Chap 7 Cell Cycle and Division Flashcards
Explain the cell cycle and the tie taken for each step.
In the cell cycle, the first growth phase (G1) includes growth and metabolic roles, and the organelles are duplicated taking about 10 hours.In the S phase (synthesis phase) DNA replication occurs and takes about 9 hours.In the second growth phase (G2) growth and preparation for mitosis occurs and takes 4 hours.The cell then undergoes mitosis or M phase and back to the G1 phase.
Explain the checkpoints on the cell cycle.
G1 checkpoint occurs in the middle of the G1 phase,it checks for if sufficient nutrients are present,if the environment is favorable/if there is a need for new cells,if the cells have sufficient growth/if the cell is a minimum size,if there is sufficient organelles,DNA not damaged and can be replicated,growth factors present.
G2 checkpoint occurs at the end of G2 and it checks if cell size and amount of nutrients (protein) is sufficient,checks if DNA has been replicated accurately and without damage.
M checkpoint occurs halfway through the mitotic phase,(metaphase) it determines if all chromosomes kinetichores are attached to the mitotic spindle,ensures alignment of all chromosomes at metaphase,allows seperation of chromosomes at anaphase.
Explain the stages of mitosis.
1.Interphase
the stage before mitosis,the “holding stage” between two successive mitotic divisions.90 % of cells time is spent here,biochemical activity is high.
2.Prophase
Chromosomes contract & become visible and each chromosome is seen to consist of two sister chromatids joined at the centromere.Centrioles move to either side of the nucleus.Assembly of spindle microtubules in cytoplasm.Nuclear envelope breaks down.
3.Metaphase
Duplicated chromosomes align themselves in the middle or equator between the poles(metaphase plate).Spindle harnesses each chromatid & pulling it in opposite directions.Chromatids begin to draw apart at the centromere region.
4.Anaphase
Sister chromatids separate at the centromeres,chromatids move towards the spindle poles close to the centrioles.This is due to the shortening spindle microtubules, which pull the chromosomes.Each chromatid now becomes a separate chromosome.
5.Telophase
Chromatids arrive at opposite poles of cell
Cell starts to constrict across the middle to prepare for cytokinesis into two daughter cells
Nuclear membrane reforms in each daughter cell
Spindle microtubules degenerate
Chromosomes return to their thread-like (chromatin) form.
6.Cytokinesis
Constriction of ring of microfilaments forms a cleavage furrow, pinching the cell apart.
Explain Meiosis 1
Meiosis 1
Cell is doubled from one to two, chromosomes reduced by half from diploid to haploid.
Prophase 1
Homologous chromosomes become paired.
Crossing over occurs between homologous chromosomes (the physical exchange between chromosome segments of non sister chromatids to increase genetic diversity)
Metaphase 1
Homologous pairs become aligned in the center of the cell.Independent assortment occurs which is a random alignment pattern.As the cell could have different alignment patterns it leads to greater genetic diversity.
Anaphase 1
Homologous chromosomes are separated to opposite poles
Telophase 1
Chromosome decondenses,nuclear envelope reforms follow by cytokinesis.
What is interkinesis?
Interkinesis is similar to interphase in mitosis except DNA synthesis does not occur.(no S phase). Centrosomes are duplicated.
Explain what causes genetic diveristy
Meiosis I: Prophase I
Synapsis (unique event in Prophase I):
Pairing of the replicated homologous chromosomes
Homologous chromosomes stick together along their lengths
Crossing over:
Two non-sister chromatids break at an identical site called a chiasma (chiasmata), and swap genetic segments at the break and may be reattached to a different homologous chromosome
Meiosis I: Metaphase I
Homologous pairs arrange themselves along the equator
Spindle microtubules harness & orientate one chromosome of each pair towards opposite poles
Random harnessing (independent assortment) of maternal and paternal chromosomes
Explain Spermatogenesis.
Spermatogonium which is a diploid undergoes mitosis to form two Primary Spermatocytes (diploid).One of the primary spermatocytes undergoes meiosis 1 and forms two secondary spermatocytes which are haploid.The two secondary spermatocytes then undergo meiosis 2 to form 4 spermatids which differentiate into sperm (haploid).
Explain Oogenesis.
