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Chapter 7: The Cell Cycle and Cell Division
Terms in this set (70)
Different Life Cycles use Different Modes of Cell production
The Life span of an organism from birth to death is intimately linked to cell reproduction. Process in which a parent cell duplicates its genetic material and then divides into similar cells. This is used in growth and repair. Additionally, it repairs and regenerates tissues.
Asexual reproduction by binary fission or mitosis results in genetic constancy
Reproduction in which the parent cells have their offspring as identical to themselves. Many multi cellular organisms can reproduce by this method like fungi and plants. (aspen trees are example.)
Genetically identical to each other and they result from asexual reproduction. If there is genetic variation it is due to mutations (alteration in the DNA.) caused by either environmental factors or errors in DNA replication.
Process which single celled prokaryotes reproduce by.
Sexual Reproduction by meiosis results in genetic diversity.
Involves the fusion of the specialized cells, gametes, can can result in the offspring have a lot of genetic diversity.
Specialized Cells used in sexual reproduction. Only contain a single set of chromosomes.
Process of cell division that results in daughter cells only having half the genetic material of the original cell. The genetic material is randomly separated and reorganized which results in the daughter cells being genetically different. This diversity leads to natural selection.
What the DNA in eukaryote cells is called. It has a double-stranded molecule of DNA and associated proteins.
The cells that are not
for reproduction. Each somatic cell contains two pairs of chromosomes. The chromosome occurs in pairs called homologous pairs.
The chromosomes that pair up are homologous pairs. One pair comes form mother, and the other from the father. Both pairs have corresponding material, but it is NOT identical.
The number of chromosomes of gamete is denoted by n and its a haploid since it only has half.
2 haploid cells that fuse to form, they do this through the process of
. It has two sets of chromosomes.
The number of chromosomes in zygote is denoted by 2n, and its a diploid as it has 2 chromosomes.
Sexual life cycles are Diverse
All life cycles involve meiosis in order to produce haploid cells. In some cases, gametes come right after meiosis and in others it occurs by mitosis by haploid cell dividing. The fusion of gametes result in a zygote.
Random Selection of half the diploid chromosomes
It makes a haploid gamete, followed by fusion of 2 haploid gametes from different parents to then produce a diploid cell.
Haplontic Life Cycle
Mature organism is haploid and zygote is only a stage in life. Found in protists and fungi (haploid is majority.)
Alteration of generations
Organism passes through haploid and then diploid stages of life which are both mulitcellular. This is found in most plants (half and half)
Diplontic Life Cycle
Organism is diploid and gametes are only haploid stage. Found in animals, brown algae. (Diploid is majority.)
Both Binary Fission and Mitosis produce genetically identical Cells
Binary Fission and Mitosis produce 2 identical cells. Prokaryotes produce by binary fission and singled celled Eukaryotas by mitosis.
Events required for an organism to divide.
1. There must be one or more
It initiates cell division and can be inside or outside the cell.
must occur so both sets of cells will have the full complement amount of genes to complete cell functions.
: Cell must distribute the replicated DNA to each cell:
: Cytoplasm must divide and each must be surrounded by a memebrane and cell wall (for plants.)
Prokaryotes divide by binary fission
Process for prokaryotes which cell division results in the reproduction of the entire prokaryote. The cells grows, replicates its DNA, and then separates the cytoplasm and DNA into new cells.
External Factors like environmental conditions and nutrient concentration are reproductive signals.
In most prokaryotes, the DNA is carried in 1 chromosome. Additionally, when chromosome ends meet, it becomes circular as they join by covalent bonds.
2 Regions of prokaryotic Chromosome that plays functional roles in cell reproduction.
: The site where the circular chromosome starts (think of ORIgin)
The site where the replication ends. (think of TERminus
It takes place is DNA is threaded by a
of proteins near the center. Begins at ori and ends at ter. When the process is complete the 2 daughter DNA molecules segregate to opposite ends, DNA replication occupies the entire time of cell divisions.
The replication begins near the center and then it goes to the ori region. DNA sequences near the ori bind proteins to the cell. Cytoskeleton forms from the segregation process.
The division of the single cell into 2 occurs right after chromosome segregation. Initally, there is pinching of the cell membrane caused by fibers. As the pinching occurs, new cell wall materials are put in, which then finally separates them.
Eukaryotic Cell divides by mitosis followed by Cytokinesis
Cell division in eukaryotes.
Although it has 4 same steps, for prokaryotes there is differentiation in those steps.
Eukaryotes do not constantly divide when the environment has good conditions like prokaryotes do. Most of the time, the signal comes from the function of the entire organism.
: Eukaryotes have more than 1 chromosome, unlike prokaryotes. It's process is like that of prokaryotes in that replication comes by threading long strands by replication complexes. It only occurs during a specific stage in the cell cycle.
