Cell Nuclear Division D2.1 Flashcards
Cell division
cells divide in two by cell division. only produced by pre-existing cells.
Mother cell
the cell that divides
Daughter cell
the cell produced from cell division
What processes require cell division?
- growth
- reproduction
- maintenance
- tissue repair
What is the role of mitosis in eukayotes?
maintain the chromosome number and genome of cells
What is the role of meiosis in eukayotes?
halves he chromosome number and generates genetic diversity
Anucleate
no nucleus
Chromosome
strand of DNA that carries genes
What is the interphase of cell life cycle?
DNA is duplicated, a single chromosome duplicated to form two identical chromatids called sister chromatids
What is the M-phrase of the cell life cycle?
sister chromatids separate and each nucleus requires one, the cohesin loops must be cut. AKA cell division
Centromere
constricted region that joins two sister chromatids
What three things must happen for cell division to occur?
- condensation of chromatin into chromosomes
- microtubule and spindle fiber organization
- movement of chromosomes
Explain the condensation of chromatin by supercoiling
long, thin chromatin strands are condensed into compact short chromosomes by wrapping the DNA double helix around proteins called histones to produce nucleosomes that continue to coil to produce ‘beads on a string’. continued coiling will result in structure of chromosomes
What are needed for movement of chromosomes?
- centrioles
- centrosomes
- microtubule fibres
- kinetochores
Explain the movement of chromosomes
chromosomes are moved to opposite sides of the cell using microtubules which are assembled at the centrosome’s microtubule organizing center.
Centriole
a cylindrical organelle in animal cells composed of microtubules made of tubulin protein
Centrosome
region close to the nucleus for cell division
Microtubule fibers
attach to chromosomes during nuclear division to form a spindle
Different types of microtubule fibers
- pull apart the sister chromatids
- push spindle poles apart to contribute to cell elongation
Kinetochore
a protein complex associated with the centromere, a microtubule motor that shortens microtubule fibers and puts them under tension causing chromatid movement
Mitosis: Prophase
- chromatin condenses and supercoils, DNA becomes shorter and compact
- the chromosomes become visible as sister chromatids
- nuclear membrane begins to break down
- centrosomes move to opposite sides of the. cell and spindle fibers begin to form
Mitosis: Metaphase
- movement of microtubule spindle fibers cause the sister chromatids to line up along the center aka the metaphase plate.
- microtubules continue to grow and attach to the kinetochores n the centromeres of sister chromatids
- sisters within each chromosome become attached to opposite poles
Mitosis: Anaphase
- microtubules link each chromosome to opposite poles of cell
- cohesin loops are cut, chromatids become separated
- kinetochores shorten the microtubules, pulling to the poles
- non-kinetochore microtubules elongate and stretch the cell
Mitosis: Telophase
- chromosomes arrive at opposite poles of cell and the nuclear membrane reforms around
- chromosomes become less condensed to form chromatin
- nucleoli reappear
- microtubule spindle fibers disappear
Mitosis: Late telophase
- plasma membrane is pulled around the equator
- two daughter cells are formed
Cytokinesis
separation of cell’s cytoplasm and daughter cell from parent
Cytotkinesis in plants
membrane-enclosed vesicles derived from the golgi apparatus migrate to the center of the cell where they fuse to form structures that will form two layers of plasma membrane. this cell plate develops until it connects with the existing cell’s plasma membrane. each daughter cell secretes cellulose to form new adjoining cell walls.
Cytokinesis in animal cells
a ring of contractile actin and myosin protein filaments forms around the cell to constrict at the equator of the cell; the cleavage furrow is formed. once cleavage furrow is reached the center of the cell, it is pinches apart to form two daughter cells.
Equal cytokinesis
both daughter cells receive same amount of cytoplasm
Unequal cytokinesis
opposite of equal, cells can still survive if receive a nucleus and at least one organelle.E
Example of unequal cytokinesis
production of female egg cells, polar bodies received after the two division contain much less cytoplasm. larger cells continue to mature into an ovum.
Meiosis
a reduction division of one diploid nuclei to produce 4 haploid nuclei
Diploid
nucleus has two chromosomes of each type, 3 copies of every gene but different versions
Haploid
nucleus contains half the genetic material, one set of genes
Prophase I
- chromatin condenses and supercoils, DNA becomes shorter, visible, and compact.
