Unit 2 Cell Structure and Function

• Some subcellular components are universal and found in eukaryotic and prokaryotic cells
• This means that they share a common ancestry and started from the beginning of life
• Ribosomes


  • Consist of two subunits that are NOT membrane-bound
  • Made of ribosomal RNA (rRNA) and proteins
  • Synthesize proteins
• Protein synthesis


  1. DNA detects what proteins are needed and has instructions on different proteins

  2. Nucleotides are organized in sequences of three called codons

  3. The order of nucleotides determines the order of codons which determines the structure and function of the protein

  4. The order (instructions) of amino acids is held by DNA and is taken by mRNA which will take it to the ribosome

  5. Ribosomes synthesize proteins using information from mRNA sequences
• Prokaryotic cells


  • Don't have membrane-bound organelles
• Eukaryotic cells


  • Have membrane-bound organelles
  • Chemical reactions that take place within membrane-bound organelles do not interfere with other organelles and reactions
  • The cell membrane around organelles creates compartments with different pHs that allow enzymes to be more efficient
  • Membrane-bound organelles allow Eukaryotic cells to be more efficient than prokaryotic cells
• Rough endoplasmic reticulum (RER)


  • Proteins made in the RER are meant to be used outside of the cell or are membrane bound
  • They are transported to the Golgi apparatus after being synthesized in the RER
  • Has a highly folded cell membrane which increases its efficiency
• Golgi apparatus


  • Modifies and packages proteins for export out of the cell
  • Has incoming transport vesicles and secretory vesicles
  • Incoming transport vesicles take proteins to the Golgi apparatus and secretory vesicles take them from the Golgi apparatus
  • Has a highly folded cell membrane which allows it to be more efficient
  • It is a series of flattened membrane sacs
• Lysosome


  • Works best in acidic conditions
  • Functions: Intracellular digestion, Recycling organic materials, Programmed cell death (apoptosis)
• Smooth endoplasmic reticulum


  Detoxifies and synthesizes lipids
• Lipids


  • Has hydrolytic enzymes (uses hydrolysis reactions to break down molecules)
  • Are used to digest macromolecules and damaged cell parts
  • Hemoglobin can be reused
• Living things


  All living things are composed of cells
• Vacuoles


  • Plant cells have large vacuoles that are filled with water until they push against the cell membrane, allowing plants to stand upright (Turgor Pressure)
  • They maintain a certain amount of water that keeps the plant upright but prevents bursting
  • Some animals have small vacuoles that are used to store water
• Cell theory


  The cell is life's basic unit of structure and function
• Ribosomes


  Synthesise Cytosolic proteins in the cytoplasm
• Cell


  The smallest unit of living material that can carry out all the activities necessary for life
• Mitochondria


  • It is where cellular respiration takes place
  • Is a double membrane-bound organelle
  • The inner membrane is highly folded with proteins embedded in it (cristae) which increases the mitochondria's efficiency by increasing the surface area
  • Electron transport and ATP synthesis takes place in the inner mitochondrial membrane
  • The outer membrane is smooth
  • The Krebs cycle (citric acid cycle) reactions occur in the matrix of the mitochondria
• Why not be a giant cell?
• Chloroplast


  • Is a double membrane-bound organelle
  • Its purpose is to carry out the process of Photosynthesis
  • The membranes of the chloroplast divide the chloroplast space into three compartments: The intermembrane space, the stroma, and the thylakoid space
• Reason for not being a giant cell

  • Specialization
  • Must maintain high surface area:volume ratio to allow cellular exchanges across the membrane
• Intermembrane space


  The region between the inner and outer membrane of a chloroplast
• Invention of electron microscopes allowed scientists to figure out the exact functions of cells
• Thylakoid space


  • It is a membrane system in the form of flattened interconnected sacs named thylakoids which has highly folded compartments
  • Thylakoids may be stacked and each stack is called a granum and is plurally called grana. Grana is filled with chlorophyll which captures light
  • Light-dependent reactions take place with photo-absorbing pigments
  • It has electron capturing used for ATP
• Types of cells


  • Prokaryotic
  • Eukaryotic
• Stroma


  • Light-independent reactions (Calvin-Benson cycle) take place
  • It is the fluid between the inner thylakoid membrane and outside thylakoids (it surrounds it)
• Chlorophyll


  It is a pigment that gives plants their green color
• Vesicles


  Membrane containers that move materials from one part of a cell to another
• Prokaryotic cells


  • Only in domains Bacteria and Archaea
  • Smaller
  • Simpler
  • Circular DNA in nucleoid region (no nucleus)
  • Cell wall made of peptidoglycans
  • Filled with semi-fluid cytosol
  • Have ribosomes
  • Can have flagella
  • May have a thick capsule
  • No membrane-bound organelles

  
• Eukaryotic cells


  • More complex
  • Organized into smaller structures called organelles
  • DNA in nucleus bounded by a membranous nuclear envelope
  • Cytoplasm between plasma membrane and nucleus

  
• Convoluted


  Complicatedly folded
• To stay alive, cells need to take in substances and get rid of waste (takes in oxygen, nutrients - get rid of heat, CO2)
• Each organelle has its own special task
• Cells that have a larger surface area compared to volume are more efficient
• Plasma membrane


  • Outer envelope
  • Complex phospholipid bilayer
  • Encloses vacuole
  • Regulates movement in/out of cell
  • Flexible due to weak bonds holding it together
  • Semipermeable - only small hydrophobic molecules can pass through unaided, anything large/hydrophilic must pass through active/passive transport, water can't move through easily due to polarity
• Fluid-mosaic model of plasma membrane


  • Peripheral proteins are loosely associated with the lipid bilayer
  • Integral proteins are firmly bound into the plasma membrane and can extend all the way through
  • Membrane peppered with different proteins/carb chains

  
• In nature, cells have different shapes and sizes (square, round, rectangular)
• Smaller cells are more efficient → As cells grow the volume of the cell increases faster than the surface area
• Plasma membrane components


  • Adhesion proteins
  • Receptor proteins
  • Transport proteins
  • Carrier proteins
  • Channel proteins
  • Cell surface markers
  • Carbohydrate side chains
  • Cholesterol

  
• The larger the ratio between surface area and volume, the more efficient the cell is
• At a certain size, cells have to divide to become smaller and more efficient