B2.3 cell specialization Flashcards
Describe the process of cell specialization by differentiation, giving a specific example
zygote
Cells are differentiated as some genes are expressed but not others. This happens when the concentration of morphogens (signal molecules) increases or decreases, where the gradient (in morphogen concentration) affects the genes expressed in different parts of the embryo.
Low ——- High concentration
A AB ABC Gene expressed
Properties of stem cells (2)
- Divide endlessly (able to self-renew), where either/both daughter cells may be differentiated, or remain as a stem cell.
- Differentiate across different pathways, able to create functional tissues
e.g. plant cells containing stem cells in regions of meristematic tissue near root and stem tips
2 locations of stem cell niches in humans and their functions
Hair follicles - Large numbers of epithelial stem cells found in the bottom, rounded area of a hair follicle. These stem cells are multipotent and are involved in hair growth, skin and hair follicle regeneration, and the production of oil-producing glands
Bone marrow - hematopoietic stem cells (stem cells that can differentiate into all type of blood cells) are found alongside self-renewing stem cells.
Differentiated blood cells produced - carried away by blood vessels - cycle repeats
Order totipotent, pluripotent and multipotent in increasing ability to produce different types of cells
multipotent, pluripotent, totiplutent
Compare and contrast totipotent, pluripotent, and multipotent cells.
Totipotent:
- Only lasts 4-6 days early in embryo stage
- Can produce any tissue in an organism, also can produce an organism
Pluripotent:
- Only lasts 4-6 days in embryo stage
- Can produce most but not all tissue in an organism, but not an organism
Multipotent:
- Exists after embryo in adult stage
- Can produce a limited number of cell types
How does SA:V ratio constrain cell size?
SA increases at a slower rate than V of a cell. SA increases by a factor involving squaring the radius whereas V increases by a factor involving cubing the radius.
Hence a large cell compared to a smaller cell, has a comparatively less SA to bring in needed materials for life processes and get rid of waste materials.
Cells that are too large do not have enough SA to get rid of waste.
2 examples of adaptations to increase SA:V ratio in cells.
Erythrocytes (red blood cells):
- biconcave disc shape = greater SA:V
- the small size + flexibility of RBC allows it to squeeze through small capillaries.
- other adaptations: contain the protein haemoglobin to combine with/release oxygen
Proximal convoluted tubules:
- cube shaped cells packed closely together to increase space efficiently
- tiny microvilli projections facing the lumen of the cell to increase SA:V
- large no. of mitochondria for active transport of ions and other substances
- channels on the side of the cell opposite to the lumen to increase surface area to help in transport
Adaptations of type I pneumocytes
Type I:
- cover 95% of the alveolar surface
- allows for gaseous exchange between alveoli and capillaries.
- thin and flat - increase SA and decrease diffusion distance.
- shared basement membrane with endothelium lining of capillaries - minimal distance for diffusion of respiratory gases
- tightly joined to one another so that fluids do not enter the capillaries
Adaptions of type II pneumocytes
Type II:
- produce pulmonary surfactant to reduce surface tension and prevent collapse and sticking of alveoli when breathing
- Cube shaped - larger cytoplasmic area for organelles producing surfactant
- microvilli oriented towards alveolar sac - increase SA for surfactant secretion
- Many organelles in cytoplasm involved in surfactant production and secretion
- Can transform into type I when needed
Adaptations of striated skeletal and cardiac muscle fibres.
Striated skeletal:
- fibres PARALLEL
- multinucleated
- membrane capable of impulse propagation, allowing for VOLUNTARY control over the large muscle fibre
- visible bands capable of shortening to produce voluntary movement
Cardiac:
- fibres BRANCHED
- Single nucleus per fibre
- connected at the ends by intercalated discs
- INVOLUNTARY movement
- bands capable of shortening
- The heart also has straited muscle fibres
Compare and contrast sperm and egg cells (6 differences, 1 similarity)
Sperm:
- One of the smallest human cells
- Flagellum for mobility, mitochondria to produce energy for flagellum
- Shape has a head and tail, streamlined for speed and efficiency
- Very few cytoplasmic organelles (RER, ER, Golgi apparatus, ribosomes)
- Continually produced in vast numbers in the male life cycle
- Head has specialised secretory vesicle called the acrosomal vesicle that contains enzymes to help sperm penetrate the egg’s outer coat
- Contains a haploid nucleus
Egg:
- One of the largest human cells
- Cell is not mobile
- Spherical, not streamlined
- Most cytoplasmic organelles present, along with specialised storage structures for initial embryo development
- All early gamete-forming cells present before birth, no new egg-forming cells produced after birth
- Has special secretory vesicles under the plasma membrane that release their contents after sperm penetration, preventing other sperms from entering
- Contains a haploid nucleus
