12.6 Cell Cycle & Cell Division Flashcards
what is the first stage of the cell cycle called
interphase
what 3 stages is interphase divided into
G1 phase (gap 1)
S phase (synthesis)
G2 phase (gap 2)
what happens in G1 phase
cell increases in size / volume and new biomass is made (proteins)
what happens in S phase
DNA replicates by semi-conservative DNA replication
what happens in G2 phase
cell prepares for division, synthesis and stores of ATP and new organelles synthesised
nuclear division (mitosis or meiosis) definition
period when the nucleus divides into 2 (mitosis) or 4 (meiosis)
cell division (cytokinesis) definition
division of the cytoplasm which follows nuclear division and is the process by which the cytoplasm divides to produce 2 new cells (mitosis) and 4 new cells (meiosis)
why does the mass of a cell in the cell cycle overall increase
- G1 -> cell gets bigger -> more mass
- S -> DNA replication
- Mitosis -> organelle replicate
why does the mass of DNA in the cell cycle increase and then decrease
increases in S phase -> DNA replication
decreases in mitosis -> DNA contents halves as cell divides into 2 during cytokinesis
gene definition
a section of DNA that codes for 1 specific polypeptide (protein)
the base sequence of DNA on the DNA codes for…
the sequence of amino acids in a protein
chromosome definition
an independent DNA molecule which has been supercoiled into a condensed form
unduplicated chromosome is called
chromatid
duplicated chromosome is called
identical sister chromatids
central point in chromosome is called
centromere
how are identical sister chromatids formed
DNA starts to coil around histones -> DNA supercoils and condenses -> Forms identical sister chromatids
why do complex organisms have a number of chromosomes
they have a large number / many different genes
what is a chromosome number
the number of different chromosomes possessed by an organism
the chromosome number is represented by the letter…
n
diploid (chromosome number)
2n
haploid (chromosome number)
n
draw a single unduplicated chromosome
draw a single duplicated chromosome
a single unduplicated chromosome. before or after S phase
before S phase
a single duplicated chromosome. before or after S phase
after S phase
(3 things) mitosis is used for…
- increasing cell numbers and growth of an organism
- repair of damaged tissues (not cells)
- replacement of worn out / dead cells
what happens before mitosis
semi conservative replication of DNA
does variation occur in mitosis
no
what can the 2 daughter cells be called in relation to their parent cell
genetically identical clones (same alleles of same genes in the same gene loci)
can mitosis be used for asexual reproduction
yes
when will mitosis occur in some organisms for asexual reproduction (what environment)
tends to occur in favourable, stable environments (no environmental change)
order of stages in mitosis
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
key points of prophase
- the nuclear membrane starts to break down
- the centrioles start to move to the poles of the cell and make spindle fibres
- the chromosomes supercoil and condense / shorten / thicken and become visible
- each chromosome appears as 2 identical sister chromatids joined at the centromere
prophase microscope hint
you first see the chromosomes properly / visible
key points of metaphase
- the centrioles complete the production of spindle fibres (contractile protein fibres)
- the chromosomes are attached to the spindle fibres by their centromere
- the chromosomes align down the equator of the cell
metaphase microscope hint
the chromosomes look like they line up in the middle / equator
key points of anaphase
- the spindle fibres contract / shorten
- the centromere splits
- the identical sister chromatids are pulled to opposite poles
- making a ‘V’ shape
anaphase microscope hint
chromosomes are pulled apart, they look v shaped
key points of telophase
- a nuclear membrane starts to reform around each set of chromosomes
- the chromatids / chromosomes unwind / uncoil / become longer / thinner and become invisible
telophase microscope hint
the chromosomes have split and clustered into 2 nuclei
what happens in cytokinesis
separation of the cytoplasm
allele definition
different version of the same gene
gene definition
section of DNA on a chromosome coding for 1 or more polypeptide
chromosome definition
independent DNA molecule in a condensed form which contains many genes (using histones)
sister chromatid definition
1 of the 2 strands of a replicated chromosome that are joined together by a single centromere prior to cell division
haploid definition
cell that contain only a single copy of each chromosome
diploid definition
cell in which the nucleus contains 2 sets of homologous chromosomes
somatic cell definition
a normal body cell
homologous chromosomes definition
same genes are in the same location
cancer definition
cells that undergo rapid uncontrolled mitosis
which control genes are used to switch cell division on and off
- tumour suppressor genes
- proto-onco genes
what do tumour suppressor genes code for
code for proteins that slow down the cell cycle
what do proto-onco genes do
code for proteins that speed up the cell cycle
formation of cancer
- if a mutation occurs in 1 if these control genes, then cell division continues, uncontrolled
- it’s often rapid and the cells produced are abnormal
- a tumour develops
- if these cells start to spread into the surrounding tissues / body, the tumour is regarded as a cancer
what is a tumour
a mass of abnormal cells
1 method used to treat cancer
give drugs that inhibit cell division (mitosis)
