mod 5: Cell Division Flashcards
cell cycle
period between cell divisions. different cells have varying cycle lengths. divided into phases
somatic cells
body cells (any of the cells forming multicellular organisms, except gametes). cycle length varies based on type of cell and environment
parent cell
original cell that divides into daughter cells
daughter cell
product of cell division
mitosis (definition)
asexual reproduction. produces two daughter cells genetically identical to the single parent cell
meiosis
sexual reproduction. produces daughter cells (gametes) genetically different from parent cell
DNA
deoxyribonucleic acid. molecule of nucleic acid that contains genetic information of a cell and governs process of heredity in cells of an organism
chromosome
length of DNA and its associates proteins (such as histones)
histone
protein that provides forms for DNA to twine around so that it can fit all its length into the confined space of the nucleus. creates a beadlike structure with DNA, where histones are the beads
chromatin
strands of the tight, beadlike structure produced by DNA in combination with histones. contains small amount of RNA
RNA
ribonucleic acid. contains instructions for making proteins
centromere
the part of a chromosome that is constricted (pinched in). a “button” that keeps sister chromatids together after the S phase and and through mitosis until anaphase, where the sister chromatids come apart. also called kinetochore
chromatid
one half of a chromosome. a chromosome divides into two separate chromatids during cell division
binary fission
cell division in prokaryotes. simple because there is only one circular chromosome so no spindle is needed. extremely similar to mitosis
advantages of mitosis
- low energy cost
- fast
- allows rapid spread and population growth
disadvantages of mitosis
daughter cells genetically identical to parent cells–very little genetic variation that only occurs due to mutations
super bugs
bacteria that mutate rapidly and develop resistance to drugs. major health concern
advantages of meiosis
genetic variation
disadvantages of meiosis
- high energy cost
- lengthy process
- requires more than one parent to produce an organism (each parent must provide a gamete)
homologous chromosomes
chromosomes that appear very similar (are officially a pair, correspond with each other) but carry different alleles
allele
different forms of the same gene
autosome
pairs of homologous chromosomes. humans carry 22 autosomes and a sex chromosome pair
sex chromosomes
grouped together but aren’t homologous if XY (XX are homologous). each somatic cell contains both sex chromosomes
X chromosome
larger, contains more genes than Y
Y chromosome
smaller, contains very little genetic information
diploid
symbol: 2n
cells that contain autosomes
haploid
symbol: n
cells that contain unpaired chromosomes (only half of every autosome–they have one of every chromosome but they do not have the corresponding homologous chromosomes)
polyploid
when there are more than two of each chromosome in a set. some organisms are naturally polyploid
karyotype (definition, organization, use)
pictorial representation of the particular set of chromosomes an individual contains. chromosomes organized according to size (longest to shortest) with the sex chromosomes last. used to diagnose chromosome abnormalities and sex chromosomes
how is a karyotype prepared?
- cell sample is collected
- cell sample frozen during the part of the sample where the chromosomes are most clearly visible under a light microscope (during cellular division)
- cells are stained to help see differences in chromosomes
- a photo of the sample is taken and a computer organizes chromosomes into homologous pairs
what characteristics help determine if two chromosomes are homologous?
- overall length
- staining properties (banding pattern/colour)
- centromere position
nondisjunction
error in meiosis (anaphase I or II) that results in non-separation of chromosomes. two chromosomes enter a single daughter cell, causing the other daughter cell to have one chromosome less than it should
what are some syndromes caused by nondisjunction?
- Down syndrome: extra chromosome 21
- Turner syndrome: one X chromosome is missing
- Klinefelter syndrome: extra X chromosome (also called triple X syndrome or trisomy X)
what are the phases of the cell cycle?
interphase, consisting of: growth 1 (G1), synthesis (S), growth 2 (G2).
and mitosis or meiosis (M), which heavily overlaps with the last stage: cytokinesis (C)
interphase
longest period of the cell when the cell is actively growing and metabolizing. consists of G1, S, and G2 phases. DNA is in loose, stringy chromatin form and not visible under the microscope
cell division
the period of the cell cycle where the cell is actively dividing. composed of mitosis and cytokinesis stages.
