiliki 2 molekul
Polimerase
DNA III + enzym pembantu (topoisomerase
DNA dan helikase) mengendurkan dan
memisahkan ikatan DNA
• Arah pembacaan 3’ – 5’
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DNA polymerase III
Newly
synthesized
leading strand
3'
5'
5'Replication fork
3'
5'
Formation of the leading strand
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� Pertama terbentuk fragmen okazaki yang
diperlukan u/ polimerase DNA dapat berfungsi
� Ada beberapa tempat fragmen okazaki dan
tidak saling
berhubungan
� Enzym polimerase DNA I menyambung dan
menutupinya
dengan enzym ligase