Module 2.1.6 Cell Division, Cell Diversity & Cellular Organisms Flashcards
What is the role of mitosis & the cell cycle?
To produce 2 genetically identical daughter cells for growth & repair of tissues
Are cells produced from mitosis genetically identical or genetically different?
Identical
What are the different processes in the cell cycle?
Interphase
Mitosis
Cytokinesis.
What is interphase?
The stage which the chromosomes in the cells replicate & start to condense
What happens during interphase?
G1
S
G2
What happens during growth 1 (G1) of interphase?
Cell synthesises proteins for replication & the cell size doubles
What happens during S of interphase?
The DNA replicates -> the chromosomes consist of 2 sister chromatids joined at a centromere
What happens during growth 2 (G2) of interphase?
The organelles in the cell divide
What happens during growth 2 (G2) of interphase?
The organelles in the cell divide
What are the 4 stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase?
Chromosomes condense & become visible
Centrioles move to the opposite poles of the cell in animals cells & the mitotic spindle fibres form
The nuclear envelope & nucleolus break down so the chromosomes are free in the cytoplasm
What happens during metaphase?
The sister chromatids line up at the cell equator & attach to the mitotic spindle by their centromeres
What happens during anaphase?
The spindle fibres contract & the centromeres divide
The sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of the cell
The spindle fibres then break down
Does anaphase require energy or not?
Yes (requires ATP)
Does anaphase require energy or not?
Yes (requires ATP)
What happens during telophase?
The chromosomes decondense & become invisible again
A new nuclear envelope forms around each new set of chromosomes -> results in 2 new nuclei with 1 copy of each chromosome
What happens during cytokinesis?
A new cell membrane forms & the cytoplasm contractiley divides
How is the cell cycle regulated?
There are checkpoints that are regulated by cell-signalling proteins
Why must the cell cycle be regulated?
To ensure that damaged cells do not progress to the next stage of the cell cycle
What happens during the checkpoint between G1 & S of interphase?
The cell checks for DNA damage & after the restriction point the cell enters the cycle
What happens during the checkpoint between G2 & M of the cell cycle?
The cell checks the chromosomes have replicated properly
What happens during the metaphase checkpoint of the cell cycle?
The cell checks that the sister chromatids have attached to the spindle fibres correctly
What is meiosis?
A form of cell division which produced 4 genetically different haploid cells known as gametes
How many stages of meiosis are there?
2
What happens during meiosis 1?
Homologous chromosomes pair to form bivalents
Crossing over occurs as the chiasmata
The cell divides into 2. The homologous chromosomes separate randomly & each cell contains either the maternal or paternal copy of the chromosome
What are homologous chromosomes?
A pair of chromosomes with genes at the same locus consisting of 1 maternal & 1 paternal
What happens during meiosis 2?
There is independent assortment of sister chromatids & each cell then divides again -> produces 4 haploid cells
Is there genetic variation in the cells produced by meiosis?
Yes
How does meiosis produce genetic variation?
Crossing over during meiosis 1 & Independent assortment of homologous chromosomes & sister chromatids during meiosis 2 -> results in new combinations of alleles
How do cells become specialised?
Some genes are expressed while others are silenced due to cell differention by transcription factors
What are transcription factors?
A protein that controls the transcription of genes so that only some parts of the DNA are expressed so cells can become specialised
How do transcription factors work?
They move from the cytoplasm into the nucleus & bind to the promoter region upstream of the target gene. This makes it easier/more difficult for RNA polymerase to bind to the gene which increases/decreases the rate of transcription
What is a stem cell?
Undifferentiated cells that can divide indefinitely & turn into other specific cells types
What are the 4 types of stem cell?
Totipotent
Pluripotent
Multipotent
Unipotent
What are totipotent stem cells?
Stem cells that can divide & produce any type of body cell
Occur for a limited time in early mammalian embryos
Can only translate part of their DNA during development which results in cell specialisation
What are pluripotent stem cells?
Found in embryos & can become almost any type of cell
Usually used in research
What are multipotent stem cells?
Stem cells that can only develop into few different types of cells e.g. bone marrow
What are unipotent stem cells?