M phase
the period of the cell cycle where the cell is actively dividing. composed of mitosis and cytokinesis stages.
locus
specific location on a chromosome
how can you tell if a cell is going through cell division by looking at it through a light microscope?
when cells go through division, DNA condenses from chromatin into tightly packed chromosomes. this condensation is visible and looks like a tight tangle in the centre of the cell. then it splits apart into two spaghetti-clump-looking masses on either side and develop into two cells
replication
occurs in S phase. copying of cell’s DNA prior to mitosis so that each daughter cell has an exact copy of the mother cell’s genetic material. results in sister chromatids.
G1 phase
“growth 1 phase”. first part of interphase. cell is actively growing and undergoing metabolism and protein synthesis. normal intended function of the cell.
CHEMICAL CHECKPOINT: the cell determines whether it will divide, delay division, or enter a resting stage
S phase
“synthesis phase”. second part of interphase. DNA replication occurs. each single chromosome makes a copy of itself and holds onto the copy (makes two sister chromatids that are joined by the centromere and considered as one chromosome when joined)
G2 phase
“growth 2 phase”. third part of interphase. growth and preparation for cell division and normal cell function continue.
CHEMICAL CHECKPOINT: evaluates whether the cell has properly duplicated its chromosomes. if not, it may attempt to carry on anyways or may self destruct
sister chromatids
two individual chromosomes that are identical to each other due to DNA replication. lie side-by-side and joined by the centromere, together making up a single chromosome
eukaryotic cell
cell with membrane-bound organelles and nucleus
prokaryotic cell
cell with no membrane-bound nucleus. DNA is just in the cytoplasm
mitosis (stage, not detailed process)
sister chromatids are divided into single separate chromosomes.
CHEMICAL CHECKPOINT: cell evaluates whether the spindle apparatus has properly attached itself to each chromosome and whether the cell is ready for physical division. if not, the cell will likely die
cytokinesis
greatly overlaps with mitosis, not a distinctly separate phase. cytoplasm is divided, forming two daughter cells from the parent cell, which then being to go onto the G1 phase and the cycle is complete
spindle apparatus
structure composed of spindle fibres. facilitates separation and movement of chromosomes in cell division. formed during mitosis (prophase) by centrioles
density dependent inhibition
property of normal cells that allows mitosis to only occur until cells touch each other–cells will only form a single layer, will not begin to grow on top of each other
anchorage dependence
property of normal cells that only allows mitosis to occur when cells are attached to a substrate or surface, not floating freely
cancer
rapid, uncontrolled division of cells, not limited by density-dependent inhibition or anchorage dependence. cells do not stop at any checkpoint in the cell cycle, have a short cell cycle, and never enter the stage where specialized function occurs. lack of cellular clock–do not age or die
metastasis
when some cancer cells leave their original site and spread to other areas through blood or lymph systems
radiation treatment
high energy radiation from radioactive isotopes is directed towards a cancerous tumour in effort to destroy it without damaging surrounding tissue too much. it damages DNA so tat the cancer can’t multiply properly, preventing growth
cellular clock
“apoptosis”. property of cells that allows the too go through a set number of divisions and then stop, causing the cell to die out. prevents mutations from building up and having too big an effect (natural safeguard against cancer)
mutagenic agents
chemicals or physical agents (such as radiation) that have the ability to mutate DNA, affecting the timing of the cell cycle, increasing rate of mitosis over time. over time, this can add up and result in cancer
chemotherapy
use of cytotoxic drugs that inhibit cell division (usually by preventing DNA replication or interfering with the spindle mechanism and supply of blood and nutrients to the tumour). applies systematically into the bloodstream. may affect normal rapidly-dividing cells (such as hair follicles)
Hodgkin’s disease
blood cancer of lymph tissue
what are the phases of mitosis? (in order)
PMAT: prophase, metaphase, anaphase, and telophase
prophase
first phase of mitosis
- chromatin condenses into tightly packed chromosomes
