2.1.6 Cell Division, Cell Diversity and Cellular Organisation Flashcards
What are the three main phases of the cell cycle?
- Interphase
- Nuclear division
- Cytoplasmic division (cytokinesis)
What happens in the G1 phase?
- Growth
- Proteins and organelles are made
What happens in the S phase?
- Replication of DNA (synthesis)
What happens in the G2 phase?
- Organelles made
- Energy stores increased
- DNA is checked for errors
What does a checkpoint do?
Verify that the previous part of the cell cycle has been completed
e.g. G1, G2, spindle assembley
What is the G1 checkpoint?
- Between G1 and S phases
- Checks for cell size, nutrients, growth factors and DNA damage
What is the G2 checkpoint?
- Between G2 and nuclear division phases
- Checks for cell size, DNA replication and DNA damage
What is the spindle assembly (metaphase) checkpoint?
- At metaphase
- Checks that chromosomes are aligned and attached to spindles at the centromeres
What is G0?
- When a cell leaves the cell cycle
- Happens when checkpoints aren’t satisfied
Why does a cell enter G0?
Differentiation:
- Cell becomes specialised
- Performs this function indefinitely
Damaged DNA:
- Can no longer replicate (senescent)
Age:
- The older you are, the more senescent cells you have
- Linked with cancer and arthritis
What is cancer and how is it caused?
- Caused by mutation of genes that regulate the cell cycle
- Uncontrolled growth of cells
- Forms a tumour
How can cancer be treated?
- Prevent DNA replicating or inhibit metaphase (interfere with spindle fibres)
- Can be done using cisplastin or vinca alkaloids
- Treating cancer also affects normal cells and can cause hair loss
What are the stages of mitosis?
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
What happens in interphase?
- Chromosomes are invisible prior to mitosis
- Long and thin
What happens in prophase?
- Chromosomes condense and become visible
- Nuclear envelope and nucleolus disappear
- Centrioles move to the opposite ends of the cell
- Spindle fibres attach to centromeres and start to move chromosomes to the equator
What happens in metaphase?
- Chromosomes arrange themselves along the equator of the cell
- Equator is known as the metaphase plate
What happens in anaphase?
- Each of the 2 threads of the chromosome (chromatid) migrates to an opposite pole by shorting spindle fibres
What happens in telophase?
- Nuclear envelope reforms
- Nucleolus reforms
- Chromosomes uncoil and become long and thin again
What happens in cytokinesis?
- Cell divides into 2 daughter cells that are identical to the parent cell
- Division of the cytoplasm
What is the difference between a chromatid and chromosome?
1 chromosome is made of 2 chromatids
What is the process of cytokinesis in animal cells?
- Cleavage furrow forms in the middle of the cell
- Cell surface membrane is pulled inwards by the cytoskeleton and fuses
What is the process of cytokinesis in plant cells?
- Plant cells have a cell wall which prevent a cleavage furrow
- Vesicles from the golgi apparatus line up along the metaphase plate
- Vesicles fuse with each other and the cell surface membrane
- New cell wall forms
What is the importance of mitosis?
- Growth
- Differentiation
- Repair
- Asexual reproduction in plants, animals and fungi
Why are plant root tips a good source of cells for mitosis?
- Continually growing at regions called meristems
- Meristems are constantly dividing
How do you calculate mitotic index?
Mitotic index = number of actively dividing cells in field of view/number of cells in field of view
What are homologous chromosomes?
- The same genes in the same positions (could be different alleles)
- One from each parent
- Same length and size
What is an allele?
Different versions/forms of a gene
What is a locus?
Where on the chromosomes the alleles are
What is a gamete?
A haploid cell involved in sexual reproduction (e.g. egg and sperm or pollen and egg)
What does haploid mean?
Half of the number of chromosomes
What does diploid mean?
Full number of chromosomes
How is genetic variation created?
- Crossing over
- Independent segregation of chromosomes (random assortment)
- Random fertilisation
What is crossing over?
- When chromatids twist around each other and swap
- Contain the same genes but different alleles
- Only within homologous pairs
What is the independent segregation of chromosomes?
- Chromosomes align on the metaphase plate randomly during metaphase (meiosis I)
- One from each pair passes into a daughter cell
What is random fertilisation?
- Any sperm can fertilise any egg
- Each individual is unlike any to have existed before or any that will exist again
What are the main stages of meiosis?
- Interphase
- Meiosis I
- Meiosis II
What happens in interphase?
- DNA duplicates during S phase
What happens in meiosis I?
- The first division
- Each chromosome is made up of two sister chromatids
- Genetic recombination takes place at random (chromosomes cross over and swap blocks of genes)
- Prophase I, metaphase I, anaphase I and telophase I
- Homologous chromosomes segregate into 2 nuclei
- Nuclear envelope forms
What happens in meiosis II?