Stem cells that can only differentiate into one type of cell
What are the different sources of stem cells in mammals?
Embryos up to 16 days after conception contain pluripotent cells -> can differentiate into any type of cell
Umbilical cord blood contains multipotent cells (similar to adults)
Placenta -> multipotent stem cells that can develop into a limited number of specialised cells
Adult stem cells -> can produce different cells to repair those within a particular tissue/organ
What are some uses of stem cells?
Repairing damaged tissues
Drug testing on artificially grown tissues
Treating neurological diseases e.g. Alzheimer’s
Development biology research e.g. formation of organs
What are the 2 groups of specialised cells in the blood?
Erythrocytes (RBC)
Leukocytes (WBC)
What are the specialised features of erythrocytes (RBC)?
Biconcave, have no nucleus & have lots of haemoglobin to carry oxygen
What are some of the different types of Leukocyte (WBC)?
Lymphocytes
Eosinophils
Neutrophils -> engulf foreign bacteria
How do RBC & WBC form in the blood?
From multipotent stem cells in the bone marrow
What is the lifespan of an erythrocyte?
Short since they cannot undergo mitosis -> no nucleus
What is the relationship between a system & specialised cells?
Specialised cells -> tissues -> organs -> organ systems
What is differentiation?
The process by which stem cells become specialised
How are sperm cells specialised for sexual reproduction?
Tail/flagellum -> facilitates movement
Many mitochondria -> supplies energy for the sperm to swim
Acrosome on the head -> contains digestive enzymes. To digest the protective layer of ovum so the spem can penetrate it
Streamlined -> swimming
What are some plant cells that are specialised for their function?
Palisade cells
Root hair cells
Guard cells
How are palisade cells specialised for their function?
Contain:
Chloroplasts -> can move in the cytoplasm & contain chlorophyll (absorb more light for photosynthesis)
Rectangular shaped -> can be closely packed together -> maximises photosynthesis
Thin cell walls -> increases rate of Co2 diffusion
Large vacuole -> maintains turgor pressure (for structure & support) & stores water (photosynthesis)
How are root hair cells specialised for their function?
Root hairs -> increase surface area (absorb more water & minerals) & thin cell wall (easier osmosis of water/active transport of minerals)
Large vacuole -> stores more water & minerals
How are guard cells specialised for their function?
Stomata -> faster gas exchange (photosynthesis)
Thicker cells walls on one side (inside) -> stomata can form as the cell doesn’t change shape symmetrically
What are some different animal tissues that are specialised for their function?
Squamous epithelial cells
Ciliated epithelial cells
Cartilage
Muscles
How are squamous epithelial cells specialised for their function?
Very thin -> one cell thick to allow rapid diffusion across a surface e.g. the lungs
How are ciliated epithelial cells specialised for their function?
Cilia -> move in a rhythmic manner & waft mucus to be excreted
Goblet cells -> secrete mucus to trap unwanted particles to avoid them getting into the alveoli
How is cartilage specialised for its function?
Contains:
Fibres of proteins (elastin & collagen) -> firm yet flexible to prevent bones rubbing together
Chondrocyte cells -> embedded in extracellular matrix
How are muscles specialised to their function?
Skeletal muscle fibres (attached to bones) -> contains myofibrils that have contractile proteins
What are some examples of plant tissues that are specialised for their function?
Epidermis
Xylem & phloem tissues
How is the plant epidermis specialised for its function?
Closely packed cells to cover the plant’s surface -> waxy waterproof cuticle -> reduces water vapour loss
Contains guard cells
What is the function of the xylem vessel?
Transports water & minerals throughout plants
How is xylem tissue specialised for its function?
Elongated vessel elements made of dead cells
Thick cell walls that are strengthened with lignin -> sustains water pressure to maintain unilateral flow & provides structure & support
What is the function of the phloem vessel?
Transports assimilates (sucrose) throughout the plant
How is phloem tissue specialised for its function?
Columns of sieve tube cells
Perforated cell walls with sieve plates
What are meristems?
Totipotent undifferentiated plant cells that can develop into various types of plant cells (including xylem & phloem vessels)
Found at the root & shoot tips
