Cell structure + Organisation

• Main points on cell theory

  1. All organisms are made out of cells
  2. All cells are made from division of preexisting cells
  3. All metabolic processes are carried out inside the cell
  4. All activities in the cell depend on the activities of the sub cellular structure
• Two types of cells

  1. Prokaryotic
  2. Eukaryotic
• Prokaryotic

  • DNA free in cytoplasm
  • No proteins
  • No mitochondria
  • 70s Ribosomes
  • No internal compartmentalization
  • Size less than 10 micrometers
• Eukaryotic

  • DNA enclosed in nucleus
  • Have proteins in the form of chromosomes
  • Have mitochondria
  • Have internal compartmentalization
  • 80s ribosomes
  • Size bigger than 10 micrometers
• Why internal membrane divide the cell into different compartments

  1. regional separateness
  2. different local environment
  3. specialization
  4. division of labour
• Nucleus

  1. Control all cell activities
  2. Essential for division of labour
  3. Double membrane
• Nucleus consist of

  1. Nuclear envelope
  2. Regulates passage of molecules
  3. Separates chemical reactions
  4. Nucleoplasm
  5. Nucleolus
  6. Directs protein synthesis
• Cell surface membrane

  1. Surrounds cytoplasm
  2. Made up of lipids and proteins
  3. Compromises of a phospholipid bilayer
  4. Partially permeable
  5. Controls substances to entering or leaving the cell
• Molecules of plasma membrane

  1. Lipids
  2. Phospholipids
  3. Cholesterol
  4. Proteins
  5. Intrinsic
  6. Extrinsic
  7. Carbohydrates
  8. Glycolipids
  9. Glycoproteins
• Plasma membrane

  1. 7 nanometers thick
  2. Made out of 75% phospholipids, cholesterol, proteins and polysaccharids
  3. In phospholipids, one fatty acid is replaced by phosphate group
• Lipids

  1. Made out of fatty acids and glycerol
• Lipids

  Glycerol

  • Made out of 3 carbon and 1 hydroxyl group

  Fatty acids

  • Made out of a long carbon skeleton which is 16/18 carbon atoms in length
  • One end has a carboxyl group
  • Three fatty acids bond with the glycerol through an ester linkage
  • Called a triglyceride

  
• Types of fatty acids

  1. Saturated
  2. All carbons connected by single bonds
  3. Solid at room temperature
  4. Unsaturated
  5. One or more double bonds between carbons
  6. Liquid at room temperature.
• Phospholipids

  1. Made out of two fatty acids and glycerol
  2. Last hydroxyl group in the glycerol connected with one phosphate group
  3. Ampipathic
  4. One end phospholipid molecule is the polar end/hydrophillic
  5. Attracts water from surroundings
  6. Other end of phospholipid molecule is non-polar end/hydrophobic
  7. Does not mix well with water
  8. Aligns to form double layer membranes
  9. Polar end on the outside and non-polar end on the inside
• Cholestrol

  1. Is a sterol, made out of steroids and alcohol
  2. Steroids are lipids characterized by their carbon skeleton consisting of four fused rings
  3. Cholesterol is a common component of animal cell membranes and it is the precursor from which steroids are synthesized.
• Effects of cholesterol on membrane fluidity

  1. Greater steroid content = less fluid
  2. Makes up 20% of all lipids in animal cells, rarely found in plant cells
  3. Different effects at different temperatures
  4. Cholesterol fits between phospholipids to increase rigidity and stability
  5. At warm temperatures, cholesterol restrains movement of phospholipids
  6. At cool temperatures, cholesterol maintains membrane fluidity by preventing tight packing
• Extrinsic proteins

  1. Sit on surface
  2. Slide across membrane very quickly and collide into one another
  3. Never flip from one side to another
  4. Proteins on internal surface maintain cell's shape
  5. Can also be enzymes catalyzing reactions in cytoplasm
• Intrinsic proteins

  1. Called transmembrane proteins
  2. Hydrophobic regions contain one or more stretches of non-polar amino acids which are coiled up into alpha helices
  3. Weak hydrogen bonds between proteins and phospholipids keep the membrane stable e.g (Channel + Carrier proteins)
• Channel proteins

  1. Hydrophilic channel for certain molecules/ions to use as a tunnel to pass through membrane.
  2. Fixed shape
  3. Highly selective
• Carrier protein

  1. Hold onto passengers and shuttle them across membrane
  2. Undergo rapid change in shape
  3. Highly selective
• Membrane proteins

  1. Some enzymes like ATPase which converts ATP to ADP, releasing energy, can be found in the membrane.
  2. Glycoproteins stick out of the membrane
  3. Important in membrane recognizing each other
  4. Some glycoproteins act as antigens
• Functions of membrane proteins

  1. Hormone binding sites
  2. Immobilized enzymes
  3. Channels for passive transport
  4. Carriers for active transport
  5. Cell adhesion
  6. Cell to cell communication
• Rough endoplasmic reticulum (RER)

  1. in layers
  2. have ribosomes attached to outer surface
  3. transport proteins made by ribosomes to golgi apparatus for secretion out of cell
• Smooth endoplasmic reticulum

  1. in circle
  2. synthesizes substances like fats and steroids
  3. converts harmful substances to harmless molecules
• Ribosomes

  1. those attached to RER outer surface will have their proteins secreted out of cell
  2. those lying freely in cytoplasm will have their proteins used up within cytoplasm of cell
• Golgi apparatus

  1. chemically modifies substances made by ER
  2. stores and packages substances into vesicles for secretion out of cell
  3. produces macromolecules
• Secretory vesicles

  1. cell secretion
  2. packaged in secretory vesicles at golgi apparatus
  3. transports to cell surface for release
• Processes in golgi apparatus

  1. vesicles transport substances within cell
  2. Small vesicles with substances made by the ER are pinched off from the ER
  3. vesicles fuse and release contents into golgi apparatus
  4. golgi apparatus may chemically modify substances
  5. Secretory vesicles with modified substances are pinched off from the golgi apparatus
  6. They will then fuse with the cell surface membrane
  7. contents are released outside cell
• Lysosomes

  1. vesicles with digestive enzymes
• Functions of lysosomes

  1. digestion in membrane bound vacuole with which lysosomes will fuse with
  2. break down large molecules - (Phagocytosis, cell eating)
  3. Found in amoeba and human macrophages
  4. recycle worn out organelles within cell- (Autophagy, self eating)
• Vacuole

  1. store substances
  2. Enclosed by partially permeable membrane

  Animal cell

  1. many, small, temporary vacuoles
  2. Store food and water

  Plant cell

  1. Large, central vacuole containing cell sap
  2. cell sap has dissolved substances
• 1. Granules
  2. Ribosomes
  3. Cristae
  4. Inner membrane space
  5. Matrix
  6. ATP synthase particles
  7. DNA
  8. Outer membrane
  9. Inter membrane

  
• 1. Thylakoids
  2. Stroma
  3. Granum