Cell Biology

• Cell theory states:

  • Cell is the smallest unit of life (Organelles cannot survive alone & carry out different functions)
  • Cells only arise from pre-existing cells (Cells multiply through division. All life evolved from simpler ancestors)
• Mitosis & Meiosis are processes of cell division
• Metabolism is the web of all enzyme-catalyzed reactions in a cell/organism
• Response means living things can respond to & interact with the environment
• Nutrition involves feeding by either synthesis of organic molecules or absorption of organic matter
• Excretion is the removal of metabolic waste
• Reproduction is when living things produce offspring either sexually or asexually
• Growth means living things can grow or change size or shape
• Homeostasis is the maintenance and regulation of internal cell conditions
• A larger surface area to volume ratio in cells allows for more efficient nutrient intake and waste removal, shorter diffusion pathways, easier concentration gradient generation, but can lead to heat loss in small warm-blooded animals and rapid water loss in desert plants with flat leaves
• Ways to maximize the surface area to volume ratio:

  • Cells divide to avoid inefficiency in large cells, allowing for cell differentiation, specialized functions, and more complex multicellular life
  • Cells compartmentalize using membranes to carry out metabolic processes (organelles), increasing the surface area for reactions
  • Some organs fold up to maximize surface area to volume ratio for efficient absorption of food (e.g., intestines)
  • Alveoli are thin membranes that maximize surface area for gas exchange
  • Roots have long branches with root hairs to maximize surface area for water uptake
• The rate of metabolism is proportional to Mass/Volume, while the rate of material exchange is proportional to Surface Area/Volume. As a cell increases in size, the ratio decreases. If the metabolic rate exceeds the rate of material exchange, the cell will die, so cells must constantly divide to maintain a viable surface area to volume ratio
• Cell exceptions (E): 

  • Striated muscle (aka fibres)
  •  > 1 nucleus per cell, fibres can be v long & are surrounded by a single plasma membrane but are multinucleated. (E is one nucleus per cell)
  • Aseptate fungal hyphae
  • > 1 nucleus, v large, continuous cytoplasm
  • Tubular system of hyphae form mycelium
  • Cell walls composed of chitin (E is no divisions btw cells)
  • Giant algae
  • Single-celled organism that is gigantic in size & complex
  • Has 3 anatomical parts
  • Bottom rhizoid (resembles roots & contains nucleus)
  • Long stalk
  • Top umbrella of branches that fuse into a cap
• Emergent properties arise from the interaction of component parts
• Multicellular organisms can perform functions that individual cells could not do because the interaction between cells produces new functions
• All specialised cells are formed from differentiation, which is the process by which a less specialised cell undergoes maturation to become more distinct in form and function
• Stem cells are unspecialised cells that can:

  • Continuously divide & replicate
  • Differentiate into specialised cell types
• All diploid cells of an individual organism share an identical genome, meaning each cell contains the entire set of genetic instructions for that organism
• In totipotent embryonic stem cells, the entire genome is active, while newly formed cells receive signals that deactivate (rarely activate) genes
• • Totipotent: differentiate into any type of cell
  • Pluripotent: differentiate into many types of cells
  • Multipotent: differentiate into a few closely-related types of cells
  • Unipotent: differentiate into their associated single cell type (can also regenerate)
• Active genes ≈ packaged in an expanded & accessible form (euchromatin), while inactive genes are ≈ packaged in a condensed form (heterochromatin). ↓ active genes → ↑ specialised. As a result of gene expression, cell differentiation begins: cells metabolism & shape Δ to carry out specialised func. 
• Stargardt’s macular dystrophy:

  1. Problem

  • Recessive genetic condition
  • Causes an active transport protein on photoreceptor cells to malfunction → cell degeneration → prod of dysfunctional protein that cannot perform E transport → progressive & eventual complete loss of central vision.

