Show Menu
Cheatography

AP Biology Unit 4 - Mitosis & Meiosis Cheat Sheet (DRAFT) by

AP Exam review for unit 4

This is a draft cheat sheet. It is a work in progress and is not finished yet.

why do cells divide

growth, repair, reprod­uction
mitosis
produces 2 geneti­cally identical daughter cells (called clones)
preserves diploid (2n) chromosome number
passes a complete genome from parent to child
genome
whole of its hereditary inform­ation encoded in its DNA, includes both the genes and the non-coding sequences of the DNA
meiosis
in sexually reprod­ucing organisms, results in haploid cells (have half the chromosome # of the parent)(n)

structure of a replicated chromosome

replicated chromosome consists of two sister chromatis where one is an exact copy of the other.

centromere is a specia­lized region that holds the two chromatids together

kineto­chore is a disc-s­haped protein on the centromere that attaches the chromatid to the mitotic spindle during cell division

cell cycle basics

bone marrow cells
always dividing to produce constant supply of red and white blood cells
liver cells
arrested in G0 (have stopped dividing) can be induced to divide about/­reg­enerate when liver tissue is damaged
human intestine cells
divide ab twice a day to renew tissue destroyed during digestion
specia­lized cell ex (nerve cells)
do not divide at all
process is regulated in any case by a complex mechanism involving kinases and allosteric intera­ctions
ratio of volume of cell to SA and capacity of nucleus to control the entire cell
limit cell size and promote cell division

ratio of cell volume to sa

as cell grows, sa increases as the square of the radius and volume increases as the cube of the radius
volume inside cell grows at faster rate than cell membrane
determines when cell divides

capacity of nucleus

nucleus must be able to provide enough info to produce adequate quantities of all substances to meet the cells needs
bc of this metabo­lically active cells are usually small
can be large active cells like paramecium
-has two nuclei that each control diff cell functions
human skeletal muscle cells
giant multin­ucleate cells
fungus slime molds
consist of one giant cell that has thousands of nuclei

cell division and cancerous cells

contact inhibi­tio­n//­density dependent inhibition
normal cells grow and divide until they become too crusaded then they stop and enter G0
anchorage dependence (ANIMALS)
to divide, cell must be attached or anchored to some surface
can be Petri dish (in vitro) or extrac­ellular membrane (in vivo)
cancer cells show none of these two things
divide uncont­rol­lably, and do not have to be anchored to any membrane
^is why cancer cells can migrate or metast­asize to other regions of body

regulation and timing of the cell cycle

cell cycle control system
regulates the rate at which cells divide
check points act as stop signals that halt cell unless overridden by go signals
checkp­oints in G1, G2, and M
G1 is most important, if receive go ahead, cell will most likely complete cycle
if it doesn't, it will go to G0 and become a non dividing cell
timing of cell cycle is initiated by growth factors and controlled by 2 molecules
cyclins and protein kinases
cyclins get name bc levels cyclicly rise and fall in dividing cells
synthe­sized during every S and G2 phase
broken down after M phase
kinases are and ubiquitous class of proteins that activate other proteins by phosph­ory­lating them
only activated when bound to a cyclin
named cyclin dependent kinases (cdk)
when cdk binds to a cyclin, cyclin cdk compels is formed
ex of this is mpf which triggers cells passage from G2 to mitosis
maturation (mitosis) promoting factor
contri­butes to molecular events required fro chromosome conden­sation and spindle formation during prophases
after M phase, during anaphase, mpf switches off by initiating process that leads to the breakdown of cyclin
cdk persists in cell in inactive form until becomes part of mpf again
 

interphase

G1
intense growth and bioche­mical activity
s
synthesis/replic­ation of DNA
G2
cell continues to grow and complete prepar­ations for cell division
more than 90% of cells life is in interphase
in interp­hase, chromatin is thread­like, not condensed
centrosome consisting of two centrioles may be seen in the cytoplasm of ANIMAL cell
centrosome is duplicated during s phase
G2 - M transition
two centro­somes separate from one another and move to opposite poles
plant cells lack centro­somes but have microt­ubule organizing centers (MTOCs)
these have the same function

mitosis

consists of the actual dividing of the nucleus

prophase

promet­aphase

metaphase

equatorial plate=­met­aphase plate

centro­somes at opp poles of cell

spindle fibers run from centrosome to kineto­chores in the centro­meres

anaphase

telophase

superc­oiled chromo­somes uncoil back to chromatin

telophase

superc­oiled chromo­somes uncoil back to chromatin

cytoki­nesis

dividing of the cytoplasm

begins during anaphase

animal cells: cleavage furrow froms down middle of cell as actin and myosin microf­ila­ments pinch in the cytoplasm

plant cells: cell plate forms during telophase as vesicles from golgi coalesce down middle of cell, daughter plant cell DO NOT separate

new cell wall forms and sticky middle lamella cements adjacent cells together

cyclin vs cdk

activity of cdk rises and falls depedning on changes in concen of cyclin

peaks of mpf activity correspond to rise in cyclin concen­tration

cyclin leves rise during S and G2 phases and then fall abrubtly during the M phase
 

meiosis

generates genetic diversity that is the raw material for natural selection and evolution
produces gametes (ova and sperm)
have haploid or monoploid chromo­somes (n)
half genetic material of parent cell
nucleus divides twice
each gamete differs geneti­cally from every other gamete
sexual reprod­uction involves fusion of two haploid gametes and restores diploid chromosome # to offspring
meiosis I reduction division
homologous chromo­somes separate
each chromosome pairs up w homologue in synapt­onemal complex by process called synapsis
forms structure called tetrad (set of 4) or bivalent (in pairs)
by aligni­ng/­binding crossing over is likely
^process by which non sister chromatids exchange genetic material
results in recomb­ination of genetic material
ensures greater variation among gametes
meiosis II like mitosis
sister chromatids separate into diff cells

prophase I

-synapsis, pairing of homologues occurs
crossing over, exchange of homologous bits of chromo­somes
-chias­mata, visible manife­sta­tions of the crossover events are visible
-sets stage for separation (segre­gation of DNA)

metaphase 1

spindle fibers from poles of the cell are attached to the centro­meres of each pair of homologues

anaphase 1

telophase 1 / cytoki­nesis 1

in telophase: each pole has haploid # of chromo­somes

cytoki­nesis occurs simult­ane­ously w telophase 1

in some species interphase occurs bet meiosis 1 and 2, in other none

NO chromosome replic­ation in bet meiosis 1 and 2

meiosis 2

same as mitosis

chromosome # remains haploid

meiosis and genetic variation

3 types of genetic variation occur from meiosis and fertil­ization
indepe­ndent assortment of chromo­somes, crossing over, random fertil­ization of an ovum by a sperm

indepe­ndent assortment of chromo­somes

homologous pairs separate depending on the random way they line up on the metaphase plate during metaphase 1
each pair of chromo­somes can line up in two possible orient­ations
50% chance receive maternal chrom
50% chance receive paternal chrom
possible # of combin­ations of chromo­somes is 2^23
bc 23 pairs of chromo­somes in humans

crossover

produces recomb­inant chromo­somes that combine genes inherited from both parents
may be 2 to 3 crossover events in humans
metaphase 2 recomb­inant chromo­somes line up on metaphase plate in random fashion
^increases possible types of gametes even more

random fertil­ization

human ovum and sperm represent 8 million possible chromosome combin­ations respec­tively
when one sperm fertilizes one ovum
8 million x 8 million recomb­ina­tions can occur