1.1 - Introduction to Cells Flashcards
Principles of Cell Theory
- All living things are composed of cells (or cell products)
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
Striated muscle fibres
Challenges the idea that cells always function as autonomous units
- Muscle cells fuse to form fibres that may be very long (>300mm)
- Consequently, they have multiple nuclei despite being surrounded by a single, continuous plasma membrane
Aseptate fungal hyphae
Challenges the idea that living structures are composed of discrete cells
- Fungi may have filamentous structures called hyphae, which are separated into cells by internal walls called septa
- Some fungi are not partitioned by septa and hence have a continuous cytoplasm along the length of the hyphae
Giant Algae - Acetabularia
Challenges the idea that larger organisms are always made of many microscopic cells
- Certain species of unicellular algae may grow to very large sizes
- Acetabularia may exceed 7 cm in length
Functions of Life
Metabolism
Reproduction
Sensitivity
Homeostasis
Excretion
Nutrition
Growth
MR SHENG
Paramecium - Sensitivity
Paramecia are surrounded by small hairs called cilia which allow it to move
Paramecium - Nutrition
Paramecia engulf food via a specialised membranous feeding groove called a cytostome
Paramecium - Metabolism
Food particles are enclosed within small vacuoles that contain enzymes for digestion
Paramecium - Excretion
Solid wastes are removed via an anal pore, while liquid wastes are pumped out via contractile vacoules
Paramecium - Homeostatis
Essential gases enter (e.g. O2) and exit (e.g. CO2) the cell via diffusion
Paramecium - Reproduction
Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation
Scenedesmus - Nutrition and Excretion
Scenedesmus exchange gases and other essential materials via diffusion
Scenedesmus - Metabolism
Chlorophyll pigments allow organic molecules to be produced via photosynthesis
Scenedesmus - Reproduction
Daughter cells form as non-motile autospores via the internal asexual division of the parent cell
Scenedesmus - Sensitivity
Scenedesmus may exist as unicells or form colonies for protection
Rate of metabolism
a function of its mass / volume - larger cells need more energy to sustain essential functions)
Rate of material exchange
a function of its surface area - large membrane surface equates to more material movement)
SA:V Ratio and Intestinal tissue
Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface area of the inner lining
SA:V Ratio and Alveoli
Alveoli within the lungs have membranous extensions called microvilli, which function to increase the total membrane surface
Calculation of Magnfication
Magnification = Image size (with ruler) ÷ Actual size (according to scale bar)
Calculation of Actual Size
Actual Size = Image size (with ruler) ÷ Magnification
Visible Features on Microscope Image of Bacteria - E. coli
Cell wall - if stained
Flagella - if stained
~ 1-10 micrometres
Visible Features on Microscope Image of Protist - Ameoba
Nucleus
Pseudopodia
Food vacuoles
~ 50-500 micrometres
Visible Features on Microscope Image of Plant Cell - Leaf
Nucleus
Chloroplast
Cell wall
~ 10-100 micrometres
Visible Features on Microscope Image of Animal Cell - Cheek
Nucleus
Mitochondria - only if stained
~ 10-50 micrometres
Emergent properties
Metabolism
undertake essential chemical reactions
Reproduction
produce offspring, either sexually or asexually
Sensitivity
responsive to internal and external stimuli
Homeostasis
maintain a stable internal environment
Excretion
exhibit the removal of waste products
Nutrition
exchange materials and gases with the environment
Growth
move and change shape or size
Differentiation
is the process during development where newly formed cells become more specialised and distinct from one another as they mature
Active gene
usually packaged in an expanded form called euchromatin that is accessible to transcriptional machinery
Inactive genes
typically packaged in a more condensed form called heterochromatin (saves space, not transcribed)
Qualities of stem cells
Self Renewal – They can continuously divide and replicate
Potency – They have the capacity to differentiate into specialised cell types
Types of Stem Cells
Totipotent, pluripotent, multipotent, and unipotent
Totipotent
Can form any cell type, as well as extra-embryonic (placental) tissue (e.g. zygote)
Pluripotent
Can form any cell type (e.g. embryonic stem cells)
Multipotent
Can differentiate into a number of closely related cell types (e.g. haematopoeitic adult stem cells)
Unipotent
Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells)
Process of stem cells replacing damaged cells
- The use of biochemical solutions to trigger the differentiation of stem cells into the desired cell type
- Surgical implantation of cells into the patient’s own tissue
- Suppression of host immune system to prevent rejection of cells (if stem cells are from foreign source)
- Careful monitoring of new cells to ensure they do not become cancerous
Stargardt’s Disease (what, caused by, treatment with stem cells)
- An inherited form of juvenile macular degeneration that causes progressive vision loss to the point of blindness
- Caused by a gene mutation that impairs energy transport in retinal photoreceptor cells, causing them to degenerate
- Treated by replacing dead cells in the retina with functioning ones derived from stem cells
Parkinson’s Disease (what, caused by, treatment with stem cells)
- A degenerative disorder of the central nervous system caused by the death of dopamine-secreting cells in the midbrain (Dopamine is a neurotransmitter responsible for transmitting signals involved in the production of smooth, purposeful movements)
- Individuals with Parkinson’s disease typically exhibit tremors, rigidity, slowness of movement and postural instability
- Treated by replacing dead nerve cells with living, dopamine-producing ones
Leukaemia and treatment with stem cells
Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy
Paraplegia and treatment with stem cells
Repair damage caused by spinal injuries to enable paralysed victims to regain movement
Diabetes and treatment with stem cells
Replace non-functioning islet cells with those capable of producing insulin in type I diabetics
Burn victims and treatment with stem cells
Graft new skin cells to replace damaged tissue
Stem cells derived from…
- Embryos (may be specially created by therapeutic cloning)
- Umbilical cord blood or placenta of a new-born baby
- Certain adult tissues like the bone marrow (cells are not pluripotent)
Ethical considerations of stem cell therapy
- Using multipotent adult tissue may be effective for certain conditions, but is limited in its scope of application
- Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising issues of availability and access
- The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism
Somatic cell nuclear transfer (SCNT) for artificial stem cells
- Involves the creation of embryonic clones by fusing a diploid nucleus with an enucleated egg cell (therapeutic cloning)
- More embryos are created by this process than needed, raising ethical concerns about the exigency of excess embryos
Nuclear reprogramming for artificial stem cells
- Induce a change in the gene expression profile of a cell in order to transform it into a different cell type (transdifferentiation)
- Involves the use of oncogenic retroviruses and transgenes, increasing the risk of health consequences (i.e. cancer)
