Cell Division Flashcards
What does DNA exist as
when a cell is not dividing?
-When a cell is not dividing the DNA exists as chromatin within the nucleus
What does chromatin consist of and where are they found?
consists of DNA and histone proteins and is found in the nucleus of eukaryotic cells
When cell division begins, what does chromatin do?
condenses to form chromosomes
What do chromosomes consist of?
Chromosomes consist of DNA, protein and a little RNA- The DNA is made up of many small sections called genes.
In diploid cells, what are are chromosomes found in?
in matching pairs called homologous chromosomes
What happens to chromosomes at the start of cell division?
the DNA replicates (during interphase) and the chromosomes are visible as two identical sister chromatids joined at the centromere.
What does a centromere do?
links two sister chromatids together
How many pairs of homologous chromosomes do humans have?
23
What does each homologous pair consist of?
one chromosome inherited from the mother (maternal) and one inherited from the father (paternal)
What is the diploid number?
The total number of chromosomes in a somatic (body) cell (2n)
What do gametes (sex cells) have?
one of each type of chromosome (i.e. half the diploid)
What is the diploid number of chromosomes for humans?
46
What is the haploid number of chromosomes for humans?
23
Where is the majority of time spent in a cell’s cell cycle?
interphase
What happens during interphase?
-a newly formed cell increases in size and performs several activities:
•DNA replicates
•Organelles are produced
•Protein synthesis occurs
•ATP synthesis occurs
What happens during G2?
-protein synthesis
-centrioles replicate
What happens during G1?
-cell gets bigger
-organelles replicated
-protein synthesis
-ATP synthesised
What happens during S phase?
DNA is replicated inside the nucleus (DNA helicase/DNA polymerase) so DNA content doubles
What are 3 process processes take place during interphase?
G1 and S and G2- cell is getting ready for entering mitosis (including replication of DNA)
What is the process of interphase?
-DNA replicates- occurs during S phase of interphase
-Organelles are produced = so daughter cells have the same number
-Protein synthesis occurs = including enzymes for cell division
-ATP synthesis occurs
what is mitosis and what are the four phases?
the division of the nucleus-
-Prophase
-Metaphase
-Anaphase
-Telophase
What happens in prophase?
•Chromatin condenses into visible sister chromatids joined at the centromere.
•Centrioles move to opposite poles, forming protein microtubules and developing the spindle.
•The nuclear envelope disintegrates, the nucleolus disappears, and chromosomes move towards the cell equator.
•Prophase is the longest stage of mitosis.
What happens during anaphase?
-A rapid stage (fastest) in which spindle fibres contract and shorten, the centromere splits, and sister chromatids are pulled apart.
-Chromatids are drawn towards opposite poles with the centromere leading.
What happens during metaphase?
Chromosomes align along the cell equator and attach to spindle fibres at the centromere
What happens during telophase?
•Chromosomes uncoil and lengthen.
•Spindle fibres break down.
•Nucleolus and nuclear envelope reform
What happens during cytokinesis?
•In animal cells, cytokinesis occurs by constriction of the parent cell from the outside inwards, forming a cleavage furrow.
•In plant cells, a cell plate forms across the equator of the parent cell from the inside outwards, and a new cellulose cell wall is laid down.
How is the time for a phase calculated?
(Number of cells in that phase/total number of cells) x time for one complete cell cycle
What is the summary for mitosis?
-Interphase
•ATP and protein synthesis
•New organelles produced
-Prophase
•Chromosomes condense
•Nucleolus disappears, nuclear membrane disintegrates
•Centrioles synthesise spindle
-Metaphase
•Chromosomes line up along the equator
•Spindle attaches to centromere
-Anaphase
•Spindle fibres shorten
•Chromatids pulled to opposite poles
-Telophase
•Nucleolus and nuclear envelope reform
•Chromosomes uncoil
•Spindle disintegrates
What are the differences in mitosis between animal cells and plant cells?
