Cell Structure

• EUKARYOTIC & PROKARYOTIC SIMILARITIES:

  • ORGANELLES: Both prokaryotic and eukaryotic cells contain organelles & other features including: a plasma membrane, cytoplasm, DNA, ribosomes (although they are smaller in prokaryotes)
  • CELL SURFACE MEMBRANE: Both have cell surface membranes made of a phospholipid bilayer

   (responsible for controlling the passage of substances across exchange surfaces)
• EUKARYOTIC & PROKARYOTIC DIFFERENCES:

  • ORGANISMS: Prokaryotic cells make up single-celled organisms (eg bacteria). Eukaryotic cells make up complex eukaryotic organisms (eg animals, plant, fungi, algae)
  • SIZE COMPARISON: Eukaryotic cells are 10-100µm. Prokaryotic cells are 0.1-5.0µm.
  • ORGANELLES: Prokaryotes do not have any membrane -bound organelles (nucleus, mitochondria, Golgi apparatus, etc)
  • DNA: In eukaryotes are found as chromosomes in the nucleus. In prokaryotes are found as a circular module in the cytoplasm.
• PROKARYOTIC DNA

  • DNA: Prokaryotic DNA is found as a circular module in the cytoplasm.
  • PLASMIDS: smaller loops of DNA not part of the main circular DNA molecule. Bacteria can exchange plasmids with other bacteria (sometimes receiving beneficial new genes that can be added to their DNA) e.g. antibiotic resistance often spreads through a bacterial economy through plasmid exchange.
• • PROKARYOTES:
  • CAPSULE: The capsule enables prokaryotic cells to attach to surfaces in its environment
  • FLAGELLA, PILI, FIMBRIAE: Flagella= tail like used for locomotion. Some prokaryotes have 0 and some more than 1. Pili= used to exchange genetic material during conjugation (a type of reproduction). Fimbriae= used by bacteria to attach to a host cell
• BINARY FISSION: How prokaryotes replicate

  1. REPLICATION OF GENETIC MATERIAL: replication of the circular DNA and plasmids
  2. MIGRATION OF GENETIC MATERIAL: The 2 sets of genetic material migrates towards opposite poles
  3. CYTOPLASM BEGINS TO DIVIDE: The cytoplasmic contents divide to give both new cells substance to sustain life
  4. FORMATION OF DAUGHTER CELLS: 2 genetically identical daughter cells formed, each with one of the circular DNA and many plasmid copies. Only difference= number of plasmid copies in each cell.
• TYPES OF EUKARYOTIC CELLS:

  • ANIMAL CELL: Organelles include mitochondria, ribosomes, endoplasmic reticulum, golgi, lysosomes, nucleus. Animal cells are enclosed by a cell membrane.
  • PLANT CELL: Contains all the organelles found in animal cells plus a vacuole (a respiratory of cell sap), chloroplasts (the site of photosynthesis), cell wall (made of cellulose and contains plasmodesmata, through which cells exchange substances with each other) 
• Viruses

  • Non- living and acellular (don't contain cells)
  • Made up of nucleic acids (DNA & RNA) surrounded by a capsid (a type of protein coat)
  • Smaller than bacteria
  • Have attachment proteins
• Virus replication

  1. Invade and hijack the reproductive mechanism of a living cell (host cells)

  2. Attachment glycoproteins bind to complementary receptors on host cells

  3. Inject DNA or RNA into the host cell

  4. Host cell divides as normal, and the virus is replicated
• Viruses

  • Non- living and acellular : no nucleus, plasma membrane, cytoplasm, or ribosomes
  • Not made up of cells
  • Cannot reproduce independently
• SPECIALISATION OF CELLS:

  • CELL SPECIALISATION: A cell specialises because the shape and contents of it help carry out its function. 
  • MUSCLE CELLS: Very active -> contain lots of mitochondria (to produce ATP)
  • RED BLOOD CELLS: Have a biconcave shape + no nucleus (to maximise space to carry oxygen)
  • PALISADE CELLS: Have long upright shape & contain chlorophyll (to absorb light for photosynthesis)
• ORGANISATION OF CELLS:

  • Specialised cells -> tissues -> organs -> organ systems (-> = organised into)
  • TISSUES: eg muscle tissue, xylem tissue
  • ORGANS: eg the animal heart, plant leaf
  • ORGAN SYSTEMS: eg the female reproductive system
• Phospholipid bilayer

  • Made up of lipids and proteins
  • A phospholipid is a lipid molecule with glycerol, 2 fatty acid chains, and a phosphate containing group
• Plasma membranes

  • Have proteins and cholesterol embedded into them
  • Proteins act as receptors which means the cell can respond to the external environments of the cell
• Cell surface membranes

  1. Controls passage of organic molecules, ions, water, oxygen in and out of the cell

  2. Excretes waste products eg carbon dioxide and ammonia

  3. Has receptor molecules so it can respond to chemical-like hormones
• CYTOPLASM:

  • STRUCTURE: The cytoplasm is made up of organelles suspended in a gel like cytosol. 70% of the cytoplasm is water and it also contains proteins, sugars, ions, fatty aids
  • FUNCTION: METABOLIC REACTIONS: take place is the cytoplasm (metabolic energy= energy released from respiration).
  • ORGANELLES: different organelles perform functions in the cytoplasm, organelles are not cells even if they are surrounded by membranes.
• Nucleus

