B2.3 Cell Specialisation Flashcards
B2.3.1 Formation of zygote and embryo
Fertilization is the fusion of a male and female gamete to produce a single cell (zygote).
The zygote divides by mitosis to form an embryo composed of genetically identical cells.
B2.3.1 How do unspecialized embryo cells develop into specialized cells?
Embryo grows, cells develop along different pathways and differentiation occurs.
B2.3.1 Gene expression in cell differentiation
When a gene is switched on and the information in it is used to make a protein/other gene product = expressed.
Cell differentiation happens because a different sequence of genes is expressed in different cell types.
B3.2.1 How does cell position effect differentiation during Embryonic Development?
Position of a cell within the embryo determines how it differentiates.
Gradients of signaling chemicals (morphogens) impact gene expression and consequently the differentiation of the cell.
B3.2.1 What is retinoic acid (Morphogen) and what role does it play in embryonic development?
Retinoic acid = morphogen important roles in cell growth, differentiation, organ/tissue development.
Diffuses throughout the embryo switching genes on and off and imparting different cell fates depending on its concentration.
B2.3.2 Properties of stem cells
Can divide repeatedly and endlessly.
Capable of differentiating along different pathways.
B3.2.3 Location and function of stem cell niches in adult humans
An area of a tissue that provides a specific microenvironment, in which stem cells are present in an undifferentiated state and maintained for proliferation and differentiation.
B3.2.3 Bone marrow
Haemopoietic stem cells are located within the bone marrow, give rise to the different types of blood cells.
Bone marrow transplants restore the haemopoietic stem cell niche after leukemia chemotherapy.
B3.2.3 Hair Follicles
The hair follicles contain a range of epidermal stem cells that are involved in cyclic bouts of hair growth, skin innervation and wound repair
B3.2.4 Totipotent stem cells
Early-stage embryos (morula= stem cells = totipotent.
Can differentiate into any type of cell including placental cells. Can give rise to a complete organism.
B3.2.4 Pluripotent stem cells
As embryonic stem cells commit to specific differentiation pathways, they transition into pluripotent stem cells. Can differntiate into all body cells but cannot develop into an entire organism (can’t form extra structures e.g. placenta).
Pluri = Plenty, but NOT the Placenta!
B2.3.4 Multipotent stem cells
Multipotent stem in the adult body only differentiate into several types of closely related mature cells.
E.g. Haematopoietic stem cells generate different types of blood cell, but not others.
B2.3.5 Cell Size as an aspect of specialisation - gametes
Sperm: 50μm long but narrow. Narrowness + small volume reduces resistance, allows swim more easily.
Egg: 110μm in diameter + spherical, largest volume. Allows large quantities of food reserves to be stored in the cytoplasm.
B2.3.5 Cell Size as an aspect of specialisation - red blood cells
6μm-8μm diameter but dent (1μm) middle. Small size + shape passage along narrow capillaries and gives a large SA:Vol, loading + unloading oxygen is faster.
B2.3.5 Cell Size as an aspect of specialisation - B-lymphocytes
10μm in diameter when inactive, enlarge up to 30μm if activated (antibody-secreting).
The extra volume is cytoplasm with rER and Golgi apparatuses for protein synthesis.
B2.3.5 Cell Size as an aspect of specialisation - cerebellar granule cells (brain)
Cell body is 4.0μm in diameter, but twin axons extend for about 3mm (3,000μm) in the cerebellar cortex. Small volume = cerebellum can house 50 billion.
B2.3.5 Cell Size as an aspect of specialisation - motor neurons
Cell body 20μm in diameter. Large size allows enough proteins to be synthesized to maintain the immensely long axon to carry signals from the central nervous system to distant body parts.
B2.3.5 Cell Size as an aspect of specialisation - striated muscle fibres
Larger than normal cells, lengths can exceed 100mm. Dimensions allow the fibre to exert greater force and contract by a greater length than smaller muscle cells.
B2.3.6 Surface area-to-volume ratio - Why is it important for metabolism?
Cells need to produce chemical energy (metabolism) to survive, requiring exchange of materials w/ the environment.
The rate of material exchange is a function of its surface area (large membrane surface equates to more material movement).
B2.3.6 Surface area-to-volume ratio - Changing metabolic rate
Cell grows, vol increases faster than SA, decreasing SA:Vol ratio. Harder for the cell to exchange nutrients + waste, so if metabolic demands exceed exchange rate, the cell dies from toxin buildup+energy shortage.
Growing cells tend to divide to maintain a high SA:Vol ratio.
B2.3.6 Surface area-to-volume ratio formula
surface area (mm2) / volume (mm3)
B2.3.7 Adaptations to increase surface
area-to-volume ratios of cells - red blood cells
Short diameter and biconcave shape reduce volume and minimize the distance from the cytoplasm to the plasma membrane, aiding rapid oxygen loading and unloading.
B2.3.7 Adaptations to increase surface
area-to-volume ratios of cells - Proximal convoluted tubule cells
Microvilli on the apical membrane and infoldings on the basal membrane increasing surface area. Allows more channel + pump proteins to efficiently reabsorb useful substances from the filtrate into the blood.
B2.3.8 Adaptations of type I pneumocytes in alveoli
Squamous (flattened) shape, very thin (~ 0.15µm) – minimising diffusion between alveoli and capillaries.
Thin bc diffusion = passive, little need mitochondria/ organelles.
Cells connected by occluding junctions, prevents leakage of tissue fluid into alveolar air space.
B2.3.8 Adaptations of type II pneumocytes in alveoli
Phospholipid synthesized in cytoplasm, stored in lamellar bodies (vesicles) with proteins -> exocytosis.
Alveolar moisture layer allows oxygen to dissolve + diffuse into the blood. Phospholipids form a surfactant layer, proteins stabilise it. Stops H20 mol. pulling together due to hydrogen bonding, reducing surface tension and preventing alveolar collapse.
B2.3.9 Adaptations of striated muscle fibres
Connect bones of the skeleton + responsible for locomotion (voluntary movement).
Long, cylindrical fibres formed, cell fusion. Fibres in muscle bundle (2-3cm).
Long fibers → Contract over a greater distance, generating more force.
Fascicle bundling → Distributes force effective + helps coordination.
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B2.3.9 Adaptations of cardiac muscle cells
Forms heart walls. Striated, short, mostly mononucleate. Intercalated discs connect branched cells, allowing rapid electrical signal transmission. This stimulus transmission ensures synchronized contraction, efficiently pumping blood.
B2.3.10 Adaptations of sperm cells: head
Streamlined shape – Minimal cytoplasm reduces resistance.
Haploid nucleus = paternal DNA for fertilization.
Acrosome cap = hydrolytic enzymes to digest protective zona pellucida, allowing penetration.
Receptors for ZP3 glycoproteins – Enable sperm binding to egg. Binding proteins then help fuse sperm and egg membranes for nucleus entry.
B2.3.10 Adaptations of sperm cells: mid-piece and tail
Mid-piece packed w/ mitochondria -> Produces ATP to power tail movement.
Paired centrioles are essential for the first cell divisions of the zygote, as egg cells lack them.
Tail (Flagellum) has Axoneme (microtubule structure) – Allows bending + movement, sperm swim to egg.
B2.3.10 Adaptations of egg cells: structures that enable them to receive one sperm
Zona pellucida – Glycoprotein layer w/ ZP3 for sperm binding; later chemically alters to block more sperm.
Binding proteins in PM aid fusion w/ sperm mem, allowing nucleus entrance.
Cortical granules – Enzyme-filled vesicles that make the zona pellucida impenetrable after fertilization.
