Cell Division, Cell Diversity And Cellular Organisation Flashcards
State what the cell cycle is and outline it’s stages
Regulated cycle of division with intermediate growth periods
1. Interphase
2. Mitosis or meiosis
3. Cytokinesis
Outline what happens during interphase
G1: cell synthesis proteins for respiration e.g. tubulin for spindle fibres and cell size doubles
S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere
G2: Organelles divide
What is the purpose of mitosis
Produces two genetically identical cells for:
• Growth
• Cell replacement / tissue repair
• Asexual reproduction
Name the stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Outline what happens during prophase
- Chromosomes condense, becoming visible. (X-shaped: two sister chromatids joined at a centromere)
- Centrioles move to opposite poles of the cell (animal cells) and mitotic spindle fibres form
- Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm
Outline what happens in metaphase
Sister chromatids line up at cell equator attached to the mitotic spindle by their centromeres
Outline what happens during anaphase
Requires energy from ATP hydrolysis
1. Spindle fibres contract = centromeres divide
2. Sister chromatids separate into two distinct chromosomes and are pulled to opposite ends of the cell (looks like V shapes facing each other)
3. Spindle fibres break down
What happens during telophase
- Chromosomes decondense, becoming visible again
- New nuclear envelope forms around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome
What happens during cytokinesis
- Cell membrane cleavage furrow forms
- Contractile division of cytoplasm
How is the cell cycle regulated
Checkpoints regulated by cell-signalling proteins ensure damaged cells do not progress to next stage of cycle
Cyclin-dependant kinase enzymes phosphorylate proteins that initiate the next phase of reactions
Describe what happens at each key checkpoint in the cell cycle
Between G1 and S, cell checks for DNA damage (e.g. via action of p53 - a gene that codes for a protein that checks the fidelity of the DNA)
Between G2 and M the cell checks the chromosome replication
At the metaphase checkpoint the cell checks that the sister chromatids are connected to the spindle properly
What is meiosis
Meiosis is a form of cell division that produces 4 genetically different haploid cells which only have half the number of chromosomes present
These are known as gamates
What happens during meiosis
- Homologous chromosomes pair to form bivalents
- Crossing over (the exchange of sections of genetic material) occurs at chiasmata
- Cell divides in two - homologous chromosomes seperate randomly to form two cells containing either the maternal or paternal copy of a gene
What are homologous chromosomes
Pair of chromosomes with genes at the same locus. 1 maternal and 1 paternal chromosome present
Some alleles may be the same but some may be different which gives variation
What happens during meiosis II
- Independent segregation of sister chromatids
- Each cell divides again which produces 4 haploid cells
How does meiosis produce genetic variation
Both crossing over during meiosis 1 and the independent assortment of homologous chromosomes and sister chromatids mix up the genes in a new way resulting in a new combination of alleles
How do cells become specialised
Some genes are expressed whilst others are silenced due to cell differentiation mediated by transcription factors
Cells produce proteins that determine their structure and function
What is a transcription factor
A protein that controls the transcription of genes so that only certain parts of the DNA are expressed e.g. in order to allow a cell to specialise
How do transcription factors work
Move from the cytoplasm into nucleus
Bind to promoter region upstream of target gene
Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases the rate of transcription
What is a stem cell
Undifferentiated cells that can divide indefinitely and turn into other cell types
Name and define the 4 types of stem cell
Totipotent - can develop into any type of cell including in the placenta and embryo
Pluripotent - can develop into any type of cell excluding in the placenta or embryo
Multipotent - can develop into only a few different types of cell
Unipotent - can only develop into one type of cell
Suggest some uses of stem cells
Repair of damaged tissue e.g.cardiomyocytes after myocardial infarction
Drug testing on artificially grown tissues
Treating neurological diseases e.g. Alzheimers or Parkinsons
Researching developmental biology e.g. formation of organs and embryos
Describe the 2 groups of specialised cells in blood
Erythrocytes (RBCs): biconcave, no nucleus, lots of haemoglobin to carry oxygen
Leucocytes (WBCs): Lymphocytes, eosinophils, neutrophils to engulf foreign material, monocytes
How do the specialised cells form in the blood
Multipotent stem cells in the bone marrow differentiate into:
Erythrocytes, which have a short lifecycle and cannot undergo mitosis since they have no nucleus
Leucocytes, including neutrophils
State the relationship between a system and specialised cells
Specialised cells —> tissues that perform specific function —> organs made of several tissue types —> organ systems
Describe the structure of squamous and ciliated epithelia
Simple squamous epithelium: single smooth layer of squamous cells (thin and flat with round nucleus) fixed in place by basement membrane
Ciliated epithelium: made of ciliated epithelial cells (column-shaped with surface projections that move in a synchronised pattern)
Describe the specialised structure of a spermatozoon
Specialised to fertilise an ovum during sexual reproduction in mammals
Haploid nucleus so fertilisation restores diploid chromosome number
Acrosome secretes enzymes to penetrate ovum coat
Spiral-shaped mitochondrion
Flagellum bound by plasma membrane propels cell
Describe the structure and function of palisade cells and guard cells in plants
Palisade cells: Specialised to absorb light energy for photosynthesis, so contain many chloroplasts. Pack closely together
Guard cells: From stoma. When turgid, stoma opens; when flaccid, stoma closes. Walls are thickened by spirals of cellulose
Describe the structure and function of root hair cells
Specialised to absorb water and low-concentration minerals from soil
Hair-like projections increase surface area for osmosis / carrier proteins for active transport
Many mitochondria produce ATP for active transport
What are meristems
Totipotent undifferentiated plants cells that can develop into various types of plant cell, including xylem vessels and phloem sieve tubes
Classified as apical (at root and shoot tips), intercalary (stem) or lateral (in vascular areas)
Describe the structure of phloem tissue
- Sieve tube elements: form a tube to transport sucrose in the dissolved form of sap
- Companion cells: involved in ATP production for active loading of sucrose into sieve tubes
Plasmodesmata: gaps between cell walls where the cytosplasm links, allowing substances to flow
Describe the primary cell types in xylem tissue
Vessel elements: lignified secondary walls for mechanical strength and waterproofing; perforated end walls for rapid water flow
Tracheids: tapered ends for close packing; pits for lateral water movement; no cytoplasm or nucleus
Describe the additional cell types in xylem tissue
Xylem parenchyma: packing tissue with thin walls transmit turgidity
Sclereids
Sclerenchyma fibres : heavily lignified to withstand negative pressure
Describe the structure of cartliage
Avascular smooth elastic tissue made of chondrocytes, which produce extensive extracellular matrix (ECM)
ECM mainly contains collagen and proteoglycan
3 categories: hyaline, yellow elastic, white fibrous (depends on ratio of cells: ECM)
Name the three muscles in the body and where they are located
Cardiac : exclusively in the heart
Smooth: walls of blood vessels and intestines
Skeletal: attached to incompressible skeleton by tendons
Describe the gross structure of skeletal muscle
Muscle cells are fused together to form bundles of parallel muscle fibres (myofibrils)
Arrangement ensures there is no point of weakness between cells
Each bundle is surrounded by endomysium: loose connective tissue with many capillaries
