140 terms

Brooker Biology Chapter 15

Cell Division
the reproduction of cells is a highly regulated process that monitors the integrity of the genetic material.
involves the microscopic examination of chromosomes and cell division. When a cell prepares to divide, the chromosomes become more tightly compacted, a process that decreases their apparent length and increase their diameter, a consequence of this compaction is that distinctive shapes and numbers of chromosomes become visible with a light microscope.
reveals the number, size and form of chromosomes found with an actively dividing cell.
Explain the microscopic examination of chromosomes?
1) sample of blood treated with drugs that stimulate cell division. The sample then subject to centrifugation.
2) the supernatant is discared, cell pellete suspended in hypotonic solution, causing cell to swell, and chromosome to spread out from each other.
3)centrifugation a second time to concentrate the cells. the cells are suspended in a fixative, stained and placed on slide
4)the slide is viewed by light microscope with camera. the chromosomes can be photographed and arranged electronically on the screen.
What type of information is learned from a karyotype?
that eukaryotic chromosomes occur in sets. Each set is composed of different types of chromosomes.
one set of human chromosomes contain?
23 different types of chromosomes, chromosomes are numbered with the largest chromosome having the smallest number. exp: 1,2,3 are relatively large, 21 and 22 and the two smallest.
sex chromosome
determines sex, does not apply to the numbering system, they are designated with the letter x and Y.
the chromosomes that are not sex chromosomes , humans have 23 different types of autosomes.
Most cells contain how many sets of chromosomes?
how many chromosomes in each set? therefore this human cell contains a total of ?
23, 46
why does a person's cell have 46 chromosomes each?
an individual inherit one from father, one from mother, known as diploid.
when the cells of an organism carry two sets of chromosomes. So diploid organisms are reffered to as 2n, where n is 23. an exception would be gametes, namely sperm and egg cells referred to a 1n, which mean they contain 1 set of chromosomes.
namely sperm and egg cells, they are halpoid or 1n which means they contain only one set of chromosomes.
When an organism is diploid, it is said to be?
homologues because the similarity of the pair of chromosomes, pairs of homologues chromosomes are derived from the same chromosome, however these chromosomes are not usually identical to each other because over many generations they have accumulated some genetic changes that make them distinct.
The X and Y chromosomes are not considered?
Homologues, certain genes found on the X chromosome are not found on the Y chromosome.
cell cycle
A cycle that eukaryotic cells that are destined to divide progress through, usually a sequence of growth, replication, and division that produces new cells.
when a mother has 3 pairs of chromosomes, for a a total of 6 individual chromosomes. what is n?
n = 3, and this cell is consider 2n diploid.
what are the phases of the cell cycle?
G1 ( first gap)
S (synthesis of DNA, the genetic material)
G2 ( Second Gap)
M Phases (mitosis and cytokinesis)
What phases are collectively known as interphase? the pause in activity b/w DNA synthesis and mitosis?
G1, S, G2, during the interphase, the cell grows and copies its chromosomes in preparation of cell division.
G0 phase?
when cells may exit the cell cycle and remain for long periods of time in a phase. The G0 phase is an alternative to proceeding through G1. A cell in the G0 phase has postponed making a decision to divide or, in the case of terminally different cells such as nerve cells in adult animals has made a decision to never divide again. G0 is a nondiving phase.
G1 phase
a period in a cell's life when it may become committed to divide. a cell in the G1 phase may accumulate molecular changes that causes it to progress through the rest of the cell cycle.
cell growth typically occurs during the G1 phase
S phase
During the S phase, the chromosomes are replicated, after replication, the 2 copies are still joined to each other and referred to as a pair of sister chromatids. When S phase is complete, it will have twice the number of Chromatids as the number of chromosomes in the G1 phase.
G1 has 46 chromosomes
G2 would have 46 pairs of sister chromatids, for a total of 92 chromatids.
G2 Phase
a cell synthesizes proteins that are necessary for chromosome sorting and cell division. This prepares the cell for the last phase of the cell cycle. Some cell grow may occur.
M phase
the first part of M phase is mitosis. During mitosis, these pairs of chromatids are separated and sorted so that each daughter cell will receive 46 chromosomes.
Mitosis purpose?
is to divide one cell nucleus into 2 nuclei, distributing the duplicated chromosomes so that each daughter cell will receive the same complement of chromosomes. each daughter cell will receive 46 chromosomes. Mitosis is the name given to this sorting process.
