Cell and Nuclear Division Flashcards
(25 cards)
How are new cells generated in living organisms?
Cell division.
Parent cell/mother cell divides to produce two daughter cells.
Three stages: DNA replication, Nuclear Division and Cytokinesis
What is cytokinesis?
Splitting of cytoplasm in parent cell between daughter cells, following the division of the nucleus
What is equal cytokinesis
Cytokinesis that produces two identical daughter cells, each receiving:
-Full copy of parent cell’s DNA
-Some of the essential organelles
- At least one mitochondrian (chloroplast in plants)
What is unequal cytokinesis?
Cytokinesis in which the cytoplasm is divided unequally -> New cell evolves as an outgrowth
E.g. oogenesis and budding
What is the difference between nuclear division during mitosis and meiosis?
Mitosis:
- Single nuclear division.
- Produces two genetically identical daughter cells
- Same number of chromosomes as the parent cell
- E.g cell proliferation
Meiosis:
- Two nuclear divisions
- Produces four genetically distinct daughter cells.
- Half the number of chromosomes as the
parent cell.
- E.g sex cells
Why does DNA replication take place before mitosis?
A complete copy of the cell’s DNA needs to be made.
Describe how chromosomes are condensed
DNA is wrapped around histone proteins, becoming chromatin.
It is coiled and then supercoiled, the coils stacking on top of each other to form a compact pair of chromatids.
How do chromosomes move?
Microtubuli from the centrosome attach to the kinetochore protein at the centromere of the chromosome
Motor proteins coordinate movement -> walk on the overlapping microtubules
What are the phases of mitosis?
Prophase, metaphase, anaphase, telophase
What occurs during prophase?
Chromatin fibres become more tightly coiled => chromosomes
Nuclear membrane breaks down
Paired centrosomes move to opposite poles of the cell and produce microtubule spindle fibres.
What occurs during metaphase?
Chromosomes line up along the centre of the cell
Kinetochores attach to the centromere.
What occurs during anaphase?
The sister chromatids seperate.
Chromosomes are pulled by spindle fibres to opposite poles of the cell
What occurs during telophase
Chromosomes arrive at the poles.
New nuclear membranes reform around each set of chromosomes
Chromosomes decondense into chromatin.
Microtubule spindle fibres dissolve.
What do the phrases ‘diploid’ and ‘haploid’ mean?
Diploid: cell has two sets of chromosomes
Haploid: cell has a single set of chromosomes
What does meiosis result in?
Four haploid nuclei from one diploid nucleus
Outline the first four steps of meiosis
Prophase I:
- The homologous chromosomes associate with each other to form bivalents.
- Crossing over between non-sister chromatids -> recombinants formed
Metaphase I:
- The homologous pairs line up at the equator.
- Random orientation occurs.
- The nuclear membrane disintergrates
Anaphase I:
- Homologous pairs are seperated and pulled to opposite poles.
- Redution division
Telophase I:
- Nuclei are haploid.
- Cytoplasm begins to divide. New nuclear membranes.
- Chromosomes decondense
Outline the last 4 steps of meiosis
Prophase II:
- Meiotic spindle fibres are produced
Metaphase II:
- Pairs of sister chromatids line up at the equator.
- Spindle fibres form, attach to centromeres
Anaphase II:
- Spindle fibres contract => centromeres are split
- Sister chromatids seperated.
- Chromosomes are pulled to opposite poles.
Telophase II:
- Four new haploid membranes are formed.
- Nuclear membranes reform.
- Chromosomes decondense. Cytokinesis begin
How does meiosis create genetic variation?
Random orientation of bivalents during metaphase I
Crossing over during prophase I
Why does cells proliferate? Give an example of cell proliferation
Growth, cell replacement, tissue repair.
Skin must continue to divide by mitosis to replace dead cells to heal a wound
What are the phases of the cell cycle
Interphase (including G1, S and G2), mitosis, cytokinesis
What occurs during interphase?
Cell growth, this is a metabolically active period.
G1: cell grows, intake of nutrients, proteins are formed
S: DNA is synthesised
G2: number of mitochondria and chloroplasts increase
What are cyclins?
Regulatory proteins that work with CDKs to control the cell cycle.
What is the function of cyclins?
When binded to CDKs they act as enzymes and cause the cell to go from one phase to the next.
A specific level of cyclins is required to pass each checkpoint in the cycle.
The number of cyclins increase and decrease during the cell cycle
What are the consequences of mutations in genes that control the cell cycle
Mutations in proto-oncogenes convert them to oncogenes which actively promote cell proliferation
Mutations in tumoursuppressor genes, result in uncontrolled cell division
