Chapter 2.2 Cell division ✓ Flashcards
Define cytokinesis
The division of the cytoplasm immediately after mitosis, meiosis 1 and meiosis 2 to create two separate daughter cells
What does the process of mitosis and meiosis allow?
The processes mitosis and meiosis allow for the replication and transfer of genetic material to the next generation
Define the cell cycle
An ordered sequence of events in the life of a cell from when it was formed from a parent cell until it own division
Describe what happens in interphase
The cell grows (G1 phase) and DNA replicates (S phase) to prepare for cell division (G2 phase).
Define centrosomes
An organelle from which spindle fibres arise.
What cells in the body do not divide?
Specialised cells such as nerve cells
Explain why the terms ‘parent’ cell and ‘daughter’ cells are used?
To differentiate between the original cell and the newly created cell.
Parent cell refers to the original cell whereas the daughter cell refers to the newly formed cell
What are the four phases ,in order, of mitosis?
-Prophase
-Metaphase
-Anaphase
-Telophase
What is produced in result of mitosis?
Two identical daughter cells
What occurs in prophase in mitosis?
-Chromatin threads condense to form chromosomes
-Chromosomes consist of two sister chromatids held together by a centromere
-The nuclear membrane disintegrate and the nucleolus disappears.
-Spindle fibres begin to form and have finished forming at the end of prophase
-The spindle fibres attach to each chromosome
-The two centromeres move towards the opposite poles of the cell.
What occurs in metaphase in mitosis?
-Chromosomes move to the centre of the cell and line up along the equator.
-The centromeres of the chromosomes are aligned on the equator.
-The centrioles are located at opposite poles of the cell.
What occurs in anaphase in mitosis?
-Spindle fibres shorten and pull on the centromeres causing the sister chromatids to separate
-The spindle fibre pull the sister chromatids to opposite poles of the cell
-The centromere is the first part of each chromosome to be pulled towards the poles.
-At the end of anaphase, each pole has a complete identical set of maternal and paternal chromosomes
-The sister chromatids are now referred to as chromosomes.
What occurs in telophase in mitosis?
-Chromosomes decondense to form chromatin
-Two new nuclear membranes form, one for each new daughter cell
-Nucleoli reappear and the spindle fibres disappear
-The cell elongates and a cleavage furrow forms to become ready for cytokinesis.
What happens during cytokinesis in plant cells?
-The cytoplasm of a plant cells divides with the formation of a structure called a cell plate
-Cellulose is deposited on to the cell plate, forming a wall that divides the parent cell into two daughter cells, each one with a cell membrane
What happens during cytokinesis in animal cells?
-Animal cells do not contain a cell wall so in cytokinesis it does not require the formation of a cell plate.
-The cytoplasm divides by a process known as cleavage. The cell membrane around the middle of the cell draws together to form a cleavage furrow.
-This cleavage furrow continues to develop until the cell membrane eventually meets at a point, and then the cell is then cleaved or split resulting in two new daughter cells
Define binary fission
The process of asexual reproduction whereby a prokaryotic cell divides into two identical daughter cells
Is the mutation rate higher in eukaryotic cells or prokaryotic cells and why?
Prokaryotic cells because binary fission occurs relatively fast compared to other cell division process so it is more susceptible to mutation which therefore has a higher mutation rate
What processes does binary fission include?
-DNA replication
-Chromosome segregation
-Cytokinesis
What is the process of binary fission?
1) Prior to binary fission, the single chromosome is tightly coiled
2) The genetic material in the chromosome and any plasmids replicates and separates
3) The original and replicate chromosomes attach to the cell membrane and are pulled to separate poles as the cell elongates
4) The new cell wall starts to grow. As this process commences. a cleavage furrow develops in the cell membrane
5) The new cell wall fully develops
6) The two cells separate (cytokinesis), forming two identical daughter cells. The chromosomes become tightly coiled again
Why is variation higher in prokaryotic cells than eukaryotic cells?
-Rapid reproduction (binary fission): More replication cycles = more mutations
-HGT introduces new genes quickly, unlike eukaryotic reproduction
-No meiosis: Variation relies on mutation and gene transfer, which happens frequently.
-Result: Faster evolution and adaptation e.g. antibiotic resistance
What causes variation in prokaryotes?
-Mutations: Occurs frequently due to rapid replication and lack of proofreading mechanisms
-Horizontal Gene transfer (HGT)
-Transformation: Uptake of free DNA from the environment
-Transduction: DNA transfer via bacteriophages (viruses)
-Conjugation: Direct transfer of plasmid DNA between cells
Define bivalent
A structure (visible in a cell during prophase 1 of meiosis) made up of two homologous chromosomes joined together (or in short a pair of homologous chromosomes)
Define synapsis
The pairing of homologous chromosomes during prophase 1 of meiosis.
Define crossing over
The exchange of genetic material between maternal and paternal homologous chromosomes (of non-sister chromatids) that occurs during prophase 1
