cell cycle and division Flashcards
cell cycle definition
a regulated process in a sequence of events which cells divide into daughter cells in complete cell division. this consists of three main stages: interphase, mitosis and cytokinesis
interphase part of cell cycle
G1, S, G2
phase between divisions
DNA is unwound as chromatin so genes are accessible for transcription
cells are metabolically active
cell growth and DNA replication occurs
S
signal received causing cell division
DNA replicates and is synthesised
amount of DNA doubles
G1 phase
cells make RNA, enzymes and other proteins for growth
organelles are replicated
G2 phase
cell continues to grow
new DNA is syhthesised and checked
mitosis products
2 genetically identical diploid daughter cells
mitosis function
growth. (increasing cell number), repair of damaged tissues and asexual reproduction
staged of mitosis in order
Prophase, Metaphase, Anaphase, Telophase
prophase
chromosomes condense (now visible if stained)
two centrioles move towards opposite poles
nuclear envelope break down (now visible on light microscope)
Nucleolus disappears
Spindle fibres form
metaphase
centrosomes reach opposite poles
spindle fibres extend from centrosome
chromosomes line up at the equator
spindle fibres reach chromosomes and attach to centromere
each sister chromatid is attached to a spindle fibre originating from opposite poles
anaphase
sister chromatids separate at the centromere
spindle fibres begin to shorten
separated sister chromatids (chromosomes) are pulled to opposite poles by spindle fibres
telophase
chromosomes arrive at opposite poles and begin to decondense
nuclear envelope reforms
spindle fibres break down
Formation of specialised cells from stem cells
Chemical stimulus (e.g. growth substance)
Genes activated
Active genes transcribed
mRNA translated to make proteins
Proteins modify cell structure and function permanently
Things which are only observed in meiosis
Chiasmata
Pairing of homologous chromosomes
Synapsis
Formation of bivalents
How generic variation occurs in meiosis
Crossing over and independent assortment
CO: crossing over sections of chromatid
IA: random selection of maternal and paternal chromosomes by spindle fibres in metaphase 1
Causing new allele combinations