3.2.2 - all cells arise from other cells Flashcards
why do we need new cells?
for growth and to replace damaged tissue
do all cells keep their ability to divide?
in multicellular organisms, not all cells keep their ability to divide
what do eukaryotic cells that do retain the ability to divide show?
Eukaryotic cells that do retain the ability to divide show a cell cycle.
when does the cell cycle start?
cell cycle starts when a cell has been produced by cell division
when does the cell cycle end?
cell cycle ends with the cell dividing to produce 2 identical cells
what does cell cycle consist of (interphase)?
cell cycle consists of a period of cell growth and DNA replication (interphase)
what does cell cycle consist of (mitosis)?
cell cycle consists of a period of cell division (mitosis)
what is interphase divided into?
interphase (cell growth) is subdivided into 3 separate growth stages: G1, S and G2
stages of the cell cycle 1: mitosis
mitosis: cycle starts and ends here
stages of the cell cycle 2 : G1
gap phase 1: cell grows and new organelles and proteins are made
stages of the cell cycle 2 : S
synthesis: cell replicates its DNA, ready to divide by mitosis
stages of the cell cycle 2 : G2
gap phase 2: cell keeps growing and proteins needed for cell division are made
what happens during interphase?
during interphase the cell carries out normal functions, but also prepares to divide
what happens to the cell’s DNA in interphase?
the cell’s DNA is unravelled and replicated, to double its genetic content
what happens to the cell’s organelles in interphase?
organelles are also replicated so it has spare ones
what happens to the cell’s ATP content in interphase?
ATP content is increased as ATP provides the energy needed for cell division
what are the 2 types of cell division?
mitosis and meiosis
what is the form of cell division that occurs during the cell cycle?
mitosis is the form of cell division that occurs during the cell cycle
what does a parent cell divide to give in mitosis?
in mitosis, a parent cell divides to produce 2 genetically identical daughter cells
daughter cell DNA
they contain an exact copy of the DNA of the parent cell
what is mitosis needed for?
mitosis is needed for the growth of multicellular organisms and for repairing damaged tissues
is mitosis a continuous process
mitosis is one continuous process but it is described as a series of division stages
what are the stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
structure of chromosomes in mitosis
what are chromosomes made of
as mitosis begins, chromosomes are made of 2 strands joined in the middle by a centromere
structure of chromosomes in mitosis
what are the separate strands called
the separate strands are called chromatids
structure of chromosomes in mitosis
sister chromatids
two strands on the same chromosome are called sister chromatids
structure of chromosomes in mitosis
why are there two strands?
there are 2 strands as each chromosome has already made an identical copy of itself during interphase
structure of chromosomes in mitosis
what happens to the chromatids when mitosis is over
when mitosis is over, the chromatids end up as one-strand chromosomes in the new daughter cells
PROPHASE
1. what happens to chromosomes during prophase
- chromosomes condense and get shorter/fatter
PROPHASE
2. centrioles
- tiny bundles of proteins called centrioles start moving to opposite ends of the cell , forming a network of protein fibres across it called the spindle
PROPHASE
3. nuclear envelope
- nuclear envelope (membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm
METAPHASE
chromosomes (reach with 2 chromatids) line up along the middle of the cell and become attached to the spindle by their centromere
ANAPHASE
1. centromeres
- centromeres divide, separating each pair of sister chromatids
ANAPHASE
2. spindles
- spindles contract, pulling chromatids to opposite poles of the spindle, centromere first. this makes the chromatids appear V shaped
TELOPHASE
1. chromatids
- chromatids reach the opposite poles on the spindle. they uncoil and become long and thin again. they are now called chromosomes again
TELOPHASE
2. nuclear envelope
- nuclear envelope forms around each group of chromosomes, so there are now 2 nuclei
TELOPHASE
3. division of the cytoplasm
division of the cytoplasm (cytokinesis, which starts in anaphase) finishes in telophase
TELOPHASE
4. daughter cells
there are now 2 daughter cells that are genetically identical to the original cell and to each other
TELOPHASE
5. end of mitosis
mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis
how long does each stage of mitosis take
time taken for each stage of mitosis varies depending on cell type/environmental conditions
what are mitosis and the cell cycle controlled by
mitosis and the cell cycle are controlled by genes
do cells stop dividing and when
normally when cells have divided enough times to make new cells, they stop
what causes cells to grow out of control
mutation in a gene controlling cell division can cause cells to grow out of control
how is a tumour formed?