Cytokinesis is?
after mitosis, which is the division of the cytoplasm to produce 2 distinct daughter cells.
Which are the shortest and longest phase? G1, S, G2, M
G1 is longest, M is shortest
Which phase make up interphase?
G1, S, G2 phase
Explain the whole Eukaryotic cell cycle in short?
1) the original diploid cell had 3 pairs of chromosomes, for a total of 6 individual chromosomes.
2) during S phase, these have replicated to yield 12 chromatids
3) after mitosis complete, 2 daughter cells each contain 6 chromosomes.
Kinetochore is?
a group of protein that are attached to the centromere and play a role during chromosome sorting.
DNA that is hidden beneath the kinetochore proteins
What main factors determine whether or not a cell will divide?
it is based on external factors such as environmental conditions and signaling molecules, second is internal controls such as cell cycle control molecules and checkpoints.
Cyclins and Cyclin-dependent kinases (CDKS)
are responsible for advancing a cell through the phases of the cell cycle, cyclins amount will vary dependent on the cell cycle. To be active, the kinases controlling the cell cycle must bind to are dependent on cyclin. The number of different types of cyclins and cdks varies from species to species.
Describe Cyclin control in various phases?
during G1, cyclin increases, the G1 cyclin binds to Cdk to form an activated G1 cyclin/cdk complex. once activated, cdk functions as a protein kinase that phosphorylates other proteins that are needed to advance the cell to the next phase in the cell cycle.

For exp: certain proteins involved with DNA synthesis are phosphorylated and activated thereby allowing the cell to carry out even in S phase. when cell passes into S phase, G1 cyclin is degraded. A different cyclin, called mitotoic cyclin, accumulates late in G2, it binds to a CDK to form an activated mitotic cyclin/cdk complex, this complex phosphorylates proteins that are needed to advance into Mphase.
3 critical regulatory points called ___ are found in the cell cycle of eukaryotic cells.
pupose of checkpoints?
at these checkpoints, a variety of proteins, referred to as checkpoint proteins act as sensors to determine if a cell is in the proper condition to divide.
Restriction check point is?
also known as the G1 checkpoint, determines if conditions are favorable for cell division. they can also sense if the DNA has incurred damage. if it is indeed damaged, the checkpoint proteins will prevent the formation of active cyclin/cdk complexes and thereby stop the progression of the cell cycle.
G2 check point does?
also checks for DNA damage and ensures that all DNA has been replicated, in addition it monitors the levels of proteins that are needed to progress through M phase.
metaphase checkpoint does?
the third checkpoint, senses the integrity of the spindle apparatus which is involoved in choromosome sorting. Metaphase is a step in mitosis during which all of the chromosomes should be attached to the spindle apparatus. if a chromosome is not correctly attached, the metaphase checkpoint will stop the cell cycle. This checkpoint prevents cells from incorrectly sorting their chromosomes during division.
The importance of checkpoint proteins?
it delay the cell cycle until problem are fixed and prevent the cell divisions when problems can't be fixed, the primary aim is to prevent the division of a cell that may have incurred DNA damage or harbors of abnormalities in chromosome number. This maintain the integrity of the genome.
The formation of activated cyclin/cdk complexes is regulated by?
checkpoint proteins
maturation promoting factor which is the factor that caused the oocytes to progess or mature from G2 to M phase, MPF is important in the divison of all types of cells, MPF is a complex made of mitotic cyclin and a cyclin-dependent kinase (CDK).
what happens in mitotic cell division?
a cell divides to produce 2 new cells ( the daughter cells) that are generally identical to the original cell (the mother cell). It involves mitosis which is the division of 1 nucleus to 2 nuclei and then cytokineses which the mother cell divides into 2 daughter cells.
why is mitotic cell division important?
one purpose is asexual reproduction. certain unicellular eukaryotic organism such as yeast and amoeba increase their numbers in this way.
2) production and maintenance of multicelluarity such in those of plants, animals and most fungi are derived from single to multicellular organisim that undergoes repeated cellular division.
a protein called cohesin is necessary to hold the sister chromatids together.
centromere serves as an attachment site for a group of proteins that form the___?
kinectochore is necessary for?
soring chromosomes
What structure is responsible for organizing and sorting the chromosomes during cell division?
mitotic spindle apparatus or mitotic spindle, it is composed of microtubules which are protein fibers that are components of the cytoskeleton.