Shape- animal cells become rounded before mitosis whereas plant cells have no shape change
Centrioles- present in animal cells, absent in plant cells
Cytokinesis-in animal cells cleavage for developed from outside inwards pinching the cytoplasm whereas in plant cells cell plates develop from the centre outwards forming a new cell wall
Spindle - in animal cells degenerates at telophase whereas in plant cells it remains throughout new cell wall formation
-Occurrence- in animal cells mitosis occurs in the epithelial tissue bone marrow and other sites was implant cells it takes place meristems (tips of roots and shoots)
what does mitosis produce?
two daughter cells with the same number of chromosomes as the parent cell
How does mitosis ensure genetic stability?
Each chromosome is an exact replica of one of the original chromosomes, so mitosis produces cells that are genetically identical to the parent cell
What does mitosis lead to?
growth of an organism, repair of damaged tissues and replacement of dead cells.
Where mitosis occur in plants?
in root tips and growing points of shoots
where does mitosis occur in animals?
In human skin, mitosis replaces dead surface cells with genetically identical cells from below.
What does asexual reproduction do?
-produces offspring through mitosis, so that the offspring are genetically identical to the parent.
-There is no genetic variation; they are clones.
(in certain flowering plants, such as strawberry runners, daffodil bulbs, and potato tubers, large numbers of genetically identical offspring are produced.)
What do most animals and plant produce?
haploid gametes, which are not identical to the parent cell, allowing for sexual reproduction.
What are the advantages of asexual reproduction?
•Offspring are genetically identical to the parent, so they are able to survive successfully if environmental conditions are stable.
•Less time and energy are required as there is no need to produce gametes and find a reproductive partner.
•The population can rapidly increase in number if environmental conditions are stable
What is the disadvantage of asexual reproduction?
lack of genetic variation means offspring cannot adapt to changing environmental conditions.
what is the length of the cell cycle controlled by what does this ensure?
by genes, ensuring mitosis occurs where and when it is needed, such as for tissue repair and replacement of tissues in adults and correct development in embryos
What can carcinogens do?
Carcinogens, such as radiation, certain chemicals, and some viruses can mutate DNA and affect the genes that control the cell cycle.
What do proto-oncogenes do?
regulate the cell cycle by signalling when cells should divide
What are the two types of tumour that can form?
Benign -non-cancerous and won’t invade nearby tissues.
•Malignant -cancerous and can spread to other tissues
What does meiosis produce?
gametes in sexually reproducing organisms, resulting in four genetically different daughter cells
What are the two stages of cell division?
•Meiosis I: Chromosome number is halved.
•Meiosis II: Haploid cells divide again, producing four genetically different daughter cells Note- this stage is similar to mitosis .
What happens at prophase l?
•Chromosomes condense into visible sister chromatids joined at the centromere.
•Homologous chromosomes pair up in a bivalent.
•Chromatids from homologous pairs wrap around each other and then partially repel each other but remain joined at points called chiasmata. A chiasmata is where homologous chromosomes can exchange equivalent sections of DNA. This swapping is called crossing over.
•Nuclear envelope disintegrates, nucleolus disappears, centrioles move to opposite poles, and spindle microtubules form.
What happens at metaphase l?
•Chromosomes align themselves either side of the equator in their homologous pairs, attached to spindle fibres at their centromeres.
•Homologous pairs of chromosomes (bivalents) align randomly along the equator, leading to independent assortment.
•This results in a random combination of paternal and maternal chromosomes in each daughter cell.
What happens at anaphase I?
•Spindle fibres contract and shorten, separating bivalents and chromosomes are pulled to opposite poles.
•Each pole receives one chromosome from each homologous pair. This results in a random mix of maternal and paternal chromosomes due to independent assortment in metaphase I.
What happens during telophase l?
•In some species, the nuclear envelope reforms around the haploid chromosomes, which uncoil and lengthen. In many species, chromosomes remain condensed.
What happens in cytokinesis?
when the cytoplasm is divided, producing two haploid cells.
