Ch 12 and 13 Flashcards
a characteristic that best distinguishes living things from non-living matter
the ability of organisms to produce more of their kind
Omnis cellula e cellula
every cell from a cell
the continuity of life is based on
cell division
cell division
the reproduction of cells
the division of a prokaryotic cell reproduces
an entire organism
dividing cells in your bone marrow
continuously make new blood cells
the cell division process is an integral part of
the cell cycle
cell cycle
the life of a cell from the time it is first formed from a dividing parent until its own division into two daughter cells
a crucial function of cell division
passing identical genetic material to cellular offspring
3 functions of cell division
- Reproduction
- Growth and Development
- Tissue Renewal
most cell division requires the distribution of
one exception
identical genetic material to two daughter cell s (meiosis)
genome
a cell’s endowment of DNA, its genetic infromation
prokaryotic genome is often
a single DNA molecule
eukaryotic genomes usually consist of
a number of DNA molecules
a typical human cell has about (of DNA)
2 m of DNA- 250,00 time the length of the diameter of the cell
before the cell can divide to form genetically identical daughter cells
all DNA must be copied of replicated
the replication and distribution of so much DNA is manageable because the DNA molecules are packaged into structures called
chromosomes
chromosomes
the structures DNA is packaged in
chroma
color
soma
body
eukaryotic chromosomes consist of
one very long, linear DNA molecule associated with many proteins
The DNA molecule contains (how many genes)
several hundred to a few thousand
genes
the units of information that specify an organisms inherited traits
chromatin
the entire complex of DNA and proteins that is the building material of chromosomes
every eukaryotic species has (in relation to chromosomes)
a characteristic number of chromosomes in each cell nucleus
somatic cells
all body cells except the reproductive cells
number of chromosomes in the nuclei of a human somatic cell
46, made up of two sets of 23, one from each parent
gametes
reproductive cells, sperm and eggs
number of chromosomes in gametes
half as many as somatic cells, one set of 23 in humans
number of chromosomes in somatic among species
varies wildly
when a cell is not dividing , and even as it replicates its DNA in preparation for cell division each chromosome is in the form of
a long thin chromatin fiber
after DNA replication, chromosomes
condense as part of cell division. each chromatin fiber becomes densely coiled and folded, making chromosomes much short and so thick they can be viewed with a light microscope
each duplicated chromosome has two
sister chromatids
the two sister chromatids are
joined copies of the original chromosome
the two sister chromatids each contain
an identical DNA molecule
the two sister chromatids are intitially attached all along their lengths by
protein complexes called cohesins
cohesins
protein complexes that attach the two sister chromatids intially along their lengths
the attachment of the sister chromatids is caleld
sister chromatid cohesion
centromere
a region containing specific DNA sequences where the chromatid is attached most closely to its sister chromatid
each sister chromatid has
a centromere
mediator of the centromere
proteins bound to the centromeric DNA sequences and gives the condensed, duplicated chromosome a narrow “waist”
arm of the chromatid
what the part of a chromatid on either side of the centromere is referred
an uncondensed, unduplicated chromosome has
a single centromere and two arms
Karotype
a micrograph of the 46 human chromosomes arranged in pairs starting with the longest chromosome
homologous chromosomes or homologs
the two chromosomes composing a pair: they have the same length, centromere position and staining pattern
Both chormosomes of each pair of homologs carry
genes controlling the same inheritance patterns
autosomes
all non-sex chromosomes
sex chromosomes
X and Y chromosome
Both of the sex chromosomes have genes
lacking on their opposite
Female Sex chromosomes
XX
Male sex chromosome
XY
only small parts of X and y chromosomes are
homologous
the two sister chromatids of each duplicated
chromosome separate and move into
two new nuclei at each end of the cell
once the sister chromatids seperate they are no longer called sister chromatids but are considered
individual chromosomes
each new nucleus receives a collection of chromosomes identical to
that of the parent cell
mitosis
the division of the genetic material in the nucleus
cytokinesis
the division of the cytoplasm
mitosis is usually immediately followed by
cytokinesis
zygote
a fertilized egg
Walther Flemming
developed dyes to observe chromosomes during mitosis and cytokinesis; named mitosis and chromatin
Mitotic (M) phase
- mitosis and cytokinesis
