Component 2 - Cell division Flashcards
What are the phases during the cell cycle?
Interphase - preparation phases for mitosis
Mitosis - cell division
What are the three phases of interphase?
G1
S
G2
When does interphase occur?
Stage before mitosis
What is the G1 phase?
First growth phase: protein synthesis, cytoplasm and number of organelles increase rapidly
What is the S phase?
Dna replicates (DNA doubles)
What is the G2 phase?
Proteins necessary for cell division are synthesised
What is meant by cell division?
Process by which a cell divides into 2 genetically identical daughter cells
Why do cells need to divide?
Asexual reproduction
Living things grow by producing more cells
Repair of damaged tissue
To replace old or worn out cells, e.g. RBCs and skin cells
What is DNA’s function and where is it located?
Controls all cell activities including cell division
It is located in the nucleus
What is a chromatin?
Long and thread-like DNA in a non-dividing cell
What is a chromosome?
Doubled, coiled, short DNA in a dividing cell
What 2 parts does DNA consist of?
Chromatid and centromere
How does chromatin change into chromosomes?
Duplicates itself
Coils up into chromosomes
Describe the structure of a chromosome and what happens to the structure when it undergoes cell division?
2 identical “sister” chromatids attached at an area in the middle called a centromere
When cells divide “sister” chromatids separate and 1 goes to each new cell
Each chromatid is an exact copy of the other due to semi conservative theory of replication
What is significant about interphase?
The cell spend most of its life cycle in interphase
What is mitosis?
Division of the nucleus into 2 nuclei, each with the same number of chromosomes
Where does mitosis occur?
In all the somatic cells
Why does mitosis occur in terms of chromosomes?
So each new daughter cell has nucleus with a complete set of chromosomes
What are the 4 phases of nuclear division, directed by the cell’s DNA?
Prophase
Metaphase (middle)
Anaphase (apart)
Telophase (two)
What occurs during prophase?
Chromosomes coil up/condense (shorten and thicken)
Nuclear envelope disappears
Nucleolus disappears
The centrioles move to opposite sides of the nucleus
Spindle fibres form
What does prophase look like under a microscope?
What occurs during metaphase?
The chromosomes arrange themselves on the equator of the spindle
The centrioles are attached to the centromeres
What does metaphase look like under a microscope?
What occurs during anaphase?
The centromere divides in two
The attached centrioles contract and pull chromatids to opposite poles of the cell, centromere first
Chromatids now called daughter chromosomes
What does anaphase look like under a microscope?
What occurs during telophase?
The daughter chromosomes reach the poles and uncoil and lengthen
Nuclear envelope and nucleolus re-form
2 new nuclei are formed
Spindle fibres disintegrate
What does telophase look like under a microscope?
What is cytokinesis?
The division of the rest of the cell (cytoplasm and organelles) after the nucleus divides
How is cytokinesis different in animal and plant cells?
In animal cells the cytoplasm pinches in whereas in plant cells a cell plate forms
What happens after mitosis and cytokinesis?
The cell returns to interphase to continue to grow and perform regular cell activities
What is cancer?
Uncontrolled cell division , i.e. uncontrolled mitosis
How is a tumour formed?
Cancerous cells divide repeatedly
What is a tumour?
An irregular mass of cells
What does cancerous cells do to the cells/organs of a human?
Prevent them from functioning
What is asexual reproduction and what living organisms does it take place in?
Results in complete offspring that are identical to the parent
This takes place in yeast and bacteria, certain flowering plants
What is the meaning of the term homologous pair of chromosomes?
Consists of one chromosomes from the mother and one from the father
Each one pair contains the same genes as the other, but may have a different allele
Comparison of mitosis and meiosis
In mitosis one division resulting in two daughter cells whereas in meiosis two division resulting in four daughter cells
In mitosis number of chromosomes is unchanged whereas in meiosis number of chromosomes is halved
In mitosis daughter cells are genetically identical wheres in meiosis they are genetically different
In mitosis homologous chromosomes are not associated in pairs whereas in meiosis they pair up
In mitosis crossing over does not occur whereas in meiosis crossing over occurs and chiasmata forms
In mitosis there is no variation between individuals wheres in meiosis there is variation
What is meant by a diploid?
A cell containing homologous chromosomes (2n)
What is meant by a haploid?
A cell containing only one of each chromosome (n)
What is a somatic cell?
A cell which contains a diploid number of chromosomes
What is a gamete and how are they produced?
A gamete is a haploid sex cell and are produced through meiosis
When does meiosis occur?
During sexual reproduction; 1 diploid cell divides to produce 4 haploid cell (gametes)
What are the two stages of cell division in meiosis?
Meiosis I and II
How is variation achieved in meiosis?
Crossing over
Random assortment
Production of haploid gametes for random fertilisation
What happens during prophase I?
Chromatin condenses, coils and thickens to become visible
Chromosomes are now visible as two chromatids
Centrioles move to opposite poles of the cell
SYNAPSIS: Each homologous pair of chromosomes come together to form a bivalent
What occurs during late prophase I and what does it look like?
Crossing over takes place between the non-sister chromatids in the bivalent
Each chromatid may break and reconnect to another chromatid
The point of crossing over is called a chiasma (chiasmata)
This process results in the recombination of maternal and paternal genetic information
What occurs during metaphase I and what does it look like?
Spindle fibres attach to the centromere and move the whole chromosome to the equator of the cell
The bivalents arrange themselves at the equator of the spindle
Homologous chromosomes arrange themselves randomly at the equator of the cell (random assortment) leading to genetic variation
What happens during anaphase I and what does it look like?
The spindle fibres attached to the centromere of each homologous chromosome shorten to pull them to opposite poles of the cell
Whole chromosomes are pulled (still made of two chromatids)
What occurs during telophase I and what does it look like? (Give full detail)
Two new nuclear envelopes reform (animals)
Each nucleus now contains half the number of original chromosomes
The chromosomes are genetically different from those in the original cell
The organelles. cytoplasm and membrane become evenly distributed in two new cells: cytokinesis
What happens during prophase II?
Chromatin condenses and chromosomes become visible
Centrioles replicate
A new spindle forms at right angles to the first
Nuclear envelope and nucleolus disappear
What occurs during metaphase II?
The spindle fibres align the chromosomes randomly on the equator of the spindle
Each chromosome is made up of a pair of chromatids
This phase again introduces genetic variation due to random assortment of chromatids at equator
What occurs during anaphase II?
The centrioles contract and the centromeres divide
Chromatids are pulled to opposite poles of the cell by the attached spindle fibres
As soon as they are separated they are called chromosomes
What occurs during telophase II?
Chromosomes uncoil: each new chromosome may be genetically different from the original one
Nuclear envelope and nucleolus reappear
Cytokinesis begins
Four haploid cells are produced
