Histology + Cells + Tissues (W1) Flashcards
minimum hours a cell cycle lasts
12h
cell cycle protein molecules
cyclins A,B,E
what do the cell cycle protein molecules (cyclins A,B,E) activate?
CDKs (cyclin dependent kinases)
interval between the end of mitosis and beginning of next is called
interphase
Period in which DNA is synthesised. What promotes this synthesis?
S phase + promoted by cyclin A and CDKs
TIME FRAME of S phase in mitosis
8h after end of mitosis
takes 7/8 hours to complete
lists some possible ways the DNA can be damaged during replication (mitosis)
- Deoxynucleotide incorporation error during replication
- by spontaneous deamination of bases
- various chemicals that interact with DNA
- x-radiation causing NICKS in the DNA
- UV irradiation
what are nicks in the DNA
single strand breaks
what is mismaatch repair (MMR)
a DNA repair mechanism that corrects errors that occur during DNA replication, specifically base mismatches and small insertions or deletions that can arise when the DNA polymerase incorporates the wrong nucleotide or slips during replication.
Prevents mutations from being passed on to daughter cells.
what is homologous recombination
refers to the exchange of genetic material between two homologous (similar or identical) DNA molecules. These homologous sequences are typically found on sister chromatids or homologous chromosomes.
xiroderma pigmentosum - changes in the skin and why
a rare genetic disorder characterized by extreme sensitivity to ultraviolet (UV) radiation, particularly from sunlight
People with XP have a defective DNA repair mechanism, specifically in the nucleotide excision repair (NER) pathway, which normally fixes DNA damage caused by UV light.
These mutations impair the ability to repair UV-induced damage, specifically thymine dimers (abnormal covalent bonds between adjacent thymine bases(thymine dimers/pyrimidine dimers) on a DNA strand, caused by UV exposure)
develop SQUAMOUS CELL CARCINOMA on the skin
As a result, individuals with XP accumulate DNA damage in their skin cells, leading to a higher risk of skin cancer and other skin-related abnormalities.
what is RAD51
DNA repare protein encoded by the gene RAD51. (it is an enzyme) - during homologous recombination
what is homologous recombination in meiosis
homologous recombination happens during meiosis I, which leads to the formation of gametes (sperm and egg cells). This process contributes to genetic diversity by creating new combinations of alleles.
ALSO
Proper Chromosome Segregation: In meiosis, it helps in the proper segregation of homologous chromosomes into gametes by ensuring they are physically connected, allowing them to align correctly at the cell’s equator.
what is homologous recombination in mitosis
DNA Repair: repair of DSB (double-stranded breaks) in DNA
How is homologous recombination used in CRISPR-Cas9
This genome-editing tool often relies on homologous recombination to integrate a desired DNA sequence after a double-strand break is induced by the Cas9 protein.
what is BRCA1/BRCA2 and what is its function
gene involved in repairing DNA through homologous recombination
its dysfunction, leads to genomic instability
increased risk of cancer
what is G1 in mitosis + what is it controlled by
between end of mitosis + beginning of S phase
cell responds to growth factors
these frowth factors, instruct the cells to undergo mitosis
once the cell decides to do so, there is no going back, irreversible process.
+ syntehsis of moelcular machinery needed for mitosis
CONTROLLED BY: Cyclin E + CDKs
what does cyclin E+CDKs control
control G1 phase in mitosis
length of time for G1 phase in mitosis
variablewh
what is G0 phase in mitosis
cells which have retained the capacity for proliferation, but are no longer dividing - QUIESCENT, they do NOT enter the S phase
this phase is between G1 and S
remembrer (M-> G1 -> (G0) -> S)
gene mutated in retinoblastoma + what is it
Rb
tumor suppressor gene
causing DISEASE x
normally, Rb blocks the mitotic cycle in G1 phase (cell becomes quiescent)
What is G2 phase in mitosis
what is it controlled by
the gap between the end of S pahse and beginning of mitosis i nthe G2 phase
cell prepares for division
this period ends with breakdown of nuclear membrane and the onset of chromosome condensation
CONTROLED by cylin B+ CDKs
what does cyclin B+CDKs control
G2 phase in mitosis
time duration of G2 phase in mitosis
2-4h to complete in mitosis - stage
interphase
a stage in which individual chromosomes are not visible - uncoiled
nucleus of cell possess a nuclear envelopes which contains a network of chromatin threads or granules + nucleolus
what happens in prophase of mitosis
- each chromosome splits longitudinally into 2 chromatids except at the centromere
- the two paired centriole are separated from each otehr by elongation of continuous microtubulues of the achromatic spindle and occupy the oppotsite poles of nucleus
what happens during prometaphase
nuclear membrane and nucleolus disappear
chromosomes entangled in a meshwork of continuous microtubules
1.5h
what happens during metaphase
+ duration
centromere region from each chromosome presents a bilateral disc KINETOCHORES
a set of chromosomal mircotbules are organized and extend from the kinetochores bialterally towards opposite centrioles
the centromere of individual chromosomes with their paired chromatids occupies equatorial plane of the spindle – facilitated by the growth of chromosomal microtubules
20 MIN
what are kinetochores and where are they found
bilateral disc present at the centromere region - arises from each chromosome
what happens during anaphase of mitosis
chromosomal microtubules contract + exert force in centromere region
centromeres split longitudinally and chromatids separate to form 2 new chromosome
spindle fibres contract, chromsomes newly formed separate and migrate to the opposite pole of the spindl
what happens during telophase (IN PROGRESS) of mitosis
new nuclear membrane forms + nucleolus appears
chromosomes uncoil
cytoplasm divides + 2 complete cells are formed
what happens during telophase (COMPLETE ) in mitosis
cleavage furrow develops around the equator region of achromatic spindle , during cytokinesis
contraction of fibrillar component of cytoplasm help in hour glass constriction of cleavage
What is non-disjunction
refers to the failure of sister chromatids to properly separate during the anaphase stage of mitotic cell division. This results in an unequal distribution of chromosomes between the two daughter cells, where one cell may receive an extra chromosome (gain) and the other may receive one less chromosome (loss).
what is iscohromosome in mitosis
a type of chromosome abnormality that occurs during cell division (mitosis or meiosis) when a chromosome divides horizontally/transversely, instead of the normal vertical separation. As a result, the two arms of the chromosome (typically referred to as the p arm and q arm) are mirror images of each other, and both halves of the isochromosome will have identical genetic material from either the short arm (p) or the long arm (q) of the original chromosome.
what is colchicine
Inhibits Microtubule Polymerization:
* X by binding to tubulin, a protein that assembles into microtubules, which are part of the cytoskeleton.
* Microtubules are essential for a variety of cellular processes, including cell division (mitosis), intracellular transport, and the maintenance of cell shape.
* X By binding to tubulin, prevents the formation of microtubules, disrupting processes that rely on them, particularly cell division.
Effect on Mitosis:
* Since X disrupts microtubule formation, it also prevents the proper separation of chromosomes during mitosis. This characteristic makes X useful in laboratory settings for studying cell division, and it has been used in karyotyping to arrest cells in metaphase so that chromosomes can be easily examined.
ALSO undeprins rationale for many types of cytotoxic drugs in cancer therapy
hernia
the bulging of an internal organ through a weak are or tear in the muscle or other tissue that holds it in place
