1.1 Introduction to Cells

• Cell Theory:

  1. All living things are composed of cells
  2. The cell is the smallest unit of life
  3. Cells only arise from other cells
• Exceptions to Cell Theory:

  1. Giant Algae (visible to the naked eye, up to 10cm unicellular organism)
  2. Aseptate Fungi (does not have cell wall or division)
  3. Skeletal striped muscle (cells are fused together and are multi-nucleated)
• MRS SHENG: Metabolism, Reproduction, Sensitivity, Homeostasis, Excretion, Nutrition, Growth
• Paramecium is a unicellular heterotrophic protist with membrane bound organelles. It is covered in cilia hairs which are an example of sensitivity and can also assist directing food into the vacuole. They also contain water vacuoles which maintain homeostasis.
• Scenedesmus are autotrophic unicellular protists which produce energy through photosynthesis.
• Cells that don't excrete waste efficiently can burst.
• Stem cells are unspecialised cells.
• The 2 main characteristics of stem cells is that they are capable of self renewal and are potent.
• Potency is the ability to differentiate into different cells
• Totipotent stem cells are the most potent type of stem cell and can form any cell type as well as placental tissue.
• An example of totipotent cells is a zygote.
• Pluripotent stem cells are the 2nd most potent type of stem cell and can form any cell type.
• An example of pluripotent cells are embryos.
• Multipotent stem cells are the 2nd least potent form of energy and can differentiate into closely related cells.
• An example of multipotent stem cells are haematopoietic adult stem cells.
• Unipotent stem cells are the least potent form of stem cell and cannot differentiate but are capable of self-renewal.
• An example of unipotent stem cells are progenitor cells and muscle stem cells.
• Stargardt's Disease is an inhereted condition where a gene mutation impairs energy transport in retinal photoreceptor cells. It can be treated by replacing dead cells with healthy stem cells.
• Leukemia/blood cancer can be treated by stem cells with a bone marrow transplant post chemotherapy.
• Stem cell therapy is the process of replacing damaged or diseased cells with healthy steam cells derived from the embryo, umbilical cord or adult tissue.
• Ethical concerns with stem cells include the destruction of life if using embryos, expensive and inaccessible storage costs if using umbilical cords and limited availability and application if using adult tissue.
• Somatic Cell Nuclear Transfer (SCNT) is the process of creating embryonic clones by fusing a diploid nucleus with enucleated egg cell. However, there is a major ethical concern that it leads to excess embryos.
• Nuclear reprogramming is the process of changing the profile of a cell through transdifferentiation. However, there are concerns it could lead to cancer.
• In cells Surface Area to Volume Ratio increases exponentially. Larger volume cells with smaller surface areas take longer to access materials and excrete them.
• 1mm = 1000 um
• Emergent properties are the collective actions on individual cells combining to create new synergistic effects. For instance, cells may be group together in tissues which form organs etc.
• All cells in an organism share an identical genome. The activation of different genes will cause it to differentiate in function.
• In the nucleus, DNA is packaged with proteins to form chromatin.
• Active genes are usually packaged in an expanded form called euchromatin so it is accessible for transcription.
• Inactive genes are usually packaged in a condensed form called heterochromatin to save space since they're not transcribed.
• Heterochromatin is dark o diagrams of a nucleus.
• Euchromatin is light on diagrams of a nucleus.