cell division Flashcards
cell cycle
- mitotic phase and interphase alternate
- highly regulated
- checkpoints determine fate of cell
interphase
- gap 1 = cell growth
- S = DNA double
- centrioles double
- gap 2 = cell growth and preparation for division, longest phase of cell cycle
checkpoints
internal and external signals provide stop and go signals at checkpoints
cyclins
cyclins and cyclin dependent kinases control the cell cycle
IE Mitosis promoting factor
- triggers mitosis in somatic cells and egg maturation
- works best with high cyclin levels
- MPF is a complex: cyclin dependent kinase and cyclin B
- this complex phosphorylates proteins needed for mitosis
checkpoint failure
- causes mutations and genomic arrangements resulting in genetic instability
- genetic instability is a major factor of birth defects and in development of many diseases, notably cancer
mitosis
- division of the nucleus of diploid (2n) somatic cells
- asexual reproduction, growth, repair
stages of mitosis
- replication, alignment, separation
- rate depends on cell type
binary fission
- cell division of prokaryotes
- DNA doubles
- cell elongates
- cell splits in half
differentiation
creates daughter cells that are different from parent
specialized cells and cell division
when a cell specializes it often enters a stage where it can no longer divide. it can reenter the cell cycle when proper cues are given but some don’t
G0
- takes place after G1
- cells get stuck and never return to the cell cycle
- cells of the CNS
cytokinesis
- plant cells = cell plate
- animal cells = cleavage furrow
Meiosis
- makes sexual reproduction possible
- creates diversity
- haploid (n) gametes are produced from germ cells
- nuclear division of gametes
- rate varies with gender (egg cells take decades to mature)
homologous chromosomes
- 2 of each chromosome exist in each cell (except gametes)
- they are identical in types/location of genes
- 1 set from mom and 1 set from dad
orientation of chromosomes in meiosis
random, ensuring a mix of genes in gametes
fertilization
- fusion of gametes
- increases variation
- restores diploid number
zygote
first cell formed after fertilization
what is the point of meiosis I?
- crossing over
- chromosomes reduced to 23 duplicated chromosomes
what is the point of meiosis II?
to turn 23 duplicated chromosomes into 23 unduplicated chromosomes
what triggers cell to divide?
- size
- demand (sperm/muscle)
- DNA signal
- cancer/damaged DNA
what stops cell division?
- DNA signal
- cells touching borders
- death
- demand changes
- gametes
Hayflick limit
- number of times a cell can divide before it dies
- ~50
- telomeres get shorter with each cell division, when telomeres are gone cell dies (the ends kind of unravel)
- this is why we age and die
telomerase
prevents the unraveling of telomeres and can lengthen them
HeLa cells
- some cancer cells produce telomerase so they are essentially immortal
- Henrietta Lacks’ cells are used for research because they don’t die
HeLa cells have been used for
- cancer
- AIDs
- effects of radiation and toxic substances
- gene mapping
