2.1 Cells as a basis of life

• Cell membrane


  Separates the cell cytoplasm from its surroundings and controls the exchange of materials, including nutrients and wastes, between the cell and its environment
• Fluid mosaic model


  Describes the structure of the cell membrane
• Characteristics of life (MRS GREN)

  • Movement
  • Respiration
  • Sensitivity
  • Control (homeostasis)
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• Cell theory


  • Cells are the smallest structural and functional unit of life
  • Cells originate from existing cells through cell division
  • Cells contain hereditary material
• Cells all contained 3 things: genetic material, metabolic machinery, and cell membranes
• Viruses display some characteristics of living things but do not have a membrane
• Cell membrane


  • Encloses prokaryotic and eukaryotic cells
  • Selectively permeable due to its chemical composition and structure
  • Composed of lipids, proteins and carbohydrates
  • Composed mostly of phospholipids arranged in a bi-layer with hydrophobic tails facing inwards and hydrophilic heads facing aqueous solutions
• Phospholipids in cell membrane

  • Packed tightly but fluid and free to move around
  • Contain sterols like cholesterol that restrain fluidity at high temperatures and stop lipids from packing too tightly at low temperatures
• Peripheral proteins


  Proteins on the surface of the cell membrane
• Integral proteins


  Proteins embedded in the hydrophobic layer of the cell membrane
• Protein functions in cell membrane


  • Transport, signaling, catalyzing specific metabolic reactions, structure and inducing cell responses
• Autotrophs


  Most living things derive energy from the breakdown of carbs and fats
• Types of autotrophs


  • Photoautotroph
  • Chemoautotroph
• Photoautotroph


  Make energy molecules from light energy
• Chemoautotroph


  Make energy molecules from chemical reactions
• Primary producers


  Also called autotrophs
• Chemoautotrophs


  Usually prokaryotes
• Heterotrophs


  Derive food from other living (or formally living) things via digestion of tissues
• Types of heterotrophs


  • Carnivores
  • Omnivores
  • Herbivores
  • Detritivores
• Consumers


  Also called heterotrophs
• Photosynthesis


  The sun is the principal energy source in most ecosystems
• Photosynthesis


  Light energy is converted to chemical energy
• Photosynthesis


  A chemical reaction that turns CO2 and water into glucose and oxygen
• Thylakoid


  Contain the chlorophyll and photosynthetic enzymes
• Thylakoids in chloroplasts


  Similar in structure and function to those found in photosynthetic bacteria
• Glucose


  An energy dense molecule made during photosynthesis or obtained through consumption
• Aerobic respiration


  Glucose is completely broken down into CO2 and H2O + energy
• Anaerobic respiration/Fermentation


  Glucose is partially broken down into lactic acid or ethanol
• Lactic acid fermentation


  Occurs in animals and some bacteria
• Alcohol fermentation


  Occurs in plants and yeast
• Adenosine triphosphate (ATP)


  Energy coupling refers to the transfer of energy in cell processes through this molecule
• ATP hydrolysis


  The bond between the 3rd phosphate group is broken creating ADP + P; and energy is released
• Nucleus


  • Usually the largest organelle in a Eu cell
  • Enclosed by nuclear envelope (double lipid bilayer)
  • Nuclear pores regulate entry and exit of macromolecules (RNA and proteins)
  • Contains chromatin that makes up the chromosomes
  • Contains nucleolus where ribosomal RNA is synthesized from DNA and assembled with proteins into ribosomes (Ribosome factory)
• ATP synthesis


  Adding the phosphate back to ADP allows the molecule to be reused over again
• Ribosomes


  • Made of rRNA and proteins - carry out protein synthesis
  • Not membrane bound (and not considered organelles)
  • Cells that secrete proteins (hormone cells or antibody cells) have more ribosomes and prominent nucleoli
  • Free ribosomes (in cytosol) and bound ribosomes (attached to ER) are identical, but their proteins are destined for different futures
  • Free ribosomes usually produce proteins destined for functions in the cytosol
  • Proteins made in the ER are generally destined to be membrane bound, or secreted
  • Signal peptide directs the SRP to escort the ribosome to the ER
• Mitochondria in eukaryotes, cytoplasm and membrane of prokaryotes

  Where ATP synthesis occurs
• Metabolism


  Refers to the total of the chemical reactions occurring in cells; required for respiration, growth and excretion etc
• Endoplasmic reticulum


  • Network of membranes making up half of the membrane volume in a Eu cell
  • Made of a single lipid bi-layer sacs called cisternae, while internal space is called ER lumen
  • Two types - smooth and rough - connected
  • Also connected to the internal space between the nuclear envelope
• Smooth ER


  • Synthesizing lipids, cholesterol, steroid hormones
  • Enzymes within detoxify drugs and poisons by adding hydroxyl groups to make them water soluble
  • Storing calcium ions required for muscle movement
• Water


  The solvent that organic and inorganic compounds are dissolved in, allowing for easy transport