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What is cytokinesis?
Cytoplasmic division after nuclear division, resulting in two new daughter cells
What is interphase?
Phase of cell cycle where the cell is not dividing but subdivided into growth and synthesis phases
What is mitosis?
Type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell
What are the purposes of checkpoints in the cell cycle?
- Prevent uncontrolled division of the cell that could lead to tumours
- Detect and repair damage to DNA
- stop the cell cycle from reversing
- Ensure DNA is only duplicated once during each cell cycle
What are the phases of the cell cycle and checkpoints?
- M Phase
- G1 phase (G0 Can occur here)
- Synthesis phase
- G2 phase
What is the interphase of the cell cycle?
- G1 phase
- S phase
- G2 phase
* G0 is not part of the interphase
What checkpoints occur in the M phase?
- Checkpoint protein before prophase
- Metaphase check point
What does the checkpoint protein do at the start of the M phase?
Triggers condensation of chromatin
What does the metaphase checkpoint do?
Ensures the cell is ready to complete mitotic cell division (cytokinesis)
What occurs in the cell during mitosis?
- Cell growth stops
- Nuclear division of mitosis consisting of
1. Prophase
2. Metaphase
3. Anaphase
4. Telopase
- Cytokinesis
Where are the checkpoint(s) near the G0 phase?
Prior to G0 in the G1 phase at the restriction point checkpoint chemical
What is triggered at G1 checkpoint that leads to the cell going to G0?
A resting phase is triggered
Do all cells have G0 phase?
No, i.e. the epithelial cells do not have G0
What occurs in the cell in the G0 phase?
Cells may undergo apoptosis, differentiation or senescence
What does the checkpoint at G1 phase do?
G1 checkpoint control mechanism; ensures the cell is
- Ready to enter the S phase
- Begin DNA synthesis
What occurs in the cells during G1 phase?
- Cells grow and increase in size
- Transcription of genes to make RNA occurs
- Biosynthesis (i.e. protein synthesis)
- Organelles duplicate
- p53 tumour suppression gene controls this phase
- G1 checks the DNA for damage
What happens when G1 detects a mutation?
Stops the cell from entering the S phase due to the damaged DNA that has been checked by G1.
Where is DNA in its lowest concentration of the interphase?
Lowest concentration of DNA is in G1
What type of "checkpoint" genes are replicated first in the S phase?
Housekeeping genes are replicated first as "checkpoints". Essential to the cell
Does the S-phase have the highest or lowest concentration of DNA?
Highest concentration of DNA
What occurs in the cell after the S phase and G2 phase?
- DNA replicates
* After duplication of all chromosomes, sister chromosomes are formed
What are important features of the S phase?
- Once the cell begins the S phase, it is fully committed to completing the cycle
- Phase is rapid as exposed DNA pairs are more susceptible to mutagenic agents
What occurs in cells of the G2 phase?
Cells grow.
What do the checkpoints do in the G2 phase?
Special chemicals stimulate proteins involved in;
- Make chromosomes condense
- Forms the spindle
If you took a sample and recorded the cells between the phases of interphase, which phase would have the highest cells recorded?
G1 phase
How do tumours form?
uncontrolled cell division
What are chromatids?
Replicates of chromosomes
Why do organisms need mitosis? (what are mitosis' roles)
- Asexual reproduction
- Growth and repair of tissues; where daughter cells are genetically identical to the parent cells and wounds can heal
- Development of a body plan
- Clonal expansion of white blood cells
- Produce new stem cells
What are the four main stages of mitosis?
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
What events occur during prophase?
After the S phase;
- DNA super coils
- Nuclear envelope breaks down
- Chromosomes condenses
- Chromosomes are now visible
- Centriole (in animal cells) divides and two daughter centrioles moves to opposite side of cell
- Tubulin cytoskeleton protein threads form a spindle in animals
What occurs during metaphase?
- Chromosomes line up on the equator
- Spindle threads attach to the centromeres of the chromosomes (do NOT call them chromatids until anaphase)
What occurs during anaphase?
- Centromere of each pair of sister chromatids splits
- Motor proteins pull each pair of sister chromatids in opposite directions towards opposite poles
- Chromatids assume a V shape as their centromeres pulled first
(YOU CAN NOW CALL THEM CHROMATIDS)
What occurs during telophase?
- Separated chromosomes reach the poles (chromatids now called chromosomes)
- New nuclear envelope forms around each set of chromosomes
- Cell contains two nuclei each genetically identical to each other
- Cell begins to divide nearing cytokinesis
What occurs during cytokinesis in animal cells?