What happens is prophase II?
•Centrioles migrate to the poles and new spindle develops at right angles to the previous one.
what happens in metaphase II?
•Chromosomes align on the equator, attached to spindle fibres at their centromere.
•Independent assortment occurs with chromatids randomly facing either pole.
What happens in anaphase II?
•Spindle fibres contract and shorten.
•Centromeres split, and sister chromatids are pulled to opposite poles.
What happens in telophase II?
•Chromosomes uncoil and lengthen and are no longer visible under the microscope.
•Spindle breaks down.
•Nuclear envelope and nucleolus reform.
What happens in cytokinesis?
Cytokinesis produces four haploid daughter cells.
The species to survive in a constantly changing environment what is essential?
sources of genetic variation are essential
In what ways does meiosis introduce genetic variation?
-crossing over
-independent assortment
-random fusion of haploid gametes
What is the process of crossing over?
•During prophase I, chromosomes condense, and homologous pairs form a bivalent (synapsis)
•Chromatids in the bivalent join at chiasmata, where parts of the chromosome may be exchanged. This process is called crossing over.
What is the process of independent assortment?
•During metaphase I and II, chromosomes randomly distribute themselves at the equator of the cell.
•This random distribution leads to independent assortment of chromosomes.
•With 3 pairs of chromosomes, there are 23 = 8 possible combinations of maternal and paternal chromosomes.
What is the process of random fusion of haploid gametes?
•At fertilization, the diploid chromosome number is restored when two random haploid gametes fuse to form a zygote.
•Half of the chromosomes in the new cell come from the maternal gamete, and half come from the paternal gamete
What are the advantages of sexual reproduction?
•Allows offspring to adapt to a changing environment, this allows natural selection to take place.
•Spores produced by fungi and seeds by plants are dispersed widely to help reduce intraspecific competition.
What are the differences between meiosis and mitosis?
-One cell division in mitosis ~two cell divisions (meiosis I and II)
-In mitosis 2 daughter cells are produced
~4 daughter cells are produced
-In mitosis Chromosomes do not associate in homologous pairs (bivalents)~chromosomes form bivalents (prophase I)
-In mitosis the chromosome number in each daughter cell is diploid ~ the chromosome number in each daughter cell is halved (haploid)
-In mitosis crossing over does not take place~crossing over does take place
-In mitosis daughter cells are genetically identical~ daughter cells are genetically different
What is a gene?
Small sections of DNA which code for specific proteins.
What are gametes?
Haploid cells produced by the ovaries and testes.
What is interphase?
the longest part of the cell cycle. DNA replication, protein synthesis and ATP synthesis occur.
What are centrioles?
These move to opposite poles of the cell and produce protein microtubules during prophase.
What is prophase?
Centrioles move to opposite poles, chromosomes condense and the spindle forms during this stage of mitosis.
What is a chromosome?
Made of DNA, protein and a small amount of RNA.
What is cytokinesis?
Constriction of the centre of the parent cell after telophase; in plant cells a cell plate is formed first.
What does homologous mean?
Matching pairs of chromosomes
What is metaphase?
Chromosomes arrange themselves at the equator during this phase of mitosis.
What is chromatin?
This condenses during cell division to form chromosomes.
What is a centromere?
Chromatids are joined by this region.
What is telophase?
The nuclear envelope reforms and nucleoli reappear during this stage of mitosis.
What are sister chromatids?
Identical copies of a chromosome, joined at the centromere.
What is anaphase?
The spindle fibre contracts and pulls the sister chromatids to opposite poles during this stage of mitosis.
What is fertilisation?
Haploid gametes fuse to form a zygote, restoring the diploid chromosome number.
What is crossing over?
During prophase I sister chromatids of homologous pairs can wrap around each other and exchange sections of DNA at the chiasmata
What is independent assortment?
During metaphase I & metaphase II it is random which side of the equator chromosomes/chromatids line up on
