1.1 Cell Introduction Flashcards
What are the 3 main 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
What are 3 examples of cells/tissues that do not conform to cell theory?
- striated muscle fibres
- aseptate fungal hyphae
- giant algae
What component of cell theory do striated muscle fibres not conform to ?
Challenges the idea that cells always function as autonomous units
How doe s a striated muscle fibre challenge cell theory?
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
How does aseptate fungal hyphae challenge cell theory?
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
What component of cell theory does aseptate fungal hyphae challenge?
Challenges the idea that living structures are composed of discrete cells
How does giant algae challenge cell theory?
Certain species of unicellular algae may grow to very large sizes (e.g. Acetabularia may exceed 7 cm in length)
What component of cell theory does giant algae challenge?
Challenges the idea that larger organisms are always made of many microscopic cells
What 7 characteristics are all living organisms capable of carrying out?
- metabolism
- reproduction
- sensitivity
- homeostasis
- excretion
- nutrition
- growth
Define metabolism
Living things undertake essential chemical reactions - a total of all the chemical reactions that take place within an organism
Define reproduction
Living things produce offspring, either sexually or asexually
Define sensitivity
Living things are responsive to internal and external stimuli
Define homeostasis
Living things maintain a stable internal environment
Define excretion
Living things exhibit the removal of waste products
define nutrition
iving things exchange materials and gases with the environment
define growth
Living things can move and change shape or size
Give an example of a unicellular heterotroph
paramecium
Explain how paramecium show sensitivity
Paramecia are surrounded by small hairs called cilia which allow it to move
Explain how paramecium show nutrition
Paramecia engulf food via a specialised membranous feeding groove called a cytostome
Explain how paramecium show metabolism
Food particles are enclosed within small vacuoles that contain enzymes for digestion
Explain how paramecium show excretion
Solid wastes are removed via an anal pore, while liquid wastes are pumped out via contractile vacoules
Explain how paramecium shows homeostasis
Essential gases enter (e.g. O2) and exit (e.g. CO2) the cell via diffusion
Explain how paramecium reproduce
Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation
Give an example of a unicellular autotroph
scenedesmus
Explain how scenedesmus shows nutrition/excretion
Scenedesmus exchange gases and other essential materials via diffusion
Explain how scenedesmus shows metabolism
Chlorophyll pigments allow organic molecules to be produced via photosynthesis
Explain how scenedesmus shows reproduction
Daughter cells form as non-motile autospores via the internal asexual division of the parent cell
Explain how scenedesmus shows responsiveness/sensitivity
Scenedesmus may exist as unicells or form colonies for protection
What is important in the limitation of cell size?
Surface area to volume ratio is important in the limitation of cell size
What do cells need to do to survive?
Cells need to produce chemical energy (via metabolism) to survive and this requires the exchange of materials with the environment
What is the rate of metabolism affected by?
The rate of metabolism of a cell is a function of its mass / volume
(larger cells need more energy to sustain essential functions)
What is the rate of material exchange affected by?
The rate of material exchange is a function of its surface area
(large membrane surface equates to more material movement)
How does the SA:VOL ratio change with increasing cell size?
As a cell grows, volume (units3) increases faster than surface area (units2), leading to a decreased SA:Vol ratio
What will happen if the metabolic rate exceeds the rate of exchange of vital materials and wastes?
If metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:Vol ratio), the cell will eventually die
How doe cells prevent the SA:VOL ratio becoming to low?
Hence growing cells tend to divide and remain small in order to maintain a high SA:Vol ratio suitable for survival
What type of cells/tissue would be adapted to have a bigger SA:VOL ratio?
Cells and tissues that are specialised for gas or material exchanges will increase their surface area to optimise material transfer
How is intestinal tissue adapted to increase SA:V ratio?
Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface area of the inner lining
How are alveoli adapted to increase SA:V ratio?
Alveoli within the lungs have membranous extensions called microvilli, which function to increase the total membrane surface
How does light microscopy work?
Light microscopes use visible light and a combination of lenses to magnify images of mounted specimens
What can be seen/looked at with a light microscope?
Living specimens can be viewed in their natural colour, although stains may be applied to resolve specific structures
What can be seen in bacteria w/ a light microscope?
- cell wall (if stained)
- flagella (if stained)
- ~1-10μm
What can be seen in a protist with a light microscope?
- nucleus
- pseudopodia
- food vaculoes
- ~50 - 500μm
What can be seen in a plant cell with a light microscope?
- nucleus
- chloroplasts
- cell wall
- ~10 - 100 μm
What can be seen in an animal cell with a light microscope?
- nucleus
- mitochondria (only if stained)
- ~10-50μm
When do emergent properties arise?
Emergent properties arise when the interaction of individual component produce new functions
How do multicellular organisms differ from unicellular organisms differ and how?
Multicellullar organisms are capable of completing functions that unicellular organisms could not undertake – this is due to the collective actions of individual cells combining to create new synergistic effects
What do cells join together to form?
Cells may be grouped together to form tissues
What do tissues join together to form?
Organs are then formed from the functional grouping of multiple tissues
What do organs work together to form?
Organs that interact may form organ systems capable of carrying out specific body functions
What do organ systems work together to form?
Organ systems collectively carry out the life functions of the complete organism
What is differentiation?
