Cell Division Flashcards
What are the roles of mitosis?
Tissue repair/replacement, organism growth, asexual reproduction and development (of embryos)
What is mitosis?
The stage of the cell cycle where the nucleus divides
What is the cell cycle?
Strict sequence of events that takes place within a cell to make two genetically identical daughter cells
What is interphase?
One of the major phases of the cell cycle that is referred to as the ‘resting’ phase
What happens in interphase?
Three stages; G1, S and G2
What happens in the G1 stage?
Protein synthesis for organelles, cell size increases, cytoplasm increases, organelles replicate
What happens in the S stage?
DNA synthesis
What happens in the G2 stage?
Cell size continues to increase, energy stores are increased and error checking occurs for the duplicated DNA
What stage comes after interphase?
Mitotic stage (mitosis)
What are checkpoints in the cell cycle?
Control mechanisms to ensure that each stage of the cell cycle are successful
When are the checkpoints in the cell cycle?
G1 checkpoint- end of G1
G2 checkpoint- end of G2
Spindle assembly checkpoint- metaphase of mitosis
What is G0?
Resting state of the cell (does not duplicate)
What are some examples of cells that enter G0?
Specialised cells, neurons, aging cells, dormant (quiescent) cells
What are chromatids?
A single DNA molecule
What are sister chromatids?
Two identical copies of a single replicated chromosome
What are chromosomes?
A pair of two chromatids joined by a centromere
What are homologous chromosomes?
Genetically identical pair of chromosomes
What are the properties of chromatin?
Loosely packed into the nucleus, occurs in non-dividing cells, accessible for transcription
What are the properties of chromosomes?
Tightly wound and condensed, can be segregated and transported easily, only for a short time, cannot be transcribed
What are the stages of mitosis?
Prophase, metaphase, anaphase, telophase
What happens in prophase?
Chromatin condense into chromosomes, nucleolus disappears, nuclear envelope disassembles, spindle fibres begin to form and centrioles align at equator
What happens in metaphase?
Chromosomes align at equator (metaphase plate), spindle fibers attach to centromeres of chromosomes
What happens in anaphase?
Chromosomes separate into sister chromatids and are pulled to either pole of the cell, spindle fibers contract to pull chromatids, organelles also seperate
What happens in telophase?
Nuclear envelope reforms, reformed chromosomes now uncoil, nucleolus reforms, spindle fibers detach from chromosomes
What is cytokinesis?
The actual division of the cells
How is cytokinesis different for animal cells?
The plasma membrane forms a cleavage furrow via an actin ring
How is cytokinesis different for plant cells?
The rigid cell wall cannot form a cleavage furrow so instead forms a phragmoplast from vesicles from the golgi
What is meiosis?
A form of cell division that forms gametes (haploid cells)
What is the role of meiosis?
Sexual reproduction
How many chromosomes does a human cell have?
46
How many chromatids does a gamete have?
23
What is an allele?
A different variation of the same gene that code for the same characteristic, e.g. eye colour, but different colours
What are the stages of meiosis?
Meiosis I and meiosis II
What happens in meiosis I?
The reduction division where the homologous chromosomes are separated into two cells
What happens in meiosis II?
Chromatids separate similar to mitosis, four haploid daughter cells are produced
What happens in prophase I?
Same as mitosis, except homologous pairs form bivalents which causes crossing over
What are bivalents?
A pair of sister chromatids
What is crossing over?
When genes cross over between the bivalents and allows for genetic variation
What happens in metaphase I?
Same as mitosis, except independent assortment occurs for whole chromosomes aligning at equator rather than chromatids
What is independent assortment?
Chromosomes align at the equator randomly and allows for genetic variation (2^n where n = number of chromosomes)
What happens in anaphase I?
Same as mitosis, except whole chromosomes are pulled to the poles. Chiasmata ensues to form recombinant chromatids
What are recombinant chromatids?
When genes swap between chromatids
What is chiasmata?
When parts of chromatids break off and rejoin, which allows for genetic variation
What happens in telophase I?
Same as mitosis
What happens in prophase II?
Same as prophase I
What happens in metaphase II?
Same as mitosis
What happens in anaphase II?
Same as mitosis
What happens in telophase II?
Same as mitosis
How is cytokinesis different for meiosis II?
4 haploid daughter cells are formed
