Terms in this set (95)
process by which a cell doubles its organelles and cytoplasm, replicates, and then divides in two
Cell division in unicellular vs multicellular
Uni - means of reproduction
Multi - method of growth, development, replacement of cells
Nuclear division divides the ____ while cytokinesis divides the ______
Genetic material in the nucleus, cytoplasm
Two courses of cell division
Mitosis or meiosis, each preceded by interphase
Do plants have MTOCs?
Yes, they are called centrosomes, but they aren't composed of centrioles
Do all eukaryotics have centrioles?
No, plant cells lack centrioles. Only lower plants will have basal bodies / flagella
Humans have ___ chromosomes, ____ homologous pairs, and _____ chromatids
46, 23, 92
What percent of its life does a cell normally send in interphase?
What is DNA called when it is uncoiled?
The central region that joins two identical sister chromatids
Stage in which cell is not dividing
Three parts of interphase?
Phase initates interphase and described as the active growth phase and can cary in length. The cell increases in size and synthesizes proteins and the length of G1 determines length of entire cell cycle
Period of DNA synthesis, and marks the time during which the second DNA molecule for each chromosome
Cell prepares to divide in G2 and grows and synthesizes proteins
Last phase of the cell cycle?
M phase (mitosis or meiosis), either resulting in 2 identical or 4 non-identical daughter cells
Division and distribution of the cell's DNA to its two daughter cells such that each cell receives a complete copy of the original genome and this type takes place in somatic cells
Somatic vs gametes
Non-sex cells vs sex cells
Karyokinesis (also known as ____) is followed by cytokinesis (also known as _______)
Nuclear division, cell division
Prophase in Mitosis
nucleus disassembles: nucleolus disappear, chromatin condenses into chromosomes, and nuclear envelope breaks down. Mitotic spindle is formed and microtubules (composed of tubulin) begin connecting to kinetochores. The kinetochores actively monitor spindle formation and prevent premature anaphase onset
Metaphase in Mitosis
chromosomes line up single file at center, each chromatid is complete with a centromere and a kinetochore, once separated, it is a chromosome (to keep track of total: count centromeres!). Centrosomes at opposite ends of cell. (note: once separated that's the end of metaphase, so to be precise the chromosome # doubles at anaphase). Karyotyping performed here.
Anaphase in Mitosis
microtubules shorten, each chromosome is pulled apart into two chromatids (once separated it is a chromosome; chromosome # doubles), pulls the chromosomes to opposite poles (disjunction); at the end of this phase, each pole has a complete set of chromosome, same as original cell before replication.
Telophase in Mitosis
nuclear division, nuclear envelop develops, chromosomes => chromatin, nucleoli reappear.
Cytokinesis: Actually begins during the later stages of mitosis (most sources indicate it begins towards the end of anaphase). Division of cytoplasm to form 2 cells.
Cytokinesis in Mitosis
The cytoplasm divides into two daughter cells, each with a complete nucleus and its own set of organelles
In animal cells, a cleavage furrow forms, and cell membrane indents along the equator of the cell, eventually punching through the cell and separating the two nuclei
In plant cells, cell plate forms, effectively splitting the plant cell in half and allowing the cell to divide
Cytokinesis in plant cells is called
Cell plate, what forms it? Vesicles from Golgi bodies migrate to the plane between the two newly forming nuclei and these fuse to form a cell plate, which subsequently become the plasma membranes for two new daughter cells. The cell walls develop between membranes
Cytokinesis in animal cells is called
Where is karyotyping performed?
What are some of the check points to make sure that things are going towards plan?