- shortest part of cell cycle
interphase
90% of the cell cycle
-cell that is about to divide grows and copies its chromosomes in preparation for cell division
3 subphases of interphase
G1 phase (first gap), S phase (synthesis), G2 (second gap)
during all 3 subphases of interphase
a cell that will eventually divide grows by producing proteins and cytoplasmic organelles
chromosomes are only duplicated during
S-phase
most variable subphase in interphase between types of cells in reference to time
G1 phase; some cells never divide
5 stages of mitosis
prophase,prometaphase,metaphase,anaphase,and telophase
when does the mitotic spindle begin to form
in prophase in the cytoplasm
mitotic spindle
fibers made of microtubules and associated proteins
when the mitotic spindle assembles
microtubules of the cytoskeleton partially disassemble in order to construct it
how does do the spindle microtubules elongate (polymerize) and shorten (depolymerize)
- polymerize by incorporating more subunits of protein tubulin
- depolymerize by losing subunits
centrosome
a subcellular region containing material that functions throughout the cell to organize the cell’s microtubules
also called the microtubule-organizing center
where does the assembly of spindle microtubules start in animal cells
centrosome
located at the center of the centrosome
a pair of centrioles ; but not necessary for division and plants don’t have them
the single centrosome duplicates when in animal cells
interphase
the two centrosomes formed in interphase in animal cells move apart during
prophase and prometaphase as spindle microtubules grow from them
by the end of prometaphase the centrosomes, one at each pole of spindle
are at opposite ends of the cell an aster extends from each centrosome
an aster
a radial array of short microtubules
the mitotic spindle include
the centrosomes, the spindle microtubules, and the asters
kinetochore
- each of the two sister chromatids of a duplicated chromosome has one
- a structure of proteins associated with specific sections of chromosomal DNA at each centromere
- each of the chromosome’s two face in opposite directions
during prometaphase what attach to the kinetochores (they are called kinetochore microtubules) (number varies wildly between species)
some of the spindle microtubules
at metaphase the centromeres of all the duplicated choromosomes are
on a plane midway between the spindle’s two poles called the metaphase plate which is an imaginary rather than real cell structure
effect of microtubules on kinetochore of a chromosome
pulls on them and counteract each others pulls which ends in a draw (like a game of tug and war)
what occurs in G2 phase of interphase
- nuclear envelope encloses nucleus
- nucleus contains one or more nucleoli
- two centrosomes formed from one
- chromosomes duplicated during S phase but not yet condensed
what occurs in prophase
- chromatin fibers become more tightly curled
- nucleoli disappear
- duplicated chromosome appears as 2 identical sister chromatids
- mitotic spindle begins to form
- centrosomes move away from each other
what occurs in prometaphase
- nuclear envelope fragments
- chromosomes more condensed
- microtubules from each centrosome invade the nuclear area
- each of the two chromatids of each chromosome now has a kinetochore
- some microtubules attach to kinetochore
- nonkinetochore microtubules interact with those from the opposite pole of the spindle
what occurs in metaphase
- the centrosomes are now at opposite poles of the cell
- the chromosomes convene at the metaphase plate
- for each chromosome, the kinetochores of the sister chromatids are attached to the kinetochore tubules coming from the opposite poles
what occurs in anaphase
- shortest stage of mitosis
- anaphase begins when the cohein proteins are cleaved . this allows the 2 sister chromatids of each pair to part suddenly; each chromatid becomes a chromosome
- two liberated daughter chromosomes move toward the opposite ends of the cell as their kinetochore microtubules shorten
- cell elongates as the nonkinetochore microtubules lengthen
- by end, two ends of cell have equivalent and complete collections of chromosomes
what occurs in telophase
- 2 daughter nuclei form, nuclear envelopes arise form the fragments of the parent’s cell’s nuclear envelope and other portions of the endomembrane system
- nucleoli reappear
- chromosomes become less condensed
- any remaining spindle microtubules are depolymerized
- mitosis is now complete (the division of one nucleus into 2 identical nuclei)
what occurs in cytokinesis
- division of cytoplasm well underway by end of telophase, so two daughter cells appear shortly after the end of mitosis
- in animal cells, cytokinesis involves the formation of a cleavage furrow which pinches the cell in two
microtubules that do not attach to kinetochores have been elongating and by metaphase
