cycle 2 Flashcards
location of DNA in eukaryotic and prokaryotic cells
in the nucleus
phases and main characteristics of the cell cycle for prokaryotic cells
B period - from birth to the initiation of DNA replication. cell grows in size
C period - replication in middle of cell where DNA enzymes are located. chromosome is replicated (begins at ori) and the resulting daughter chromosomes move to opposite ends
D period - cell division begins. new cell wall is synthesized. cell divides by binary fission and forms two daughter cells
phases and main characteristics of the cell cycle for eukaryotic cells
G1 - period of growth before DNA replicates. gap where no DNA is synthesized, cell continues to function.
S - DNA replication and chromosome duplication occur. continues synthesis
G2 - second gap where cell growth continues and cell prepares for mitosis. no DNA synthesis, continues to synthesize RNAs and proteins. marks the end of interphase
M - mitosis
stages and main characteristics of mitosis
prophase - chromosomes condense
prometaphase - nuclear envelope disappears, spindle fibre enters, microtubules from opposite poles attach to the kinetochores of each chromosome
metaphase - chromosomes align at midpoint
anaphase - sister chromatids separate and move to opposite poles
telophase - chromosomes unfold, return to interphase state, nuclear envelopes form, cytoplasm divides by furrowing
interphase - two daughter cells are genetic duplicates
stages and main characteristics of meiosis I
prophase I - chromosomes condense, homologous chromosomes pair together
prometaphase I - nuclear envelope breaks down, spindle enters the former nuclear area. chromosomes attach to kinetochore microtubules
metaphase I - random alignment of chromosomes (independent assortment)
anaphase I - two chromosomes of each homologous pair separate and move to opposite spindle poles
telophase I - transitory stage, little or no change in the chromosomes. cell division (cytokinesis) in telophase I creates truly haploid cells
stages and main characteristics of meiosis II
prophase II - chromosomes condense
prometaphase II - nuclear envelope breaks down. spindle enters the former nuclear area, spindle microtubules leading to opposite spindle poles attach to the two kinetochores of each chromosomes
metaphase II - movements of the spindle microtubules align the chromosomes on the metaphase plate. independent assortment
anaphase II - sister chromatids of each chromosomes separate from each other and move to opposite spindle poles. separated chromosomes (now chromatids) have been segregated to the two poles
telophase II - chromosomes begin decondensing, spindles disassemble, new nuclear envelopes form around the masses of chromatin. cells divide. result is four haploid cells with half the number of chromosomes.
basic mechanism of DNA recombination in prophase of meiosis
homologous chromosomes pair
crossover between non-sister chromatids
takes place at random
randomness of alignment of homologous pairs in metaphase I
accounts for the second major source of genetic variability
reason why G1 and G2 phases exist
gap for growth. no DNA synthesis. synthesis of RNAs and proteins
location of actively cycling cells in multicellular animals
specialized tissues that produce gametes and spores respectively
purpose of cell division and risk if cells grow too large in size
needs a high SA:V ratio
able to satisfy demands of the cell - easier diffusion
main role of cell cycle checkpoints
ensure accurate cell division by preventing critical phases from beginning until the previous phases are completed correctly (no replication or division of mutations
positive regulation at cell cycle checkpoints
cyclins and CDKs
phosphorylation cascade - cyclin binds to CDK. cyclin-CDK complex is phosphorylated. activated cyclin-CDK complex phosphorylates target protein. phosphorylated target protein changes to active form. moves cell into next stage of cell cycle.
negative regulation at cell cycle checkpoints
p53, p21, Rb
p53 detects DNA damage and increases p21 (cyclin-DCK inhibitor) production by binding to p21 promoter. cyclin-CDK complex inactivated, cannot phosphorylate proteins involved in cell cycling
inhibits the cell cycle
apoptosis - if DNA damage can be repaired, positive regulation pathway stimulated. if DNA damage cannot be repaired, p53 triggers apoptosis
risk of any protein involved at the cell cycle checkpoints not functioning properly
mutations replicate and divide - cancer