Explain the structure of mitotic spindle?
formed by the centromsomes which produce 3 types of microtubules. the astral microtubules emanate away from the region bw the poles. the polar microtubules project into the region b/w the 2 poles. the kinetochore microtubules are attached to the kinetochores of sister chromatids.
what are the functions of the 3 types of microtubules?
The astral microtubules which extend away from the chromosomes are important for positioning the spindle apparatus within the cell. the polar microtubules project into the region b/w the 2 poles, polar microtubules that overlap with each other play a role in the separation of the 2 poles. kinetochore microtubules are attached to kinetochores at the centromemeres and are needed to sort the chromosomes.
With regards to chromosome composition, how does the mother cell compare to the 2 daughter cells?
the mother cell in G1 phase and the daughther cells have the same chromosome composition. they are also gentically identical.
Prior to mitosis, the cells are in?
interphase, which includes G1, S, and G2 phase, during interphase, the chromosomes are decondensed and found in the nucleus.
the start of mitosis, the chromosomes have already replicated to produce 12 chromatids, joined as 6 pairs of sister chromatids, as prophase proceeds, the nuclear envelop begins to dissociate into somall vesicles, at the same time, the chromatids condense into highly compacted structures that are readily visible by light microscopy.
the nuclear envelops has completely dissociated into vesicles, and the mitotic spindle is fully formed. sister chromatids attach to the spindle via kinetochore microtubules.
during prometaphase, as it grows, if a microtubule happens to make contact with a ____, it is said to be ____, and remains firmly attached to the ____.
kinetochore, captured, kinetochore.
eventually the pairs of sister chromatids are aligned in a single row along the metaphase plate- which a plane half way b/w the poles. when this alignment is complete, the cell is in metaphase of mitosis. the chromatids can then be equally distributed into 2 daughter cells.
the connection b/w sister chromatids are broken, each chromatid now an individual chromsome is linked to only 1 of the 2 poles by one or more kinetochore microtubules. as anaphase proceeds, the kinectochore microtubules shorten, pulling the chromosomes toward the pole to which they are attached. in addition, the 2 poles move farther apart b/c the overlapping polar microtubules lenghthen and push against each other, therby pushing the poles farther apart.
the chromosomes have reached their respective poles and decondense. the nuclear envelope now re-forms to produce 2 separate nuclei, each contain 6 chromosomes each.
two nuclei are segregated into separate daughter cells. in animal cells, cytokinesis involves formation of a cleavage furrow, which constricts like a drawstring to separate cells, in plants, vesicles from the golgi appartus move along microtubules to the center of the cell and coalesc to form a cell plate, which then forms a cell wall b/w the 2 daughter cells.
Sexual reproduction requires?
a fertilization event in which 2 halpoid gamestes unite to form a diploid cell called a zygote.
the process by which halpoid cells are produced from a cell that was orginally diploid. " to make smaller", refers to the fewer chromosomes found in cells following this process. for this to occur, the chromosomes must be correctly sorted and distributed in a way that reduces the chromosome number to half its original diploid value.
When a cell begins meiosis, it contains chromsomes that are found in _____ ____. When meiosis is completed, a single ___ cell with ___ ___ of chromosomes has produced 4 ___ cells.
homologous pairs, diploid, homologous pairs, haploid
Like mitosis, meiosis begins after?
a cell has progressed through G1, s, G2 phase
2 key events that occur at the beginning of meiosis that do not occur at mitosis?
1) first homologous pairs of sister chromatids associate with each other, lying side by side to form a bivalent also called a tetrad. the process of forming a bivalent is termed synapsis.
2) crossing over - which involves a physical exchange b/w chromosome segments of the bivalent, after crossing over occurs, the arms of the chromosomes tend to separate but remain adhered at a crossover site, this connection is called chiasma, but it physically resembles the greek letter chi, x.
Mitosis phases?
Prophase, prometaphase, metaphase, anaphase, telophase
Interphase and Cytokinesis are before and after mitosis
Meiosis 1 phases?