they overlap and interact with other nonkinetochore microtubules from the opposite pole of the spindle (called polar microtubules)
by metaphase the microtubules of the asters have
grown and are in contact with the plasma membrane; the spindle is now complete
anaphase commence when
the cohesins holding together the sister chromatids of each chromosome are cleaved by an enzyme called separase
separase
enzyme which cleaves the cohesins of the sister chromatids
once the chromatids become full fledged chromosomes they move
towards the opposite ends of the cell
how do the chromosomes move
they walk along the kinetochores via motor proteins on the kinetochore
in animal cells what is responsible for elongating the whole cell
the nonkinetochore microtubules; while they may be extensively overlapped, their motor proteins push them apart via ATP; expanding the cell
in animal cells, cytokinesis occurs via
cleaveage
first sign of cleavage
the cleavage furrow
cleavage furrow
shallow groove in the cell surface near old metaphase plate
deepens until cell splits into two
on the cytoplasmic side of the cleavage furrow is
a contractile ring of actin microfilaments associated with molecules of the protein myosin
actin interacts with myosin causing contraction
in plant cells cytokinesis occurs via
cell plate
cells plate
formed via vesicles from the Golgi apparatus which move along microtubules to the middle of the cell
- fuses with plasma membrane
- new plasma membrane forms in daughter cells and cell plate begins cell wall
binary fission
type of reproduction in prokaryotes where cell doubles in size and then divides and asexual reproduction in eukaryotes (but in eukaryotes this includes mitosis)
in bacteria most genes are carried on
a single bacterial chromosome which consists of a circular DNA molecule and associated proteins
in ecoli cell division:
-initiated when DNA of bacterial chromosome begin to duplicate at a specific place on the chromosome called the origin of replication producing 2 origins
-the 2 origins move to opposite ends
-cell expands
-plasma membrane pinches
-cell divided into two daughter cells
way of moving is a mystery
intermediaries between binary fission and mitosis:3
dinoflagellates diatoms and some yeasts
yeast and diatom division
nuclear envelope in tact
spindle formed inside nucleus
microtubules separate chromosomes and nucleus splits into 2 nuclei
dinoflagellates division
chromosomes attach to nuclear envelope
nuclear envelope remains intact during division
microtubules pass through nucleus inside cytoplasmic tunnels
then divides in binary fission style process
when fused cells from earlier stages
jump to the farthest state of the 2
cell cycle control system
a cyclically operating set of molecules in the cell that both triggers and coordinates the key events in the cell cycle
checkpoint
a control point where stop and go signals can regulate the system
animal cell checkpoints are generally
built in, many are internal, but may be from outside the cell
three major checkpoints
G1, G2, and M phases
dubbed the restriction checkpoint in mammalian cells
the G1 checkpoint is most important- if given go ahead, division will probably occur
if no go ahead given at G1
cell goes into G0 phase which is non-dividing
regulatory cell cycle molecules
mainly two proteins of 2 types: protein kinases and cyclins
protein kinases
enzymes that activate or inactivate other proteins by phosphorylating them
-particular protein kinases give go ahead signals at the G1 and G2 checkpoints
-many are present at constant concentration, but inactive much of the time
-
cyclin
activates kinases;attachs to them
cyclically fluctuates concentration in the cell
cyclin dependent kinases (Cdks)
kinases which need cylcin
MPF
the cyclin dependent complex that was discovered first in frog eggs
m phase promoting factor-triggers cell’s past G2 checkpoint into M phase
when cyclins that accumulate during G2 associate with Cdk the resulting MPF complex phosphorylates a variety of proteins initiating mitosis; nuclear lamina is phosphorylated fragmenting N envelope
during anaphase cyclin destroyed and Cdk dormant
M phase checkpoint
will not begin until the kinetochores of all the chromosomes are attached to the spindle
growth factor
a protein released by certain cell that stimulates other cells to divide
density-dependent inhibition
a phenomenon where crowded cells stop dividing due to a surface-inhibiting protein which sends a growth inhibiting signal to both cells
anchorage dependence
in most animal cells, to divide, they must be attached to a substratum like a culture jar
cancer cells
do not heed normal signals that regulate cell cycle
which cells are immortal
cancer cells: they divide indefinitely
transformation
the process that converts a normal cell to a cancer cell, normally destroyed by body, but if not can form a tumor
benign tumor