Differentiation is the process during development whereby newly formed cells become more specialised and distinct from one another as they mature
What do all cells of an organism share?
share an identical genome i.e each cell contains the entire set of genetic instructions for that organism
What causes cells to differentiate?
The activation of different instructions (genes) within a given cell by chemical signals will cause it to differentiate
What occurs in the nucleus of a eukaryotic cells to form chromatin?
DNA is packaged with proteins to form chromatin
How are active genes packaged?
packaged in an expanded form called euchromatin that is accessible to transcriptional machinery
How are inactive genes packaged?
Inactive genes are typically packaged in a more condensed form called heterochromatin (saves spaces, not transcribed)
Will differentiated cells have same regions of DNA packaged the same way?
NO
differentiated cells will have different regions of DNA packaged as eurochromatn and heterochromatin according to their specific function
What ability does a cell lose when it becomes specialised?
When a cell differentiates and becomes specialised, it loses its capacity to form alternative cell types
What type of cells are stem cells?
unspecialised cells
What 2 key properties do stem cells have?
- Self Renewal – They can continuously divide and replicate
2. Potency – They have the capacity to differentiate into specialised cell types
What are the 4 main types of stem cell?
totipotent
pluripotent
multipotent
unipotent
What does it mean if a stem cell is totipotent?
– Can form any cell type, as well as extra-embryonic (placental) tissue (e.g. zygote)
What does it mean if a stem cell is pluripotent?
Can form any cell type (e.g. embryonic stem cells)
What does it mean if a stem cell is multipotent?
– Can differentiate into a number of closely related cell types (e.g. haematopoeitic adult stem cells)
What does it mean if a stem cell is unipotent?
Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells)
What role do stem cells play in embryonic development?
Stem cells are necessary for embryonic development as they are an undifferentiated cell source from which all other cell types may be derived
What role do stem cells in therapeutic medicine?
Cell types that are not capable of self-renewal (e.g. amitotic nerve tissues) are considered to be non-stem cells
As these tissues cannot be regenerated or replaced, stem cells have become a viable therapeutic option when these tissues become damaged
What 4 things does the process of stem cell therapy need?
- the use of biochemical solutions
- surgical implantation
- impression of host immune system
- careful monitoring of new cells
Why does stem cell therapy need biochemical solutions?
to trigger the differentiation of stem cells into the desired cell type
Where are the cells surgically implanted in stem cell therapy?
Surgical implantation of cells into the patient’s own tissue
Why must the host’s immune system be suppressed in stem cell therapy?
to prevent rejection of cells (if stem cells are from foreign source)
Why do cells need to be carefully monitored in stem cell therapy?
Careful monitoring of new cells to ensure they do not become cancerous
What are 6 examples of stem cell therapy? (diseases used to treat)
- stargardt’s disease
- parkinson’s disease
- leukemia
- paraplegia
- diabetes
- burn victims
What type of disease is stargardt’s disease?
An inherited form of juvenile macular degeneration
What does stargardt’s disease cause?
causes progressive vision loss to the point of blindness
What causes stargardt’s disease?
Caused by a gene mutation that impairs energy transport in retinal photoreceptor cells, causing them to degenerate
how can stargardt’s disease be treated?
Treated by replacing dead cells in the retina with functioning ones derived from stem cells
What is parkinson’s disease?
A degenerative disorder of the central nervous system caused by the death of dopamine-secreting cells in the midbrain
What is dopamine?
Dopamine is a neurotransmitter responsible for transmitting signals involved in the production of smooth, purposeful movements
What type of symptoms do people with Parkinson’s disease exhibit, due to the lack of dopamine?
Consequently, individuals with Parkinson’s disease typically exhibit tremors, rigidity, slowness of movement and postural instability
how can parkinson’s disease be treated?
Treated by replacing dead nerve cells with living, dopamine-producing ones
How can leukemia be treated using stem cell therapy?
Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy
How can stem cell therapy be used to treat paraplegia?
Repair damage caused by spinal injuries to enable paralysed victims to regain movement
How can stem cell therapy be used to treat diabetes?
Replace non-functioning islet cells with those capable of producing insulin in type I diabetics
How can burn victims be treated using stem cell therapy?
Graft new skin cells to replace damaged tissue
What 3 sources can stem cells come 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)
What are three ethical considerations associated with the therapeutic use of stem cells?
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
How can stem cells be artificially derived? 2 ways
Stem cells can be artificially generated via NUCLEAR TRANSFER or NUCLEAR REPROGRAMMING, with distinct benefits and disadvantages
What does somatic cell nuclear transfer (SCNT) involve?
Involves the creation of embryonic clones by fusing a diploid nucleus with an enucleated egg cell (therapeutic cloning)
What ethical concerns are raised with SCNT?
More embryos are created by this process than needed, raising ethical concerns about the exigency of excess embryos
What does nuclear reprogramming involve?
Induce a change in the gene expression profile of a cell in order to transform it into a different cell type (transdifferentiation)
What ethical consideration is involved with nuclear reprogramming?
Involves the use of oncogenic retroviruses and transgenes, increasing the risk of health consequences (i.e. cancer)
What is an advantage of SCNT?
stem cells produced which are indistinguishable from embryo-derived cells
What is an advantage of nuclear reprogramming?
Stem cells autologous to adult donor
