Topic 4 (pre-exam) Flashcards
how often does the cell cycle occur, and how long does each stage last?
once approximately every 24 hours (circadian rhythms)
interphase - G1: 11 hours; S: 8 hours; G2: 4 hours
mitosis - 1 hour
role of S phase and G2 phase in the cell cycle
prepare the cell for division (mitosis)
what is the best way to distinguish living/nonliving matter?
cell division; continuity of life based on the reproduction of cells
cell division in unicellular organisms
cell division is reproduction; division of one cell replicates the entire organism
purpose of cell division in multicellular organisms
needed for:
- development of a fertilized cell
- growth
- repair (i.e. tissue renewal)
what is the result of mitotic vs meiotic cell division?
mitotic: daughter cells with identical genetic info (DNA) and 2 sets of chromosomes
meiotic: nonidentical daughter cells (gametes aka sperm and egg cells) with only 1 set of chromosomes
genome
all of the DNA in a cell (including in mitochondria and/or chloroplasts)
*can consist of a single DNA molecule (prokaryotes) or a number of DNA molecules eukaryotes)
function and significance of chromosomes
DNA is condensed and packaged into chromosomes (with proteins) during prophase
*every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
somatic cells vs gametes
somatic cells: non-reproductive; 2 sets of chromosomes
gametes: reproductive; half the chromosomes
chromatin
complex of DNA and protein that condenses into chromosomes during cell division; makes up eukaryotic chromosomes
what occurs in preparation for cell divison?
DNA is replicated and chromosomes condense
sister chromatids
the 2 identical copies of a chromosome after it’s been duplicated that separate during cell division
centromere
the narrow waist of a duplicated chromosome, tightly attaches sister chromatids
two phases of eukaryotic cell division
mitosis - division of nucleus
cytokinesis - division of cytoplasm
historical breakthrough in observing the cell cycle
Walter Flemming developed dyes to observe chromosomes and see their change in form, called the “father of cytogenics”
*various staining techniques today to observe chromosomes
two parts of the cell cycle and their functions:
Mitotic (M) phase - mitosis and cytokinesis
Interphase - cell growth and copying of chromosomes in preparation for cell division
phases of mitosis
prophase, prometaphase, metaphase, anaphase, telophase
- cytokinesis underway by late telophase
- process is still a continuum!!
prophase
assembly of mitotic spindle
- DNA condenses into chromosomes
- nuclear envelope disappears
- centrosome (outside of nuclear envelope) replicates in 2; migrates to opposite ends of cell
- spindle microtubules are assembled and begin to grow out of centrosomes
- asters extends from each centrosome
centrosomes
- both create and control microtubules
- discovered by Walther Flemming; only in animal cells (unknown where plant microtubules come from)
mitotic spindle
made of up centrosomes, spindle microtubules, and asters
asters
radial array of short microtubules extending from each centrosome
types of microtubules
spindle microtubules
- kinetochore: attach to kinetochore of chromosomes during prometaphase to pull chromosomes apart during anaphase
- nonkinetochore: overlap and push against eachother during telophase to elongate cell
other microtubules
- asters: short microtubules that anchor spindle posts to cell membrane
prometaphase
spindle microtubules attach to kinetochores of chromosomes and begin to move them
kinetochores
complex of proteins associated with the centromere of chromosomes where spindle fibers attach
metaphase
chromosomes lined up at metaphase plate (cell equator) midway between spindle’s 2 poles
anaphase
sister chromatids separate and move along kinetochore microtubules towards opposite ends of cell
- microtubules shorten by depolymerizing at kinetochore ends
telophase
nonkinetochore microtubules from opposite poles overlap and push against each other, elongating cell
- genetically identical daughter nuclei form at opposite ends of cell
how did scientists learn how kinetochores depolymerize?
- scientists used a pig kidney cell in early anaphase
- spindle microtubules dyed and part was lasered to remove fluorescence
- they monitored change in length on either side of the mark as the chromosomes moved towards the poles
- microtubules on kinetochore side shortened, so depolymerization happens at kinetochore end
cytokinesis (plants vs animals)
- in animal cells: cleavage furrow forms
- in plant cells: more rigid, so a cell plate forms to divide them
binary fission
- method of prokaryote reproduction
- chromosome replicates and 2 daughter chromosomes actively more apart
evolution of mitosis
- mitosis evolved form binary fission because prokaryotes existed before eukaryotes
- some protists exhibit “in-between” types of cell division
what is the molecular control system?
chemical signals in the cytoplasm cause the frequency of cell division to vary with cell type
evidence for regulation of cell division coming from the cytoplasm
- mammalian cells at different phases of the cell cycle were fused to form a single cell with 2 nuclei
- when cells in S and G1 fused, nucleus of G1 cell immediately entered S phase and DNA synthesized
- when cells in M and G1 fused, nucleus of G1 cell began mitosis (spindle formed and chromatin condensed) even though chromosomes had not been duplicated
cell cycle control system
directs the sequential events in the cell cycle (like a clock)
- both internal and external controls
- specific checkpoints control where cell cycle stops until go-ahead signal received
important checkpoints in cell cycle control system
most important: G1 checkpoint
- cells that get go-ahead will complete other phases and divide; cells that don’t get go-ahead signal will exit the cycle and switch into a non-dividing state called G0 phase
G2 checkpoint
- gives ok for cell division; right before M phase
G0 phase
non-dividing state if no go-ahead signal is received at the G1 checkpoint
regulatory proteins involved in cell cycle control
cyclins and cyclin-dependent kinases (Cdks)
- actively fluctuate levels during the cell cycle
role of MPF
MPF (maturation-promoting-factor) is a cyclin-Cdk complex that gives the cell the go-ahead past the G2 checkpoint, stimulating the mitotic (M) phase
- once mitosis completed, cyclins degrade from MPF
equation for determining concentrations
C1V1 = C2V2
examples of internal cell signaling
when kinetochores not attached to the spindle, a signal is sent to delay anaphase
examples of external cell signaling relating to mitosis
growth factors - proteins from some cells stimulate other cells to divide
- platelet-derived growth factor (PDGF) - stimulates division of human fibroblast cells
density-dependent inhibition - crowded cells stop dividing
anchorage dependence
cells must be attached to a substratum in order to divide (most animal cells)
*cancer cells often don’t have this
characteristics of cancer cells
- no density-dependent inhibition nor anchorage dependence
- don’t respond to cell cycle control mechanisms
- may not need growth factors to divide (make their own growth factor, convey growth signal without factor, or have abnormal control system)
transformation
process by which normal cells transformed to cancerous cells
what do cancer cells do? why are they dangerous?
form tumors - masses of abnormal cells within otherwise normal tissue
***can invade healthy tissue (disrupting functions of organs) and take resources away from the cell