Cell splits into two;
Cell surface membrane folds inwards, nips in the cytoplasm
What occurs during cytokinesis in plant cells?
Cell splits into two;
- End plate forms where the equator of the spindle was
- New cell surface membrane and cellulose cell wall material laid down along the end plate
What is a haploid?
having a single set of unpaired chromosomes. symbol "n"
What are (two) homologous chromosomes?
Matching chromosomes containing genes in the same loci (place). They may contain different alleles
What is meiosis?
Type of nuclear division that results in formation of gametes with half the number of chromosomes from the parent cell
Why is meiosis important?
Increases genetic variation
Why is genetic variation important?
Increases chances of survival when the environment changes as some individuals will have better adapted characteristics
What are the body cells usually referred as?
Diploid
For sexual reproduction what must sex cells be?
Haploid gametes
When two gamete nuclei fuse together, which is the product called?
Zygote
What can gonads be?
- Ovaries
- Testes
What are the two chromosomes received from the mother and the farther?
- Maternal chromosomes
- Paternal chromosomes
What are the maternal and paternal chromosomes known as?
Homologous chromosomes.
How does meiosis proceed?
- Two divisions of meiosis with each having four stages;
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
- Short Interphase
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2
- Cytokinesis
What occurs during prophase 1?
- Chromatin condenses
- Chromosomes supercoils
- Nuclear envelope breaks down
- Spindle thread forms from the centriole
- Chromosomes come together in homologous pairs each containing two chromatids
- Crossover of points between the two non-sister chromatids, swapping of sections, alleles exchanged
What occurs during Metaphase 1?
- Pairs of homologous chromosomes in crossed over state attach along the equator to the spindle by the centromeres
- Independent assortment. Homologous pairs arranged randomly, members of each pair facing opposite poles of the cell
- Way they lined up randomly will determine independent segregation
What occurs during Anaphase 1?
- Members of each pair of homologous chromosomes are pulled apart by motor proteins
- Centromeres do not divide
- Cross-over areas separate from each other; Swapped areas of chromosomes and further allele shuffling
What occurs during Telophase 1 in most animal cells?
- Two new nuclear envelopes form around each of chromosomes
- Cell divides by cytokinesis
- Short interphase and chromosomes uncoil
- Each new nucleus contains half the original chromosomes with each chromosome containing two chromatids (from maternal and parental)
What occurs during Telophase 1 in most plant cells?
Cells go straight from anaphase 1 to prophase 2
What occurs in prophase 2?
- If the nuclear envelopes have reformed, they break down again
- Chromosomes coil and condense, each with two chromatids
- Chromatids of each chromosome not identical due to crossover and independent assortment
- Spindle fibres form
What occurs in metaphase 2?
- Chromosomes align on the equator and attach by their centromeres to the spindle
- Chromosomes are randomly arranged though this arrangement will determine how they are pulled apart
What occurs in Anaphase 2?
- Centromeres divide
- Chromatids of each chromosome are pulled apart by motor proteins and dragged along tubular threads to opposite poles
- Chromatids are randomly segregated
What occurs in telophase 2?
Nuclear envelope forms around each of the haploid nuclei
How does cytokinesis occur after telophase 2 in animal cells?
Two cells divide to give four haploid cells
How does cytokinesis occur after telophase 2 in plant cells?
Tetrad of four haploid cells is formed.
In summary, how does the steps during meiosis produce genetic variation?
- Cross over during prophase 1 shuffles alleles
- Independent assortment of chromosomes in metaphase 1. Random distribution of maternal and paternal genetic material
- Independent assortment of chromosomes in metaphase 2 leads to further random distribution
How can genetic variation increase after meiosis has already been completed?
Random fertilisation
What is the definition of differentiation?
Process where stem cells become specialised into different types of cell
What is the definition of an erythrocyte.
Red blood cell
What is the definition of epithelial cells?
Cells constituting a lining tissue
What is the definition of a neutrophil?
Type of white blood cell that is phagocytic
What is the definition of a stem cell?
Unspecialised cells able to express all of its genes and divide by mitosis.
Why does the body need specialised cells?
Multicellular organisms are larger and have a small SA:V ratio.
- Most cells are not in contact with the external environment
- Therefore multicellular organisms need specialised cells to carry out particular functions
What is a zygote, are they specialised?
- It is a stem cell
- they are not specialised
- All genes in it's genomes is able to be expressed
- After multiple mitotic divisions, an embryo can form containing multiple undifferentiated embryonic stem cells.
Why, after the zygote is formed, the nuclear division is mitosis and not meiosis?
