Cell division Flashcards
Differences between mitosis and meiosis
- In mitosis the daughter cell has same or full number of chromosomes 46 .
- in meiosis the daughter cell contains half the chromosomes 23 .
- in mitosis each chromosome splits into two chromatids and each one moves towards each pole of the dividing cell
- while in meiotic cell division “ meiosis “ the chromosomes arrange themselves in pairs and half of their number 23 moves towards each pole of the dividing cell .
The cell cycle
- Are the changes which occur in the cell during its division ( mitosis ) and during its rest ( interphase ) .
Parts of cell division
- mitosis part
- interphase part
The mitotic part of the cell cycle
Is the period of cell division in which each cell divides by mitosis to give two daughter cells
The interphase part of the cell cycle
Is the period of cell rest in which the cell is in a resting condition before starting another cell division
The interphase period is divided into
G1-phase
S-stage
G2-stage
Gap one stage
- in this stage , the nucleus of each daughter cell has 46 chromatids which are called interphase chromosomes
- the period of gap one happens between the end of mitosis and the beginning of the next S-Stage
Synthesis stage
In this stage - DNA is duplicated through the process of synthesis and replication of DNA molecules
- so that we have 46 identical pairs of chromatids
Gap two stage
- very short period of time lies between the S-Stage and the beginning of mitosis
- the two chromatin threads of each pair become shorter and thicker —> each pair of the identical chromatids becomes joined together at the centromere to form the chromosomes of the next cell division “ mitosis “ —> the two centrioles are also duplicated into two pairs in this “ gap two stage “ —> now the cell contains 46 pairs of identical chromatids and four centrioles .
Cells of type one according to their cell cycle
- can not divide —> remain outside the cell cycle —> their number is kept constant —> the die cell is rarely replaced by new ones .
The cell of type two according to their cell cycle
- unable to divide —> when they die they are replaced by daughter cells —> arising from stem cells of the same family —> this stem cells are present in the same region
The cell of type three according to their cell cycle
- normally are not divide —> but at a time of need —> they can divide and renew their kind of cells
Give example about type one cells
The nerve cells
Give example about type two cells
The absorbing and secretory cells of the intestine
Give example about type three cells
Liver cells and hormone secreting cells of the endocrine glands
Give the exception from cell division
The nerve cells and cardiac cells are exception from cell division
Types of cell division
- Amitosis “ direct cell division “
- mitosis “ indirect cell division “
- meiosis “ reduction cell division “
Tell me about Amitosis cell division
- it is a simple division of the nucleus and cytoplasm
- it occurs in lower animals like amoeba and certain cells of the placenta and embryo
- it is a process of Asexual reproduction of cells
Tell me about mitosis cell division
- it occurs in the general cells of the body “ somatic cells “
- the term mitosis —> mitos = thread , osis = process .
- Example —> process in which threads of chromosomes appear during the stages of mitosis
- it gives each daughter cells full number of chromosomes
- the daughter cells will have the same amount of genetic material as the mother cells
Tell me about meiosis cell division
- it occurs in germ cells —> which present in the testis and ovary during formation of gametes .
- it gives each daughter cells the half number of chromosomes “ haploid number “
When the cell begins to divide by mitosis certain changes occur in its cytoplasm what they are ?
- a spindle - shaped structure is fused by the microtubules which originate from the cytoplasm —> this spindle plays an important role in bringing the chromosomes at the middle of the dividing cell —> it is also important in the movements of chromosomes towards each end of the elongated dividing cell
When the cell begins to divide by mitosis certain changes occur in its nucleus what they are ?
- the chromatin granules change into 46 chromosomes . Each chromosomes is formed of two chromatids which separate from each other during cell division —> each chromosome divides normally in a longitudinal manner into 2 chromatids .
- the half number of these chromatids moves towards each pole of the dividing cell
- in each new daughter cell and during its interphase , each chromatid changes into a chromosome , thus 46 chromatids form again the full number of chromosomes which are 46 chromosomes .
The period of mitosis
The whole process takes from one to two and half hours according to the cell type
The prophase period compared to otger phases in mitosis
It takes the linger time than any phase —> takes about one and half hours
Early prophase in mitosis
- Each pair of centrioles move to one pole of the dividing cell
- chromosomes formed of two similar elements nts which very closes to each other and called chromatids
- if the centrioles does not divide in previous gap two stage —> the centrioles duplicate
- the cytoplasm surrounding each centriole to form ASTRAL RAYS
- the cytoplasm between the two centrioles also modifies to form SPINDLE FIBERS
- the nucleoli and nuclear envelop —> disappear
Metaphase of mitosis
- the mitotic spindle is well formed and its cytoplasmic microtubules are attached to the centrioles
- each chromosome in formed of two chromatids which are connected with each other at a point called centromere —> at this centromere there are two rounded bodies called kinetochores —> which form another type of microtubules called chromosomal microtubules
- the chromosomal microtubules and cytoplasmic microtubules both are forming the mitotic spindle .
- cytoplasmic microtubules —> arise from cytoplasm —> attached to the centrioles
- chromosomal microtubules —> arise from kinetochores of chromosomes —> attached to chromosomes .
