Cell Cycle Flashcards
Schleiden, Schwann, Virchov - cell theory
1) All living things are made of cells
2) Cell is the basic unit of structure & function in all organisms
3) Every cell comes from another cell that lived before it
Cell cycle
Replication of chromosomes (DNA) & cell growth
Separation of chromosomes
Cell division
Cell Cycle (Phases)
Interphase G1 S G2 M=Mitosis
G1
First gap
Growth of cell - duplication f organelles, synthesis of proteins
S
Synthetic
Replication of nuclear DNA - duplication of chromosomes
G2
Second gap
Growth of cell continues
Mitosis
Cell divides its nucleus
Cell cycle checkpoints
Monitor & regulate cell cycle allowing verification of necessary phase processes & repair of DNA damage
Prevent uncontrolled cell division
Cyclins
Control cell cycle
Help drive events at certain phase
Group of related proteins
Increase level at stage where it is needed
Cdks
Control cell cycle
Inactive enzymes that phosphorylate (add P group) to specific target proteins
P group act like “switch” - make target protein more or less active
Control processes in the cell cycle
Promoting factors (complex)
Cyclins + Cdks
APC
Anaphase promoting complex
Starts destruction of cohesions thus allowing the sister chromatids to separate
G0 phase
Cell cycle is stopped in response to a lack of growth factors or nutrients
Cyclins & Cdks disappear
Mitosis
Division of somatic cells, results in 2 daughter cells with identical genetic material (1 set of chromosomes from mother, the other from father)
Mitosis (mitochondria & chloroplasts)
Are duplicated & randomly distributed into the daughter cells
Mitosis (ER, GA)
Are fragmented & randomly distributed into the daughter cells
Prophase
Identical sister chromatids (cohesions) Chromosome condensation by CONDENSINS Nucleolus become invisible Kinetochore is formed Mitotic spindle is formed
Mitotic spindle is composed of
Centrosome
Kinetochore microtubules
Polar microtubules
Astral microtubules
Prometaphase
Nuclear envelope breaks down
Kinetochore microtubules attach to sister chromatids
Metaphase
Chromosomes line up in the middle of the cell
Anaphase
Sister chromatids by enzyme SEPARASE (previously blocked by SECURIN)
K MT pull chromatids to opposite poles
Identical sets of chromosomesd
Telophase
Nuclear envelope forms
Chromosomes decondense
Creates 2 daughter cells (cytok.)
Cytokinesis
Cytoplasm is dividing
Begins in anaphase & continues through telophase
Cytokinesis in animal cell
Cytoplasm is divided by a contractile ring of actin & myosin II - forms cleavage furrow
Cytokinesis in plant cell
Guided by phragmoplast
Vesicles from GA are transported along MT to the equator of phragmoplast
Vesicles fuse to form membrane enclosed structure, which expands until it reaches the plasma membrane & cell divides in 2
Phragmoplast
Formed by remains of polar microtubules at the equator of old mitotic spindle
Meiosis
Division of sexual cells (gametes)
Results in 4 daughter cells with non-identical genetic material
Haploid (1 set of chromosomes)
Meiosis I
Different from mitosis
Recombination of genetic information
Meiosis II
Similar like mitosis
Prophase I (“stages”)
Leptotene Zygotene Pachytene Diplotene Diakinesis
Leptotene
Chromosomes begin to condense
Zygotene
Homologous chromosomes combine to form bivalent (tetrad), forming synaptonemal complex (synapis)
Pachytene
Nonsister chromatids of homologous chromosomes randomly exchange segments of genetic information -crossing over
Results in recombination of genetic information
Diplotene
Synaptonemal complex degrades
Homologous chromosomes separate, a little
Chiasmata
Diakinesis
Nucleolus disappears
Nuclear membrane disintegrates into vesicles
Mitotic spindle begins to form
Metaphase 1
Homologous chromosomes align along an equatorial plane
Anaphase I
K MT pull homologous chromosomes toward opposite poles (random segregation of chromosomes - recombination)
Nonk. MT lengthen, cell elongates
Telophase I
Each daughter cell is haploid (half # of chromosomes each consisting of a pair of chromatids)
