Cell cycle and Cell Division (mitosis and meiosis) Flashcards
what is the goal of cell division
partition 2 identical (more-or-less) copies of genetic material between two daughter cells
Difference between prokaryotes and eukaryotes in cell division
binary fission(pros) mitosis (euks)
Why are prokaryotic cells simpler to divide
comparatively simple; only 1 chromosome, so have a relatively easy time sorting daughter chromosomes to daughter cells
why are eukaryotic cells more difficult to divide
longer DNA & multiple chromosomes
what are the steps of binary fission
1) Prokaryote chromosome replicates & cell stretches
2) Produce 2 circular chromosomes at opposite ends of cell
3) Cell membrane stretches & breaks apart → form 2 cells
Each cell has now has 1 full chromosome
4) Randomly distributed cytosol, plasmids, & ribosomes end up in both cells
what are the two methods of asexual reproduction>
binary fission and mitosis
explain loose chromatin
Unwound DNA
Found throughout Interphase
DNA is being used for macromolecule synthesis
explain condensed chromosomes
Tightly packaged DNA
Found only during cell division
DNA is not being used for macromolecule synthesis
why do eurkaryotes do mitosis?
they have a nucleus so dna cannot simply move to either side of the cell
they have multiple chromosomes meaning need to ensure that each daughter cell has exactly 1 copy of each chromosome
chromosomes are formed from what
2 sister chromatids with an identical sequence
where are sister chromatids attached
at the centromere
where to microtubules attach to?
The kinetochore
what is another name for the microtubules that split the sister chromatids
mitotic spindle
What pulls apart the sister chromatids in mitosis
microtubles
where are the two centrosomes?
at opposite poles of the nucleus
what is the centromere?
dna sequence that links sister chromatids
what are the 3 functions of the centromere?
adhesion
kinetochore formation
pairing of homologous pairs
what is the kinetochore?
protein structure that assembles at centromere
what are the functions of the kinetochore?
links chromosome to microtuble polymers from the mitotic spindle
used in mitosis and meiosis
what does the cell cycle include?
Includes DNA replication, cell division & cell growth
What are the 4 phases of the cell cycle?
g1 (gap phase 1)
s (synthesis)
g2 (gap phases 2)
m (mitosis)
explain gap phase 1 (g1)
lasts approx 11h growing performs transcription and translation produces proteins and organelles at a certain phase, s is initiated
explain s phase
lasts approx 8h period of dna replication little growth occurs nucleus contains double the dna once celel has replicated all its dna, g2 is initiated
does protein synthesis occur in s phase
NO not enough space/energy to do both
how many chromosomes do humans have
46 (23 pairs)
are the two chromosome pairs identical?
no because we have one copy from each parent therefore they have genetic differences
they are a homologous pair
why are the two chromosomes (1 from each parent) called a homologous pair
because although they aren’t genetically identical, they code for the same proteins (ie. hair colour, height)
what does the s phase entail and what does it give you
entails dna synthesis
gives two identical sisters chromatids attached at the centromere
why do we have two homologous pairs?
because one from mom is copied and one from dad is copied
explain g2 phase
lasts approx. 4 h
growing
produces more organelles and proteins
once a certain size, mitosis is initiated
why must the cell cycle be tightly regulated?
to ensure division does not happen prematurely or too late\ee
what are the proteins that regulate the cell cycle
cyclins
what do cyclines do?
family of proteins that regulate transition of cells from one stage of the cell cycle to the next.
Specific cyclins control transition from S to G2: send signals within the cell to know when replication is complete
what happens if cyclins do not functionn properly?