- nucleolus and nuclear membrane disappear
- (animal cells:) pair of centrioles move apart to opposite poles, forming spindle apparatus between them (plant cells:) contain no centriole, spindle apparatus anchors to cell wall
centrioles
organizing bodies of the spindle. form the spindle apparatus between them when they move apart
metaphase
second phase of mitosis
- spindle fibres guide the chromosomes (which are made up of two sister chromatids at this point) the equator of the cell
- spindle fibres attach to centromeres so that one sister chromatid faces one pole and the other faces the other
anaphase
third phase of mitosis
- centromere of each chromosome splits
- spindle fibres pull their sister chromatids toward their pole
- microtubules of the spindle apparatus that are unattached to chromatids lengthen and push the poles away
result: sister chromatids are split and there is a complete diploid in each hemisphere
telophase
fourth phase of mitosis
- chromatids unwind into chromatin strands
- spindle apparatus breaks down
- nuclear membrane forms around each set of chromosomes
- nucleolus forms within each nucleus
cytokinesis (in animal cells)
cleavage furrow forms on either side of the cell, “pinching through” until the parent cell is divided into two daughter cells
cytokinesis (in plant cells)
cell wall prevents it from occurring like in animal cells. a new cell wall forms between the two daughter cells (called a cell plate)
telomere
section on each end of chromosome that that protects chromosomes. shortens with each mitotic division, preventing division from occurring when its too short, therefore preventing cancer from occurring
an excess of which two substances can negatively affect cells
too much glucose or too many oxidants can bind to DNA and cause cells to die, reduce in function, or develop into cancer
what are the two key outcomes of meiosis?
- reduction division: another name for meiosis because meiosis is a form of cell division that produces daughter cells with fewer chromosomes than in the mother cell
- recombination: products of meiosis have different combinations of genes, giving rise to genetically distinct offspring
what are the phases of meiosis? (in order)
- interphase: the same as in mitosis
- meiosis I: consists of prophase I, metaphase I, anaphase I, and (possibly) telophase I
- meiosis II: consists of prophase II, metaphase II, anaphase II, and telophase II
ploidy
refers to chromosome number of a cell or how many sets of chromosomes are present
what is the goal of meiosis I?
to separate homologous pairs, halving the amount of chromosomes
prophase I
synapsis occurs
synapsis
homologous chromosomes that had been duplicated and now each consist of two sister chromatids entwine and synapse together, forming tetrads
tetrad
formed in prophase I (meiosis I) during synapsis. consists of four chromatids where there are two sister chromatid pairs. non-sister chromatids are beside each other in the middle, allowing crossing over to occur
crossing over
occurs in prophase I when chromosomes are in a tetrad. two non-sister chromatids may exchange pieces, resulting in a completely different chromosome from the original set. can occur at several points along the chromatids. this creates a new chromatid because homologous pairs have different alleles
metaphase I
spindle fibre attaches to the centromere of each chromosome within a tetrad and lines them up in two lines along the equator, where each homologous chromosome is across the equator to its corresponding chromosome.
anaphase I
spindle fibres separate the tetrads, sister chromosomes stay together. this means each pole contains a haploid set, but each chromosome in a haploid set is made up of two sister chromatids (which aren’t identical because crossing over happened)
telophase I
some cells skip this phase. essentially the same as telophase in mitosis. replication does NOT occur before meiosis II
meiosis II
follows the exact same pattern of steps as mitosis–sister chromatids are split apart and result daughter cells without any duplicated chromosomes. results in four haploid daughter cells. replication DOES NOT occur between meiosis I and II.
two sources of genetic recombination (variation)
independent assortment and crossing over
independent assortment
in metaphase I, tetrads line up randomly on the equator so it doesn’t matter which side receives the maternal or parental version of the chromosome, the orientation of one chromosome/tetrad is completely independent of the organization of the others.
