2.1.6 Cell division, cell diversity and cellular organisation Flashcards
what is the cell cycle?
The cell cycle is the repeating sequence of events whereby a cell’s genetic information is replicated (during a stage called interphase) and then the cell undergoes division, via mitosis followed by cytokinesis, to produce two genetically identical daughter cells. Each of these cells then itself goes through the cell cycle.
what is the longest pahse in the cell cycle
interphase
what is included in interphase?
G1, S and G2
Can the cell cycle ever go in reverse?
cell cycle cannot ever go into reverse, e.g if damaged DNA is detected
at the G2 checkpoint, the cell cycle is halted and the cell tries to repair the damage. The cell
cannot return to an earlier stage, if it cannot be repaired, the cell will enter the G0
What is G0, why does it enter this phase?
The name given to the stage in the cell cycle, where the cell leave the cycle temporarily or permenatnly, and stops divinding
Cell differentiation
Failed G1 checkpoint: DNA may be damaged, or cell’s nutrients/size were not sufficient. The cell is not allowed to go into S phase
What occurs at the G1 checkpoint? 4
checks for: Adequate cell volume/size nutrients Absence of DNA damage Growth factors
What occurs at the S checkpoint? 2
checks for:
Absence of DNA damage
All DNA has been replicated
What occurs at the G2 checkpoint? 4
checks for: Adequate cell volume/size nutrients Absence of DNA damage Growth factors
What is interphase?
The first (and by far the longest) stage in the cell cycle is called interphase. Interphase is made up of three phases: G1, S and G2.
is interphase a stage of mitosis?
NO! It is the stage which prepares a cell so it can then divide by mitosis.
What occurs in S phase of interphase? 3
- Chromosomes are replicated via semi‐conservative DNA replication: following this process, each chromosome will now have two chromatids (of identical DNA base sequence) that are held together by a centromere.
- Aerobic repsiration to produce ATP
- Checking of the newly‐replicated DNA, i.e. proofreading: some mutations can be
corrected at this stage, e.g. if a base is identified as being wrongly paired.
Draw a chromose before and after semi conservative replication.
look at notes :)
What occurs in G1 phase of interphase? 6
- Production of more organelles, e.g ribosomes and mitochodnria
- Replication of the centrioles (Animal cells only, made of microtubules), they are replicated during interphase and then used later in the cell cycle to organise the spindle fibres during mitosis (or meiosis).
- Protein synthesis via transcription and translation
- Aerobic repsiration to produce ATP
- Increase in cell volume due to increased surface area of plasma membrane (cell surface
membrane) and increased volume of cytoplasm, more phospholipids are inserted into the plasma membrane, enabling an increase in cell volume to occur as the membrane surface area expands; the increase in cell volume is necessary so that when the cell eventually
divides, the two daughter cells will receive enough cytoplasm and organelles. - Checking of the newly‐replicated DNA, i.e. proofreading: some mutations can be
corrected at this stage, e.g. if a base is identified as being wrongly paired.
What occurs in G2 phase of interphase? 6
- Production of more organelles, e.g ribosomes and mitochodnria
- Replication of the centrioles (Animal cells only, made of microtubules), they are replicated during interphase and then used later in the cell cycle to organise the spindle fibres during mitosis (or meiosis).
- Protein synthesis via transcription and translation
- Aerobic repsiration to produce ATP
- Increase in cell volume due to increased surface area of plasma membrane (cell surface
membrane) and increased volume of cytoplasm, more phospholipids are inserted into the plasma membrane, enabling an increase in cell volume to occur as the membrane surface area expands; the increase in cell volume is necessary so that when the cell eventually
divides, the two daughter cells will receive enough cytoplasm and organelles. - Checking of the newly‐replicated DNA, i.e. proofreading: some mutations can be
corrected at this stage, e.g. if a base is identified as being wrongly paired.
what is the definition of mitosis?
nuclear division stage in the mitotic phase of the cell cycle, producing two genetically identical daughter cells
When does mitosis occur?