a tumor that cannot expand due to too few genetic and cellular challenges to survive at another site
malignant tumor
can spread to new sites
metastasis
the spread of cancer from their original site, spread by blood vessels and lymph vessels which may be signaled to grow towards it
heres
heir
heredity or inheritance
the transmission of traits from one generation to the next
variation
the opposite of inherited similarity
genetics
the scientific study of heredity and hereditary variation
genes
hereditary units
genetics is written in
DNA and read via the nucleotides
gametes
reproductive cells that are the vehicles that transmit genes from one generation to another
humans have how many chromosomes in somatic cells
46
somatic cells
all non gamete cells in the body
locus
from Latin; place- a gene’s specific location along the length of the chromosome
asexual reproduction
single organism, all DNA passed down
offspring of asexual reproduction
a clone
sexual reproduction
2 parents
unique combinations of genes
life cycle
the generation to generation sequence of stages in the reproductive history of an organism from conception to reproduction of its own offspring
diploid cell
any cell with two chromosome sets; 2n
the number of chromosomes in a single set is represented by
n
for humans the diploid number is
46 (2n=46) the number in our somatic cells
haploid cells
one set of chromosomes; i.e gametes
human haploid number
23 (n=23): 22 autosome and 1 sex chromosome (sperm may have X or Y, while an egg must have X
each sexually reproducing organism has a characteristic
diploid and haploid number
fertilization
union of gametes culminating in the fusion of their nuclei
zygote
fertilized egg, is a diploid
only cells in the human body not produced by mitosis
gametes, develop from specialized cells called germ cells in the gonads and ovaries respectively
if gametes were produced by mitosis
the number of chromosomes would keep doubling forever each generation
meiosis
what gametes use- reduces the number of sets of chromosome sets from 2 to 1 occurs in germ cell in reproducing animals
alternation of generation
life cycle of some algae and plants, both diploid and haploid types and are multicellular
in alternation of generation; diploid
sporophyte, meiosis of sporophyte produces spores; a type of haploid cell
unlike a gamete
a haploid spore doesn’t fuse with another cell, but divides mitotically generating a multicellular haploid stage called the gametophyte which if fuse results in the next sporophyte beginning the cycle over
life cycle of most fungi and some protists
- gametes fuse and forma diploid zygote
- meiosis occurs without a multicellular diploid offspring developing
- meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to either unicellular descendants or a haploid multicellular adult organism
- haploid completes further mitoses producing cell that develop into gametes
- only diploid stage is single celled zygote
either haploid or diploid cells can divide using what depending on the life cycle
mitosis
only diploid cells can undergo
meiosis
two divisions of meiosis
meiosis I and Meiosis II; results in 4 daughter cells
for a single pair of homologous chromosomes in mitosis
both members duplicated and the copies sorted into 4 haploid daughter cells
an allele
different versions of a gene
homologs appear alike but
may have different alleles at corresponding loci
What happens in Meiosis I
separation of homologous chromosomes
What happens in Meiosis II
separation of sister chromatids
What happens in early Phrophase I
- chromosomes begin to condense and homologs loosely pair along their lengths aligned gene by gene
- paired homologs become physically connected to each other along their lengths by a zipper-like protein structure; the synaptonemal complex; this state is synapsis
- Crossing over- a genetic rearrangement between non-sister chromatids involving the exchange of corresponding segments of DNA molecules, begins during pairing and synaptonemal complex formation and is completed while homologs are in synapsis
What happens in main prophase I
- synapsis has ended with the disassembly of the synaptonemal complex in mid-prophase and the chromosomes in each pair have moved slightly apart
- each homologous pair has one or more X-shaped regions called chiasmata (chiasma,singular) which exists where a crossover occurred. It appears as a cross because sister chromatid cohesion still holds the original sister chromatids together, even in regions beyond the crossover point, where one chromatid is now part of the other homolog
- centrosome movement, spindle formation, and nuclear envelope breakdown occur as in mitosis
What happens in late prophase I
-microtubules from one pole or the other attach to the two kinetochromes, protein structures at the centromeres of the homologs. The homologous pair then move toward the metaphase plate.
