K6- Replikasi DNA

8/13/2019 K6- Replikasi DNA

1/31

as c

Science

Departemen


2/31

The nucleus contains a blueprint for all cells structures & activities

encoded in DNA

The information that makes each individual life unique must be

preserved & then passed on to progeny

Cells divisions does not stop with the formation of mature organism

but continous in certain tissues throughout life

New cells originate from other living cellscells division

More than 1013cells form a human bodythe whole organism has

been generated by cell divisions from a single cell

One of the hallmarks of life is its ability to reproduce

Introduction


3/31

Tissues of the body divided into three

groups base on proliferative activity

of their cells:

Continuously

dividing tissues

(labile tissues)

Quiescent

tissues (stable

tissues)

Nondividing

tissues

(permanent

tissues)


4/31

Example:

Surface epithelia

i.e. stratifiedsquamous

epithelia of skin,

oral cavity, vagina& cervix

The lining mucosa

of all excretoryducts of glands

(e.g., salivary

glands, pancreas,biliary tract)

The columnar

epithelium of the

GI tract & uterus

The transitionalepithelium of urinary

tract, and cells of

bone marrow &

hematopoietic

tissues

Cells proliferate throughout life Replacing that destroyed

Continuously dividing tissues (labile tissues):


5/31

Example :

Parenchymal cells of

liver, kidneys, &

pancreas

Mesenchymal cells

such as fibroblasts &

smooth muscle

Vascular endothelial

cells; & lymphocytes

& other leukocytes

Normally have a low level of replication but cells can undergo rapid

division in response to stimuli & capable of reconstituting the tissue

of origin

Quiescent tissues (stable tissues)


6/31

Example : neurons & skeletal & cardiac muscle cells

Contain cells that have left the cell cycle & cannot undergomitotic division in postnatal life

Nondividing tissues(permanent tissues)

t


7/31

ynt es s occurs ns e

the nuclues


8/31

Cell nucleus contain 3 major components:

Nuclearenvelopecomposed of two

parallel unit membranes that fuse witheach other at certain regions to form

perforations known as nuclear pores

Chromatin: a complex of DNA and

proteins and represents the relaxed,

uncoiled chromosomes of the interphase

nucleus

Nuclelolus: the deeply staining-non

membrane bounded structure within

nucleus that is involeved in rRNA synthesisand in the assembly of small and large

ribosomal units

CELL NUCLEUS


9/31

Chromatin: a complex of DNA and

proteins and represents the relaxed,

uncoiled chromosomes of the interphasenucleus

DNA: the cells genetic material

Like a computer tape that stores many

programs

DNA present in each cell in the form of anumber of chromosomes

Chromosomesare chromatin fibers that

becomes so condensed and thightlycoiled during mitosis and meiosis that

they become visible with the light

microscope

Chromatin


10/31

Chromatin Depending on

transcriptional activity:

Heterochromatin:

Condensed inactive form of chromatin

Located mostly at periphery of nucleus

Euchromatin:

Active form of chromatin where the

genetic material being trancribed intoRNA

Composed of thread like material 30

nm thick: Nucleosomes: unwound material

resembling beads on stringconsist

of histone

DNAmoleculesthin filament

resembling string

Chromatin contd


11/31

The Nucleus


12/31

Chromatin-Histone


13/31

Genome: is total number of genes within one mature cell (60 -

100.000).

Genes:

Basic unit of genetic information.

They determine the inherited characters

Each gene is a part of DNA sequences that contains genetic information

coding for synthesis of a certain protein

Chromosomesstorage units of genes.

Most human cells contain 46 chromosomes:

22 pairs of chromosomes , named autosomes.

1 pair of sex chromosomes (X and Y):

XYin males, XXin females

Genom & Gene


14/31


15/31


16/31

Interphase (G1-S-G2)

may extend for days,

weeks or longer

depending on the celltype

M phaseusually lasts

only an hour or so

S PHASE


17/31

DNA contains all informations for human.