Once interphase is complete
what are the 4 stages of mitosis, and how to remember order
Prophase, Metapahse, Anaphase, Telophase
PMAT
How can we easily view the stage of mitosis? What stain do we use? How do we prepare it?
A stained onion root tip squash, viewed by light microscopy, is often used to study mitosis
because the root tip contains meristem tissue, a site of active cell division. All the stages of the mitotic cell cycle are therefore likely to be visible (though most cells will appear to be in interphase since it is the longest phase).
Methylene blue
Preparing the root tip as a squash means that the cells are spread into a single layer, giving an
image without overlapping cells, straightforward to interpret and easily allowing light to pass
through.
what is the name of the first stage of mitosis and what occurs? 3 parts
Prophase
Chromosomes condense as DNA becomes more tightly coiled; the chromosomes become shorter and fatter and hence become visible as distinct structures. (Nucleolus dissapears)
Centrioles move to opposite poles of the cell (in animal cells only); their role is to organise the spindle fibres.
Spindle fibres (made of microtubules) begin to form; these are considered to be a component of the cytoskeleton.
what is the name of the second stage of mitosis and what occurs?
Metaphase
The nuclear envelope breaks down, such thatthe chromosomes are released into the cytoplasm.
The spindle fibres are completed; each spindle fibre attaches to one individual chromosome at its centromere.
Each spindle fibre then pulls its attached chromosome to the equator of the cell; this results in the chromosomes lining up on the equator in a single row (in a random order, which has no significance).
what is the name of the third stage of mitosis and what occurs?
Anaphase
The centromeres divide, releasing the twochromatids of each chromosome so that they are now separate from each other; each of these will now become a chromosome in its own right.
Spindles fibres shorten and so pull each of the two chromatids to opposite poles of the cell.
what is the name of the fourth and final stage of mitosis and what occurs?
Telophase
IMPORTANT: A full (diploid) set of chromatids (now called chromosomes again) has reached each pole ofthe cell.
New nuclear envelope forms around the chromosomes at each pole, giving the cell has two identical nuclei (though this is usually
temporary, as the cell will go on to divide by cytokinesis).
Chromosomes decondense (disappearing as individual structures) and a new nucleolus forms in each nucleus.
What is the step after Mitosis?
Cytokinesis
What is cytokinesis?
It is the division of the cell itself, into two daughter
cells, each of which receives one nucleus plus a share of cytoplasm containing the other
organelles.
What are the steps of cytokinesis in an animal cell?
- In a plane corresponding to the cell equator, microtubules pull the plasma membrane
inwards until it fuses with itself in the centre of the cell. - This causes the cell to be divided into two daughter cells (usually of similar sizes), each with one nucleus.
- The cytoplasm (including organelles, e.g. ribosomes and mitochondria) has been shared out and divided to form the two daughter cells.
Why are the steps in cytokinesis in plant cells different to animal cells?
Because a plant cell must for a new cell wall
What are the steps of cytokinesis in an plant cell?
- Along the plane of the cell equator, vesicles containing cellulose line up (moved into
position using microtubules as tracks). - These vesicles start merging together; the structure that forms is called the cell plate,
and it eventually divides the cell in two, by forming a complete new cellulose cell wall
to separate the two daughter cells. - However, narrow threads of cytoplasm usually remain in connecting pores that link the two cells; these are called plasmodesmata.
Are you able to recognise photos of each stage of mitosis?
look at photos :)
What is significant about mitosis?
generates genetically identical daughter cells
chromosome number is maintained (original cell is diploid i.e. has two sets of chromosomes then both daughter cells formed will also be diploid.)
eukaryotic cells
how do prokaryotes divide?
binary fission
What are 3 general roles of mitosis?
- Growth: mitosis increases cell numbers and hence causes growth (the increase in size
of the organism’s body) in multicellular eukaryotes.