what do these drugs stop
DNA replication, spindle formation, cytokinesis
where does binary fission occur
in prokaryotic cells
what type of reproduction is binary fission
asexual reproduction
process of binary fission
- replication of the circular DNA (not associated with histones) and of plasmids
- cell elongates from the middle separating the 2 DNA molecules attached to different parts of the cell membrane
- a new murein cell wall is formed down the middle of the elongated cell which eventually meets, dividing the cell in 2
- division of the cytoplasm to produce 2 daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids
which organelles are NOT used in binary fission
no nucleus, no chromatids, no centrioles, no spindle fibres
how long does the process of binary fission take
- its very fast
- bacteria doubles every 20 mins
what is the endosymbiont theory
- mitochondria and chloroplasts can also replicate by binary fission
- gives evidence that these organelles perhaps were once prokaryotes
are viruses cellular (living) or acellular (non-living)
acellular (non-living)
where do viruses replicate
can only replicate inside host cells
process of viral replication
- attachment proteins on the virus attach to the receptors on the cell
- the virus nucleic acid enters the cells cytoplasm
- reverse transcriptase makes DNA from viral RNA
- the viruses DNA is inserted into the host cells own nuclear DNA / genome
- the viral DNA is transcribed (viral mRNA) and translated into viral proteins (capsids / enzymes / attachment proteins)
- the cell replicates the viral DNA
- the genetic material and proteins coats are assembled into virions
- eventually these virions burst out of the cell, often destroying the host cell
why is the plant sample soaked in 50C HCl (mitosis -> practical skills)
to break down the cellulose cell walls (breaks H bonds that hold microfibrils together), ensuring the stain can enter the tissue and the root tissue can be squashed into a single layer, 1 cell thick, so that light passes through the thin sample of tissues / cells
why is the plant sample soaked in ethano-orcein stain / potassium iodide (mitosis -> practical skills)
to stain the chromosomes (adds contrast) so they can be viewed under the microscope
equation of mitotic index =
(number of cells in PMAT) / (total number of visible cells)
the greater the MI value =
faster rate of cell division
dilution series equation
M1 x V1 = M2 x V2
equation for the length of time each stage of mitosis takes by using a variation of mitotic index
(total number of cells in mitosis - visible chromosomes) / (total number of visible cells) x time of 1 cell cycle (minutes)
(dilution series equation) where V1 equals…
desired volume (cm3)
(dilution series equation) where M1 equals…
desired diluted concentration (mol dm-3)
(dilution series equation) where M2 equals…
original concentration (mol dm-3)
(dilution series equation) where V2 equals…
unknown volume of stock solution (cm3)
draw and label the stages of meiosis with 2 homologous pairs of chromosomes
draw and label the stages of meiosis with 3 homologous pairs of chromosomes
stages of meiosis (P1 & M1 -> meiosis 1 -> nuclear division 1)
- chromosomes supercoil, condense (around histones) and become visible
- homologous pairs of chromosomes pair up (form a bivalent) and align along the equator
- spindle fibres attach to the centromere
- crossing over and independent segregation occurs here
stages of meiosis (A1 -> meiosis 1 -> nuclear division 1)
spindle fibres contract and separate homologous chromosome pairs, pulling 1 of each pair to opposite poles of the cell
stages of meiosis (T1 -> meiosis 1 -> nuclear division 1)
nuclear membrane reforms around the separated homologous chromosomes
stages of meiosis (conclusion -> meiosis 1 -> nuclear division 1)
each daughter cell is now HAPLOID (n)
stages of meiosis (P2 -> meiosis 2 -> nuclear division 2)
each daughter cell only contains 1 chromosome from each homologous pair (haploid)
stages of meiosis (M2 -> meiosis 2 -> nuclear division 2)
each chromosome aligns along the equator
stages of meiosis (A2 -> meiosis 2 -> nuclear division 2)
non-sister chromatids are split by their centromere and pulled to opposite polls of the cell
stages of meiosis (T2 -> meiosis 2 -> nuclear division 2)
nuclear membrane reforms
stages of meiosis (conclusion -> meiosis 2 -> nuclear division 2)
4 genetically different haploid daughter cells are produced
key points of crossing over
- chromosomes being moved during P1 and M1 of meiosis 1
- the homologous chromosomes associate / bivalent is formed
- chiasmata form (chromosomes entangle / twist)
- equal lengths of non-sister chromatids / alleles are exchanged
- producing new combinations of alleles
key points of independent segregation
- during M1 of meiosis 1
- homologous chromosomes attach to the spindle fibres
- they pair up side by side
- can be reshuffled in any combination
- on equator of the cell
equation for calculating the possible number of different combinations of chromosomes following meiosis, without crossing over
2^n where n = the number of different pairs of homologous chromosomes
5 differences between meiosis and mitosis
MEI -> genetically different (daughter cells)
MIT -> genetically identical (daughter cells)
MEI -> homologous chromosomes associate in pairs
MIT -> chromosomes do not pair
MEI -> reduced the chromosome number
MIT -> maintains the chromosome number as in the parent nucleus
MEI -> crossing-over / chiasmata formation
MIT -> no crossing-over
MEI -> 2 divisions OR -> 4 offspring (daughter) cells
MIT -> 1 division OR -> 2 offspring (daughter) cells