cell may go uncontrolled growth which leads to cancer
are all cells in the cell cycle at all times
no , some cells are in g0
are cells not going through the cell cycle considered dead>
no, they still transcribe and translatee
they just aren’t actively dividing
what are the two types of cells (Q vs D)
Quiescent cells vs Differentiated cells
explain quiescent cells
they are reversible and can change (skin cells)
explain differentiated cells
they can never go back (brain cells)
mitosis is used for what kind of cells
somatic (non sex cells)
what are the 5 phases of mitosis
1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase
components of prophase
nucleoli disappears and dna condenses (see thick visible lines, dna is no longer long unravelled fibres)
sister chromatids are attached at centromere
kinetochore proteins attaches to centromere
centrosomes (that we’re replicated) seperate and migrate to oppsotive sides of the cell
microtubles extend and attach to each other and as these grow, the cell stretches
what is the centrosome
microtubule organizing centre
components of prometaphase
nuclear envelope breaks down
spindles fibbers attach to kinetochore
other spindle fibres extend to provide tracks for migrateing organelles
components of metaphase
chromosomes align at cell equator (metaphase plate) in nice row
kinetochores of sister chromatids are facing opposite poles (each attached to a spindle from different sides of cell)
components of anaphase
sister chromatids are pulled apart (each now considered a daughter chromosome)
microfibres (spindles) shorten
cell elongates
each pole has.a copy of each chromosome
components of telophase
nuclei begin to form at each pole
nuclear envelope forms around chromosomees
chromatin uncoils/decondenses and become less distinct
what is the last process of mitosis called
cytokinesis
what is the goal of cytokinesis
separation created two identical daughter cells)
explain cytokinesis in animals
formation of cleavage furrow (growing gap between two daughter cell)
pinching in caused by microfilaments inside cell which tightens til cell splits
explain cytokinesis in plants
plants have cell wall therefore cannot do cleavage furrow
must form cell plate that will form with cell wall then divide
vesicles from golgi bring small pieces of cell wall
difference between animal and plant mitosis
1) cleavage furrow vs cell plate
2) animals have centrioles, plants do not
aspects of asexual reproduction
- reproduction without sex
- binary fission or mitosis
- involves only one parent
- offsprings are genetically identical (clones) or parent
aspects of sexual reproduction
- union of 2 gametes (sex)
- meiosis and fertilization
- involved 2 parents
- offspring are genetically different from parents (recombination)
mitosis creates what kinds of cells
diploid somatic cells
meiosis creates what kinds of cells
haploid gametes
meiosis creates how many daughter cells and are they identical
makes 4 cells which are genetically similar but still different
what is a somatic cell and what kinds are somatic
Non-reproductive cell
Almost all the cells in your body are somatic cells (except sperm / eggs)
what is a gamete and where are they produced
Reproductive cells (e.g. eggs / sperm) Produced in ovaries / testes through meiosis
haploids are human…
gametes
diploids are human…
somatic cells
what is a haploid cell
cell that possesses one set of chrmosomes
what is a dimploid cell
cell that possesses two sets of chromos
when u inherit one set from each parent
define sex chromosome
Determine sex (dissimilar chromosomes – not homologous)
Humans: X & Y chromosomes
Humans have 1 pair of sex chromosomes (XX or XY)
are sex chromosomes homolgous?
no
define autosome
Any chromosome that is not a sex chromosome
Humans have 22 pairs
define homologous chromosomes
Pair of chromosomes with the same size, centromere position, staining pattern
Inherit 1 homologue from each parent
Autosomes: same genetic loci (sites) – code for same genes
Note: sex chromosomes have different sizes & loci (X vs. Y) but they do pair during meiosis
define karyotype
- Shows chromosomes in a somatic cell at metaphase
- Arranged in a standard sequence (size, centromere location, colours from staining)
- Use to screen for chromosomal abnormalities
meiosis forms what in comparison to mitosis
Meiosis forms 4 unique haploid cells
Compare this to mitosis, which forms 2 identical diploid cells
components of meiosis 1 prophase 1
chromosomes condense
sister chromatids associated with one another
homologous pairs also associate
centrosomes extend microtubules and move apart
explain homologous recombination
homologous chromosomes (non sisters) can cross over and recombine
where does recombination occur
chiasmata
what is the result of meiosis prophase1
4 chromatids cluster around centromere (tetrad is formed)
(pair of homologous chromosomes)
associate with a kinetochore
components of meiosis 1 pro metaphase 1
nuclear envelope breaks down
tetrads associate to mitotic spindle fibers
centrosomes localist to opposite poles of the cell
components of meiosis 1 metaphase 1
tetrads align at centre of cell (metaphase plate/equator)
kinetochores of homologous chromosomes face opposite cells (Each attached to a spindle fibre originating from a different side of the cell)
components of meiosis 1 anaphase 1
- pairs of sisters chromatids REMAIN ATTACHED (ie. sister chromatids do not separate yet to go to a different centrosome)
- each homologous chromosome pair DOES separate from its other pair memeber
what is the result of anaphase 1
one copy of each chromosome is passed to a different cell (this is a random choice)
-daughter cells are haploid because despite having.2 sister chromatids they are lacking one different copy from each chromosome)
in anaphase 1, are you supposed to have both a copy from mom and dad?