totipotent cells
cells that have not specialized or differentiated (ex: morula, zygote) and all genes have the potential to be expressed
prenatal genetic testing
sampling and testing of embryonic cells to determine chromosome number and gender
spermatogenesis (process)
starts with a diploid spermatogonium, which are contained in the testes at birth. they undergo mitosis start at puberty. one daughter cell may take the place of the parent cell and continue producing more daughter cells while the other (called a primary spermatocyte) undergoes meiosis I, transforming into two secondary spermatocytes that then undergo meiosis II, resulting in four spermatids altogether, which are completely developed but not mature
spermatogonium
diploid. cell in the testes that duplicate themselves and produce primary spermatocytes through mitosis
primary spermatocyte
diploid. produced by spermatogonium (essentially it is exactly the same as any spermatogonium but it chooses to continue developing into a sperm rather than duplicate). undergoes meiosis I to create two secondary spermatocytes
secondary spermatocyte
haploid. produced by primary spermatocytes. undergoes meiosis II where each secondary spermatocyte will create two spermatids
spermatid
haploid. produced by secondary spermatocytes. a completely developed but not-yet-mature sperm cell
oogenesis
diploid oogonium undergoes mitosis prenatally until about 2 million primary oocytes are produced, which begin prophase I but stop there until puberty, at which point one primary oocyte continues meiosis I each month, producing one secondary oocyte and the first polar body, which may or may not produce two second polar bodies. secondary oocyte only starts meiosis II after fertilization and results in an ovum and a second polar body.
oogonium
diploid. undergoes mitosis to create primary oocytes prenatally
primary oocyte
diploid. begins prophase I prenatally and continues meiosis I after puberty once a month (one oocyte per month).
asymmetrical cytokinesis
unequal distribution of cytoplasm. causes oogenesis to result in oocytes and polar bodies. egg cells need cytoplasm to support a developing embryo so polar bodies have much less cytoplasm and are therefore smaller.
polar body
haploid. essentially oocytes/ovum with less cytoplasm. are used as a place to dump unneeded chromosomes during oogenesis. reabsorbed by the body after creation
types of nondisjunction?
monosomy–when one chromosome is lost (human has 45 chromosomes)
trisomy–when one extra chromosome is gained (human has 47 chromosomes)
why is an older woman more likely to give brith to a child with a nondisjunction as she gets older?
since until they start developing themselves, primary oocytes are frozen in the prophase I stage for many years, as they age the apparatus to complete meiosis properly deteriorates.
also: with age, the womb becomes less selective and is more likely to carry an embryo with a genetic disorder to term.
three ways to test fetuses for genetic problems?
- amniocentesis–needle sampling of amniotic fluid
- cordiocentesis–sampling of umbilical cord blood
- chorionic villus sampling (CVS)–vaginal sampling of chorionic villi
parenthogenesis
rare type of asexual reproduction in animals. haploid unfertilized egg divides by mitosis, producing a complete multicellular organism in which all cells are haploid. (ex: bees, Komodo dragons)1
conjugation
bacteria transfer genetic material from one cell to a different one with different genes. produces one genetically unique daughter that can undergo binary fission and create an new colony
alternation of generations (definition and process)
a plant life cycle where two distinct diploid and haploid multicellular forms occur in a generation and reproduction alternates between sexual and asexual. all plants do this and this is exclusive to plants (animals such as jellyfish may alternate between sexual and asexual reproduction but between haploid and diploid)
the sporophyte (diploid generation) creates haploid spores through meiosis, which aren’t fertilized, instead grow into the haploid generation. the gametophyte (haploid generation) produces male and female gametes through mitosis that fuse (fertilize) and form a zygote that grows into a sporophyte, restarting the cycle.
vascular plants
plants that have a transport system of conducting tubes (ex: coniferous trees). in vascular plants, the sporophyte generation is dominant (in coniferous trees, the sporophyte is the tree itself)
non-vascular plants
plants that do not have a transport system to conducting tubes (ex: moss). in non-vascular plants, the gametophyte is dominant (in moss it’s the part identifiable as moss)