Near the end of G1 -> cell growth is ssessed and favorable conditions are checked. If fails, then enters the G0
End of G2 -> checks for sufficient Mitosis Promoting Factor (MPF) to proceed
M checkpoint (metaphase checkpoint) during mitosis triggers the start of G1
A nuclear membrane forms around each set of chromosomes and nucleoli reappear
Telophase - mitosis
Chromosomes line up along the equatorial plane
Metaphase - mitosis
Sister chromatids separate at the centromere and migrate to opposite poles
Anaphase - mitosis
Nucleolus disappears and MTOC start to move towards opposite sides of cell
Prophase - mitosis
homologous chromosomes pair at plate, migrate to opposite poles (no separation of sister chromatids).
nucleus disassembles: nucleolus disappears and nuclear envelop breaks down, chromatin condenses, spindle develops. MT's begin attaching to kinetochores. Crossing over means genetic recomb, NT seq. might change!
homologous chromosomes pair up. These pairs are referred to as tetrads (group of 4 chromatids) or bivalents.
region where crossing over occur of non-sister chromatids.
protein structure that temporarily forms between homologous chromosomes: gives rise to the tetrad w/ chiasmata and crossing over
5 main steps of Prophase 1?
Prophase I has 5 steps: leptotene (chromosomes start condensing) à zygotene (synapsis begins; synaptonemal complex forming) à pachytene (synapsis complete, crossing over) à diplotene (synatopnemal complex disappears, chiasma still present) à diakinesis (nuclear envelope fragments, chomosomes complete condensing, tetrads ready for metaphase
homologous pairs are spread across metaphase plate. Microtubules attached to kinectochores of one member of each homologous pair. Microtubules from other site attach to 2nd member of pair.
homologues within tetrads uncouple and pulled to opposite sides (disjunction)
nuclear membrane develops. Each pole forms a new nucleus that has half number of chromosomes (from homologous pair to each chromosome = 2 sister chromatids). Chromosomes reduction phase to haploid.
- Interphase may occur in between here, depending on the species.
chromosomes spread across metaphase plate and sister chromatids separate and migrate to opposite poles. It is similar to mitosis
nuclear envelop disappears and spindle develops etc, no chiasmata and no crossing over.
chromosomes align on plate like in mitosis but now with half number of chromosomes (no extra copy).
each chromosome is pulled into 2 separate chromatids and migrate to opposite poles of cell
nuclear envelope reappears and cytokinesis occurs => 4 haploid cells (each chromosome = 1 chromatid).
Where is the second chromatid made to make a complete set of chromosomes at the end of mitosis?
S phase of interphase
The fern life cycle where plants will undergo meiosis to make spores
Spores: haploid or diploid?
Haploid cells that divide by mitosis to become a multicellular haploid structure called the gametophyte
When the gametes fuse and produce a diploid cell that grows by mitosis
Alternation of generations
Alternation of diploid and haploid stages
· Crossing over during prophase I
· Independent assortment of homologues during metaphase I (which chromosome goes into which cell)
Random joining of gametes aka germ cells (which sperm fertilizes which egg - genetic composition of gamete affects this)
What are some functional limitations of the cell cycle, aka how do we regulate it?
Surface to volume ratio
& Genome to volume ratio
Genome to volume ratio
genome size remains constant throughout life; as cell grows, only volume increases.
G/V will be small and thus exceed the ability of its genome to produce sufficient amounts of regulator of activities. Some large cells (paramecium, human skeletal muscle) are multinucleated to deal with this.
Surface to volume ratio
volume gets much larger when cells grow (4/3 πr^3) vs. SA (4 πr^2). When S/V is large, exchange becomes much easier. When S/V is small, exchange is hard, leads to cell death or cell division to increase SA.
aka restriction point, the most important one. At the end of G1 phase, if cell is not ready to divide it may arrest here (G0 phase - nerve and muscle cells remain here, rarely divide after maturing) and never proceed or wait until it is ready.
What types of cells typically remain in the G0 phase?
Nerve and muscle cells
end of G2 phase, evaluates accuracy of DNA replication and signal whether to begin mitosis.
during metaphase, ensures microtubules are properly attached to all kinetochores. Prevents anaphase if not.
What cell specific factors influence the onset of cell division?
Checkpoints, cyclin-dependent kinases, growth factors, density-dependent inhibition, and anchorage dependence
Cyclin dependent kinases - Cdk enzyme activates proteins that regulate cell cycle by phosphorylation; Cdk's are activated by protein cyclin.
What activates CDK's?