- centrosome movement, spindle formation and nuclear membrane breakdown
- homologous chromosomes pair up, aligned gene by gene
- the sister chromosomes of non homologous pairs perform crossing over at the chiasmata
- microtubules begin to attach to the two kinetochores of each homolog
Metaphase I
- homologous pairs of sister chromatids AKA tetrads or bivalents align on the equator of the cell, one chromosome in each pair facing each pole
- both chromatids of one homolog are attached to microtubules at the kinetochore from one pole
Anaphase I
- spindle microtubules contract and pull the homologous pairs apart
- the homologs move toward opposite poles (disjunction)
- one chromosomes from each tetrad moves to either 2 poles
Telophase I
- each half of the cell has a haploid nucleus
- each chromosome is composed of two sister chromatids
- cytokinesis occurs and new nuclear membrane forms
- cleavage furrow
Meiosis II
during another round of cell division, sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes. this meiosis II works like mitosis
Tetrad
homologous pair of sister chromatids
Reasons for variation in meiosis
- random orientation
- crossing over
Random orientation as source of variation in meiosis
random alignment of homologous sister chromatids during metaphase promotes genetic variability because of the orientation of one tetrad doesn’t influence any others
Crossing over as source of variation in meiosis
during prophase I leads to an exchange of genes between homologous pairs of sister chromatids, increasing genetic variability
Recombinants
chromosomes with the new combination different from parents
Non-disjunction
failure of homologous chromosomes or sister chromatids to separate during meiosis I or II.
What does non-disjunction cause?
chromosome abnormalities
Down syndrome
has three copies of chromosome 21. during meiosis the sister chromatids have not been separated so gametes has 24 chromosomes
What only happens in mitosis?
- 2 daughter cells produced
- 2 cells produced are genetically identical
- only in somatic cells
- one stage
- no change in no. of chromosomes
- no crossing over
- diploid product
What only happens in meiosis?
- 2 stages
- 4 haploid products
- daughter cells genetically different
- reproductive cells
- tetrads formed
- sister separate only in meiosis II
- crossing over
- independent assortment
What happens in both mitosis and meiosis?
- microtubules used o move chromosomes
- starts with diploid
- use kinetochores for shortening of microtubules
- nuclear membrane breakdown
Cell proliferation
rapid incerase in the number of cells by mitosis.
What is cell proliferation needed for?
in multicellular organisms for growth, cell replacement, and tissue repair
Cell proliferation for growth in animals
during embryonic development there is cell proliferation throughout the animal embryo. some areas of the human body cell still proliferate during juvenile years
Cell proliferation for growth in plant
confined to growth regions called meristems
Meristems
group of cells that retain the ability to divide by mitosis
Apical meristems and where it is
responsible for primary growth and occur at the tip of stem and root
Shoot apical meristems
produce new cells that elongate and extend the length of the axis of the shoot, forms cells that give rise to lateral organs
Root apical meristems
less complex than shoot apical meristems
Lateral meristems
mesistematic tissue that give rise to new cells in the center of vascular bundles
What does growth of lateral meristems do?
increase circumference and strength of the stem by causing secondary growth of plant.
Cell replacement example
on skin cell division happen in the basal layer of the epidermis. cells produced here are displaced toward the skin surface by continued cell division and large amounts of hydrophobic protein keratin is formed, therefore cells dry out
Tissue repair
after a wound, stem cells in the dermis can repair the damage unless it is very deep. following blood clotting, inflammation causes increased blood flow to the wound, enabling white blood cells and fibroblasts to appear at the damaged skin
Fibroblasts
produce proteins that help wound closure
What is interphase considered?
a very active phase of the cell cyle with many processes blurring in the nucleus and cytoplasm
What phases does interphase include?
G1 phase
S phase
G2 phase
G1 phase
cell increases in size and prodices proteins and enzymes required for DNA replication
S phase
DNA is duplicated in order to provide each daughter cell with one full set of chromosomes
G2 phase
after DNA replication, cell continues to grow, organelles increase in numbers, microtubules begin to form
G0 phase
some cells grow and differentiate for specific role as a specialized cell
How is the cell cycle controlled by cyclin?
for cell cycle to continue, proteins called cyclins become active when coupled with enzymes called cyclin dependent kinases (CDK). once bound to the CDK, the complex becomes phosphorylated, allowing it to activate other proteins that advance the cell cycle by carrying out tasks specific to one of the phases of the cell cycle.
Which 3 points of the cell cycle is controlled by cyclin
G1 checkpoint, G1 cyclin tells the cell to grow and get ready for replication of DNA
Mitotic cyclin tell the cell to make microtubules.
Correct chromosome duplication is assessed at G2
unless cyclin reach a threshold concentration, the cell does not progress to the next stage
What does mutations in the cell cycle result in?
cancer
Tumor supressor gene
produce regulatory proteins which stop or prevent uncontrolled cell division and stimulate apoptosis in case of damaged DNA
Oncogene
proto-oncogenes that become mutated and lead to uncontrolled cell division and may continue to cancer
Proto-oncogene
code for proteins which enhance the cell cycle and prevent cell death
Beign/malignant tumors
abnormal groups of cells that develop at any stage of life in any part of the body. benign tumors do not spread to other tissues and organs by metastasis
malignant tumors spread to other tissues and organs by metastasis to form secondary tumors
Metastasis
cell invades neighboring tissue or organ and adhere to each other
Primary tumor
place where cancer statrs
Secondary tumor
when cancer cells break away and settle in another part of the body
Mitotic index
a measure for the proliferation status of a cell population. the ratio between the number of cells in mitosis and the total number of cells.
mitotic index = number of cells in mitosis/total number of cells
