CELL BIOLOGY: 1.1 introduction to cells Flashcards
Cell Theory
- All organisms are made up of cells
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
Striated muscle fibres
- Muscle cells fuse to form fibres that may be very long (>300mm)
- Multinucleated fibres surrounded by a single, continuous plasma membrane
- Challenges the idea that cells always function as autonomous units
Aseptate fungal hyphae
- Have filamentous structures called hyphae, which are separated into cells by internal walls called septa
- Some fungi does not have cellular partitions and therefore has continuous cytoplasm along the hyphae
Unicellular Organisms
- Smallest organism capable of independent life
- Single cell that can carry all 7 life functions
Paramecium (heterotroph):
- Unicellular protozoa (eukaryotes)
- Usually less than 0,25mm in size
- Widespread in aquatic environments, specially in stagnant ponds (less oxygen)
- Heterotrophs: feed on food participles they find in their environment
-Challenges the idea that living structures are composed of discrete cells, that cell is a single unit
Giant Algae
- Large in size (eg: Acetabularia may exceed 7 cm in length)
- Challenges the idea that larger organisms are always made of many microscopic cells
Functions of Life: Mr. SHENG
- Metabolism: living things undertake essential chemical reactions
- Reproduction: living things produce offspring either sexually or asexually
- Sensitivity: living things are responsive to internal and external stimuli
- Homeostasis: living things maintain a stable internal environment
- Excretion: living things exhibit the removal of waste products
- Nutrition: living things exchange materials and gasses with the environment
SA:Vol Ratio
- The rate of metabolism of a cell is a function of its mass/volume
- Larger cells → more energy for sustaining essential functions
Surface area
- Determined by cell membrane
- Cell membrane regulates what goes in and out of the cell
- Large surface area → more exchange
Volume
- Determined by cytoplasm
- Most metabolic reactions take place in the cytoplasm
- Metabolic reactions require gases and chemical nutrients and produces waste products
SA vs Vol:
- The larger the cell → the larger the cell membrane + volume
- However volume increases more rapidly than surface area therefore decreasing SA:Vol
- If metabolic rate > rate of exchange → low SA:Vol → cell die
Who has a larger and a smaller SA:VOL ratio
- Small cells have a larger surface area → Molecules have a shorter distance to diffuse within the cell → more effective
- Large cells have smaller surface area → Within the cell molecules have a larger distance to diffuse → less effective
Magnification
For drawing microscopic structures:
- A title including the identity specimen: name of organism, tissue or cell
- Magnification or scale should be included to indicate relative size
- Identifiable structures should be labelled
Emergent properties
- Multicellular can complete functions that unicellular organism cannot
- The collective action of individuals cells combined creates new synergistic effects
Differentiation
- Process during development where newly formed cells become more specialised and distinct from one another as they mature
- All cells of an organism share an identical genome
- But the activation of certain genes within a given cell by chemical signals causes differentiation
Types of genes
- Active: Packaged in an expanded form called euchromatic , Accessible to transcriptional machinery
- Inactive: Packaged in a more condensed form called heterochromatin
This saves space and cannot be transcribed
Stem Cells
unspecialised cells with two key qualities:
- Self renewal - they can continuously divide and replicate
- Potency - they have the capacity to differentiate into specialised cells types
Types of Stem cells
Stem Cells Therapy
Stem cells are self-renewal so they can replace damaged or diseased cells with healthy, functioning ones
Ethical concerns of stem cell use
Derived from Embryos:
- Advantage: greatest yield of pluripotent stem cells
- Disadvantage: destruction of a potential living organism
Derived from umbilical cord blood of new-born babies:
- Disadvantage: need to be stored and preserved at cost, raising issues of availability and access
Derived from adult tissues (eg: bone marrow):
- Advantage: effective for certain conditions
- Disadvantage: limited in its scope of application and differentiate