Protein called cyclin
Density dependent inhibition
Many cells will stop dividing once the cell density reaches a certain maximum
Most cells only divide when they are attached to an external surface, such as the flat surface of a neighboring cell (or the side of a culture dish)
plasma membrane has receptors for growth factors (external molecules) that stimulate cell for division. One such growth factor is produced by damaged cells, stimulating other cells to divide. More than 50 different growth factors are known
Cells that have become cancerous and defies the factors that influence cell division
Cancer cells that inhibit mitosis do so how?
By disrupting the ability of microtubules to separate chromosomes during anaphase, stopping replication
Are sperm cells equally competitive?
No, joining of gametes is random, but some sperm cells contain genetic material that gives them a competitive advantage - so they aren't "equally" competitive
What does it mean to have 2n chromosomes?
We have two full sets of chromosomes, for example, we as humans have 2 sets of 23 chromosomes, giving us a grand total of 46
What does it mean to be diploid?
A cell that has both sets of chromosomes. Most eukaryotic cells have one set from each parent. Denoted by 2n
What does it mean to be haploid?
A cell that has only one set of chromosomes, denoted n. We would say the haploid # of chromosomes in humans is 23
What are homologues?
Pairs of the chromosomes. For example, we have 46 chromosomes, but there are actually only 23 distinct chromosomes.
Sex cells are haploid/diploid?
Haploid. The gametes will be paired with a set from another parent to produce a new diploid cell, or zygote
What is the main difference between mitosis's prophase and prophase I of meiosis?
Synapsis - where the chromosomes line up side by side with their counterparts. And during synapsis, the corresponding regions along nonsister chromatids form close associations called chiasmata and these are sites where genetic material is exchanged between nonsister homologous chromatids (crossing over)
These pairs are called tetrads / bivalents (group of 4 chromatids)
By the end of prophase, the homologous chromosomes are held together only at specialized regions called ______
Synapsis involves 2 sets of chromosomes that come together to form a ____ or _____. This consists of 4 chromatids. Synapsis is followed by ________ the exchange of segments between homologous chromosomes
Tetrad / bivalent
Main difference between anaphase I and anaphase from mitosis?
The chromosomes don't separate at the centromere, those are in fact. Rather, one pair within a tetrad separates and moves to opposite poles
After telophase I, the nucleus has diploid or haploid?
Haploid, but the chromosome is duplicated
What's most similar: meiosis I, meiosis II or mitosis?
Mitosis and meiosis II
Occurs when a set of chromosomes has an extra or missing chromosome. The chromosomes failed to separately properly during meiosis and this results in the wrong # of chromosome in a cell, results in serve genetic defect
23 pairs of chromosomes are normal in humans, but individuals have 3--instead of 2 copies of the 21st chromosome
Transposons, DNA segments that have the ability to move around the genome and sometimes when they move, they leave behind mutations and can cause mutations by inserting into a gene
4 parts of an operon
Structural genes, regulatory gene, promoter gene, and operator
Genes that code for enzymes needed in a chemical reaction and these genes will be transcribed at the same time to produce particular enzymes.
In lac operon, three enzymes (beta galactosidase, galactose permease, and thiogalactoside transacetylase involved in digesting lactose are coded for
Is the region where the RNA polymerase binds to begin transcription
Region that controls whether transcription will occur
Codes for a specific regulatory protein called the repressor and the repressor is capable of attaching to the operator and blocking transcription
If repressor binds to operator, transcription will not occur. On the other hand, if the repressor does not bind to the operator, RNA polymerase moves right along the operator and transcription occurs.
In the lac operon, the inducer, lactose, binds to the repressor, causing it to fall off the operator, and turns on transcription
A high level of tryptophan does what in terms of the further synthesis?
When tryptophan combines with the trp repressor protein, it causes the _____ to bind to the _____, which turns the operon off, thereby blocking transcription
Fusion of 2 haploid gametes
Fertilization / syngamy -> diploid zygote.
The zygote will then divide by mitosis to produce a multicellular organism
_____ in somatic cells and ____ in gametes?
What exactly are gametes?
Sperm, egg, pollen (sex cells)
Somatic cells are typically (diploid/haploid). What about gametes?