Week 5 Flashcards
Cell division - importance
in growth and repair of multicellular organisms
Asexual reproduction
offsprings are clones
genetically identical to parents
any genetic variation is due to mutations
single celled prokaryotes - reproduction
binary fission
Single celled eukaryotes - reproduction
mitosis and cytokinesis
mulitcellular eukaryotes - reproduction
reproduce by asexual
Sexual reproduction
involves fusion of gametes
results in genetic variation
gametes formed by meiosis
somatic cells
body cells
contains 2 sets of chromosomes that occur in homologous pairs
Gametes
sex cells
one pair of chromosomes
fertilisation
2 haploid cells form a zygote
Sexual reproduction - essence
random selection
fusion of haploid gametes to make dipliod cell
Four events of cell division
reproductive signals
DNA replication
DNA segregation
Cytokinesis
Replication
ocurs as the DNA is threaded through a replication complex of proteins at center of the cell
Segregation
as replication proceeds, the ori complexes move to opposite ends of the cell
DNA spequences adjacent to ori region bind to proteins for segregation using ATP
Actin protien provide filaments along which ori and other proteins move
ori
where replication starts
ter
where replication ends
important regions of circular chromosome
ter
ori
cytokinesis
after chromosome segregation, cell membrane pinches in and new cell walll is made
Mitosis
one nucleus produces 2 daugther nuclei containing same number of chromosomes
continuous
M phase: mitosis
segragation of chromosomes into 2 nuclei, followed by cytokinesis
Interphase: Mitosis
cell nucleus is visible and cell functions occur, including DNA replication
Interphase mitosis subphases
G1 - variable
S pahse - DNA is replicated
G2- cell prepares for mitosis , synthesises microtubules for segregating chromosomes
Prophase
3 structures appear
condensed chromosomes
reoriented chromosomes
spindle
Karotype
the condensed chromosomes distinguished by their sizes and centromere positions
centrosome
determines orientation of spindle
consists of 2 centrioles
poles at which the chromosomes move twards
centrioles
hollow tubes formed by microtubules
spindle
made up of polar microtubules
astral microtubules
Kinetochore microtubules
polar microtubules
overlap in middle region of cell and keep poles apart
Astral microtubules
interact with proteins attached to cell membrane, keeps poles apart
Kinetochore microtubules
attach to kinetochores on chromatid centromeres
Prometaphase: mitosis
nuclear envelope breaks down and chromatids attach to kinetochore microtubules
Metaphase: mitosis
the chromosomes line up at midline of cell
Anaphase: mitosis
chromatids separate and daughter chromosomes move towards poles
Telophase: mitosis
nuclear envelopes form around each set of chromosomes and nucleoli appear, and spindle breaks down and chromosomes become less compact
Cytokinesis: mitosis
in animal cells, cell membrane pinches in between nuclei
in plant cells, vesicles appear along plane of cell division and fuse to form new cell membrane
Cyclin dependent kinases
trigger substances
catalyse phosphorylation of proteins that regulate cell cylce and are activated by binding to cyclin, which exposes the active site
Meiosis
two nuclear division
reduces chromosome number to haploi
generates diversity
Meiosis 1
chromosomes come together and line up along lengths
pairs seperate but individual chromosomes made up of 2 chromatids remain together
Meiosis 2
not preceded by DNA replication
sister chromatids seperate
4 haploid cells are produced
crossing over
prophase 1 - chromosomes repel each other but remain attached at chiasmata
genetic material is exchanged between non sister chromosomes
increases genetic variation
Independent assortment
at anaphase 1, matter of chance which member of homologous pair goes to which daughter cell
Nondisjunction
homologous pairs fail to separate at anaphase 1
sister chromatids fail to separate at anaphase 2
aneuploidy
abnormal numbers of chromosomes
polyploidy
organisms with triploid, tetraploid or higher can form
can occur through extra round of DNA replication or lack of spindle formation
Translocation
crossing over between non homologous chromosomes
necrosis
cell is damaged or starved for oxygen or nutrients
cells swell and burst
Apoptosis
genetically programmed cell death