no, it will either be one copy from mom OR. a copy from dad
components of meiosis 1 teleophase 1
sister chromatid pairs reach the centrosome
some cells show chromosome decondensing, some dont
components of meiosis 1 cytokinesis/interkinesis 1
formation of cleavage furrow (like mitosis)
pinching caused by microfilaments
more centrosomes are produced for meiosis round 2
components of meiosis 2 prophase 2
almost identical to meosis 1 except tetrads to not form since there are not homologous chromosome pairs (only have pairs of sisters chromatids)
components of meiosis 2 pro metaphase 2
nuclear breaks apart again (if it has reformed)
pairs of sister chromatids attach to spindle fibres via centromeres
centrosomes go to opposite poles of cell
components of meiosis 2 metaphase 2
chromosomes align at metaphase plate
kineetichores face opposite sides attached to a spindle from different side of cell)
just like mitosis except sister chromatids may not be identical due to recombination
components of meiosis 2 anaphase 2
sister chromatids seperate and move to opposite centrosome
(separated sisters are now considered to be individual chromosomes)
these cells are already haploid but this seperation ensures only 23 chromosomes per game)
components of meiosis 2 telophase 2
chromos research centrosomes at each pole
nuclei reforms and dna decondenses
cytokinesis 2
same as cytokinesis 1
but now we have 4 daughter cells1
meiosis recap
2 rounds of chromosome seperation and cell division
forms 4 unique haploid cells
end up with only 1 copy of each chromosome in a single gamete
components of meiosis in males
Spermatogenesis (formation of sperm)
Primary spermatocytes undergo meiosis I
Produce 2 secondary spermatocytes
Secondary spermatocytes undergo meiosis II
Produce 4 different spermatids
Spermatids are modified so they can survive the journey needed to achieve zygote formation
Result: produce 4 distinct mature spermatocytes (“sperm cells”)
what is the process of meiosis called in males
spermatogenesis
what is the process of meiosis called in females
oogenesis
process of meiosis in females
Primary oocyte undergoes meiosis I
Produce secondary oocytes
Larger secondary oocyte (non-polar body) is destined to become an egg cell (gamete)
Stores much larger portion of cytosol & cellular organelles
Smaller secondary oocyte (polar body) will eventually be eliminated
Larger secondary primary oocyte undergoes meiosis II
Produces 2 more cells from the non-polar body - also different sizes
Larger cell is the mature oocyte (mature ovum)
Mature ovum will fuse with mature sperm cell to produce a zygote
what is the difference between the two oocytes?
1 secondary oocyte is larger than the other
what does the process of oogenesis create?
1 mature ovum
3 polar bodies
meiosis in human females (table)
- All oocytes are made before birth
- Meiosis is completed only if the egg is fertilized
- 1 large egg & 3 other small cells (polar bodies) are the result of one oocyte undergoing meiosis → the polar bodies die
- Egg has half the DNA of a normal body (somatic) cell.
- Egg’s diameter is 140 mm or larger
- Egg has enormous cytoplasmic storehouse of proteins, ribosomes, tRNA, mRNA (25,000-50,000 different types of mRNA), & morphogenetic factors.
meiosis in human males (table)
- Spermatocytes are made under the influence of testosterone, starting at puberty, and continuing throughout life
- Meiosis is completed before sperm leave the testes (within the seminiferous tubules).
- 4 small equal-sized functional cells are formed during and after meiosis.
- Sperm has half the DNA of a normal body (somatic) cell.
- The sperm’s head is about 5 mm
Sperm designed for specialized function:
- locating the egg
- fusing with the surface of the egg
- injecting the sperm nucleus (DNA) into the egg cell’s cytoplasm.
what are the 3 sperm functions
- locating the egg
- fusing with the surface of the egg
- injecting the sperm nucleus (DNA) into the egg cell’s cytoplasm.
what are the three ways of introducing genetic variation during meiosis
1) independant assortment
2) random fertilization
3) recombination
explain independent assortment
decision of which chromosome goes to while cell is completely random
approx (8.3 million combos)
explain random fertilization
there are so many possibilities as to which games will fuse (70 trillion combos)
how is a zygote formed?
fusion of two games (egg and sperm)
explain recombination?
Homologous chromos (non sisters) can cross over and form chiasmata
both strands of dna trade fragments of the chromosomes so sisters are no longer identical
what is is called when something goes wrong in cell division
non-disjunction
What is an aneuploidy
cell that ends up with the wrong number of chromos
what happens in a non disjunction
when seperation of chromatids or chromosomes does not occur meaning some gametes will have too many chromes and some will have too few
when can a non disjunction happen
anaphase in either meiosis 1 or 2
what happens when a non disjunction occurs during meiosis 1?
entire tetrad migrates towards 1 centrosome
All 4 gametes affected
what happens when a non disjunction occurs during meiosis 2?
both sister chromatids migrate towards 1 centrosome
2 of 4 gametes affected
DIAGRAM I NSLIDES
will an XYY male show any differences from a normal XY male?
no
will an XXX female show any differences from a normal XX female?
no
what are the 4 common conditions caused by aneuploidy
Down Syndrome:
Edwards Syndrome
Klinefelter Syndrome:
Turner Syndrome:
explain down syndrome
have 3 copies (“trisomy”) of chromosome 21
As a result, have 47 chromosomes
Leads to a large # of physical differences & intellectual disability
explain edwards syndrome
(trisomy of chromosome 18) & Patau Syndrome (trisomy of chromosome 13) are 2 other relatively frequent cases of trisomy in humans
Both have increased mortalities associated with them.
explain klinefelter syndrome
males with an additional copy of the X chromosome (XXY or even XXXY)
Display a cross between male and female traits (small testes, enlarged breasts, reduced facial hair) and tend to be infertile
Associated with learning difficulties & co-ordination problems
explain turner syndrome
females with only 1 copy of the X chromosome (X)
Only non-lethal case of monosomy in humans
Have distinct body frames (certain regions are underdeveloped, including reproductive organs)
