Chapter 7: The Cell Cycle and Cell Division Flashcards
Cell division is the basis of _____, ______, _______ & ______ of living organisms
growth, development, tissue repair, and reproduction
How do prokaryotic cells reproduce?
binary fission
What are the two mechanisms of reproduction?
Mitosis (reproduction or growth/repair), Meiosis (specialized reproductive cells)
What is the main function of cell division?
Duplicating the chromosome(s) completely and sorting a copy to each daughter cell
How many chromosomes do prokaryotes have? How many molecules of DNA?
one chromosome, one DNA (usually circular)
Two important regions in DNA replication
ori (where replication starts), ter (where replication ends
What four events must occur for cell division?
reproductive signal, replication, segregation, cytokinesis
What are the signals that initiate prokaryotic cell division?
nutrient availability, and environmental conditions
What does reproductive signal do?
initiate cell division
What gets replicated?
DNA
What does segregation do?
Distribute the DNA into the two new cells
What is cytokinesis?
Separation of the two new cells
Do most cells of a fully developed multicellular organism divide?
Rarely, because most cells are specialized
What does mitosis do?
Coordinates nuclear division in eukaryotic cells to produce genetically identical daughter cells
Interphase
Begins after cytokinesis, ends when mitosis starts; The cell nucleus is visible and cell functions occur, including DNA replication
What are the subphases of interphase? What are they determined by?
G1, S, G2; defined by DNA replication status
M (Mitosis) Phase
Nuclear membrane usually dissolves, DNA condenses and divides, cytoplasm divides
How does DNA exist in Interphase?
long, threadlike “chromatin”
How does DNA exist in G1
each chromosome consists of one dsDNA molecule (one double helix)
How does DNA exist in S
DNA replication produces two identical dsDNA molecules (Sister chromatids) for each chromosome
How does DNA exist in G2
each chromosome consists of two associated dsDNA molecules (sister chromatids)
How does DNA exist in the M-phase
chromosomes become visible as dense, compact rods, each consisting of two chromatids held together at the centromere (up until separation)
What are the five phases of Mitosis
Prophase/Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis
Prophase/Prometaphase
compaction of replicated DNA into visible chromosomes; breakdown of nuclear envelope
Metaphase
duplicated chromosomes line up in middle of cell
Anaphase
sister chromatids separate and move to opposite sides of the cell (now are daughter chromosomes)
Telophase
decompaction and formation of a new nuclear envelope around the two separated sets of daughter chromosomes
Cytokinesis
division of the cytoplasm (forms two cells)
What do microtubules do for cell division?
They function as the spindle fibers, which orient and move chromosomes in the dividing cell
Positions of the centrosomes define ________ and ________
the poles and plane of division
Polar microtubules
form spindles; overlap in the center
Kinetochore microtubules
attach to kinetochores on the chromatids; sister chromatids attach to opposite halves of the spindle
When do microtubules form and attach to chromosomes
during prometaphase
What does MTOC stand for?
microtubule organizing center
What does MTOC do?
forms/orients the mitotic spindle that will attach to and move the duplicated chromosomes during M-phase
What is MTOC surrounded by?
a high concentration of tubulin dimers
What is a centrosome?
MTOC of animal cells
what does a centrosome consist of?
two centrioles (hollow tubes formed by microtubules) at right angles
Centrosome doubles during ___ phase. Where do they go?
S phase; each will move to opposite ends of the nuclear envelop during G2-to-M transition
What do Centrosome positions determine?
the spindle orientation and plane of cell divison
Do plants have centrosomes?
no, they have MTOCs instead
Metaphase Plate
a plane through the cell equator
Chromosome Segregation
division of nuclear content and movement to opposite cellular poles
Cytokinesis in animals cells
a contractile ring of actin and myosin microfilaments pinches in the cells membrane
Cytokinesis in plant cells
vesicles from the Golgi apparatus appear along the plane of cell division and fuse to form a new cell membrane; contents of vesicles contribute to forming the new cell wall
Eukaryotic cell cycle
interval between cell divisions, divided into interphase and mitosis/cytokinesis
What triggers the transition from one phase to another?
specific molecular signals
When are most somatic cells of a multicellular eukaryote arrested?
G1 phase
What restriction point occurs in the G1 phase?
DNA Damage; to be ready for DNA replication and division
What restriction point occurs in the S phase?