Oogonium (diploid) undergoes mitosis to form two primary oocytes (diploid).The primary oocyte undergoes meiosis 1 to form a secondary oocytes (haploid) and a polar body (haploid).Both then undergo meiosis 2 where the polar body forms two haploid polar bodies and the secondary oocyte forms an ovum and a polar body (both haploid).The ovum the differentiates into a mature egg.
What are the differences between mitosis and meiosis?
Mitosis occurs in somatic cells while meiosis occurs in reproductive cells.
Mitosis gives rise to 2 daughter diploid cells, meiosis gives rise to four haploid (n) daughter cells.
In Mitosis Homologous chromosomes do not pair and chromosomes align themselves in single file along the equator during metaphase.In Meiosis Homologous chromosome pair-up during prophase 1 and align themselves as homologous pairs along the equator during metaphase 1.
In mitosis no crossing over which produces identical offspring,in meiosis crossing over produces variations in offspring.
Explain Meiotic Non Disjunction in M1 and M2 and Mitosis.
Homologous chromosomes or sister chromatids failed to separate properly during cell division
Results in daughter cells with abnormal chromosome numbers (aneuploidy)
In M1 nondisjunction causes the 2 cells to have one extra chromosome and one missing chromosomes.They then undergo M2, the cell with extra chromosome produces 2 trisomic gametes while the one missing a chromosome produces 2 monosomic gametes.
In M2 non disjunction one of the 2 cells produced after M1 will produce a trisomic and monosomic gamete while the other cell will produce normal gametes.
In mitosis, nondisjunction will form a trisomic and monosomic cell which will continue to divide to form clones of the trisomic/monosomic cell.
Explain Patau Syndrome,Down Syndrome and Edwards Syndrome.
Patau syndrome (trisomy 13) Extra chromosome 13 Disrupts normal development, causing multiple and complex organ defects
Down syndrome (trisomy 21) Extra chromosome 21 Physical growth delays, characteristic facial features and mild to moderate intellectual disability
Edwards syndrome: (trisomy 18)
Extra chromosome 18
Small babies with heart defects, small head and jaw, clenched fists with overlapping fingers, and severe intellectual disability
Explain Klinefelter and Turner Syndrome
Turner Syndrome
A female with only one X chromosome.
Developmental delays, nonverbal learning disabilities, and behavioral problems
Klinefelter Syndrome
A male with 2 X chromosome and one Y chromosome.
affect physical and intellectual development.
Boys and men withKlinefelter syndrometypically have small testes that produce a reduced amount of testosterone, leading to breast enlargement, a reduced amount of facial and body hair, altered genital development.
Why is DNA Replication considered semi conservative?
Replication is called semi-conservative, because one half of the original strand is always saved, or “conserved”
What are 4 things needed for DNA Replication and give examples.
deoxyriboNucleosideTriPhosphates (dNTP)
Building blocks for DNA (dATP, dTTP, dGTP, dCTP)
Energy source
ATP
Enzymes and Proteins
DNA polymerases, Helicase, SSBP (Single-stranded DNA binding proteins), Gyrase/Topoisomerase, Primase, Ligase.
Template DNA
Parent base sequence that specifies the complementary sequence of the new daughter DNA
Explain how DNA replication occurs.
- DNA helicase (enzyme) unwinds the DNA into single strand allowing each strand to be copied. The junction between the unwound part and the open part is called a replication fork.
- Topoisomerase/Gyrase creates nicks which help in the unwinding of double helix - DNA polymerases elongates the leading and lagging strands in the 5’ to 3’ direction. The template DNA is the original DNA strand.Primase creates an RNA primer which serves as a starting point for the DNA polymerase to synthesize the new strand of DNA.
3.For Leading Strand, the synthesis is straight forward, as the polymerase travels in the same direction as the helicase.For Lagging Strand, multiple fragments of newly-synthesized DNA will be generated - Okazaki Fragments.
Okazaki Fragments are joined together by DNA ligase.
Single-stranded DNA binding proteins: Stabilize the unwound parental DNA and make the templates available to primase and DNA polymerase. (keeps the strands seperated)
During replication, there are many points along the DNA that are synthesized at the same time (multiple replication forks)