Anaphase of mitosis
- each chromosome ( two chromatids ) split at the centromere by normal longitudinal division —> now we have 92 chromatids
- half of 92 chromatids move to one pole of the cell and the other 46 to the other pole
Telophase of mitosis
- construction begins to develop at mid point of the elongated cell
- the chromatids “ know as chromosomes “ reach pole of the cell
- chromosomes become thinner , more elongated and faintly stained
- nuclear membrane will develop around each set of chromosomes
- two daughter nuclei are formed
- process accompanied by cytokinesis or division of cytoplasm
The characteristics of meiosis
- occur only in germ cells of the testis and ovary
- each mother cell give rise to four cells —> each one have haploid number of chromosomes “ 23 “
- in males , the 4 daughter cells are all viable spermatozoa
- in females only one of the 4 daughter cells is a viable egg cell , and the other 3 fail to envelop and are known as polar bodies
- consists of two nuclear divisions
meiosis consist essentially of two nuclear division which follow each other tell me about them .
- The first one —> involves the separation of chromosomes leading to the formation of two haploid nuclei ( each one contains 23 chromosomes )
The second one —> involve the longitudinal separation of chromatids in each one of the previous two haploid nuclei —> leading to the formation of four haploid nuclei ( each nucleus contains 23 chromatids which will be transformed into chromosomes )
The prophase of first meiosis
- leptotene phase —> the 46 chromosomes appear as thin threads and long filaments
- zygotene phase —> 46 chromosomes arranged in 23 pairs of homologous chromosomes called Bivalents, one number is from the father and the other one is from the mother
- pachytene phase —> chromosomes becomes shorter and thicker —> nucleus appear at this stage
- diplotene phase —> each chromosomes of each bivalent start to separate from each other —> separation not yet complete —> every two chromosomes remain in contact with on another for some time and touching at certain points known chiasmata —> number of chiasmata generally reduced —> chromosomes continue their separation
- diakinesis —> in which the nuclear membrane and nucleolus disappear and a mitotic spindle is formed
Metaphase of first meiosis
The mitotic spindle is well developed across the cell —> the 23 bivalent homologous chromosomes become arranged in the equatorial plane
The anaphase of first meiosis
- the bivalent chromosomes separate from one another —> 23 chromosomes move towards the corresponding poles of the dividing cell
The telophase of first meiosis
- at each pole of the dividing cell , the 23 chromosomes become surrounded by a nuclear membrane to form the nucleus of the daughter cell
Give the exception from cell division
The nerve cells and cardiac cells are exception from cell division
Types of cell division
- Amitosis “ direct cell division “
- mitosis “ indirect cell division “
- meiosis “ reduction cell division “
Tell me about Amitosis cell division
- it is a simple division of the nucleus and cytoplasm
- it occurs in lower animals like amoeba and certain cells of the placenta and embryo
- it is a process of Asexual reproduction of cells
Tell me about mitosis cell division
- it occurs in the general cells of the body “ somatic cells “
- the term mitosis —> mitos = thread , osis = process .
- Example —> process in which threads of chromosomes appear during the stages of mitosis
- it gives each daughter cells full number of chromosomes
- the daughter cells will have the same amount of genetic material as the mother cells
Tell me about meiosis cell division
- it occurs in germ cells —> which present in the testis and ovary during formation of gametes .
- it gives each daughter cells the half number of chromosomes “ haploid number “
When the cell begins to divide by mitosis certain changes occur in its cytoplasm what they are ?
- a spindle - shaped structure is fused by the microtubules which originate from the cytoplasm —> this spindle plays an important role in bringing the chromosomes at the middle of the dividing cell —> it is also important in the movements of chromosomes towards each end of the elongated dividing cell
When the cell begins to divide by mitosis certain changes occur in its nucleus what they are ?
- the chromatin granules change into 46 chromosomes . Each chromosomes is formed of two chromatids which separate from each other during cell division —> each chromosome divides normally in a longitudinal manner into 2 chromatids .
- the half number of these chromatids moves towards each pole of the dividing cell
- in each new daughter cell and during its interphase , each chromatid changes into a chromosome , thus 46 chromatids form again the full number of chromosomes which are 46 chromosomes .
The period of mitosis
The whole process takes from one to two and half hours according to the cell type
The prophase period compared to otger phases in mitosis
It takes the longer time than any phase —> takes about one and half hours
Early prophase in mitosis
- Each pair of centrioles move to one pole of the dividing cell
- chromosomes formed of two similar elements nts which very closes to each other and called chromatids
- if the centrioles does not divide in previous gap two stage —> the centrioles duplicate
- the cytoplasm surrounding each centriole to form ASTRAL RAYS
- the cytoplasm between the two centrioles also modifies to form SPINDLE FIBERS
- the nucleoli and nuclear envelop —> disappear
Metaphase of mitosis
- the mitotic spindle is well formed and its cytoplasmic microtubules are attached to the centrioles
- each chromosome in formed of two chromatids which are connected with each other at a point called centromere —> at this centromere there are two rounded bodies called kinetochores —> which form another type of microtubules called chromosomal microtubules
- the chromosomal microtubules and cytoplasmic microtubules both are forming the mitotic spindle .
- cytoplasmic microtubules —> arise from cytoplasm —> attached to the centrioles
- chromosomal microtubules —> arise from kinetochores of chromosomes —> attached to chromosomes .
Anaphase of mitosis
- each chromosome ( two chromatids ) split at the centromere by normal longitudinal division —> now we have 92 chromatids
- half of 92 chromatids move to one pole of the cell and the other 46 to the other pole
