3 fertilisation/gastrulation

• When analysing markets, a range of assumptions are made about the rationality of economic agents involved in the transactions
• The Wealth of Nations was written

  1776
• Rational


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Producers act rationally by


  Selling goods/services in a way that maximises their profits
• Workers act rationally by


  Balancing welfare at work with consideration of both pay and benefits
• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit you get total utility
• Cleavage stages of the embryo (to blastocyst)

  Stages
• Mitosis is the process by which cells proliferate
• Cell cycle


  The orderly sequence of events by which a cell duplicates its contents and divides into two genetically identical cells
• Phases of the cell cycle

  • G0/G1/S/G2/M
• Robert Hooke discovered that a piece of cork was composed of cells
• Rudolf Virchow proposed the cell theory, that all living organisms are made up of basic units called cells
• Cells are the basic building blocks of all living things, from micro-organisms to humans
• There is only one way to make more cells - by the division of those that already exist
• Proliferation


  • Growth: Cells are produced so that multicellular organisms can grow
  • Replacement: Any cells in multicellular organisms that have been worn out or have been damaged need to be replaced by cellular division
• Renewable tissues


  Cells that die or are exported must be replaced
• Goal of the cell cycle

  To produce two genetically identical cells from one precursor cell
• Sequence of events in the cell cycle

  1. The cell duplicates its contents

  2. The cell physically divides in two
• Interphase


  G1/S/G2 phases
• Mitosis


  M phase
• Regulation of the cell cycle

  • Integration of external signals
  • Internal "clock" of the cell
  • Checkpoints to determine whether cells continue through the cycle, or enter the cell death pathway (apoptosis)
• G1 phase


  Longest period of the cell cycle, where the cell functions normally and protein and organelle synthesis occurs
• Cyclins and cyclin-dependent kinases (CDKs)


  Regulatory molecules that determine a cell's progress through the cell cycle
• G1/S phase control


  1. Cyclin D is produced, and binds to CDK4

  2. Cyclin E-CDK2 complexes bind and activate, preparing the cell for S phase
• S phase


  DNA is replicated to produce two identical copies of each Chromosome
• S Phase control


  Active S cyclin-CDK complexes phosphorylate proteins that make up the pre-replication complexes on DNA replication origins
• G2 phase


  The cell prepares itself for mitosis by synthesizing components to ensure the survival and functionality of each daughter cell
• Mitosis


  Mitotic cyclin-CDK complexes are activated, and promote chromatin condensation, mitotic spindle formation, degradation of chromosomal structural proteins, and procession through the stages of mitosis
• Cyclins


  1. Cyclins drive the cell cycle
  2. Cyclins interact with kinase proteins called the cyclin-dependent kinases (CDKs)
  3. The CDKs phosphorylate and activate proteins needed for the cell cycle
  4. The G1/S phase cyclin/CDK pairs
• Stages of mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• At the metaphase stage of mitosis, the chromosomes are most compacted
• Karyotypes may be disrupted in situations like cancer
• In females, germ cells ultimately become oocytes with 23X genotype; in males germ cells become sperm with either 23X or 23Y genotype
• Capacitation, acrosome reaction, and fast/slow (cortical reactions) block to polyspermy of fertilisation
• The fertilising sperm produces the mitotic spindle enabling first cleavage of fertilised egg
• Early stages of embryogenesis - zygote -> blastocyst
• The derivation and importance of the inner cell mass