: Unlike prokarytes, for eukaryotes there is a nuclear envelope and multiple chromosomes. When a cell divides, one copy of each chromosome must end up in each cell. At first, the pairs are attached to each other, then condensed and then are segregated apart when they form 2 new nuclei. (Cytoskeleton is involved in this.)
The process for plants and animals vary.
The period from one cell division to the next
Cell Cycle for Eukaryotes
: Set of processes in which the chromosomes become condensed and then segregate into new nuclei.
Cytokinesis occurs right after mitosis, and both of these are called
Occurs after M Phase, and this is when the nuclei becomes visible and typical cell functions occur (DNA Replication.) The chromatin is not yet condenses.
Sub Phases of Interphase
: It is variable and the cell may be here for a while as it carries out its function
This phase is when the DNA is replicated.
Cell prepares itself for mitosis (example is synthesis of micro tubules that will move the chromosomes to opposite ends.)
A single nucleus gives rise to 2 daughter nuclei that each contain the same number of chromosomes as parent nucleus.
Prophase sets the stage for DNA Segregation
Prophase and three structures that appear during it
The beginning of mitosis
1. Condensed Chromosomes: In S phase of interphasem the DNA is packaged tightly, but during Prophase, the chromosomes become more tightly coiled and condensed. After replication occurs, 2 DNA molecules called
occur in each chromosome. Until their separation they are at the
. Chromosomes are visible during prophase.
assemble on the ceontromere which are used for movement. The
is determined by the number and size of condensed chromosomes.
2. Reoriented Centrosomes: The oreietation of chromosomes is determined by the
which are holo tubes. S phase is when chromosome is duplicated and G2-M is when centrosomes serparate and move to opposite sides. The position of chromosome is important as if it isn't the cell wont function properly.
3. Spindle: The
forms from during prophase and prometaphase and it is created by microtubules attaching to centrosomes.
3 Types of Microtubules in spindle
overlap in the middle and keeps poles apart
interact with proteins attached to cell membrane and also keep poles apart.
They attach to kineochores on chromosomes which ensures that chromatids will move to opposite ends.
Sister chromatids after separation and this completes the cell cycle.
Differences between Chromatidds and Chromosomes
1. Chromotids share centromere
2. Chromosomes have their own centromere.
Chromosome separation and movement is highly organized
What occurs in the Phases of: prometaphase, metaphase, anaphase, and Telophase
Nuclear envelope breaks downand chromosomes attach to kinetochore microtubules
chromosomes line up at the middle of cell
: Chromatids separate and daughter chromosomes move to the poles.
Nucleaur enevlope forms around the new chromosomes, nucleoli appears, and the spindle fibers disappear.
2 Mechanisms that move chromosomes for Anaphase
1. Kinetochores have molecular proteins that use energy from ATP hydrolsis to move chromosomes along microtubules.
2. Kineotochore microtubules shorten form the poles
Cytokinesis is the division of the cytoplasm
CytoKinesis in aniimals vs plant cells
: Begins with the furrowing of cell membrane. A ring forms on the cytoplasmic surface of the cell membrane. These proteins also produce a contraction (causes the pinching) and microfilaments assmebly is controlled by calcium ions.
As spindle breaks down, vesicles come from Golgi Aparatus which go near microtubule my kinesine and fuse to make a new cell membrane. They also contribute to the cell plate (beggining of new cell wall)
What occurs to Cell after Cytokinesis
After cytokineses, each daughter cell has all components of a complete cell. Chrosomes are distributed equally but not all organelles are.
Summary of Eukaryotic Cell Cycle Events
Phase and Events
; specialized cell f functions
: DNA Replication
:Spindle synthesis begins; prepares
:Condensation of chromosomes; spindle assembly
:Nuclear envelope breaks down; chromosomes attach to spindle
: Alignlment of chromosomes at e equatorial line
: Separation of chromatids; migration to poles
:Chromosomes decondense; n u nuclear envelope-reforms
: Cell separation; cell membrane a n and or cell wall (plants) formation
Cell Reproduction is Under Precise Control
In mutlicellular organism, cell reproduction is controlled to maintain the forms and function of parts of body.
Role of enviornmental factors of reporduction
When there is good enviornmental factor, prokaryotes constantly divide, but eukaryotes do not.Specialed cells for mutlicellular organism may never divide.
Substances that stimulate cell division which mammals produce.
Eukaryotic Cekk division if regulated internally
is a key point that menas that cell will proceed with the rest of the cycle (called R, restriction point)
Events that cause cells to enter S Phase or M phase
There are substances that control these transitions like cell in S phase makes substance to start replication, also a molecular enter makes cell go to M phase.
