Cell specialisation and differentiation

• What is cell specialisation?

  In multicellular organisms, cells are specialised to carry out different functions. Instead of every cell doing everything, each cell becomes specialised in a specific task.

  Cells can also create proteins needed to carry out specific metabolic reactions.
• What is a stem cell?

  They are able to develop into different types of specialised cells. There is no limit to the number of times a stem cell can divide. There are four main types
• What is a totipotent stem cell?

  Totipotent- Can become any body cell, including placenta (entirely potential). A zygote (plant and animal) is an example of a totipotent stem cell.
• What is a pluripotent stem cell?

  Pluripotent- Can become any body cell, excluding placenta (many potentials). The inner mass of a blastocyst (the stage at which the embryo becomes a hollow ball of cells) is pluripotent. Meristems of plants also contain pluripotent stem cells, the SAM (shoot apical meristem) and the RAM (root apical meristem) are responsible for the plant's longitudinal growth, the RAM at the root, and the SAM at the tip. Adult stem cells, which are multipotent, may be reprogrammed to form pluripotent stem cells, which are known as induced pluripotent stem cells (iPSC). they are typically derived from skin or blood cells, and may be used in treatment.
• What is a multi-potent stem cell?

  Multipotent- Can become multiple related cell types despite being partially differentiated (multiple potentials). Adult stem cells, which are also present in foetuses and children, are multipotent.
• What is a unipotent stem cell?


  Unipotent- Can become one cell type
• What is cell differentiation?

  Cell differentiation is the process where cells develop into specialised types, and this happens when certian genes are turned on and off (gene expression). This gives cells their unique features. Size and shape of cells are essential for their function, as a cell's surface area to volume ratio affects ow well it can take in nutrients and remove waste.
• What is gene expression?

  Gene expression is the process by which the information encoded in a gene is turned into a function. Often in gene expression, a sequence of DNA (the gene) is transcribed to form RNA which is then translated to form a protein.
• What is a stem cell niche?

  Adult stem cells are located in what are known as stem cell niches. Stem cell niches receive physical and chemical signals that interact and integrate to influence the fate of the stem cell. Sometimes the conditions allow the stem cells to remain undifferentiated for years. However in other cases, the conditions of the stem cell niche allow the adult stem cells to begin to differentiate and divide rapidly. This typically occurs in instances such as tissue injury or disease.
• What is the hematopoietic stem cell niche?

  The hematopoietic stem cells are found in the hematopoietic stem cell niche in bone marrow. It is a multi-potent adult stem cell, and may form RBCs, platelets and immune cells. The hematopoietic stem cell niche provides protection to the stem cells and provides the physical and chemical signals necessary for the cells to differentiate.
• What is the hair follicle stem cell niche?

  Epithelial skin cells (melanocytes and keratinocytes) originate from the same type of pluripotent adult stem cell known as the hair follicle stem cell. This hair follicle stem cell is located in the hair follicle stem cell niche, which is found in a bulge region of a hair follicle. The niche provides protection to the stem cells, alongside the physical and chemical signals necessary for the cells to differentiate into different types of skin cells.
• What is the size of the human sperm cell?

  Long (50 micrometres) and narrow with a strong flagellum for propulsion.
• What are some benefits of the specialisation of the human sperm cell?

  Adapted to reduce resistance as the cell moves towards the egg DNA in the nucleus is tightly packed, so volume is minimised for transport. It is narrow as it does not contain ribosomes, ER or Golgi. They contain many mitochondria, which are efficiently placed to best power the flagellum Flagellum tail propels the sperm to the egg, allowing it to burrow through the egg coat
• What is the function of the human sperm cell?

  To deliver DNA to an egg cell during sexual reproduction
• What is the size of the human egg cell?

  Large (110 micrometres) and spherical
• What are the benefits of specialisation of the human egg cell?

  Several times larger than a typical body cell, and around 10000 times larger than sperm cells, allowing storage of essential nutritional reserves large cells are the result of unequal division of cytoplasm during cytokinesis
• What is the function of the human egg cell?

  To store all of the materials and nutritional reserves needed for initial development of the embryo
• What is the size of the human RBC?

  Biconcave disc with a width of 6-8 micrometres and a thickness of 1 micrometre
• What are the benefits of specialisation of the human RBC?

  Able to fit through narrow capillaries as they are small and flexible Contains lots of haemoglobin and no nucleus, in order to carry out its function of transporting oxygen High surface area to volume ratio allowing faster loading and unloading of oxygen
• What is the function of the human RBC?

  To load and unload oxygen, transporting it through narrow capillary vessels and other arteries and veins
• What is the size of the B-Lymphocyte (WBC)?

  Small when inactive (10 micrometres) but increase in size to 30 micrometres during active infection
• What are the benefits of specialisation of the B-lymphocyte?

