The Cell cycle & Cell division Flashcards
What are chromosomes made of? Describe their structure
DNA and a protein called histone
- the DNA molecule is a double helix, running the length of the chromosomes, with sections along its length called genes
When do chromosomes become visible?
- when chromatin condense prior to cell division, aftear each DNA molecule has replicated and made an exact copy of itself
What are sister chromatids?
Two copies of a chromosome
Chromatids are joined at a specialised region, what is this region called?
The cenromere
Different species have different numbers of chromosomes, normal human body cells have how many chromosomes?
46
23 pairs
Define haploid
what is the symbol?
The number of chromosomes in 1 complete set
The simple is ‘n’
Define homologous pairs?
Many organisms receive one complete set of chromosomes (which are identical in size and shape) from each parent and so chromosomes occur in matching pairs (they carry genes for the same characteristics)
define diploid what is the symbol
define triploid what is the symbol
Having 2 compete sets of chromosomes~ 2n
Having 3 complete sets of chromosomes~ 3n
Define ploidy level
Organisms with more than two sets of chromosomes are described as what?
The number of complete sets of of chromosomes in an organism
Polyploid
Why do we have two copies of every gene?
The chromosome sets from the two parents carry genes for the same characteristics so we have two copies of every gene
- They may be however be different versions of the same gene (alleles)
What is the regular patterns of evens that the cell undergoes called?
The cell cycle
Define mitosis?
A type of cell division in which the two daughter cells have the same number chromosomes and are genetically identical to each other and the parent cell
state and explain the 3 main stages in interphase
Interphase is the longest part of the cell cycle with much metabolic activity
- G1: the cell grows and its organelles replicate
- S: The DNA replicates (its quantity doubles)
- G2: proteins such as histones and enzymes are synthesised requring energy from ATP
Describe some of the events that occur in Prophase of Mitosis
Prophase is the longest of the 4 stages of mitosis, whe one of the following changes happen:
- The chromosomes condense. They coil, getting shorter and thicker and become visible as long thin threads. They become distinguishable as a pair of chromatids
- Centrioles are present in animal cells; the pairs separate and move to opposite poles of the cell, organising a partner as they move
Describe some of the events that occur in Metaphase of Mitosis
- At Metaphase, chromosomes attach to the spindle fibres and align on the equator
- If the cell is viewed from the pole then they appear spread out
- If the cell is viewed from the side, the chromosomes appear in a line
Describe some of the events that occur in Anaphase of Mitosis
- Anaphase is a very rapid stage
- The centromere separates and the spindle fibres shorten (contract)
- pulling the now separated chromatids to the poles, centromere first
Describe some of the events that occur in Telophase of Mitosis
This is the final stage of mitosis. Chromatids have reached the poles of the cell and are referred to as chromosomes again
- Chromosomes uncoil and lengthen
- The spindle fibres break down
- The nuclear envelope reforms
- The nucleolus reappears
What happens during cytokinesis of Mitosis?
The division of the nucleus by Mitosis is followed by cytokinesis, the division of the cytoplasm to make two cells
- In animal cells, cytokinesis occurs by constriction of the parent cell around the equator (from the outside inwards)
- In plant cells, droplets of cell wall material, a cell plate, forms across the equator of the parent cell from the centre outwards and they extend an join to form a new cell wall
the differences between Mitosis in animal cells and plant cells
~SHAPE:
Animal cells- cell becomes rounded before mitosis
Plant cells-No shape change
~CENTRIOLES:
Animal cells- present Plant cells- absent
~CYTOKINESIS:
Animal cells-Cleavage furrow develops from the outside inwards
Plant cells- cell plate develops from centre outwards
~SPINDLE:
Animal cells- degenerate at telophase
Plant cells- remains throughout new cell wall formation
~OCCURRENCE:
animal cells- in epithelia, bone marrow etc
Plant cells- in meristems
The significance of mitosis: chromosomes number
- Mitosis produces two cells that have the same number of chromosomes as the parent and as each other
- Each chromosome in the daughter cells is an exact replica of those in the parental cells
- So mitosis produces cells that are genetically identical to the parent, giving genetic stability
The significance of mitosis: Growth, repair & replacement
By producing new cells, an organism increases its cell number and can grow , repair tissues and replace dead cells
- In mammals some tissue are constantly worn away e.g skin so identical cells are able to replace them
The significance of mitosis: Asexual reproduction
- Asexual reproduction produces offspring that are genetically identical to the parent
- It takes place in unicellular organisms
- It takes place in some flowering plants
- There is no genetic variation
What could happen if genes that control the cell cycle are damaged?
Cells may fail to divide or may divide too frequently or at the wrong time
What can radiation do to DNA?
Mutate DNA