- Mitosis is for the growth of the zygote
- Cells produced from a zygote needs to be genetically identical
- There is no halving of chromosomes, haploid cells are not produced after the formation of a zygote
What are the effects of differentiation on a cell?
- Proportions of organelles differ between different cells
- Shape of the cell changes
- Some contents of the cell changes
What is a cell after differentiation?
Specialised
What is the function of erythrocytes?
To transport oxygen from the lungs to respiring cells
What is the function of neutrophils?
To ingest invading pathogens
Where do erythrocytes derive from?
Stem cells in the bone marrow
How is the structure of erythrocytes adapted to carry out their function?
- Very small, 7.5 micrometers in diameter; large SA:V, high diffusion of oxygen
- Biconcave shape also increases SA:V ratio
- Well developed cytoskeleton allow erythrocytes to be flexible, especially beneficial towards capillaries
- Organelles lost to differentiation; no nucleus, mitochondria, endoplasmic reticulum, little cytoplasm; provides space for haemoglobin molecules
What tissues is muscle made from?
- Connective tissue
- Blood tissue
- Nervous tissue
Can neutrophils undergo mutation during differentiation?
No, they cannot
How is the structure of neutrophils adapted to their function?
- Multilobed nucleus; flexibility
- Attracted to infection sites via chemotaxis
- Contain many lysosomes with hydrolytic enzymes
- Ingest microbes (i.e. bacteria) by phagocytosis
How is the spermatozoa specialised to its function?
- Many mitochondria to carry out aerobic respiration as ATP is needed for the undulipodium for movement
- Spermatozoa are small and thin and can therefore move easily
- Once at the ovum, spermatozoa release enzymes are released from acrosome (specialised lysosome); enzymes digest the out layer of the ovum
- Head of sperm contains the the haploid male gamete nucleus
How are squamous epithelial tissues specialised for their function?
- Have a flattened shape
- One cell thick
- These provides short diffusion for CO2
How are cilliated epithelial tissues specialised for their function?
- Have hair-like Cilla which move in rhythm
- Cilla moves mucus up the trachea
What are guard cells?
in leaf epidermis, cells that surround stomata
What are palisade cells?
Closely packed photosynthetic cells within leaves
What are root hair cells?
Epidermal cells of young roots with long hair-like projections.
How are palisade cells' structure adapted for photosynthesis?
- Long and cylindrical with spaces
- Large vacuole; chloroplasts are positioned on near the edge of the cell
- Multiple chloroplasts
- Contains cytoskeleton threads and motor proteins
Why do palisade cells contain long and cylindrical spaces?
For CO2 to travel through
Do palisade cells have thin or thick walls?
Thin walls, to allow a greater diffusion rate of carbon dioxide
Why do palisade cells have a large vacuole near the edge of the cell with chloroplasts? (Not to do with pressure or support btw)
Shortens diffusion distance for CO2
Why do palisade cells contain multiple chloroplasts?
Gives a higher rate of photosynthesis per plant cell
Why do palisade cells contain cytoskeletal threads and motor proteins?
Move chloroplasts depending on the present light intensity
Do guard cells photosynthesise?
No
(well they kind of do; they undergo a process in the light dependent stage called cyclic photophosphorylation, but they do not contain Ribulose Bisphosphate Carboxylase Oxygenase or RuBisco for short, for now say NO, FYI you will learn about this in year 2)
Do guard cells absorb light energy?
Yes
Why do guard cells absorb light energy?
For cyclic-photophosphorylation; generation of ATP
Why do guard cells need energy from the form of ATP?
To actively transport potassium ions from surrounding epidermal cells, lowering water potential
What happens to the guard cells after their water potential is lowered?
More water enters the guard cells via osmosis from neighbouring epidermal cells, causing swelling
What does the swelling cause of the guard cells? What structure doesn't follow the guard cells movement?
Causes guard cell to open. The tips have more rigid cellulose walls therefore do not open. Stomata therefore opens
What happens when the stomata opens?
- Air can enter the places beneath the palisade cells
- Gaseous exchange occurs; CO2 diffuses into palisade cells, being used for photosynthesis
- CO2 concentration gradient maintained
- Oxygen produced during photosynthesis can diffuse out of the palisade cells, into air spaces and out of the open stomata
How are root hair cells specialised?
- Hair like projection increases SA:V ratio to absorb water and mineral ions from the soil
- Root hair cells contain special carrier proteins in cell surface membrane for active transport
What is tissue?
Group of cells the work together to perform a specific function
What are the four main tissue types?
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue
Where are epithelial tissues found?
- Skin
- Cavities of the digestive and respiratory systems
- Blood vessels
- Heart chambers
- Walls of organs
