5.1 The Mitotic Cell Cycle Flashcards
Genome
the complete set of genes or genetic material (haploid set) present in a cell or organism.
Chromatin
Combination of DNA and histone proteins that makes up eukaryotic chromosomes (loosely coiled form of chromosomes)
Chromatid
Two threadlike strands into which a chromosome divides longitudinally during cell division - each contains one molecule double helix of DNA
Centromere
Narrow region where two chromatids are joined together
Heterochromatin
Eukaryotic chromatin remains highly compacted (easier to separate) & generally not transcribed - genes mostly inactive
Euchromatin
Less condensed form of eukaryotic chromatin available for transcription
Chromosome
A molecule of DNA, associated with histones (protein) carrying genetic information in the form of genes. The DNA is tightly coiled around the histones, so that the long DNA molecule packs into a very small space
Telomere
Regions of non-coding DNA at end of chromosomes which prevents loss of DNA
Diploid nucleus
Contains 2 sets of chromosomes; 1 set = 23 chromosomes (2n = 46)
Autosomes
All chromosomes except sex chromosomes
Haploid nucleus
Contains 1 set of chromosomes (n = 23)
Interphase
Phase of the cell cycle in which a typical cell spends most of its life in this phase - cell copies its DNA in preparation for mitosis
Interphase stages
- G1: cell makes RNA, enzymes, proteins for growth and at end of G1 the cell becomes committed to dividing or not dividing
- S: DNA replication - each chromosome replicates to have two identical chromatids
- G2: cell continues to grow and new DNA checked for any errors repaired before proceeding to mitosis
Mitosis (M Phase)
Nuclear division in which two cells are genetically identical with diploid nucleus
Importance of mitosis
- Asexual reproduction
- Cell replacement
- Repairment of damaged tissues
- Cell growth
Early prophase
1) Centrioles replicate just before prophase
2) Chromosomes start to appear as the chromatin condenses and coils up, becoming shorter
3) Intact nuclear envelope
Late prophase
1) Chromosomes are seen to consist of two identical chromatids; each chromatid contains one DNA molecule
2) Centrioles move to opposite ends of nucleus where they form poles of the spindle
3) Nuclear envelope disappears (it breaks up into small vesicles which are not visible with light microscope)
4) Nucleolus disappears (forms part of several chromosomes)
Metaphase
1) Nuclear envelope disappears
2) Each centriole reaches a pole
3) Spindle (microtubules) is completely formed by centrioles
4) Chromosomes continue to condense
5) Spindle fibres attach to the cetromeres of the chromosomes
6) Spindle fibres pull on the centromeres, arranging them at the equator
Anaphase
1) Links between sister chromatids break
2) The centromeres of sister chromatids move apart, pulled by the spindle fibres to the poles of the cell
Telophase
1) Sister chromatids (now separate chromosomes) reach opposite poles
2) The chromosomes decondense
3) Nuclear envelope begin to form around the chromosomes at each pole
4) The spindle disappears
Cytokenesis
The cell divides into 2 cells, either by the infolding of the cell surface membrane in animal cells, or by the formation of a new cell wall and cell surface membrane in plants
Mitosis Stages
1) Interphase
2) Early Prophase
3) Late Prophase
4) Metaphase
5) Anaphase
6) Telophase
7) Cytokenesis
Significance of Telomeres
1) Rich in base guanine G
2) Proposed that shortening of telomere is somehow connected to ageing process
3) Prevents loss of genes
4) Allows continual cell replication
Stem Cells
cells can divide an unlimited number of times - each new cell has a potential to remain a stem cell or to differentiate into a specialised cell
