B2.3: Cell Specialization Flashcards
What is fertilization?
Multistep process where sperm and egg fuse -> zygote -> embryo (mitosis)
Occurs in sexually reproducing organisms that produce haploid gametes (ex: plant and animals)
What is cell specialization?
Cell specialization allows cells to preform a function with increased efficiency (shape and size, creating protein, etc.)
What are embryonic stem cells?
Cell in the zygote/embryo that are unspecialized cells
As cells of embryo continue to divide -> specialize into structures and gain function
Explain differentiation during embryonic development
Positon of cell in embryo -> determines how it differentiates
Gradients of signaling chemicals (morphogens) impact gene expression -> differentiation of cell
- morphogens -> signaling molecules that determine the function of a cell by its concentration (more v less will have different genes activated)
- Retinoic acid = morphogen
-> results in different cells in different postions
They control -> proliferation, differentiation, patterning during embryonic development to orchestrate formation of tissue and organs
What are stem cell niches? What is their function?
The specific location/tissues a stem cell remains in in the human body
(Ex: epithelial skin cell and hair follicle stem cell (niche); blood cells and bone marrow (niche))
Function:
Presence of stem cells -> all that tissue to regenerate and repair
In niches -> cells get physical and chemical signals that interact/integrate to influence the fate of the stem cell
Niches give protection and symbols
Conditions can all stem cells to remain undifferentiated/dormant for many years
What are the different types of stem cells?
Totipotent (entirely potential)
Pluripotent (many potentials)
- induced pluripotent cells (adult cells reprogrammed to form pluripotent stem cells)
Multipotent (multi potentials)
Unipotent (one potential)
What are the characteristics of a totipotent stem cell?
Can differentiate into any type of cell
Only found in embryos up to 16 cell stage
Can also differentiate into placenta cells
(Ex: found in zygotes)
What are the characteristics of pluripotent stem cells?
Can differentiated into any type of cell in an embryo
- just no placenta
(Ex: found in inner cell mass of a blastocyst)
What are the characteristics of a multipotent stem cell?
Can differentiated into a few closely related types of cells
(Pre-partially differentiated)
(Ex: found in adult stem cells (bone marrow cells -> RBC, WBC, platelets etc.)
What are the characteristics if unipotent stem cells?
Can regenerate but only differentiate their associated cell type
(Ex: heart muscle cells can generate new heart muscle cells (cardiomyocyte) but nothing else)
Give examples of:
Cell type
Their size
And the benefit of their size specialization
(Sex cells and blood cells)
Sperm cell:
50 micrometers with flagellum (5x3 micrometers body)
- faster/more efficient movement
- narrow head -> reduce resistance
- no organelle except mitochondria for energy -> volume minimization
Egg cell:
120 micrometer
- stores materials and nutritional reserve needed for development of embryo
- mitochondria for energy -> growth
RDC/erythrocyte:
6-8 micrometers, 1 micrometer thick
- small+flexible -> fit through capillaries
- biconcave shape -> SA:V high
WBC (B-lymphocyte):
Inactive -> 10 micrometers, active (infection) -> 30 micrometers
- extra volume -> increase in RERs and Golgi’s used to make and secrete antibodies
Give examples of:
Cell type
Their size
And the benefit of their size specialization
(Neuron and muscle)
Cerebellum neuron cell:
Small body -> 4 micrometers, long narrow axons -> up to 3000 micrometer
- muscle control (interneurones that function in the integration of sensory info and motor activity)
- small -> densely packed (3/4 of the brains neurons)
Motor neuron cell:
Large body -> 20 micrometers, long narrow axon up to 1 meter
- base of spinal chord -> toes
- rapid transmission of info across long distances
- large cell body -> many organelles to synthesize protein for electrical impulses and neurotransmitters to signal receiving cell
Striated muscles fiber cell:
Long -> 10cm and narrow -> 20-100 micrometer (cylindrical)
- generate force and contact -> movement
- long and narrow -> good for contraction
Why is a low SA:V ratio bad for cells?
Cells to survive -> metabolic processes -> rely on materials being constantly exchanged across plasma membranes
Metabolic requirement rely on the volume/mass of cytoplasm (where reaction takes place) -> larger volume higher metabolic needs and vice versa
Cell increase in size -> SA:V decrease (less surface area in relation to volume)
Increase in volume -> increase cell metabolic requirements -> lower ability to carry out these metabolic reactions
How does SA:V ratio limit cell size?
Single celled organisms -> high SA:V ratio
- survive by exchanging substances with environment by simple diffusion
- metabolic requirements low
- SA large enough to allow sufficient absorption for nutrients and secretion of waste
- small volume -> diffusion distance short
Larger cells-> lower SA:V ratio
- at some point ratio too low to survive using only diffusion at cell surface
- metabolic requirements higher
- SA doesn’t increase at the same rate as metabolic requirements -> not high enough rate of exchange with environment
- large volume -> diffusion distance longer -> substance cannot diffuse quick enough to get to needed organelles
This means…
Ratio too low -> growth stops -> divide -> multicellular organisms
Multicellular organisms have evolved to have adaptations to help exchange:
- gas exchange systems
- digestive systems
- efficient transport of substance in the body (circulatory system)
What are 3 adaptations that can increase SA:V ratio?
1) microvilli
Proximal convoluted tubule (PTC) of kidney nephron -> absorbs useful molecules from blood before kidney remove waste products
Cell lining tubules ->have microvilli to max. rate of absorption
2) invagination (folding back to form a cavity)
Biconcave shape of RBC -> max. SA:V ratio -> optimum absorption of oxygen
3) flattening
Pneumocytes in alveoli -> flattened to max. SA for gas exchange -> increase SA:V ratio
