Cell Cycle Flashcards
What is the cell cycle overview?
Highly coordinated process that allows the cell to divide into 2 daughter cells in an orderly manner
3 roles of the cell cycle
Reproduction of the organism, growth and development, tissue repair
Somatic cells
All body cells except reproductive cells, during mitosis when cells are dividing and chromosomes are visible, somatic cells contain 46 chromosomes in 23 pairs, DIPLOID
Gametes
Reproductive cells, during phase when chromosomes are visible, gametes contain 23 chromosomes HAPLOID
What is the main purpose of mitosis and meiosis
Distribute genetic material to offspring accurately with few mistakes, genetic material in nucleus is depicted and moved towards poles of cells then plots into two daughter cells
Main series of the cell cycle
Interphase (G1, S, G2) and M-phase (mitosis and cytokinesis), non dividing/resting phase is G0
% of cell cycle stages
40% G1, 39% S, 19% G2, 2% M, G0 is variable, cell enters G1 from G0
Interphase overview
The cell continues to grow during interphase and it may last for hours to weeks depending on the cell type
G1 phase overview
First gap, the cell grows and accumulates the substrates required for DNA replications, movement of one centriole in the centrosome away from the other
S phase overview
DNA synthesis., the amount of DNA present in the cell doubles as the DNA strands are replicated, centrosome divides to give 2 daughter pairs
G2 overview
Second gap, cell continues to grow and produce the proteins and other molecules required for mitosis to occur
Checkpoints in cell cycle (overview)
The cell cycle does not proceed unchecked, various points where the cycle stops until the correct signal s present to allow it to proceed to the next part, cyclic-dependent kinases (CDKs) activate other proteins to allow the next phase to proceed
G1 checkpoint
Cell proceed to S-phase or it leaves the cycle for the G0 phase
G2 checkpoint
Controls entry into the M-have, checks to see if chromosomal DNA is damaged or poorly replicated
M-checkpoint
Presence of correct signals ta this point allows the chromatids to separate (occurs during mitosis)
Control mechanisms of cell cycle
Cyclin-dependent kinases (CDKs) and cyclins
CDK overview
Kinase enzymes that are required for the cell cycle, they DO NOT vary in concentration throughout the cycle, however, they are inactive until the bind with proteins cyclins
Cyclins overview
The concentrations of these proteins do vary throughout the cell cycle, their rate of synthesis varies as the cell cycle progresses, cyclins and CDK bind complexes that control the progression of the cell cycle
Maturation (M-phase) promoting factor (MPF)
Protein allows cell to progress past the G2 checkpoint and enter mitosis, it is formed when cyclin binds to CDK, activated MPF is a kinase and controls some of the processes associated with mitosis, including the breakdown got he nuclear membrane, ONLY a transiently active molecule, it also initiates. Sequence that leads to its separation back into a cyclin and the inactive CDK, cyclin is broken down and levels remain low until correct signal occurs to increase cyclin concentration
kinase activity during cell cycle
MPF activity increases as cyclin concentration increases (same with decreases)
Cell cycle cell componentes involved
Cytoskeleton (micro tubules for cell division and micro filaments), nucleus (contains genetic material and must be replicated faithfully to provide daughter cells with a functional genome)
Microtubules are essential for cell division
Centrosomes are the point at which microtubules are formed in some but not all cells, in animals cells they contain a pair of centrioles that may contribute to for microtubule formation
Nucleus in cell cycle, nucleolus
Ribosomes and RNA, is well developed in cells with a lot of active protein synthesis, site of synthesis of ribosomes
Nucleus in cell cycle, chromatin
Consist of DNA, his tones, other associated proteins, histones are4 structural proteins closely associated with DNA, man regulatory proteins have functions in controlling gene expression
Packaging of DNA non-dividing
in non-diving, DNA not organized into easily visible structure, chromosomes not present DNA found in chromatic, DNA and histones and other protones are found in nucleus of non-dividing cell throughout the cell
Packaging of DNA dividing
Chromatin organized into readily recognizable structures (chromosomes), compromised of single strand of DNA, in somatic cell, two sister chromatids (identical) joined at centromere (where pulled apart), during cell division, the centromere develops a kinetochore (microtubules) attached to and pull chromosome apart
genetic material
Chromatin, chromosomes, sister chromatid
How is DNA organized within the nucleus?
Accomplished y a complex folding process that involves a close association of the DNA with a series of proteins
Packaging of DNA process
DNA couple helix wraps around histones (now nucleosomes) and wrapped tighter (30.nm fiber) then loops and scaffolds (looped domains 300nm fiber) until replicated chromosome (1,4000 nm made up 2 chromatids of 700 nm)
Centriole
Paired microtubular structures found in some centrosomes
Centromere
The waist of a chromosome, the structure where mitotic spindles attach to the kinetochores
Centrosome
Organelle where microtubules are formed in some cells
Chromatid
One of the pairs structures that constitute a chromosome after DNA replication is he S phase
Chromatin
Uncondensed DNA whic together with histone proteins is how DNA is packaged during G0 and interphase of the cell cycle
Chromosome
The condensed form of DNA seen during mitosis and meiosis, ca be single structure or consist of two sister chromatids
How many strands of DNA does each chromatic hold
1 strand per chromatids (genes are same as one of the strands is replicated from the others)
Key events that occur after the cell enters S phase
DNA is replicated, the centrosome replicates (controlled by cyclin-CDK, concentration peaks at G1 to S and is key event in directing cell towards mitosis)
How many DNA molecules through cell cycle?
