WEEK 2: cell division and differentiation Flashcards
2 types of cell division are?
mitosis and meiosis
Cell division is essential for?
tissue development/growth + restoration/regenration of damaged tissues
cell division can lead to what type of diseases?
neurodegenration, autoimmune diseases, metabolic diseases, cardiovascular diseases, haematological and malignancy
how many chromosomes in the human body?
23
what is a chromatid?
a chromatid is one of two identical halves of a replicated chromosome- they are referred to as sister chromatids
Mitosis
Cell DNA content is duplicated & cell divides into 2 identical diploid daughter cells
Diploid VS Haploid
diploid= paired chromosomes, one from each parent
haploid= single set of chromosomes
Cell Cycle consists of?
Interphase, Mitosis, Cytokinesis
Interphase
cell performing normal function, not actively focused on division, can be indefinite, preparation for mitosis, most cells are in interphase- consists of G1, S and G2 -> end of interphase is preparation for mitosis
Mitosis
replicated chromosomes are separated into new daughter cells, 1-3 hours
cytokinesis
the physical separation into two daughter cells
G1 phase
step between division and synthesis
normal cell function
generation of organelles
8-12+ hours
S phase
- duplication of chromosomes
- DNA replication
- synthesis of histones and nuclear proteins
- centriole replication
- 6-8 hours
G2 phase
- 2 - 5 hours
- final protein synthesis
- cell contents organise for mitosis
G0 phase
- normal cell function
- not preparing for division
Prophase
Early:
- DNA coils and chromatin condenses + nuclear membrane disappears
Late:
- centrosomes migrate to opposite sides of the cell
Metaphase
chromosomes align in the centre and attached to microtubules held by centrosomes (centrioles)
Anaphase
microtubules pull the chromatids away from the centre
Telophase
- nuclear membranes reform
- DNA uncoils
Cytokinesis
- cytoplasmic division of the daughter cells
what are the 3 different checkpoints?
G1 -> S: Is your DNA intact?
G2-> M: Have you completed DNA replication?
Metaphase -> Anaphase: Are all your chromosomes aligned at the equator?
What are cyclins?
they are at the core of regulating the cell cycle and their level of fluctuations determine which part of the cell cycle that the cell enters
Cyclin dependent kinase (CDK)
is an enzyme that plays a crucial role in regulating the cell cycle, they are inactive on their own and need to bind to specific cyclins to function , they help in checkpoint regulation as well as regulate DNA replication
G1 Phase
Cyclin D + CDK2/4/6 + helps in cell cycle entry and progression through G1
S phase (DNA Synthesis Phase)
Cyclin E + CDK2
Initiates DNA replication
G2 Phase (prepares for Mitosis)
Cyclin A + CDK2/1
Helps in the transition to mitosis
M Phase (Mitosis/Cell division)
Cyclin B + CDK1
Regulates mitotic entry + progression
what do p16, p21, 27 do
they inhibit the CDK and stop the cell cycle at that particular stage
what is p53?
this protein is a transcription factor, it binds the DNA and it regulates expression, it can turn genes on/off depending on the gene, it maintains genomic stability and initiates apoptosis/inhibits angiogenesis. it is generally induced in response to error, it arrests cells and stops cell growth, it also activates DNA repair.
what kind of anti cancer drugs exist?
viblastin, taxol, pacalitaxel, docotaxel
what do anti-cancer drugs do?
they disrupt microtubule formation, spindle formation, chromosome misalignment and target breast, ovarian, head and neck cancer
Define meiosis
a type of cell division that produces gametes (sperm/egg cells in animals) with half the number of chromosomes (haploid) compared to the original cell (diploid). it ensures genetic diversity.
What occurs in Meiosis I?
separation of homologous chromosomes (pairs of chromosomes, one from each parent)
What occurs in Meiosis II?
seperation of sister chromatids (identical copies of a chromosome) forming 4 haploid cells
Meiosis only occurs in?
germ cells - reproductive cells that give rise to gametes
How many rounds of cell division in meiosis?
Two, Meiosis I and Meiosis II. DNA replication only occurs once, but the cell divides twice.
What would happen to chromosome numbers across generations without meiosis?
Chromosome numbers would double each generation, hence meiosis ensures that offspring have the same chromosome number as parents.