  1. Treatment 

  • Embryonic stem cells are treated to divide & differentiate to become retinal cells (cells are injected into retina) → retinal cell attach to retina → central vision ↑ as there are ↑ functional retinal cells

  1. Future

  • Uncertain cus still in development
• Leukaemia:

  1. Problem

  • Blood/ Bone marrow cancer → v high levels of poorly functioning white blood cells

  1. Treatment 

  • Hematopoietic stem cells (HSCs) are harvested from bone marrow, peripheral/ umbilical cord blood. Chemo & radio used to destroy all white blood cells. HSCs transplanted back into bone marrow & they differentiate to form new, healthy white blood cells

  1. Benefit

  • Use of patients own HSCs → ↓ immune rejection risk
• Stem cell sources:

  • Embryo
  • Cord blood
  • Adult
• Extraction ease:

  • Embryo: Can be obtained from excess embryos from IVF
  • Cord blood: Easily obtained & stored but limited amount available
  • Adult: Difficult to obtain because they are very few and buried in deep tissues
• Ethics:

  • Embryo must be destroyed
  • Cord blood is thrown away at birth even if left unharvested
  • Adults can give consent for cells to be extracted
• Growth potential:

  • Embryo: Almost unlimited growth potential (totipotent)
  • Cord blood and Adult stem cells have lower growth potential compared to embryonic stem cells
• Tumour risk:

  • Embryo: Higher risk of tumour development
  • Cord blood and Adult stem cells have a lower risk of tumour development
• Differentiation:

  • Embryo: Totipotent
  • Cord blood: Can only naturally divide into blood cells with limited differentiation capacity
  • Adult stem cells' differentiation capacity depends on the source tissue with limited differentiation capacity
• Genetic damage:

  • Embryo and Cord blood have lower genetic damage risk compared to adult stem cells
  • Adult stem cells have a higher risk due to the accumulation of mutations over time
• Compatibility:

  • Embryonic stem cells are not genetically identical to the patient
  • Cord blood and Adult stem cells are fully compatible because they are genetically identical
• E- microscope > light microscope (EM has shooter λ → ↑ resolution). Ultrastructure is all the struc of a of a biological specimen that are ≥ 0.1 nm in their smallest dimension. Light microscopes let us see the struc of cells. EM lets us see the ultrastructure of cells. EM can see viruses but LM cannot. 
• Ultrastructure of E.Coli (typical prokaryote):

  • Cell wall (peptidoglycan layer that protects & maintains cell shape)
  • Plasma membrane (phospholipid layer w embedded proteins that control entry & exit of substances)
  • Pili (protein filaments that facilitate adhesion & conjugation)
  • Ribosome (70s)
  • Nucleoid (region containing a single, free, circular strand of DNA)
  • Plasmid (Independent, small circle of DNA)
  • Flagella
• Prokaryotes repro asexually using binary fission.

  Process:

  1. DNA is replicated
  2. 2 loops of DNA attach to membrane
  3. Membrane elongates & pinches off (cytokinesis) forming 2 separate cells
  4. 2 daughter cells are genetically identical
• Compartmentalise advantages:

  • Efficiency of metabolism (enzyme & substrate can localise → ↑ conc)
  • Localised conditions (optimal factors [pH] for one process in one part of cell)
  • Toxic/ dmg substances isolated (digestive enzymes stored in lysosome)
  • No. & locations of organelles can be changed depending on cells req
• Nucleus:

  • Spherical with two membranes and pores present
  • Contains genetic information in chromosome form, which can be uncoiled into chromatin
  • mRNA is transcribed in the nucleus before protein synthesis and leaves via pores
• Mitochondria:

  • Has two membranes (smooth outer and folded inner), with folds known as cristae
  • Varies in shape and is the site of ATP production by aerobic respiration
  • Can digest fat if it is used as an energy source
• Free ribosomes:

  • 80s ribosomes are larger than ribosomes found in prokaryotes
  • No membrane, involved in protein synthesis
• rER (rough endoplasmic reticulum):

  • Made up of flattened membrane sacs called cisternae, located close to the nucleus
  • Has 80s ribosomes attached to the outside of cisternae
  • Synthesizes proteins for transport via vesicles to the Golgi apparatus for modifications before secretion outside the cell
• Vesicles:

  • Single membrane with fluid inside, used to transport materials inside the cell
  • Very small in size