Biology Chapter 10: Cell Biology and Development

Introduction to Embryonic Development

• A multicellular organism develops from a single cell (the zygote) into a collection of diverse cell types, organized into tissues and organs.
• Development involves cell division, body axis formation, tissue and organ development, and cell differentiation (acquiring a specific cell type identity).
• During development, cells use both intrinsic (inherited) information and extrinsic (neighboring cell signals) to determine their behavior and identity.
• Cells become progressively more restricted in their developmental potential (the kinds of cell types they can become) as development progresses.

Embryonic Stages

• Zygote (fertilized egg): a single-celled structure.
• 2-celled zygote: cleavage begins after fertilization.
• 4-celled zygote: further cell division.
• Morula: a solid mass of cells.
• Blastula: a hollow ball of cells with a fluid-filled cavity (blastocoel).
• Gastrula: a three-layered embryo with a developing gut (archenteron).
• Neurula: an embryo with a neural tube developing.
• Organogenesis: formation of organs from the respective germ layers.

Gametogenesis

• The process of forming gametes (sperm and ova).
• Undergoes meiosis, undergoing chromosomal and morphological changes to produce mature haploid gametes.
• Spermatogenesis (in testes): leads to sperm production.
• Oogenesis (in ovaries): leads to ovum production.

Common Terms

• Animal pole: the pole of the egg with the least yolk concentration.
• Animal hemisphere: the hemisphere of the egg containing the animal pole.
• Vegetal pole: the pole of the egg with the most yolk concentration.
• Vegetal hemisphere: the hemisphere of the egg containing the vegetal pole.

Fertilization

• The fusion of two gametes (sperm and ovum) to form a zygote.
• Involves several steps, including sperm-egg contact, sperm entry, and fusion of the nuclei.
• Results in combining of genes from both parents- creating a new organism.

Cleavage

• A series of rapid mitotic cell divisions of the zygote to form a multicellular structure (morula).
• Blastomeres are the cells produced during cleavage, becoming increasingly smaller with each division.
• The type and pattern of cleavage differentiate between species.

Blastulation

• The production of a multicellular blastula as a result of cleavage.
• Blastomeres (cells) within the blastula arrange to form a hollow ball (blastula) with a fluid-filled cavity (blastocoel).

Gastrulation

• Rearranges the blastula's cells, creating a three-layered (triploblastic) embryo called a gastrula.
• The gastrula features a primitive gut (archenteron), and cell movements (invagination, ingression).

Neurulation

• The formation of the neural tube in chordates (animals with a notochord).
• Ectodermal cells form a neural plate, which then sinks and forms a neural groove; the groove edges then fuse to create the neural tube.
• The anterior end of the neural tube becomes the brain and the posterior end becomes the spinal cord.

Organogenesis

• The formation of organs from the three germ layers (ectoderm, endoderm, and mesoderm).
• The process involves differentiation of embryonic stem cells into more specialized cell types.
• Signaling cascades guide the differentiation process.
• Ectoderm, involved in nervous and epidermal systems
• Mesoderm, involved in circulatory, musculoskeletal, excretory, and reproductive systems
• Endoderm, involved in digestive and respiratory systems

Cell Injury

• Cells facing stress or injury may undergo changes, classified as reversible or irreversible cell injury (death).
• Causes include oxygen deprivation, physical agents, chemical agents, infections, immunologic reactions, genetic defects, and nutritional imbalances.
• Important targets for injury include aerobic respiration, cell membranes, protein synthesis, cytoskeleton, and the genetic apparatus.

Cell Death

• Necrosis: tissue death by enzymatic digestion of damaged cells, involving inflammation.
• Apoptosis: programmed cell death that occurs during development and in response to certain signals, causing no inflammation.

Apoptosis

• A programmed form of cell death characterized by morphological changes.
• Involved in development, removal of damaged cells, and maintaining a healthy cell population.
• Regulated by a cascade of molecular events (e.g., caspase activation).

Autophagy

• A regulated process for removing damaged proteins and organelles within cells under certain conditions (e.g., starvation).
• Involves the formation of autophagosomes, which then fuse with lysosomes for degradation.

Homeotic Genes (Hox Genes)

• Master regulator genes that control the development of body segments or structures.
• Mutations in Hox genes can significantly alter body plan development.
• Crucial role in specifying the identity of different body regions.

Metamorphosis

• A transformation in the body form and characteristics of organisms during their development.
• Complete metamorphosis: egg -> larva -> pupa -> adult (e.g., butterfly).
• Incomplete metamorphosis: egg -> nymph -> adult (gradual changes, e.g., grasshopper).

Cell Signaling

• Cells communicate via chemical signals (ligands).
• Signaling involves ligand binding to receptors initiating a chain of events inside the target cell(signal relay pathways).
• Different pathways involving phosphorylation or second messengers relay signals.
• Types of signaling include paracrine, autocrine, endocrine, and juxtacrine.

Membrane Proteins

• Integral proteins span the membrane with hydrophobic regions and often coiled within.
• Plays roles in transportation (channels and pumps), receptors for signal reception, and enzymes localized at the membrane.
• Additional roles include cell-cell recognition and linking to the cytoskeleton.

Cell Junctions

• Structures that connect cells providing contact, adherence, interactions, and communication, both in plants (plasmodesmata) and animals (tight junctions, desmosomes, and gap junctions).
• Cell walls and ECM play supporting roles.

Plasma Membrane

• A selectively permeable boundary separating the internal and external environments of a cell.
• Composed of a phospholipid bilayer with hydrophobic tails and hydrophilic heads.
• Also includes proteins and carbohydrates.
• Fluid nature allows flexibility in the membrane.

ECM (Extracellular Matrix)

• Extracellular structural components found outside the cell membrane.
• In animals, it's made up of proteins like collagen, elastin, and fibronectin along with proteoglycans (large molecules with specific carbohydrates and proteins)
• Provide mechanical support to cells, help with cell adhesion and migration processes, and play a signaling role.

Transport Across Membranes

• Simple diffusion: movement of substances down their concentration gradient- passive, no energy required
• Facilitated diffusion: passive movement of substances through specific membrane proteins, no energy required.
• Active transport: movement of substances against their concentration gradient, requiring energy (ATP).

This quiz covers key concepts in cell biology and organogenesis, focusing on processes such as phagocytosis, endocytosis, and the roles of different cell types in embryonic development. Participants will explore the significance of growth factors and the distinctions between various cellular mechanisms. Additionally, the quiz addresses morphological changes during organogenesis.