Introduction to cells

• • All organisms, including those consisting of only one cell, carry out all functions of life in that cell, including:
  • Nutrition
  • Metabolism
  • Growth
  • Response 
  • Excretion
  • Homeostasis 
  • Reproduction.
• • Surface area of a cell is the plasma membrane, which controls the exchange of materials and heat.
  • Volume represents the cytoplasm, which is where metabolism occurs, using and producing materials and generating heat.
  • As the cell grows, greater demands are made for the exchange of materials and heat
• • When a cell becomes too large,  it will not be able to exchange sufficient materials and release heat fast enough to meet the cell’s metabolic requirements.
  • The cell is now inefficient and will have to divide
• • Multicellular organisms have properties that emerge from the interaction of their cellular components.
  • Emergent properties arise from the interaction of component parts. The whole is greater than the sum of its parts.
  • Multicellular organisms are capable of completing functions that individual cells cannot. This is due to the interaction between cells producing new functions!
• Specialised tissues can develop by cell differentiation in multicellular organisms.

  Differentiation involves the expression (turning on) of some genes and not others in a cell’s genome.

  The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
• Stem cells are not differentiated, and retain the capacity to divide and differentiate into all other cell types
• Ethics and Stem cells: For

  1. Cells can be removed from embryos that would die anyway
  2. Stem cells can be used to save lives and reduce suffering
  3. Cells are removed at a stage where they is no nervous tissue – no pain
• Ethics and Stem cells: For

  1. Destruction of potential life/ against some religious beliefs
  2. More embryos are produced than are needed
  3. There is a danger of stem cells developing into tumour cells
• • According to the cell theory, living organisms are composed of cells.
  • Organisms consisting of only one cell carry out all functions of life in that cell.
  •  Surface area to volume ratio is important in the limitation of cell size.
  • Multicellular organisms have properties that emerge from the interaction of their cellular components.
• • Specialized tissues can develop by cell differentiation in multicellular organisms.
  • Differentiation involves the expression of some genes and not others in a cell’s genome.
  • The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
• Typical cells have DNA as genetic material, a cytoplasm composed mainly of water, which is enclosed by a plasma membrane composed of lipids.
• Prokaryotic - Have free DNA and no membrane-bound organelles
• Eukaryotic - Have a nucleus and membrane-bound organelles
• Organelles - small structures within a cell that perform specific functions.
• Prokaryotic cell diagram

  
• How do Prokaryotic cells divide: Binary fission

  1. The circular DNA is copied in response to a replication signal.
  2. The two DNA loops attach to the membrane.
  3. The membrane elongates and pinches off (cytokinesis), forming two cells.
• Cytoplasm - gel-like fluid inside the cell membrane where metabolic reactions occur
• Cell wall - made of cellulose and a rigid structure that surrounds bacterial cells?
• Peptidoglycan - what bacterial cell walls are made of
• 70S ribosomes - the organelles that direct protein synthesis in prokaryotes
• A single celled organism without a nucleus or membrane bound organelles is called a prokaryote
• The basic structural and functional unit of all organisms - cell
• Flagella - a long, whip-like structures that enable movement
• Sperm cell - one eukaryotic cell that has a flagellum
• Pili are hair-like protein structures that allow bacteria to attach to things