- The second division
- Identical to mitosis
- Prophase II, metaphase II, anaphase II and telophase II
- Chromatids from individual chromosomes are pulled to opposite poles
- Independent assortment
- 4 haploid gametes form
- Known as reduction division
How are erythrocytes (RBCs) specialised?
- No nucleus, mitochondria, Golgi apparatus or RER
- Biconcave discs for a large surface area
- Flexible so it can fit through small gaps
- Contain haemoglobin
How are neutrophils specialised?
- Lobed nucleus which allows them to fit through small gaps
- Flexible shape for engulfing pathogens/foreign particles
- Lysosomes contain digestive/hydrolytic enzymes
How are squamous epithelial cells specialised?
- Flat and thin to allow for rapid diffusion
How are ciliated epithelial cells specialised?
- Have cilia (hair like structure)
- Line the trachea and waft mucus away from the lungs
- Work in conjunction with goblet cells which produce mucus
How are sperm cells specialised?
- Flagellum for movement
- Acrosome contains digestive enzymes to penetrate the egg
- Lots of mitochondria to provide energy
- Less cytoplasm to reduce mass
How are palisade cells specialised?
- Chloroplasts to absorb light for photosynthesis
- Elongated (tall and thin) so it’s further to travel before going through a second cell wall (maximise light absorption)
How are root hair cells specialised?
- Long projection increases surface area to absorb water and mineral ions from soil
- Thin permeable cell wall
- Lots of mitochondria to provide energy for active transport of mineral ions
How are guard cells specialised?
- In light, guard cells take up water into their vacuole and become turgid (stoma opens)
- Inner wall becomes thicker and outer wall thinner so they bend
How is squamous epithelia tissue specialised?
- Single layer of flat cells
- Thin surface allows easy exchange of substances
How is ciliated epithelia tissue specialised?
- Found on surfaces where things need to be moved
E.g. trachea or oviduct
How is cartilage tissue specialised?
- Protects and strengthens
- Found in connective tissue in joints, ears, nose, trachea
- Chondrocytes produce an extracellular matrix of collagen fibres (strength) and elastin fibres (flexibility)
How is muscle tissue specialised?
- There are 3 types of muscle: skeletal, smooth, cardiac
- Made up of bundles of elongated cells called muscle fibres
- Contains contractile protein myofilaments called actin and myosin which form structures called myofibrils
How is xylem tissue specialised?
- Transports minerals and water up the stem
- Supports the plant
- Impregnated with lignin
- Xylem cells are dead and have no cytoplasm
- Parenchyma cells fill gaps between the other cells
- Water transporting cells with wide lumen (vessel elements)
- Fibres for support (made of lignin)
- Tracheids for the transport of water and support in angiosperms (flowering plants)
How is phloem tissue specialised?
- Transports organic nutrients up and down the plant
- Sieve tube elements: reduced cytoplasm, few organelles, end walls from sieve plates
- Companion cells help the sieve cells with their functions using plasmodesmata which allow molecules to pass between cells
What are the properties of stem cells?
- Self renewal (make copies of themselves)
- Differentiate (make other types of specialised cell)
What are totipotent stem cells?
- Has the potential to form any and every type of human cell
- Found in a fertilised egg cell
What happens when a fertilised egg cell divides?
- Eventually certain genes will be turned on that a specific to a cell function
- When becoming specialised, only the relevant gene will be translated from the DNA
What are pluripotent stem cells?
- Have the ability to differentiate into almost any type of cell
- Can form all tissue types but not whole organisms
- Found only in embryos
What are multipotent stem cells?
- Have the ability to differentiate into a limited number of specialised cell types
- Can only form a range of cells within a certain type of tissue
- Found in bone marrow (e.g.)
What cells are
derived from a common stem cell in bone
marrow?
- Erythrocytes
- Neutrophils
What are examples of distinct, differentiated
outcomes derived from a common stem cell in
meristems?
- Xylem vessels
- Phloem sieve tubes
What is meristematic tissue?
- Contains plant stem cells where the plant is growing
- Found between phloem and xylem tissue and at the tips of roots and shoot
- Contains dividing cells which can differentiate
How can stem cells be used in medicine?
- Can be transplanted into any area of the body that needs new healthy growth and they’ll adapt
- Adaptation of stem cells and the following growth stimulates more new healthy growth which replaces or repairs damage or illness in the area
- This can cure disease and improve quality of life
What are the ethics associated with stem cells?
- Objection to using stem cells
- Destruction of embryo
- Religious objections as some believe that life begins at conception
- Embryo has rights
- Ownership of genetic material
Where could stem cells be gathered from?
- Embryos left over from fertility treatment or abortions that were going to be discarded anyway
- Embryos are now created to supply stem cells
