2.2 All cells arise from other cells Flashcards
What is the cell cycle?
The regulated sequence of events that occurs between one cell division and the next.
What are the 3 phases of the cell cycle?
Interphase, nuclear division (mitosis), cytokinesis.
What happens during interphase?
Organelles double, cell grows and DNA replicates.
What are the phases of interphase?
G1, S, G2.
What happens during the G1 phase?
Growth.
What happens during the S phase?
DNA synthesis.
What happens during the G2 phase?
Growth and preparation for mitosis.
What is a chromosome during mitosis?
2 chromatids attached by a centromere.
What are the 4 stages of mitosis?
Prophase, metaphase, anaphase, telophase.
How many divisions are there in mitosis?
1.
What does mitosis produce?
2 genetically-identical daughter cells.
What is the purpose of mitosis?
Growth and repair.
What happens to the chromosomes during prophase?
Chromosomes condense and become visible.
What happens to the centrioles during prophase?
Centrioles separate and move to opposite poles of the cell.
What happens to the chromosomes during metaphase?
They line up along the equator of the cell.
What happens to the spindle fibres during metaphase?
They are released from poles and attach to the centromere and chromatid.
What happens to the spindle fibres during anaphase?
They retract.
What happens to the centromere during anaphase?
It divides in 2.
What happens to individual chromatids during anaphase?
They are pulled to opposite poles.
Name the three phases of mitosis shown by C, D and E on the figure above.
Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases.
C = prophase
D = metaphase
E = anaphase
(5)
- in prophase, chromosomes condense
- in prophase/ metaphase, centromeres attach to spindle fibres
- in metaphase, chromosomes line up at the equator of the cell
- in anaphase, centromeres divide
- in anaphase, chromatids are pulled to opposite poles of the cell
What does anaphase require?
ATP.
What happens to the chromosomes during telophase?
They decondense.
What happens to the spindle fibres during telophase?
They disintegrate.
Mitosis is important in the life of an organism.
Give two reasons why. (2)
growth/increase in cell number
- replace cells/repair tissue
What stage of mitosis does the nuclear membrane break down?
Prophase.
What happens to the nuclear membrane during telophase?
It reforms.
What happens during cytokinesis?
Cytoplasm divides.
What is the equation for the mitotic index?
The number of cells in mitosis/total number of cells.
In which phase of the cell cycle does DNA replication take place? (1)
interphase
Describe the role of the spindle during mitosis. (2)
- attachment of centromeres/chromatids
- separation of chromatids
Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly. Explain why. (2)
- to spread out cells
- so light could pass through
Other students in the class followed the same method, but calculated different mitotic indices.
Apart from student errors, suggest two explanations why. (2)
- grown for different lengths of time
- The root tips from different plants
Meosis key words (6marker)
2- divisions - meiosis 1, meios 2
DNA Replication in late interphase
Seperation of homologous chromosoemes - 1st division
Seperation of sister chromatids - 2nd division
produce 4 haploid cells
Mitosis
The process that produces two daughter cells and have the same number of chromosomes as the parent cell
binary fission simple
produces 2 daughter cells
replication of circular DNA
happens in prok cells
Describe binary fission
Circular DNA and plasmids replicate (circular DNA replicates once, plasmids can be replicated many times).
Cytoplasm expands (cell gets bigger) as each DNA molecule moves to opposite poles of the cell.
Cell membrane grows between two DNA molecules.
Cytoplasm divides and new cell wall forms.
2 daughter cells formed, each with a single copy of DNA and a variable number of plasmids
What does binary fission produce?
two daughter cells
each with a single copy of the circular DNA
and a variable number of copies of plasmids
By what process do prokaryotic cells replicate?
binary fission
Centromere
The central region of a chromosome that holds the two chromatids togethe
Chromatid
Half a chromosome
compare and contrast mitosis and meisois (6marks)
both - PMAT (phrophase, metaphase, anaphase, telophase)
- contraction of spindle fibres seperates chromatids or chromsomes
- chromosomes line up at equator of cell and there is movement towards poles
- process ends with cytokinesis/ new cell is produced
- DNA must be copied during interphase
Mitosis
- genetically identical daughter cells
- individual chromosomes line up at equatoe in metaphase
- no idependent segregation
- no bivalents and crossing over
- diploid cells produced
- 2 daughter cells
Meiosis
- genetically different daughter cells
- homologous pairs line up at equator in metaphase 1
- independent segregation of homologous chromosomes
- Bivalents form- crossing over occurs
- Haploid cells produced
- 4 daughter cells
Define sister chromatid.
one half of a duplicated chromosome
Describe and explain how using chemotherapy to block enzymes involved in DNA synthesis affects cancer cells.
prevent synthesis of enzymes in G1 phase of interphase
cell is unable to enter the S phase
cell cycle is disrupted
Cell has to kill itself.