Prophase 1, prometaphase1, metaphase 1, anaphase 1, telophase 1
Prophase 1
the repliacted chromosome condense, the homologous chromosomes for bivalents, and crossing over occurs. the nuclear envelope then starts to fragment into small vesicles.
prometaphase 1
the nuclear envelope is completely broken down into vesicles, and the spindle apparatus is entirely formed. a pair of sister chromatids is attached to just 1 pole via kinetochore microtubles as where in mitosis, it was attached to 2 poles.
metaphase 1
the bivalents are organized along the metaphase plate, in particular the sister chromatids are aligned in a double row rather than a single row ( as in mitosis). the arrangement of sister chromatids within this double row is random. When meiosis is complete, it is very unlikely that any 2 human gametes will have the same combination of homologous chromosomes.
anaphase 1
the segregation of homologous occurs, and the connection b/w bivalents break, but not the connection that hold sister chromatids together. each joined pair of chromatids migrates to one pole, and the homologous pair of chromatids moves to the oppposite pole. both pulled by kinetochore microtubules.
telophase 1
at telophase 1, the sister chromatids have reached their respective poles, and they then decondense. the nuclear envelope now re-forms to produce 2 separate nuceli.
2 cells produced as a end result of meiosis 1 and cytokinesis are consided ?
halpoids, they do not have pairs of homologous chromosomes.
Meiosis 2
the two cells that begin meiosis 2 each have 6 chromatids that are joined as 3 pairs of sister chromatids. sister chromatids are separated during anaphase 2 unlike anaphase 1 which bivalents are separated.
Life cycle
for any given species, the sequence of events that produces another generation of organisms
Animals are viewed as diploid-dominant species, why?
most species of animals are diploid, and their haploid gametes are considered to be a specialized type of cell. certain diploid cells in the testes and ovaries undergo meiosis to produce haploid sperm or eggs. during fertilization, sperm and egg unit to form diploid zygote which then undergoes repeated mitotic cell divisions to produce a diploid multicellular organism.
Most fungi and some protists are?
halploid-dominant species, in fungi the multicellular organism is halpoid (1n). haploid fungai cells are most commonly produced by mitosis. during sexual reproduction, halpoid cells unit to form a diploid zygote, which then immediately proceeds through meiosis to produce 4 halploid cells called spores. each spore goes through mitotic cellular divisions to produce a haploid multicellular organism.
plants and some algae have life cycles that are intermediates b/w the extreme cases of diploid or haploid dominance. such species exhibit?
alternation of generations, the species alternate b/w diploid multicellular organisms called sporophytes and halpoid multicellular organisms called gametophytes.
Unicellular organisms reproduce by?
cell division, exp: amoeba a single cell eukaryote
Multicellular organisms depend on division for?
development from a fertilized cell
Chromosomes are made of?
DNA and Protein
Human somatic (body) cells are?
Diploid - which consists of 2 complete sets of chromosomes, each set is 23 chromosomes, for a total of 46 chromosomes.
Human gametes (egg and sperm) cells are ?
Haploid - only 1 set of chromosomes = 23 total
these games sperm and egg cells chromosomes are for?
blood type, height etc.
Human Karyotype - 46 _ , 23 _ 22 _, 1 _
46 chromosomes, 23 pairs, 22 pairs autosome, 1 pair sex chromosome.
Chromosomes structure are ?
double stranded with 2 identical sister chromatids attached at the centromere.
each duplicated chromosome has 2 _, which separate during _?
sister chromatids, cell division
before duplication, each chromosome has a ?
single DNA molecule
Once duplicated, a chromosome consists of ____ connected at the centromere, each ___ contains a ____.
2 sister chromatids, chromatids, copy of the DNA molecule.
Mechanical processes separate the ___ into 2 chromosomes and distribute them to __?
sister chromatids, two daughter cells.
Double stranded means? Single stranded means?
double = one chromosome duplicated like sister chromatids.
single = just one chromosome, it's not duplicated. these are distributed to daughter cells after cell division.
In metephase chromosome?
highly compacted radial loops remain anchored to a scaffold formed from proteins in the nuclear matrix.
What happens in preparation for cell divison?
DNA replicated
sister chromatids tightly associated at centromere
serves as an attachment site for kinetochore used in sorting chromosomes.
Eukaryotic chromosomes consists of?
chromatin, a complex of DNA and protein that condenses during cell division
In animals, somatic cells have ___? Gamestes have ___?
2 sets of chromosomes, 1 set of chromosomes.
in mitosis, one cell divides into ___? each cell is ___?
2 cells, each cell is genetically identical to the original cell.
the basic cell cycle is?