when cells keep on dividing to make more and more cells, a tumour can form
cancer
cancer is a tumour that invades surrounding tissue
what are some treatments for cancer designed to do
some treatments for cancer are designed to control the rate of cell division in tumour cells by disrupting the cell cycle which kills the tumour cells
what is the problem with cancer treatments
treatments don’t distinguish tumour cells from normal cells so also kill normal body cells that are dividing
why are cancer treatments still more likely to kill tumour cells than normal cells
tumour cells divide more frequently than normal cells, so treatments are more likely to kill tumour cells
what are some parts of the cell cycle that cancer treatments include
- G1 (cell growth and protein production)
- S phase (DNA replication)
cancer treatments targeting G1
example of chemical drug and what do they prevent
some chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for DNA replication
cancer treatments targeting G1
what does this prevention mean
if these aren’t produced, the cell is unable to enter the synthesis phase (S), disrupting the cell cycle and forcing the cell to kill itself
cancer treatments targeting S phase
what do radiation/some drugs do
radiation and some drugs damage DNA
cancer treatments targeting S phase
what happens if DNA is damaged as a result of this treatment for cancer
at several points in the cell cycle, the DNA is the cell is checked for damage. if severe DNA damage is detected, the cell will kill itself, preventing further tumour growth
what is the practical investigating mitosis
root tip cell squash
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 1
- add enough 1M HCl into a boiling tube that would just cover the root tip and put this in a 60 degrees Celsius water bath
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 2
- use scalpel to cut 1cm from the tip of a growing root. needs to be the tip as this is where growth and so mitosis occurs
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 3
- transfer the root tip into the boiling tube containing HCl and incubate it for around 5 minutes
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 4
- use tweezers to remove root tip from boiling tube. use a pipette to rinse it with cold water and leave the tip to dry on a paper towel
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 5
- put root tip on microscope slide and cut 2mm from the very tip of it and get rid of the rest
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 6
- use mounted needle to break the tip open and spread the cells out thinly
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 7
- add a few drops of the stain e.g. methylene blue (makes chromosomes easier to see under microscope)and leave for a few minutes
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 8
- place cover slip over cells and put piece of folded filter paper on top. push down firmly to squash the tissue
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
why do you squash the tissue in step 8
makes tissue thinner and allows light to pass through it. don’t smear coverslip sideways or you’ll damage the chromosomes
ROOT TIP CELL SQUASH REQUIRED PRACTICAL
step 9
- now look at the slide under an optical microscope
how to calculate mitotic index
number of cells undergoing mitosis /
total number of cells
USING AN OPTICAL MICROSCOPE
step 1
- clip slide onto the stage
USING AN OPTICAL MICROSCOPE
step 2
- select lowest power objective lens (lowest magnification)
USING AN OPTICAL MICROSCOPE
step 3
- look down eyepiece and use coarse adjustment knob to move stage downwards until image is roughly in focus
USING AN OPTICAL MICROSCOPE
step 4
- adjust focus with fine adjustment knob until you get a clear image
USING AN OPTICAL MICROSCOPE
step 5
- if you need to see the slide with greater magnification, swap to a higher powered objective lens and refocus
what does binary fission in prokaryotic cells involve
part 1
- replication of the circular DNA and of plasmids
what does binary fission in prokaryotic cells involve
part 2
- division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids
do viruses under go cell division
no as they are non living
how do viruses replicate
Following injection of their nucleic acid, the infected host cell replicates the virus particles.
