Transcript Mitosis - Zanichelli

1
Sylvia S. Mader
Immagini e
concetti
della biologia
2
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
A6 - Cell
Duplication
3
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Reproduction
ASEXUAL
REPRODUCTION
SEXUAL
REPRODUCTION
4
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Reproduction
During ASEXUAL REPRODUCTION each daughter cell
receives a copy of the parental cell DNA.
During SEXUAL REPRODUCTION two gametes (an
egg and a sperm cell) unite and the offspring receive a
combination of its parents DNA.
5
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cell division
The process by which a parent cell divides into two or
more daughter cells is called
cell division.
multicellular organisms
growth
unicellular organisms
reproduction
6
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Reproduction in Prokaryotes
For unicellular organisms
cell division is equivalent
to reproduction and is
called binary fission.
7
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
The cell cycle
INTERPHASE: the cell performs the functions that make it
unique and prepares to division.
MITOSIS: the cell divides into two daughter cells.
8
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Somatic cells and stem cells
Somatic cell: any cell forming the body of an adult
organism.
Stem cell: cell that can divide and differentiate into diverse
specialized cell types.
Stem cells act as a repair system for the body
9
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Interphase
G1 phase
first growing phase
Production of proteins
and enzymes.
S phase
synthesis phase
Proteins and DNA in the
nucleus replicate.
G2 phase
second growing phase
The cell prepares for
mitosis. DNA organizes
into chromosome.
10
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
M-phase: mitosis and cytokinesis
PROPHASE ➡ METAPHASE ➡ ANAPHASE ➡ TELOPHASE
• The nuclear material (chromatin) becomes visible
• Chromosomes organize in the center of the cell
• Chromosomes separate and move into each new cell
• Cytokinesis: the cytoplasm divides into two separate
cells
11
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Chromosomes
In Eukaryotes, during cell division
chromosome become visible.
12
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Haploid or diploid?
Somatic cells are diploid (2n): have two sets of chromosomes.
Gametes are haploid (n): the sperm and egg cells contain only
one chromosome of each kind.
During S phase DNA is copied, so two
copies of each chromosome exist.
13
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Mitosis
Mitosis maintains the original
chromosome number
14
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Mitosis
Prophase
15
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Mitosis
Metaphase
16
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Mitosis
Anaphase
17
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Mitosis
Telophase
18
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cytokinesis divides the cytoplasm
In animal cells, cytokinesis occurs when the cell membrane forms
a cleavage furrow.
In plant cells, cytokinesis involves the formation of a cell plate
from vesicles and a cell wall.
Animal cell
Plant cell
19
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cell cycle is controlled by checkpoints
If the cell misses one of the checkpoints, apoptosis (the
programmed cell death) occurs.
20
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cell cycle is controlled by signals
Checkpoints respond to specific signal molecules that
stimulate or inhibit the cell cycle.
Internal signal molecules
External signal molecules
Kinases and Cyclin
Growth factors and hormones
Contact inhibition
when two cells come in contact
the cells arrest the growth
21
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cell cycle is controlled by signals
Internal signals
kinases and cyclins
combine and drive the
cell cycle
22
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cell cycle is controlled by signals
External signals
1. Signaling molecules
come from outside the cell
to a receptor.
2. The signal is transmitted
to the nucleus.
3. The control system in
the nucleus receive the
signal .
23
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cancer cells have anomalies in the
cell cycle
Cancer cells lack differentiation and have abnormal nuclei.
Cancer cells undergo metastasis when form tumors far
from the original site.
24
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Homologous chromosomes
Chromosome pairs of the same length and centromere
position with genes for the same characteristics.
25
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis
After meiosis, one chromosome from each homologous
pair is in the haploid daughter cell.
26
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis: synapsis
The pairing of two homologous chromosomes is called
synapsis and forms tetrads.
27
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis: crossing-over
After synapsis, DNA segments from
one chromatid pass to another
chromatid in the tetrad.
The result are two genetically new
chromatids.
28
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Genetic variability
Crossing-over allows recombination of genes in chromosomes
and contributes to the genetic variation of the offsprings.
29
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis requires two division cycles
Meiosis I: Homologous pairing and crossing-over occur
30
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis requires two division cycles
Meiosis II: chromatids from meiosis I separate into 4 cells
31
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Meiosis requires two division cycles
The life cycle of most multicellular organisms include both
mitosis and meiosis.
Mitosis is involved in growth.
Meiosis is involved in the
production of gametes
(spermatogenesis and oogenesis).
32
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Chromosomal abnormalities
Nondisjunctions occur when there are anomalies in the
separation of chromosomes (meiosis I) or chromatids
(meiosis II).
Those mistakes can lead to
monosomy (2n-1) or trisomy
(2n+1) conditions.
33
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Chromosomal abnormalities
Structural abnormalities may be caused by different
mechanisms.
Deletion
Duplication Inversion
Translocation
34
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Trisomy 21
Down syndrome, also known as
“trisomy 21”, is a chromosomal
condition caused by the presence
of a third copy of chromosome 21.
35
Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012