Cell Division in Prokaryotic and Eukaryotic Organisms Flashcards
What is cell division?
When a parent cell divides into two or more daughter cells
Do all cells divide?
Yes
Are daughter cells genetic clones or genetically distinct from parent cells?
Either depending on the cell
What is cell division used for in unicellular organisms(prokaryotes)?
Asexual reproduction
What is cell division used for in multicellular organisms(eukaryotes)?
tissue growth, tissue homeostasis(maintenance), repair and sexual reproduction
What reproduction strategies to prokaryotes use to divide?
- binary fission
- budding
- fragmentation
- sporulation
Do prokaryotes use asexual or sexual reproduction?
asexual reproduction
Do eukaryotes use asexual or sexual reproduction?
sexual or asexual reproduction
What programmes do eukaryotic cells divide by?
asexual - mitosis
sexual - meiosis
The regulation of cell division is crucial for maintaining what?
the balance between growth and tissue homeostasis
What can errors and disruptions lead to in cell division?
uncontrolled cell division
What is control of cell division mediated by?
external and internal ‘signals’
What must DNA have for replication to occur?
- available nutrients
- no DNA damage
- cell size to have increased sufficiently
How fast do unicellular organisms divide and grow?
as fast as they can
When do cells of a multicellular organisms divide?
only when more cells are needed
Growth factors and mitogen stimulate what?
cell growth and division without crossing the cytoplasmic membrane
What is PDGF?
small chemical molecules which interact with specialised proteins on the cell to activate events in the cell
What are the steps of binary fission?
- prokaryote parent cell initiates replication
- a copy of the cells DNA is created
- cell elongates and cross wall forms
- cross wall forms completely and daughter cells seperate
Is binary fission a continuous process?
yes
Do the events of cell growth, DNA replication and cell division occur simultaneuosly?
Yes
What role does FtsZ play in regulating binary fission in bacteria?
FtsZ polymerises into a dynamic ring that defines the division site, recruits downstream proteins, and directs peptidoglycon synthesis to drive construction and cell division
Describe Budding
a small bud forms at one end of the mother cell or on prosthecae, as growth proceeds the size of the mother cell remains about constant but the bud enlarges, when the bud is about the same size as the mother is separates
Types of horizontal gene transfer
- conjugation
- transformation
- tranduction
What are transposons?
a class of genetic elements that can ‘jump’ to different locations within a genome
Describe interphase
most eukaryotic cells are held in G1 until they are instructed to divide
mitogens trigger G1 arrested cells to commit to cell division
Describe M phase
nuclear + cell division
different processes for mitosis vs meiosis
What are the 4 stages of the cell cycle in a eukaryotic cell?
- G1
- S
- G2
- M
Describe G1
two separate or independent copies of each chromosome
2n chromosomes
Describe S
each chromosome is copied, or replicated, to result in two chromatids for each original chromosome
between 2n and 4n chromosomes
Describe G2
chromosomes exist as pairs of chromatids
4n chromosomes
Describe M
sister chromatids are separated into daughter cells
4n to 2n chromosomes in daughter cells
5 Stages of mitosis
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
Describe prophase
the nucleolus disappears, the nuclear envelope starts to fragment and the DNA asscoiated proteins within a cell start to coil up and condense
What are microtubule fibres in the cytoskeleton organised by?
the microtubule organising centre(MTOC)
During mitosis, the cytoplasmic microtubule complex is resorbed, and…
each of the replicated centrosomes assembles a radial ‘astral’ array of microtubules that separate to define a the mitotic spindle and its poles
Why is breakdown and regrowth of the cytoskeleton microtubule network and its reassembly essential?
its essential for accurate chromosome segregation during M phase
What is microtubule growth mediated by?
addition of GTP-bound tubulin dimers to the plus end of a microtubule fibre
What is microtubule shrinkage modulated by and what does it produce?
- hydrolysis of GTP
- to produce GDP-bound tubulin dimers which dissociate from the plus end of a microtubule fibre
Describe prometaphase
during prometaphase in cells other than fungal, the nuclear membrane breaks down fully. microtubules reorganise into the the mitotic spindle and attach to chromosomal centromeres, at regions known as kinetochores.
Describe metaphase
during metaphase the replicated chromosomes line up along the equator of the dividing cell. cells arrest in metaphase until all chromosomes are attached to the mitotic spindle correctly
Describe anaphase
at anaphase, the sister chromatids synchronously seperate to form two daughter chromosomes; each is pulled towards opposing spindle pores
Describe telophase
separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells
What is cytokinesis?
the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells
Are all forms of mitosis the same?
no
Describe budding
a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site
2 errors in chromosomal segregation during mitosis and/or meiosis
- failure to correctly separate the pairs of chromosomes or sister chromatids to different daughter cells is referred to as non-disjunction
- this can be a result of numerical aberrations(too many or too few chromosomes, aneuploidy)
Describe features of mitosis
- asexual form of reproduction
- daughter cells are genetic clones
- daughter cells contain the same amount of genetic material as the parent
Describe features of meiosis I
- sexual form of reproduction
- daughter cells are genetically unique
- daughter cells contain half the amount of genetic material as the parent cell
Describe the features of meiosis II
- sexual form of reproduction
- daughter cells are genetically unique
- daughter cells contain half the amount of genetic material as the parent cell
Meiosis I is a reduction division…
it halves the number of chromosomes within the resulting daughter cells. recombination between non-homologous sister chromatids(crossing over) occurs -> increase in genetic variation
Phrophase I is similar to mitosis…
nuclear envelope breakdown; formation of the microtubule spindle and chromatin condensation occurs. each homologous pair of duplicated chromosomes align closely together. the homologous pairs are initially linked together along their entire length by a protein scaffold called synaptonemal complex. sections of non-sister chromatids may exchange with each other through a process known as crossing over ->increased genetic variation
Metaphase I the homologous chromosome pairs are…
aligned at the central plane of the cell by the spindle microtubules. kinetochores assemble on one side of each chromatid in meiosis I. independent assortment of maternal and paternal chromosomes occurs, increasing genetic diversity in daughter cells
Does meiosis cause genetic diversity in gametes?
yes
Each gamete has a unique genetic makeup due to:
- crossing over events in meiosis I
- random(indepedant) sorting of homologous chromosomes in meiosis I
- random(independant) sorting of sister chromatids in meiosis II
