Cell specialisation and differentiation Flashcards
Stem Cells
Unspecialised cells which have the potential to form more specialised different cells
Benefits of cell specialisation
- Can perform functions more efficiently
- Cells can develop into specific sizes and shapes which are beneficial
- Cells can create only certain proteins needed for specific metabolic reactions.
Differentiation
When different cell types express different genes
What causes cells to specialise in an embryo?
Morphogens, specifically Retinoic acid
What are morphogens?
Signalling molecules which direct cell fate in a concentration - dependant way
How does Retinoic acid specialise cells?
- Certain inducing cells in embryo release morphogen
- Other cells recieve it and it causes certain genes to be expressed
- Cells further from the source have lower rates of differentiation.
Stem cell niches
Areas within adults where a pool of stem cells are kept in preparation for future differentiation and proliferation
Examples of stem cell niches?
Bone marrow, hair follicle
What stem cells do the bone marrow store?
Haemopoietic stem cells which make blood cells
What stem cells do the hair follicle store?
Epidermal stem cells which repair wounds and control sporadic bursts of hair growth.
Totipotent
Can differentiate into any type of cell. e.g. first eight cells of morula
Pluripotent
Can differentiate into all body cells, but not placenta or umbilical cord etc. e.g. inner cell mass of blastocyst
Multipotent
Can differentiate into a few closely related cells in the body
Unipotent
Can only differentiate into associated cell type e.g. liver stem cells.
Liver stem cells
Can repair itself with liver stem cells, but they are unipotent
How do sperm cells’ sizes help with function
long, narrow, small volume, reduces resistance - easy movement
How do egg cells’ sizes help with function
large, spherical, large volume, can store lots of food reserves
How do red blood cells’ sizes help with function
small size and shape - can pass through capillaries
biconcave, high SA:Vol - lots of haemoglobin can be stored and faster transport of oxygen
How do white blood cells’ sizes help with function
B - lymphocytes grow 3X their size when activated
How do cerebellar granule cells’ sizes help with function
small cell body, long pair axons extended in cerebullar cortex. Small volume allows cerebellum to accomodate lots of these at once
How do motor neurons’ sizes help with function
Long axons can pass signals from CNS to distant muscles
Large size allows enough protein synthesis to maintain long axon
How do striated muscle fibres’ sizes help with function
larger cells allow fibre to exert greater force and contract by greater length than other muscle fibres
What is the ideal SA:Vol ratio for cells and why?
High SA:Vol ratio, so they remain small because if ratio is too small nutrients and waste products cannot be exchanged from the cell fast enough.
Different adaptations to increase SA:Vol ratio
- cells dividing instead of infinetly growing
- Tissue surfaces have folds (villi) while cells have membranous extentsions (microvilli) to increase SA
- Cells that are flat and long (squamous) have higher SA relative to Vol
Examples of cells specialised for material transport and their adaptations for high SA:Vol
Red blood cells - biconcave shape - increases SA, no nucleus - more haemoglobin can be stored
Tubule cells (cells in kidney where selective reabsorption happens) - cells have microvilli - increased SA - more efficient nutrient uptake
Pneumocytes
Cells that line alveoli and make up majority of inner lung surface
How are pneumocytes type 1 and 2 adapted for their functions?
Type 1 - involved in gas exchange between alveoli and capillaries - squamous shape - reduced diffusion distance - cells connected by occluding junctions, which prevents fluid leakage into alveolar space
Type 2 - Secretes pulmonary surfactant, which reduces surface tension in alveoli - cuboidal in shape - have folds - have granules called lamellar bodies to store surfactants
Adaptations of cardiac muscle cells + location
- Within heart tissue - responsible for beating
- Branching which allows faster signal transmission and 3D contractions
- small, narrow, rectangular
- Cells connected by gap junctions which allows electrical conduction between cells
Adaptations of striated muscle fibres + location
- connected to bones and is responsible for voluntary movement (locomotion)
- Multiple nuclei and continuous plasma - made from fusion of cells
- long cylindrical fibres
- Packed together in strands to form muscle bundle
Adaptations of sperm cells
- Small, motile, only donates male haploid nuclus to zygote
- 3 parts - head, mid-piece and flagellum
- Head contains male haploid nucleus, acrosome cap which contains hydrolitic enzymes to penetrate egg, and paired centrioles needed for division of zygote
- Mid-piece contains many mitochondria to produce ATP for movement
- Flagellum made of axoneme which bends to move
Adaptations of egg cells
- large, non motile and donates all organelles and cytoplasm to zygote
- Zona pellicuda - outer layer made of glycoprotein matrix which is a sperm barrier
- Corona radiata - external follicular cells which provide nourishment
- Contains cortical granules which release contents once fertilised to prevent multiple sperm binding