what happens in metaphase I
- pairs of homologous chromosomes are now arranged at the metaphase plate , with one chromosome in each pair now facing the plate
- both chromatids of one homolog are attached to kinetochore microtubules from one pole; those of the other homolog are attached to microtubules from the opposite pole
what happens in anaphase I
- breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
- the homologs move toward opposite poles,guided by the spindle apparatus
- sister chromatid cohesion persists at the centromere causing chromatids to move as a unit toward the same pole
What happens in telophase I and cytokinesis
- at the beginning, each half of the cell has a complete haploid set of duplicated chromosomes. each chromosome is composed of two sister chromatids; one or both chromatids include regions of nonsister chromatid DNA
- Cytokinesis usually occurs simultaneously with telophase I forming 2 haploid daughter cells
- in animal cells a cleavage furrow forms and in plant cells a plate forms
- in some species chromosomes decondense and N envelope forms
- no chromosome duplication occurs between Meiosis I and II
What happens in Prophase II
- spindle apparatus forms
- in late prophase II chromosomes each still composed of 2 chromatids associated at their centromere move towards the metaphase II plate
What happens in Metaphase II
- chromosomes positioned at metaphase plate
- because of crossing over in Meiosis I , the sister chromatids of each chromosome are not genetically identical
- the kinetochore of sister chromatids are attached to microtubules extending from opposite poles
What happens in Anaphase II
-breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate. the chromatids move toward opposite poles as individual chromosomes
What happens in Telophase II and Cytokinesis
- nuclei form, the chromosomes begin condensing and cytokinesis occurs
- the meiotic division of one parent cell produces four daughter cells, each with a haploid set of (unduplicated) chromosomes
- the 4 daughter cells are genetically distinct from one another and the parent cell
Mitosis vs Meiosis:DNA replication
mitosis;occurs during interphase before mitosis begins
Meiosis;occurs during interphase before meiosis I begins
Mitosis vs Meiosis:Number of divisions
mitosis: one, including the 5 stage
meiosis: two including each of the 4 steps
Mitosis vs Meiosis: synapsis of homologous chromosomes
mitosis: doesn’t happen
meiosis: occurs during prophase I along with crossing over between non-sister chromatids ,resulting chiasmata hold pairs together due to sister chromatid cohesion
Mitosis vs Meiosis: number of daughter cells and genetic composition
mitosis: 2 each diploid (2n) and genetically identical to parent cell
meiosis: 4, each haploid (n) containing half as many chromosomes as the parent cell , genetically different from parent cell and each other
Mitosis vs Meiosis: role in animal body
mitosis: enables multicellular adult to rise from zygote: produces cells for growth, repair, and in some species, asexual reproduction
Meiosis:produces gametes; reduces number of chromosomes sets by half and introduces genetic variability among the gametes
3 unique events of meiosis I
Synapsis and crossing over, homologous pairs at the metaphase plate, separation of homologs
synapsis and crossing over Mitosis vs Meiosis
during prophase I, duplicated homologs pair up, and the formation of the synaptonemal complex between them holds them in synapsis. Crossing over also occurs in prophase I. neither occur in the prophase of mitosis
homologous pairs at the metaphase plate Mitosis vs Meiosis
at metaphase I, chromosome are positioned at the metaphase plate as pairs of homologs, rather that individual chromosomes, as in the metaphase of mitosis
Mitosis vs Meiosis: separation of homologs
at anaphase I of meiosis, the duplicated chromosome of each homologous pair move toward opposite poles, but the sister chromatids of each duplicated chromosome remain attached. In anaphase of mitosis, by contrast, sister chromatids spate.
sister chromatids are attached along their length by protein complexes called
cohesins
reductional division
Meiosis I- it halves the number of chromosome set per cell
equational division
Meiosis II-sister chromatids separate producing haploid daughter cells
in sister chromatids, it is a coin flip whether
the maternal or paternal end will face a given pole: it is a 50:50 chance
independent assortment
each pair of homologous chromosomes is positioned independently of the other pairs at metaphase I
number of combination is
2 to n (n=haploid cell number) ex. human is 2 to the 23rd or about 8.4 million
recombinant chromosomes
individual chromosomes that carry genes (DNA) from two different parents; result of crossing over
random fertilization
random nature of fertilization increases variation
asexual reproduction pros
- protects good gens in stable environment
- less energy used
successful asexual animal
bdelloid rotifier -compensate by absorbing other rotifier DNA and other species DNA while in suspended animation during dry periods called horizontal gene transfer; adds variability
crossing over process
- in prophase I
- homolog genes align with corresponding gene
- in a single event the DNA of two nonsister chromatids -one maternal and one paternal- is broken by specific proteins at corresponding points and the two segments beyond the crossover point are joined to the other chromatid