  Activation during infection increases cell size, which is due to the increase in rough ER and Golgi which make and secrete antibody proteins
• What is the function of the B-Lymphocyte?

  To produce and secrete antibodies- proteins that inactivate pathogens
• What is the size of the cerebellum neuron cell?

  Small body of 4 micrometres, with long, narrow axons extending to 3000 micrometres
• What are the benefits of specialisation of the cerebellum neuron cell?

  Small volume allows the brain to densely pack them, they are the most numerous neurons in the brain
• What is the function of the cerebellum neuron cell?

  To control and regulate muscle control, including balance and movement, functioning in the integrations of sensory information and motor activity
• What is the size of the motor neuron cell?

  Large cell body of 20 micrometres with a long narrow axon extending to 1000000 micrometres (around a metre)
• What are the benefits of the specialisation of the motor neuron cell?

  Longest axons in the body that can stretch from the base of the spinal chord to the toes, allowing rapid transmission of information large cell body contains many organelles for the synthesis of proteins needed to transmit electrical impulses
• What is the function of the motor neuron cell?

  To send information from the CNS to the muscles and glands
• What is the size of the striated muscle fibre cell?

  long (100000 micrometres), narrow (20-100 micrometres) and cylindrical
• What are some benefits of specialisation of the striated muscle fibre cell?

  Long, narrow dimensions allow for greater length of contraction Multinucleation supports the synthesis of large amounts of proteins and enzymes necessary for repair, maintenance, and contraction.
• What is the function of the striated muscle fibre cell?

  To generate force and contract in order to cause movement
• What is fertilization?


  Fertilization occurs in sexually reproducing organisms that produce haploid gametes (a reproductive cell that contains only one set of chromosomes) such as plants and animals. It is a multi-step process in which a sperm and egg fuse to form a single cell. This is a zygote. The cells in the zygote are unspecialised stem cells.

  The zygote then divides by mitosis to form an embryo composed of genetically identical cells. The cells are still unspecialised stem cells, but when the cells continue to divide, they begin to specialise in structure and function.
• What is a morphogen and how do they work?

  Morphogens are signalling molecules that influence the fate of cells based on their concentration gradients within the developing embryo. These molecules are secreted by a group of cells (a source) and diffuse through surrounding tissues, establishing a concentration gradient that provides positional information to cells close to them.

  After fertilization, the zygote begins to divide and form a multicellular embryo. Morphogens are distributed in gradients across the embryo, and the concentration of these molecules at different locations within the embryo acts as a signal for cells to activate or repress specific genes. These may be known as morphogenic fields.

  The gradient allows cells to "sense" their position within the developing embryo and respond accordingly. For example, cells that are exposed to high concentrations of a morphogen may activate different genes than those exposed to lower concentrations of the same morphogen.

  Morphogens not only provide spatial information but also regulate the timing of gene expression during development. Temporal control ensures that the correct genes are activated at the right developmental stage.

  Morphogen gradients are also regulated by feedback mechanisms that help maintain stability and prevent disruption of the patterns of gene expression.
• What is an example of a morphogen?

  Retinoic acid is a morphogen that plays important roles in cell growth, differentiation and organ development. Retinoic acid diffuses throughout the embryo, switching genes on and off and imparting different cell fates depending on its concentration.
• What is the surface area of the cell?

  The surface area is the lipid bilayer of the cell membrane, which regulates exchange of materials into and out of the cell

  Oxygen gas and nutrient molecules must be absorbed, and waste products must be eliminated through the cell membrane.
• What is the volume of a cell?

  The internal regions of the cell is what is known as the volume. Many metabolic reactions occur in the volume, which require gases and chemical nutrients, producing waste.
• What is surface area to volume ratio and how does it affect the cell?

  To calculate ratio, divide the SA by the V

  The larger the volume, the smaller the SA/V ratio- large volumes require more metabolic nutrients and waste to be transported via the SA, and there is a larger distance for the molecules to diffuse to it.

  The smaller the volume, the larger the SA/V ratio- the smaller volume requires fewer metabolic nutrients and waste to be transported via the SA, and there is less distance for the molecules to diffuse to it.

  As cells grow larger, the internal volume increases and the cell membrane (surface area) expands. The volume increases more rapidly then the surface area does, so the amount of surface area relative to the volume - the SA/V ratio decreases. Eventually the SA can no longer serve the requirements of the cell, which stimulates cell division.
• What is the cube model and what are some strengths and weaknesses of it?

  Cubes are typically used to model SA/V ratios- models are representations of and idea, an object, a process or a system that is used to describe and explain phenomena. Whiles cubes may be manipulated, visualised and easily measured in comparison to actual cells, most cells are not actually cubic so it may not be accurately representative.
• What are cytokines?

  Cytokines are signalling proteins that regulate immune cells like macrophages, and control inflammation. Higher cytokine levels suppresses inflammation more effectively