The Cell cycle is controlled by cyclin-dependent kinases
Cyclin dependent kinases
or CDKS, catalyze phosphoraltion of target proteins that regulate the cell cylcle. They are activated by bind to protein
which changes CKD;s shape to make active site exposed. (allostrsotic regulation). The synthesis and breakdown of cyclin controls the transition of cell cycle phases. They form as a result of molecular signals (growth factors)
Cell cycle chekckpoints
CKDs function differently at each of these checkpoints. Signaling pathways regulate the process of the cell cyle.
1.. G1 Checkpoints is triggered by DNA damage
2. S checkpoint is triggered by incomplete DNA replication or damage to DNA
3. G2 Checkpoint is triggered by DNA damage
4. M checkpoint is triggered by chromosome failing to bind to spindle
Meiosis Halves the nuclear Chromosome content and generate diversity
Even though nucleus divides twice, DNA is replicated once. It has 2 nucleaur division, and each haploid cell is genetically different from each other.
Functions of Meiosis
1. Reduce the chromosome number from diploid to haploid
2. Ensure that each haploid has a complete number of chromosomes
3. Generate genetic diversity (gametes)
Meiotic Division reduces the chromosomes
Features of meiosis I
1. Homologous chromosomes come together and line up along their entire lengths
1. The homologous chromosome pairs separate, but individual chromosomes are intact.
Like mitosis, Meiosis I in preceded with interphase with S phase, when chromosome is replicated, causing 2 sister chromatids to form. At the end of meiosis I, 2 nuclei form each with 1/2 chromosomes of original. However, they ave 2 sister chromatids. In
sister chromatids are separated but DNA replication does not precede it. Products of both Meiosis results in 4 genetically unique cells. Meiosis takes a much longer time than mitosis does.
Crossing over and independent assortment and generate diversity
Diploid organism has 2 sets of chromosomes (2n) (one from each parent). Unlike mitosis which has daughter nucleus have identical set of chromosomes, meiosis has unique Chromosomes.
2 processes of meiosis that cause genetic shuffling to make unique cells.
: Meiosis I beings with Prophase I. The homologous pairs adhere to their lengths by
This lasts from Prophase I to metaphase I end. A
forms from 4 chromatids of each homolgous chromosomes. Throughout this, the chromatin coils and each pairs repel each other but they remain attached in a X point called
. Chiasma is where genetic material is exchanged thorugh
and any of the chromatins can exchange material at many points. The crossing over results in
chromatids, which increases genetic diversity.
: It occurs from the homolgous chromosomes forming with one another, and receiving from paternal and maternal. A greater amount of chromosomes make mamore genetic diversity but lowers paternal combination.
Meiotic errors lead to abnormal chromosome structures and numbers
gametes formed from meiotic errors have abnormal chromosomes and when they are in fertilization, the offspring will have consequences.
Different types of meiotic errors
A homologous chromosomes fails to separate at anaphase I or pair of chromatids fail to separate at Anaphase II. The impact of failure at Anaphase I is 2 of the 4 daughter nuclei will have memebers of homoglous pair, while other 2 wont. If it happens at anaphase II then only 2 will be affected while one have have extra chromosome and one will be missing one.
Usually a organism is haploid (1n) or diploid (2n) but when it has more, polyloidy occurs. It may happen from extra DNA replication or no spindle in meiosis II. Those with 3n cant undergo meiosis because 1/3 would lack partners. It is used in agriculture as it leads to bigger plants.
It occurs when
pairs break and rejoin. If it occurs in meiosis, it will carry this on to its offspring in fertilization.
Conditions of having abnormal amount of chromosomes and consequences.
is having abnormal amount of chromosomes. Having am extra is
and missing one is
Prengancies that have trisomy or monosomy are miscarried due to this.
Programmed Cell Death Is a Necessary Process in Living Organisms
2 Methods in which cells die
it occurs when cells are damagged in mechanical means or lack oxygen or nutrients. (leads to swelling and burting, infalmmation)
genetically programmed events that cause cell death. The events consist of cell detaching from neighbors, hyrdolizing DNA into fragments, then forms "blebs" that break into cell fragments. Surrounding cells may ingest it by phagocytosis, (lyzosomes)
2 Reasons for Aptosis in animal cells
Cell is no longer needed by the organism
(example is weblike tissue that connects fingers and hands is destroyed)
The longer cells live, the more prone they are to genetic damage that could lead to cancer
Aptosis use in Plant Cells
Use it in defense mechanism called hypersensitive response, which they under aptosis at site of disease which prevents bacteria from spreading.
Signal transduction pathways for aptosis.
Cell death is controlled by signals inside or outside. Internal signa;s can be linked to cell age or damaged DNA. External signals can be detected by receptors which activates signal transduction pathway.
Enzymes that form from both internal and external signals.
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