(Note that the term growth refers here to the increase in number of cells NOT to an
increase in the size of each cell.) - Tissue repair and cell replacement: mitosis produces more (genetically identical) cells,
which can be used to repair a tissue (e.g. if injury has caused damage) or replace worn
out cells (e.g. stem cells in bone marrow must constantly divide by mitosis to produce
new red blood cells, as this cell type only remains functional for around 100 days). - Asexual reproduction: in unicellular eukaryotes, and some multicellular eukaryotes, cell
division by mitosis generates new individuals who are clones of a single parent
organism, with genetically identical cells.
Asexual reproduction does not involve meiosis or the fusion (fertilisation) of gametes;
only one parent is required; there will be no genetic variation amongst the offspring
(except for rare, random mutations).
What are 4 specific roles of mitosis?
- Development of the body plan: mitosis produces new cells to contribute to the
formation of a specific body plan during the development of an organism (though
selected cells are then removed by apoptosis (programmed cell death). - Clonal expansion of B and T lymphocytes: during a specific immune response, selected
B and T lymphocytes are stimulated to repeatedly divide by mitosis in order to increase
the number of cells able to specifically attack the pathogen that has been detected. - Producing gametes from haploid cells: in a minority of species (including male ants and
honeybees), the adult body cells are haploid (i.e. contain only one set of
chromosomes); this means that haploid gametes can be produced by mitosis in this case
(to maintain the same chromosome number, rather than using meiosis to halve it). - Renewal of stem cells: stem cells are unspecialised, however when a stem cell divides,
usually one daughter cell differentiates and the other divides again, maintaining a
population of stem cells at the appropriate level.
Specialised
What is a sepecialised cell?
Specialised cells develop structures and produce (only) the proteins relevant to that cell’s specific role.
How do sepecialised cells arise?
differentiation
is differentiation reversable?
Generally no
What are the 5 specialised animals cells you must know?
- Erythrocytes
- Neutrophils
- Squamous epithilial cells
- Ciliated epithelial cells
- Sperm cell
What are the 3 specialised plant cells you must know?
- Palisade mesophyll cell
- Root hair cell
- Guard cells
What is an Erythrocytes, what is its functions and how is it specialised?
What:
Red blood cells
Function:
Transport oxygen from the lung alveoli to body cells, for use in respiration
Specialisations:
No organelles, e.g no nucleus, no ribosome and no mitochonsria (Organelles present in immature erythrocytes, but are broken down once enough haemoglobin is produced, it is then mature. This is good as there is more space for heamoglobin so more oxygen can be carried
Biconcave disk shape, increases SA and therfore rate of diffusion increases, plus allows the cell to be flexible
Small, 7 um, therefore is able to fit through narrow blood capillaries, also creates a large SA:V ratio, increasing the rate of diffusion
What is a Neutrophil, what is its functions and how is it specialised?
What:
Type of white blood cell, and hence is part of the immune system.
Function:
Its specific role is to engulf pathogens by phagocytosis
Specialisations:
Multi-lobed nucleus, allos for more flexibility during phagocytosis, and can squeeze through small gaps
plasma membrane contains many receptors (which antibodies on the antigens of the pathogens) can fit into, triggering phagocytosis
Granular cytoplasm, contains many lysososmes, to break down pathogens , mitochondria to provide energy, and RER + Golgi apparatus to produce hydrolytic enzymes and packaging them into lysosomes
What is a Squamous epithilial cell, what is its functions and how is it specialised?
What:
Squamous epithelial cells are flattened, smooth cells.
Function:
Forms the protective lining of the inner cheek, and gives a short diffusion distance to gases by forming the thin walls of the alveoli in the lungs.
Specialisations:
Smooth surface, (in blood vesssels, it reduces friction to blood cells)
Flat and thin, (in the alveoli walls it allows for a short diffusion diustance for gases)
Basement membrane, made of collagen, holds the cells in a single layer without any gaps between them creating a continuous surface of cells