G1 - cell growth
S - chromosome duplicated
G2 - cell prepares to divide
The cell cycle consists of the?
mitotic phase
Cell life cycle of the M phase consists of Mitosis, and Cytokinesis which are?
mitosis - division of nucleus
cytokinesis - division of cytoplasm.
nondividing cell consists of?
nuclear envelope, nucleolous, chromatin
dividing cell consists of?
no nuclear envelope or nucleolus
Difference b/w chromatin vs Chromosome?
Chromatin - DNA in dispersed form, granular appearance.
Chromosome - condensed form, thick worm like
Animal cell mitotic spindle have?
1) centrosome - microtubule organizing center
2) Single centrosome duplicates at the beginning of M phase
3) have centrioles ( not found in many other eukaryotes).
Cytokinesis occurs?
late anaphase through telophase
Animal cell cytokinesis have?
cleavage furrow
Plant cell cytokinesis have?
cell plates
If we start with 4 chromosomes in the original cell, how many do we end up with in each DAUGHTER CELL?
4 in each.
Human Karyotype have 23 pairs of chromosomes, how do you know when it is a male or female?
XX - if female
XY - if male
Chromosomes are identified by?
size, location of centromere, banding patterns
based on centromere location, each chromosome is classified as?
metacentric - middle
submetacentric - off center
acrocentric - near one end
telocentric - at the end
because the centromere is not exactly in the center of a chromosme, each chromosome has a short arm and long arm. short arm is designated with letter ___? and long arm designated with letter __?
short - P
Long - Q
Meiosis follows ___, and includes?
follows interphase
interphase includes cell growth, DNA duplication, chromosomes replicated, becoming double stranded.
Meiosis occurs only in the?
gonads (ovaries, testes)
produce gametes (sex cells: eggs and sperm)
Meiosis known as?
reduction division, and includes 2 separate divisions.
In meiosis, one diploid cells usually divides into ?
4 haploid cells (eggs OR sperm)
each cell is genetically different from each other and from the original cell.
Diploid dominant species
Animals are diploid
Haploid gametes are a specialized type of cell
Haploid-dominant species
many fungi and some protists, also mulicellular organisms.
Haploid cells unite to form diploid zygote, then proceeds immediately through meiosis to make 4 haploid spores.
Plants and some algae have life cycles that are intermediate b/w the extreme cases of diploid or haploid dominance such species exhibit?
alternation of generations
diploid multicellular organism known as___, haploid multicellular organism known as___?
Homologous chromosomes?
control identical traits
are the same size and shape
make up a "pair" of chromosomes
zygote receives 1 homologue from each parent
process of meiosis?
interphase - homolgous pair of chromosomes in diploid parent cell replicated into 2 sister chromatids.
meiosis 1 - 2 homologus chromosome separate
meiosis 2 - sister chromatids separate into 4 single chromatids.
in meiois we start with how many chromsomes?
4 , then homologous chromsomes pair up, crossing over occurs when pieces are exchanged b/w homolgous chromosomes.
describe the steps of prophase 1 in meiosis ?
1) homologous chromosomes condense
2) Synaptonemal complex forming
3) bivalents form
4) crossing over occurs
5) chiasma becomes visible as chromosomes arms separate during late prophase.
Why is crossing over important?
it ensures genetic variation
each sperm cell is gentically unique
each egg cell is genetically unique
in metaphase 1
pairs of homologous chromosomes line up, it is a double line.
describe the result of independent assortment?
positioning of chromosomes in metaphase 1 determines which chromosomes will be packaged together in the haploid daughter cells.
How many chromosomes in each cell after meiosis 1?
2 double stranded chromosomes in each cell
How many chromosmes in each cell after meiosis 2?
2 single -stranded chromosomes.
How many cells do we end with after meiosis 2?
4 cells
Human egg formation?
known as oogenesis
one egg and 2 polar bodies from the end of meiosis.
segment missing, deletion
section occurs 2 or more times in a row
change in direction along a single chromosome
one segment becomes attached to another chromosome. simple or reciprocal.
Explain euploid, polypoid?
euploid - normal chromosome number like diploid 2n organism, 2 sets is normal
polyploid - 3 or more sets of chromosomes such as triploid 3n, or tetraploid 4n.
alternation number of particular chromosome
total number not an exact multiple of a set.
normal 2 copies of a chromosome plus a 3rd, 2n + 1
2n - 1
chromosomes do not sort properly during cell division, during meiosis can produce gametes with too many or too few chromsomes.
Abnormal chromosome inheritance ?
down syndrome - individual inherits an extra autosome
the number 21 karyotype is a "3"