Before any cell division, a cell must duplicate all its DNA.Replication occurs during S phase of cell cycle (synthesis

phase of interphase)

Cells also synthesize the additional histones (needed asthe cells double the nucleosomes in its chromosomes)

S-PHASE

DNA R li i


18/31

DNA Replication

Replication means making a

replica(an exact or identicalcopy)

DNA replication is the process of

making an exact copy of DNA byusing one of the parent DNA

strands as templateThe

original DNA strands are used as

templates for the synthesis of

new strands

DNA functions to :

Store genetic information &

transferring it to daughter cells during

mitosis by replication &

Transferof genetic information from

DNA to RNA to be expressed as

proteins

It occurs very quickly, very

accurately and at the appropriate

time in the life of the cell


19/31

Models of DNA Replication

In the late 1950s, three different

mechanisms were proposed for the

replication of DNA

Conservative

model

Both parental

strands stay together

after DNA replication

Semiconservative

model

The double-stranded

DNA contains one

parental & one

daughter strand

following replication

Dispersive model

Parental & daughterDNA are

interspersed in both

strands following

replication


20/31

Models of DNA Replication


21/31

replication

1. Semi-conservative mode2. Ordered and sequential

3. Semi-discontinuous

One strand synthesized continuously(Leading strand)

Other strand synthesized

discontinuously ( Lagging strand)

Fragments called Okazaki fragments

4. Accurate

5. Bi-directional


22/31

Three Steps for Replication

1. Initiation

2. Elongation

3. Termination


23/31

DNA template

Nucleotides : A ,T & G, and C

RNA primers

Enzymes

DNA Helicase

RNA polymerase ( Primase)

DNA polymerases

Topoisomerase I , II

Ligase

Some Additional factors

SSB proteins (Single-strand binding proteins (SSBs)

Requirements

DNA l T


24/31

DNA Ploymerase

Synthesis of lagging strand & gap filling

DNA polymerase

DNA repair

DNA polymerase

Mitochondrial DNA synthesis

DNA polymerase Synthesis of leading strand

DNA polymerase

DNA repair

DNA polymerase Types

rep ca on s n a e a or g ns


25/31

rep ca on s n a e a or g nsof replication

Hetereochromatin replicateslater in S Phase than

euchromatin Replication initiated at

multiple points known asReplications origins

DNA double helix is split open

by DNA helicase to expose thebase sequences

The resulting separation ofDNA strand are calledReplication bubbles

Two replication complexesform at each origin. One ateach end of the bubble and isa Y-shaped structure calledReplication fork

DNA R li ti I iti ti


26/31

The two DNA strands are separated

SSB proteins stabilize the single stranded DNA

Two replication forks are created

Each strand acts as a template

Replication proceeds from 5 to 3 end

DNA Replication Initiation

DNA El ti


27/31

1. DNA polymerase clamps to the leading strand & adds DNA

nucleotides to the RNA primer2. DNA polymerase proofreading activity checks and replaces

in correct bases

3. Continous (Leading) strand synthesis produces new

fragments on the 3to 5 template but in a 5 to 3

direction

4. Discontinous (lagging) strand synthesis produces okazaki

fragments but in 5 to 3 direction5. Replication proceeds along the single strands about 40-50

nucleotides persecond simultaneously in both directions

6. DNA Ligasejoined Okazaki fragment together

DNA Elongation


28/31

Replication orientation: 5 3

Movement of Replication fork

3

553

35

3

5

Okazaki fragment

Leading strand

(continous)

Lagging strand

(discontinous)Replication fork

1. Continous (Leading) strand synthesis produces new fragments on

the 3to 5 template but in a 5 to 3 direction

2. Discontinous (lagging) strand synthesis produces okazaki fragments

but in 5 to 3 direction

3. Replication proceeds along the single strands about 40-50

nucleotides persecond simultaneously in both directions

4. DNA Ligasejoined Okazaki fragment together


29/31


30/31


31/31

Documents

K6- Replikasi DNA