2.1.6 Cell division, cell diversity and cellular organisation Flashcards
what is the cell cycle
- the cell cycle is when cells divide in order to make new cells
what are parts of the cell cycle
- Interphase (G1 phase, S phase, G2 phase)
- mitosis
- cytokinesis
what occurs during G1 phase
- the cell is growing and carrying out its normal functions ( eg producing energy)
what is the main goal in G1 phase
- to increase the size of the cell and make sure it has all the resources needed for DNA replication
What does the cell check before entering S phase
- the cell checks whether the cell is large enough, has enough nutrients and is in good condition to replicate DNA
what occurs in S phase
- cell makes an exact copy of its DNA every chromosome is replicated, so the cell now has two sets of chromosomes
( one for each daughter cell)
what is the main goal of S phase
- the DNA is synthesised to ensure that when the cell divides the daughter cell will have identical genetic material
What occurs during G2 phase
- the cell continues growing and and the new DNA which was synthesised ( during s phase) is checked for any errors.
- other preparations are made for cell division such as production of tubulin protein.
what are the 4 stages of mitosis
- prophase
- metaphase
- anaphase
- telophase
what is the centromere
a region of a chromosome where the spindle fibres attach during cell division
what does each chromosome consist of
- two sister chromatids joined at the centromere
what is a chromatid
one of the two identical halves of a chromosome that have been replicated for cell division
what occurs during prophase
- chromosomes condenses (visible when stained)
- the nuclear envelope break down
- nucleolus disappears
- the centrioles go to opposite side of the cell and proteins form spindle fibres attached to the centromeres of each chromosome
- the spindle fibres move the chromosomes to the equator (center) of the cell
what occurs during metaphase
- the spindle fibre is fully formed
- the chromosomes are now lined up at the equator of the cell
what occurs during anaphase
- chromatids are pulled to opposite sides of the cell
- the centromeres divide into two and the spindle fibres shorten
- this pulls the sister chromatids towards opposite poles of the cell.
what occurs during telophase
- the chromatids( now called chromosomes) have reached the poles of the cell.
- the spindle apparatus breaks down and the nuclear membrane reforms
- the chromosomes uncoil back to a chromatid
- the nucleolus reappears in each cell.
- the nuclear membrane surrounds the chromatids to form a nucleus
what occurs during cytokinese
- the central cell membrane is pulled inwards by the cytoskeleton.
- this creates a groove which deepens.
- eventually the membranes fuse to form two independent cells
the significance of mitosis in life cycles
- important for growth
- tissue repair
- asexual reproduction in plants, animals and fungi
what is meiosis
a type of cell division to produce gametes that produce four genetically different haploid daughter cells from one parent cell.
what is the significance of meiosis in life cycles
- it produces 4 haploid gametes.
- there cells are genetical different by independent assortment and crossing over
what are the mainstages of meiosis
- interphase
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
define homologous chromosomes
two chromosomes with similar genes but different alleles, one inherited from each parent
what occurs during prophase 1
- chromatin condenses
- nuclear envelope breaks down and spindle fibres made from centrioles
- chromosomes pair in homologous pairs
- crossing over between non-sister chromatids occur where alleles are exchanges
what occurs during metaphase 1
- homologous chromosomes line at chromosomes line at equator to spindle the centromeres at the sides of the cell
- pairs are arranged randomly