1.1 Introduction to cells Flashcards
Cell theory
Cell theory
- Living organisms are composed of cells (or cell products)
- The cell is the smallest unit of independent life
- Cells can only arise from pre-existing cells
Cell theory
Exceptions to cell theory
- Striated muscle – composed of fused cells that are multinucleated
- Giant algae – unicellular organisms that are very large in size (~7 cm)
- Aseptate hyphae – lack partitioning and have a continuous cytoplasm
Functions of life
Functions of life
Organisms consisting of only one cell carry
out all the life functions in that single cell.
* Metabolism
* Reproduction
* Sensitivity
* Homeostasis
* Excretion
* Nutrition
* Growth
Cell size
Cell size
Cells need to exchange materials with the environment in order to produce the chemical energy required for survival (via metabolism)
The rate of metabolism is a function of a cell’s mass / volume
* The rate of material exchange is a function of a cell’s surface area
As a cell grows, volume increases faster than surface area
* If metabolic requirements exceed material exchange, a cell will die
* Hence, cells must stay small or increase their SA:Vol ratio to survive
Cell size
Small SA:Vol Ratio
⇧ metabolic rate
⇩ material exchange
Low survival chances
Ccell size
Large SA:Vol Ratio
⇩ metabolic rate
⇧ material exchange
High survival chances
Magnification
Calculating Magnification (MIA)
Magnification = Image Size ÷ Actual Size
Magnification
Calculating Actual Size (AIM)
Actual Size = Image Size ÷ Magnification
Microscopes
Light microscopes
Use lenses to bend light
* Can view living specimens in natural colour
* Have lower magnification and resolution
Microscopes
Electron microscopes
Use electromagnets to focus electrons
* Can only view dead specimens in monochrome
* Have higher magnification and resolution
* Can show cross-sections (TEM) or surface renderings (SEM)
Cellular Organization
In multicellular organisms
- Cells may be grouped together to form tissues
- Tissues may interact to form functional organs
- Organs may combine to form body systems
Emergent Properties
What are emergent properties?
A function that is present in multicellular organisms, but is not present in its individual component cells.
Emergent properties arise from synergistic interactions between
the individual cells to produce entirely new aggregate functions
An example of an emergent property is the increased levels of
antibiotic resistance that can be seen in bacterial biofilms
Stem cells
What are stem cells and what qualtites do they have?
Stem cells are unspecialised cells that have two key qualities:
1. Self-Renewal – They can continuously divide and replicate
2. Potency – They have the capacity to differentiate
Stem cells
Main types of stem cells
Totipotent
Pluripotent
Multipotent
Unipotent
Stem cells
Totipotent
Can form any cell type, as well as extra-embryonic tissue
Stem cells
Pluripotent
Can form any cell type (e.g. embryonic stem cells)
Stem cells
Multipotent
Can differentiate into closely related cell types
Stem cells
Unipotent
Cannot differentiate, but are capable of self-renewal
Stem cells
Stem Cell Therapy
Stem cells can replace damaged or diseased cells with healthy ones
Stem cells
Therapeutic use of stem cells
Harvesting stem cells from appropriate sources
* Using biochemical solutions to trigger cell differentiation
* Surgically implanting new cells into patient’s own tissue
* Suppressing the host immune system to prevent rejection
* Monitoring new cells to ensure they do not become cancerous
Stem cells
Therapeutic use of stem cells examples
Example → Condition → Treatment
Stargardt’s disease → Macular degeneration → Replace defective retinal cells
Parkinson’s disease → Death of nevre tissue → Replace damaged nerve cells
Lukemia → Cancer of blood →Replacement of bone marrow
Ethics of stem cell use
Embryo
High growth potential (pluripotent)
Higher tumor risk
Can be generated artificially by SCNT
Requires destruction of the embryo
(results in the loss of a potential life)
Ethics of stem cell use
Umbilical Cord Blood
Low growth potential Low (multipotent)
Lower tumor risk
Easily obtained and stored / preserved
Cells must be stored from birth at cost
(raises issues of financial accessibility)
Ethics of stem cell use
Adult Tissue
Low growth potential(multipotent)
Lower tumor risk
Invasive to extract
May be restrictions in scope / availability
Differentiation
Differentiation
All cells of an organism contain an identical genome – each cell
contains the entire set of genetic instructions for that organism
Differentiation involves the expression of some genes and not
others in the cell’s genome (i.e. selective gene expression)
The activation of different genes within a given cell will cause it
to develop differently from other cells
Gene Packaging
Gene Packaging
Within the nuclei of eukaryotic cells, gene instructions
(DNA) are packaged with proteins as chromatin
* Active genes are loosely packed as euchromatin
* Inactive genes are packed tight as heterochromatin