Cytokinesis completes the creation of 2 daughter cells
Interkinesis
Interphase II
Period of rest, no DNA replication
Prophase II
Disappearance of nucleoli & nuclear envelope
Shortening & thickening of chromatids
Centrosomes move to poles & arrange spindle fibers
Metaphase II
Chromosomes align along an equatorial plane
Anaphase II
Centromeres are cleaved
MT to pull sister chromatids apart (sister chromatids -> sister chromosomes)
Telophase II
Uncoiling & lengthening of chromosomes
Disappearance of MT
Nuclear envelopes are formed
Cytokinesis produces a total of 4 daughter cells
Significance of meiosis
1) Meiosis facilitates stable sexual production
2) Meiosis produces genetic variety in gametes
Regulation of cell # in multicellular organisms
By signals for proliferation & differentiation of cell
By programmed cell death
Apoptosis
Programmed cell death (“cellular suicide”) -> tidy
Apoptosis manifestation
Cell shrink & develop “blebs” on surface
DNA in nucleus is chopped up into pieces & some organelles (i.e. ER) break down into fragments
Entire cell splits up into chunks, each enclosed in a package of membrane
Chunks release signals that attract cells from immune system (phagocytes) which eats them
NO INFLAMMATION
Apoptic bodies = “chunks”
Necrosis
Accidental cell death (cells die due to injury) - messy
Necrosis manifestation
Cells damaged by harmful factors “spill their guts” as they die
Cell swells up due to no control in passage of water & ions
Damaged plasma membrane explodes & release its contents through holes in membrane
OFTEN cause INFLAMMATION in tissue surrounding the dead cell
Severe damage of 1 system in the cell leads to secondary damage in other systems
Apoptosis triggers
Internal signals
External signals
Apoptosis-inducing factors
G1 checkpoint
Cell size - large enough
Nutrients - enough energy reserves
Growth factors
DNA damage
G2 checkpoint
DNA damage
DNA replication completeness (from S phase)
Error/damage)
Repair
If irreparable: apoptosis
M checkpoint
Chromosome attachment to spindle at metaphase plate
Proteasome
Protein complexes that degrade unneeded/damaged proteins by proteolysis (chemical reaction that breaks peptide bonds)
Attachment of cyclin to Cdk
Activates Cdk as a kinase
Directs Cdk to specific target proteins
Cdk process (G1)
G1 cyclin send Cdks to S phase target
Promote DNA replication
Cdk process (M)
M cyclins send Cdk to M phase targets
Make nuclear membrane break down
Cue
Signal for an action
Positive cue (cell regulation) example
Growth factors
Normally increase activity of Cdks & cyclins
Negative cue (cell regulation) example
DNA damage
Normally decrease or block activity
Kinase
Enzyme that adds P groups to other molecules
Condensins
Large protein complex
Play central role in chromosome assembly & segregation during mitosis & meiosis
Cohesions
Hold 2 sister chromatids together
Kinetochore
Protein structure that forms on a chromatid during cell division
Allows for attachment of MT on a chromosome
Anaphase (APC/C) process
APC/C adds Ub tag to protein securin (normally binds to inactive separase)
When securin is sent for recycling, separase become active & can do its “job”
-> Separase chops up cohesion that holds sister chromatids together = allow them to separate
Synapsis
Fusion of chromosome pairs (zygotes)
Synaptonemal complex
Holds together homologous chromosomes
Crossing-over
Exchange of genetic material
PACHYTENE
Role of nonkinetochore microtubules
Lengthen & push centrioles further apart
Proliferation
Increase in number of cells
Balance between cell divison & cell loss through cell death or differentiation
Proliferation process
Growth factors
Receptors
Signalling molecules (transmit message from receptor to nucleus)
Transcription factors (binds to DNA, turn on/off production of proteins)
Differentiation
Less specialized cells -> more specialized cells
OFTEN during development of multicellular organisms
Change from single zygote to complex system of tissues & cell types