DNA Replication; check if DNA was replicated correctly
What restriction point occurs in G2 phase?
DNA Damage; check again for DNA damage
What restriction point occurs in M phase?
Spindle Attachment
What enzymes do transitions depend on?
Cdks = cyclin-dependent kinases
When is Cdk active?
when it is bound to it’s partner protein called cyclin
What does active Cdk do?
catalyzes the transfer of a phosphate from ATP to another protein; changes the shape/activity of other proteins, leading to cellular changes
T/F Cyclins are unstable
T
What two things control the progression through the cell cycle, ensuring the cell is ready to proceed past critical checkpoints?
Cyclins, Cdks
What does unphosphorylated RB protein do?
active; inhibits the cell cycle at the restriction point; cell does not enter the S phase
What does phosphorylated RB do?
inactivated; does not block the cell cycle and continues to DNA replication
What inhibits RB phosphorylation?
p16
How do cancer cells differ from ‘normal’ cells?
-not regulated by extracellular signals or internal check points
-cells migrate (metastasize) to other tissues
What regulator molecules does the cell cycle involve?
positive regulators: growth factors or their receptors (HER-2) that stimulate the cell cycles
negative regulators: p16 and RB, inhibit the cell cycle
Oncogene proteins
overactive or excessive positive regulators of cancer cells
Tumor suppressors
negative regulators in both cancer and normal cells, but in cancer cells they are inactive
Sexual reproduction in eukaryotes involves _____ and the formation of _____
meiosis
haploid gametes
Binary Fission and Mitosis
- DNA copied and a complete copy segregated to each ‘daughter cell’
- product identical to the ‘mother cell’
Meiosis
- DNA copied, followed by two rounds of division and nuclear segregation
- DNA content reduced by 1/2
- Each product is unique
Binary Fission: function in the life cycle, impact on chromosome number, genetic relationship with the parent cell
Reproduction, no change, essentially identical
Mitosis: function in the life cycle, impact on chromosome number, genetic relationship with the parent cell
reproduction, growth, repair, and more, no change, essentially identical
Meiosis: function in the life cycle, impact on chromosome number, genetic relationship with the parent cell
production of gametes, reduced by 1/2, unique subset of parents genotype
Sexual Reproduction
the systematic joining of gametes to produce a diploid phase of the life cycle, coupled with meiosis that reduces chromosome number in the haploid phase
Meiosis
a specialized cell division where a single round of DNA synthesis is followed by two stages of chromosome segregation
Diploid mother cell
pairs of chromosomes
Haploid daughter cells
each with one of each kind of chromosome
Sexual life cycles have alternation of fertilization producing a ______ phase and meiosis producing a _____ phase
diploid
haploid
Diplontic Life Cycle
- gametes are the only haploid cells in the life cycle
-life cycle dominated by the diploid (2n) phase
Haplontic Life Cycle
- Diploid zygites (2n form and undergoes meiosis to produce haploid spurs
- spurs divide by mitosis to produce the mature organism
- life cycle dominated by the haploid (n) phase
Alternation of Generations
- a multicellular haploid stage and a multicellular diploid stage
- life cycle is nearly half haploid have diploid
What is 2n?
number of chromosomes established by fertilization
What is 2n composed of?
- one member of each pair inherited from each parent
homologous chromosomes
appear the same and contain the same genes; except for sex chromosomes
homologs
a pair of chromosomes
somatic cell equation
2n = 8
gamete equation
n = 4
Meiosis transmits a ______ of each homologous pair to gametes
single member
Human Karyotype
23 pairs of homologous chromosomes (2n = 46) and a pair of sex chromosomes
Meiosis has __________ resulting in daughter cells with half the number of chromosomes as the parent cell
two consecutive nuclear divisions
Meiosis I phases
Prophrase 1, Metaphase 1, Anaphase 1, Telophase 1 & cytokinese
Prophase 1
The chromosomes condense and the nuclear envelope breaks down. Crossing-over occurs
Metaphase 1
Pairs of homologous chromosomes move to the equator of the cell.
