Cell Cycle Flashcards
What is a cell cycle ?
Sequence of events that leads to the reproduction of the cell
What occurs in the cell cycle before a new division ? (4)
- Chromosome replication and segregation
- Cell growth - expansion of volume, usually coordinated with cell division
- Separation of organelles is mostly random except for the centrosome / spindle body which is duplicated and migrates to opposite cell poles
- Gap phases occur which are important regulatory phases and provide time for cellular growth
What triggers chromosomes to replicate when newly divided cell is growing ?
- Mass increases, DNA stays the same – DNA/mass ratio is decreasing
- Triggering of chromosome replication
– DNA duplication increases DNA/mass ratio and cell must double in size before it can divide.
What does antiparallel mean ?
Base pairs with non-covalent binding to each other e.g AT , GC
What is a replication bubble ?
Before replication an imitator protein binds to origin which then forms a replication bubble and is formed locally
What occurs during helices activity ?
DNA helicases cause DNA to untwist forming a Y shaped replication fork by breaking the hydrogen bonds between bases. This forms 2 single-stranded template strands
What is the function of SSB proteins ?
Single stranded DNA-binding proteins bind to each single-stranded DNA molecule holding them in place and stopping the 2 strands re-joining.
What is the function of topoisomerase ( DNA backbone being released ) ?
DNA topoisomerase moves ahead of the replication fork and help relieve the tension created by unwinding the DNA.
The enzyme binds to DNA and cuts the phosphate backbone of either one or both the DNA strands. This intermediate break allows the DNA to be unwound or untwisted, and then the DNA back bone is released again
What are three different enzyme activities in DNA polymerase ?
- POLYMERASE SITE - DNA synthesis on a 5’ to 3’ direction.
- EXONYCLEASE SITE( 5’ TO 3’ ) - Degrades faulty DNA including RNA primer.
- PROOFREADING SITE ( 3’ TO 5’) - Cuts out any “wrong” nucleotides which are inserted by the polymerase site.
What kind of chromosome does e.coli ?
Single circular
What is e.colis single origin of replication called ?
oriC, from which the replication forks move bidirectionally
If E.Coli was a prokaryote what would its c,d and b period be?
C Period = 40 mins, almost independent of the growth rate, corresponds to a rate of DNA synthesis of about 10*5 nucleotide pairs min-1. Once DNA replication starts, the cell must go through one complete cell cycle
D period = 20 mins ; independent of the growth rate
B Period = Dependent on external conditions.
Describe the first 3 phases of Mitosis ?
1- INTERPHASE
2- PROPHASE - Chromatin condenses to have the classical chromosome structure with 2 sister chromatids
3- METAPHASE - Chromatin align at the metaphase plate and spindle fibres attach to the chromosomes.
Describe the last 3 and end result of mitosis ?
- ANAPHASE - Sister chromatids separate and move to opposite poles
5.TELOPHASE -
- chromosomes decodense
- Reappearance of nucleolus and nuclear membrane - CYTOKINESIS -
- Divides the cytoplasm of the cell through formation of contractile ring - END RESULT -
- Two genetically identical daughter cells.
What do homologous chromosomes have in common ?
size
structure
length
position of genes
What occurs in the first and second phase of meiosis and what occurs to the starting diploid cell ?
MEIOSIS 1
Separates homologous chromosomes
MEIOSIS 2
Seperates the sister chromatids
diploid cells turn into haploid cell
What are the 5 stages of meiotic prophase ?
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
What are 3 sources of genetic variation ?
- Crossing over
- Random assortment of chromosomes ( in metaphase 1)
- Random fusion of gametes from different parents.
How does crossing over occur in the prophase 1 ?
As a consequence of recombination, all four chromatids at the end of meiosis will be genetically different. Chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent.
Note 9 differences between mitosis and meiosis ?
- Mitosis occurs in somatic or body cells and meiosis only occurs in reproductive cells
- Mitosis is Used as a mode of asexual reproduction for healing and repairing of cells, growth and development of body whereas meiosis only used for sexual reproduction
- Mitosis involves one cell division whereas meiosis involves 2 successive cell divisions
- Mitosis forms genetically identical daughter cells whereas meiosis forms genetically different daughter cells
- Mitosis forms diploid daughter cells whereas meiosis forms haploid daughter cells
- There’s 4 stages of cell division in mitosis and 8 stages of cell division in meiosis
- Prophase is shorter as no crossing over whereas prophase 1 is longer in meiosis
- There is no independent assortment at metaphase in mitosis but there is independent assortment of homologous chromosomes at metaphase 1
- Separation of sister chromatids at anaphase in mitosis whereas separation of homologous chromosomes at anaphase I and sister chromatids at anaphase 11 in meiosis
What are the 4 different periods in the cell cycle ?
- G1 - Growth
- S - DNA synthesis
- G2 - Growth and preparation for mitosis
- M - Mitosis ( cell division )
What are the 3 new stages that Howard and pelt defined in the cell cycle ?
- G1 phase
- The S period
- G2 phase
Explain what the G1 phase is ?
- This is the only period that varies in length as the cell generation time varies. It is analogous to the bacterial b period
- Cells that stop dividing due to starvation
What 3 events occurs during G1 ?
- Cell growth
- Preparation of chromosomes for replication
- Duplication of cellular components