What occurs in the DNA replication stage (before Meiosis)
chromosomes duplicate and form sister chromatids (identical copies)
What occurs in prophase I (synapsis and crossing over)
Homologous chromosomes pair up and exchange genetic material, hence increasing genetic diversity
- chromosome condensation
-cross over and recombination between non sister chromatids
Name 3 differences between mitosis and meiosis
Number of daughter cells: Mitosis is two identical diploid cells and meiosis is 4 genetically unique haploid cells
Chromosome number: Mitosis maintains chromosome number whereas meiosis reduces the chromosome number by half
Location: Mitosis occurs in somatic body cells whereas mitosis occurs in germ cells
What is the first sub-stage of prophase I?
Leptonema (Stage 1)
What occurs in Leptonema (Stage 1)?
- Diploid chromosomes condense forming long thin threads, attach to nuclear envelope, individual chromatids not visible as they are closely attached, appearing as a single unit
& search for homologous pair begins
what occurs in zygonema?
Synapsis occurs
- homologous chromosomes (one from each parent) come together and begin to pair up side by side - highly specific and aligns corresponding genes on each chromosome
- chromosomes align side by side known as a tetrad (4 chromatids)
-homologs now aligned and set the stage for crossing over (genetic recombination) - genetic material will be exchanged at points known as chiasma
what occurs in pachynema? (stage 3)
- all chromosomes have aligned
- genetic recombination occurs
-exchange of material between two non-sister chromatids creates diversity
what occurs in dyplonema? (stage 4)
- sister chromatids move away from each other and sister chromatids are visible as they continue to shorten and thicken
-homologs remain attached at specific points (chiasma) - chiasma hence becomes visible
what occurs in diakinesis (stage 5)
- chromosomes condense, thicken
- detach from nuclear membrane
- nuclear envelope disintegrates
- sister chromatids join at centromere
- non-sister chromatids join via chiasmata
What occurs in metaphase I?
- spindles form between centrioles at opposite poles of the cell
- tetrads line up on the spindles on the metaphase plate
-centromeres form homologous chromosomes on opposite sides
-random assortment introduces diversity
What occurs in Anaphase I?
spindles pull homologus chromosomes apart,
each cell has one of a pair of chromosomes (with crossed over material) and one sex chromosome
What occurs in Telophase I?
- Nuclear membrane develops between each set of chromosomes
-Cytoplasmic division in males is equal whereas in females it is unequal - Daughter cell with more cytoplasm becomes the egg
- two haploid cells form, chromosomes are still double
-cleavage furrow
What occurs in Prophase II (Meiosis II)
- nuclear envelope disintegrates
- each cell is haploid
What occurs in Meiosis II- Metaphase II?
- Spindle fibres line up the chromosomes on the equatorial plate
What occurs in Anaphase II?
- Centromeres split and sister chromatids pulled apart to opposite poles
what is cellular differentiation
the process by which a less specialised cell becoes a more specialised cell type with specific functions
What changes can occur in a cell for it to differentiate?
cell size
shape
membrane potential
metabolic activity
what is a stem cell?
it is a type of cell that has the unique ability to develop into various different cell types in the body
-undifferentiated
- can divide and either create more stem cells (self renewal)
What is a totipotent stem cell?
- most powerful
- can diff into all cells including placental tissues and germ cells
eg. zygote
what is a pluripotent stem cell?
it can diff into almost any cell type but cannot form extra embryonic tissues or germ cells
eg. embryonic stem cells (cannot form the placenta)
what are multipotent stem cells?
- more limited in diffing
-eg. adult stem cells: can form diff types of blood cells but not other cell types like nerve/muscle cells
what are unipotent stem cells?
- ultra specialised
- only produce one type of cell
-can self-renew - germ line stem cell
-epidermal stem cell
what are ogliopotent stem cells?
restricted but can diff into a limited number of cell types
eg. lymphoid progenitor cells that can diff into lymphocytes - crucial for immune response
what is Induced pluripotent stem cell
created by reprogramming adult, differentiated cells to behave like embryonic stem cells- hence they can diff into almost any type of cell in the body -extremely valuable for medical research by correcting mutations in diseases also useful for drug discovery