Anaphase 1
Homologous chromosomes move to the opposite poles of the cell
Telophase 1 & cytokinesis
Chromosomes gather at the poles of the cell. The cytoplasm divides
Meiosis 2
Prophase 2, Metaphase 2, Anaphase 2, Telophase 2 & cytokinesis
Prophase 2
A new spindle forms around the chromosomes
Metaphase 2
Metaphase 2 chromosomes line up at the equator
Anaphase 2
Centromeres divide. Chromatids move to the opposite poles of the cells.
Telophase 2 & cytokinesis
A nuclear envelope forms around each set of chromosomes. The cytoplasm divides
Functions of Meiosis
Reduce chromosome number from diploid to haploid, ensures each haploid cell has a complete set of chromosomes, generates diversity in daughter cells
in Meoisis there are ___ nuclear divisions and ____ DNA replications. It begins in a ____ cell and ends with ____ products
two
one
diploid
haploid
What happens in Meiosis 1?
Homologous chromosomes pair and exchange genetic information, then segregate from each other
What happens in Meiosis 2?
Sister chromatids separate from each other
In what phase does the pairing of chromosomes occur? What is it called?
Prophase 1; synapsis
At what phase do the homologous pairs separate?
Metaphase 1
What are the functions of meiosis?
reduce chromosome number from diploid to haploid, ensure that each haploid cell has a complete set of chromosomes, generate diversity among the daughter cells
Where does meiosis start? Where does it end?
Begins in a diploid cell (meiocyte) with all chromosomes in pairs, ends with a haploid cell
What happens in Meiosis I?
homologous chromosomes pair and exchange genetic information, then segregate from each other
What happens in Meiosis 2?
Sister chromatids separate from each other
Pairing (also called _____ ) occurs during _____
synapsis
Prophase 1
Cells at end of Meiosis 1 are haploid, but each chromosome still contains ___ chromatids
2
What is crossing over? When does it occur?
exchange of genetic material occuring during Prophase 1
What are chiasmata?
sites of exchange between non-sister chromatids
what is the main difference between meiosis and mitosis?
Meiosis is similar to Mitosis except it splits chromosomes not centrimeres
What is the critical event of Meiosis 2?
separation of the sister chromatids
What is the metaphase 2 plate?
Where the chromosomes divide
Products of Telephase 2 are _____
genetically distinct
Which Meiosis is Mitosis most similar too?
Meiosis 2
In Mitosis 1, Prophase, homologs are formed by chromosomes lining up ____
horizontally
Describe Prophase 1 in human males
lasts for1 week, and 1 month for the entire meotic cycle
Describe Prophase 1 in human females
begins in utero, pauses, then resumes at puberty; each month one or a few cells that were arrested in prophase 1 resume the process and complete Meiosis 1
In males, ____ haploid cells from meiosis can become function sperm. In females ____ haploid cells from meiosis becomes functional egg nucleus
all 4
1 of 4
What happens to the 3 eggs that do not become functional?
they disintegrate
What is nondisjunction? What does it result in?
Homologous pairs fail to separate at Anaphase 1 or sister chromatids fail to separate at Anaphase 11. Either results in aneuploidy (chromosomes missing or present in excess)
What are potential causes of aneuploidy
lack of cohesins that hold homologous pairs together, failure to undergo crossingover
The frequency of nondisjunction goes ___ as a female ages. Why?
up
Eggs are set up early, and as you age you lose eggs, increasing concentration of nondisjointed
T/F it is more likely for sperm to have an extra chromosome than to be lacking any chromosomes
F; very rarely does sperm have an extra copy of chromosomes
Monosomic Zygotes
A normal egg that has been fertilized by a sperm lacking a copy of chromosome, each egg only has one chromosome
Trisomic Zygotes
A normal egg that has been fertilized by sperm with an extra copy of chromosome, each egg has one chromosome from a normal egg and two chromosomes from sperm.
Non-disjunction in meiosis 1 results in two _____ chromatids in ___ the cells
non-sister
half
Non-disjunction is meiosis 2 results in two _____ chromatids in ____ the cells. What else?
sister
half
two cells with one chromatid
What are trisomic cells? What are two conditions that result from it?
both homologs go to the same pole and that egg is fertilized; Down syndrome, Edwards syndrome
What are monosomic cells? What is a condition that results from it?
A fertilized egg does not receive a copy of a particular chromosome; usually lethal except for Turner syndrome
T/F Nondisjuction and aneuploides are very common in human zygotes
T; survival of the embryo is very uncommon, so more aneuploides result in miscarriage