Hence the growth rate of cancer cells is reduced.
Describe and explain how using chemotherapy to disrupt spindle activity/formation affects cancer cells.
chromosomes can’t attach to spindle by their centromere → sister chromatids can’t be pulled to opposite poles of the cells → prevent/slow mitosis
so growth rate is lower/no growth
Describe and explain how using radiotherapy (radiation) and chemotherapy to damage DNA affects cancer cells.
Radiation and some chemicals damage DNA. In S phase cell is checked for damage. If damage is severe the cell will kill itself and the tumour is prevented from futher growth.
Describe the appearance and behaviour of chromosomes during mitosis.
Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.
1 chromosomes shorten / thicken / supercoiling;
2 chromosomes (each) two identical chromatids / strands / copies
(due to replication);
3 chromosomes / chromatids move to equator / middle of the spindle / cell;
4 attach to individual spindle fibres;
5 spindle fibres contract / centromeres divide / repel;
6 (sister) chromatids / chromosomes (separate)
move to opposite poles / ends of the spindle;
7 each pole / end receives all genetic information /
identical copies of each chromosome;
8 nuclear envelope forms around each group of chromosomes /
chromatids / at each pole;
Describe and explain the arrangement of genetic material in prophase:
1- Chromosomes visible
2- still condensing
3- chromosomes arranged randomly/ not lined up
4- Because no spindles
Describe the structure of chromosomes and how this changes in interphase.
made of strands of DNA tightly coiled around proteins called histones
Interphase- chromosomes replicate and become sister chromatids
joined together at a centromere
Describe viral replication.
1- attachment proteins attack to receptors
2- viral nucleic acid enters cell - engulfment, injection for enters
3 - necleic acid replication in cell
4- reverse transcriptase makes DNA from RNA
5- Cells produces viral protein/ capsid/ enzymes
6- Virus assembled and released from cell - bursts/ lysis
Give 5 ways chemotherapy can be targeted to kill cancer cells.
preventing synthesis of enzymes involved in DNA synthesis
preventing DNA unwinding so preventing DNA replication
inhibiting synthesis of new nucleotides
preventing formation of spindle
damaging DNA (using radiation or chemicals) so cell is forced to kill itself when DNA is checked for damage in S phase of interphase
Give one advantage and one disadvantage of chemotherapy drugs that target cell division.
more effective - cancer cells are dividing rapidly
disrupts cell cycle of normal cells
Homologous Chromosomes
Identical chromosome
In which stages of the cell cycle are chromosomes visible as two sister chromatids?
prophase and metaphase
In which stages of the cell cycle are chromosomes visible?
prophase (as sister chromatids)
metaphase (as sister chromatids)
anaphase (as separated chromatids in a V shape)
meiosis def
produces daughter cells that are genetically different from each other
What causes cancer?
uncontrolled cell division
caused by a mutation in genes that control mitosis and cell growth
What do chromosones look like in the anaphase?
Are they visible?
visible chromatids (in two sets) being separated to opposite poles by spindles,
V shape shows sister chromatids have been pulled apart at their centromeres
What do chromosones look like in the interphase?
Are they visible?
not visible (although nucleus is visible - chromatin)
What do chromosones look like in the metaphase?
Are they visible?
chromosomes visible as sister chromatids lined up along the equator
What do chromosones look like in the prophase?
Are they visible?
chromosones visible as sister chromatids but randomly arrange
What do chromosones look like in the telophase?
Are they visible?
individual chromosomes not visible (nucleus/chromatin is visible instead)
What is the equation for calculating the mitotic index?
Mitotic index = (Number of dividing cells / Total number of cells) x 100
What stage of the cell cycle is cell A in?
How can you tell?
telophase
chromosomes in two sets, one at each pole
Why do viruses not undergo cell division?
What do they undergo instead?
because they are non-living
viral replication
What stage of the cell cycle is cell B in?
How can you tell?
prophase
chromosomes visible but randomly arranged
What stage of the cell cycle is cell C in?
How can you tell?
interphase
no chromosomes visible (visible nucleus)
What stage of the cell cycle is cell D in?
How can you tell?
metaphase
chromosomes are lined up along the equator
What stage of the cell cycle is cell E in?
How can you tell?
Anaphase
chromatids (in two sets) being separated to opposite poles by spindles
V shape shows sister chromatids have been pulled apart at their centromeres
How do cancerous cells cause a tumour?
By dividing repeatedly or uncontrollably
how do cancers start?
When a mutation in the gene that causes cell division occurs
What causes mutations?
carcinogens- UV rays- X - rays- Some infectious agents
Suggest why hair loss is often a common side effect for people receiving treatment for cancer:
- treatments cannot distinguish between healthy cells and cancerous cells- Therefore it stops all cells from replicating- because hair cells have a rapid rate of cell division, they are destroyed aswell.
