Mitosis Flashcards
define what the cell cycle is
a regulated sequence of events that occurs between one cell division to the next
list the three phases of the cell cycle
interphase
nuclear division (mitosis)
cell division (cytokinesis)
interphase itself has three phases
what are they?
G1 phase
S phase
G2 phase
G1 phase (2)
growth
- cells make the RNA, enzymes and other proteins required for growth
- a signal is received telling the cell to divide again
S phase (3)
synthesis
- DNA replicates semi-conservatively
- each chromosome now consists of two identical sister chromatids
- relatively short
G2 phase (3)
growth
- cell continues to grow in preparation for mitosis
- centrioles form microtubules, also known as spindle fibres
- the new DNA that has been synthesised is checked and any errors are usually repaired
nuclear division or mitosis also has its own 4 distinct stages
what are they?
- prophase
- metaphase
- anaphase
- telophase
what occurs in prophase (5)
- chromosomes condense and are now visible
- chromosomes consist of two identical “sister chromatids” ; they are joined by centromeres
- two centrioles move towards opposite poles of the cell
- spindle fibres begin to emerge from the centrioles
- the nuclear envelope breaks down into small vesicles
metaphase (2)
- chromosomes line up at the equator of the cell
- chromosomes attach to the spindle fibres by their centromeres
anaphase (3)
- spindle fibres shorten and centromeres split
- this pulls the sister chromatids to opposite poles of the cell
- they are now in more of a prominent ‘V shape’
telophase (3)
- chromosomes arrive at opposite poles and begin to uncoil
- spindle fibres break down
- nuclear envelopes begin to form around each set of chromosomes
the last stage of the cell cycle is cytokinesis
what happens during this stage? (2)
- the cytoplasm divides, forming two genetically identical cells
- a cleavage furrow forms (in animal cells) ; separates the daughter cells
how is the mitotic index calculated?
number of cells that have visible chromosomes divided by the total number of cells
how does cancer come about?
due to uncontrolled cell division/uncontrolled mitosis
define a tumour
an abnormal mass of cells
how does the mutation of a cell occur?
a change in the base sequence of a gene is known as a mutation
in which gene does the mutation have to happen for it to cause cancer?
the gene that controls cell division
what is the name for a mutated gene that causes cancer?
an oncogene
why is it that not all mutations lead to cancer? (3)
- mutations are common events
- most either result in early cell death or the cell being destroyed by the body’s immune system
- these events usually have no harmful effect on the body
what is the name for an agent that may cause cancer?
a carcinogen
how exactly can carcinogens possibly lead to cancer?
by increasing the rate of mutations
“almost half the people with cancer possess a mutated ______ gene”
p53
name the two types of current cancer treatments and describe what they do
methotrexate
inhibits the synthesis of DNA nucleotides in cells
vincristine and taxol
prevent the formation of the mitotic spindle
define binary fission
the process of cell division in prokaryotic cells
how is binary fission different to mitosis? (2)
- there is no nuclear envelope to break down and there are no spindle fibres present
- much simpler because prokaryotic cells do not possess a nucleus, chromosomes etc.
describe the process of binary fission (4)
- the single strand of DNA undergoes DNA replication
- any plasmids present undergo DNA replication
- the parent cell divides into two cells, with the cytoplasm roughly halved between the two daughter cells
- the daughter cells each contain a single copy of the circular DNA molecule and a variable number of plasmids