1 strand n G0 and G1 before S, 2 connected exit from S, G2, M phase until cytokinesis, 2 separate strands exit from cytokinesis
G2 to M transition
2 new centrosomes separate from each other and move to opposite ends of the nuclear envelope, the orientation of the centrosomes within the cell determines the cells plane of division
When does the clel begin mitosis
From G2 phase to interphase
Mitosis phases
Prophase, prometaphase, metaphase, anaphase, Telophase
Occurs after mitosis
Cytokinesis, separation of the cytoplasm and the formation of the two daughter cells
Prophase
Chromosomes and centrosomes and microtubules involved, chromosomes become visible distinct structures (kind of elongated), chromosomes consist of two sister chromatids held by cohesins, centromere is the region where the chromatids are the closest and the site where microtubules will attach to chromatids, kinetochore distinct structure located close to the centromere and is site where microtubules attach ro chromatids, polar microtubules extend from each centrosome complex in asteroid (star) and they develop into mitotic spindles, microtubules are formed by addition of tubulin dimers to end of each microtubule, polar microtubule runs from centrosome to a point where it overlaps and interacts with microtubule form other side, mitotic spindles serves as a track along which chromosomes will move later in mitosis
Prometaphase
The chromosomes become more tightly coiled and appear shorter and fatter remain together by cohesins
Nuclear lamina disintegrates and nuclear envelope fragments to allow spindle microtubules to infiltrate nuclear negion
Some spindle microtubules associate with kinetochores (kinetochore microtubules), none attached are non-kinetochore microtubules
microtubules from one ole associate with the kinetochore of one sister chromatids of each chromosome, microtubules from other pole associate with other kinetochore of other chromatid
Singles from cell poles move chromosomes toward center of cell, the METAPHASE PLATE, chromosomes demonstrate jerky back and form motion as they are organized
Metaphase
Kinetochores on each chromosomes are attached to a kinetochores microtubule and are aligned along the metaphase plate
Nuclear membrane and laminate has completely disintegrated
Cohesins that hold chromatids together are broken down
Anaphase
Sister chromatids of each chromosome (daughter) are pulled apart
Molecular motors at kinetochore move daughter chromosomes towards the pols along kinetochore microtubules (75% of motion)
Lengthening of the non-kinetochore tubules that extend the length of the cell
10 to 60 minutes for daughter chromosomes to move to opposite poles
At end, each pole has an identical complement of genetic material
microtubules are NOT pulling the daughter chromosome
The kinetochore is breaking down microtubules, EATING it, as it goes towards pole
Telophase
Separation of the genetic material is COMPLETE
Lengthening of non-kinetochore microtubules elongates the cell further
New nuclear membranes and nucleoli begin to form around each group of daughter chromosomes
Chromosomes become less tightly coiled and the chromatin again begins to form
Cytokinesis
Mitosis is now COMPLTE
M phase includes cytokinesis, 2 complete daughter cells are formed
Involved the formation of barrier between new 2 cells
ANIMAL CELL cleavage furrow forms require actin micro filaments
PLANT CELLS formation of a cell plate and ultimately a new plant cell wall
Formation and spear it on of all the organelles required for independent existence
Diploid number
2n equals 46
Haploid number
N equals 23
Asexual reproduction
New individual that is basically genetically identical to parent, MITOSIS (bacterial reproduction, rapid reproduction of offspring), genetic variation from random mutations or environmental affects
Sexual reproductions
Two parents contribute a gamete that fuse during fertilization to produce an individual that is genetically different from either parent, meiosis, more genetic variation and less damaging than spontaneous mutations or environment factors
How much genetic material do gametes have
Half of the genetic material of either parent
Meiosis cycle overview
Diploid cells in ovary and testis, meiosis to form haploid gametes, after fertilization, diploid zygote (embryo)
Synapses
In beginning of meiosis 1, homologous chromosomes fuse together
Homologous chromosomes
Pairs of chromosomes from each set of parent
Sex chromosomes
X, y, XX female, XY male
Synaptonemal complex
Bring together the two homologous chromosomes, proteins generated that physically hold them together,
Meiosis 1
Separation of homologous chromosomes
Prophase 1
Homologous chromosomes go through synapsis, go together
Metaphase 1
Homologous chromosomes line up at center
Anaphase 1
Homologous chromosomes are pulled apart, they are separated, each pole has same genetic material
Telophase 1 and cytokinesis
Move from diploid to haploid, 2 cells with haploid number
Meiosis II
Sister chromatids separate
Prophase II
Chromosomes with two sister chromatids in new 2 cells
Metaphase II
Chromosomes line up in equator of cell
Anaphase II
Separation of two sister chromatids
Telophase II and cytokinesis
4 cells are produced, gametes, haploid number
Fertilization
From gamete to zygote, from diploid to haploid
3 sources of genetic material
- Random assortment of chromosomes at Metaphase I, independent assortment
- Crossing over in Prophase I (distribution of genetic material)
- The random nature of fertilization
Crossing over
At prophase 1 of meiosis, non-sister chromatids of homologous chromosomes can exchange genetic material, occurs at a chiasmata between two non-sister chromatids
Random fertilization
Each male or female gamete represents 1 of approximately 223 (8.4million) possible chromosome combinations, zygote (2 23 tomes 223, 70 trillion)
Cells that exert meiosis
Are somatic, become gametes by end of meiosis