  • A large organelle that contains the cell's DNA and controls the cell's activities
  • The nucleoplasm is the semi-solid fluid inside the nucleus where the chromatin and nucleolus are found
  • In eukaryotes the nucleus contains linear chromosomes made up of DNA
  • The nucleolus is the area within the nucleus
• Nuclear envelope

  • The nucleus is surrounded by a nuclear envelope and it's a double membrane structure that controls the entry and exit of materials from the nucleus that has pores
  • Both the inner and the outer membranes of the nuclear envelope are phospholipid bilayers
• Nuclear pores

  Allow the passage of large molecules
• Nucleoplasm

  The jelly-like material that makes up the bulk of the nucleus
• Nucleolus

  A small spherical region of the nucleus within the nucleoplasm that manufacturer rRNA and assembles ribosomes, there can be more than 1 nucleolus in a nucleus
• Chloroplasts

  • Have their own DNA
  • Have their own ribosomes
  • Have inner & outer membranes for quick manufacturing of proteins needed for photosynthesis
• Chloroplast envelope

  A double plasma membrane surrounding the organelle, controls what enters & exits the organelle
• Thylakoids

  • Interconnected & stacked fluid -filled membranes in the space enclosed by the inner membrane that contains chlorophyll
• Granum

  Each stack of thylakoids
• Grana

  Plural of granum, linked by lamellae
• Lamellae

  Thin, flat parts of the thylakoid membrane
• Stroma

  Fluid-filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place, contains starch grains
• Photosynthesis

  Use carbon dioxide, water, light to make glucose + oxygen
• Chloroplasts are found in plant and algal cells but not in animals or fungi
• GOLGI APPARATUS:

  • STRUCTURE: A series of flattened membrane sacs. CISTERNAE: stack of membranes that make flattened sacs. VESICLES: small rounded hollow structures
  • FUNCTION: Transport vesicles form at ER and fuse with Golgi apparatus. The transport vesicles empty proteins and lipids into the lumen of the Golgi apparatus. As the proteins and lipids travel through the Golgi apparatus they are sorted, packaged, and tagged so they are sent to the right place
• GOLGI VESICLES:

  • STRUCTURE: Are membrane -bound, fluid -filled vesicles located in the cytoplasm. They are small, round and seen in a high density near the edges of the sacs . Lysosomes are a type of Golgi vesicle .
  • FUNCTION: Store and transport modified proteins & lipids from Golgi apparatus to target cells. LYSOSOMES: are a special Golgi vesicle . They contain the enzyme lysozymes that aid the breakdown of proteins, polysaccharides ,lipids nucleic acids, and old organelles .
• LYSOSOMES:

  • STRUCTURE: Type of Golgi vesicle/ enzymes formed when the vesicles by the Golgi apparatus contain enzymes eg protease and lipase and lysosomes. Lysosomes isolate enzymes before releasing them (to the outside or into a phagocytic vesicle within the cell). Contains enzyme lysozyme
  • FUNCTION: Hydrolyse material ingested by phagocytic cells (eg white blood cells & bacteria). Release enzymes to outside cell to destroy material outside the cell. Digest worn out organelles (so chems in them can be reused). Hydrolyse the cell walls of some bacteria.
• RIBOSOMES:

  • STRUCTURE: Small cytoplasmic granules that can be free-floating in the cytoplasm attached to the cytoplasmic side of the endoplasmic reticulum (ER). Ribosomes are very small organelles made up of protein subunits. This means they are not covered by a membrane.
  • FUNCTION: Are in charge of protein synthesis. Protein synthesis is an essential function of all cells, which is why ribosomes are found in mostly any cell.
• Endoplasmic Reticulum

  A series of interconnected sheet-like membrane sacs and tubes, continuous with the outer nuclear membrane
• Endoplasmic Reticulum

  • Cisternae: the membranes that enclose the network of tubes and flattened sacs
  • The membrane of the ER is a phospholipid bilayer embedded with proteins
  • The smooth ER membrane has no ribosomes while the rough ER membrane has many ribosomes on its surface
• Rough Endoplasmic Reticulum (RER)

  1. Responsible for processing and folding proteins

  2. Providing a pathway for transport of materials especially proteins throughout the cell
• Smooth Endoplasmic Reticulum (SER)

  Responsible for making, processing, transporting carbohydrates & lipids
• CELL WALL:

  • STRUCTURE: Is a rigid covering that protects the cell. Plant, fungal, algal cells have cell walls. The major organic molecule in fungal cell walls is chitin while plant and algal cell walls are made of cellulose (a polysaccharide made up of glucose units) embedded in a matrix. MIDDLE LAMELLA: a thin layer that marks the boundary between adjacent cell walls and joins adjacent cells together
  • FUNCTION: Provides structural support and gives shape to the cell (eg prevents bursting from osmosis). Allow water to pass along it
• Tonoplast

  • Single membrane surrounding the vacuole
• Cell sap

  Weak solution of salts and sugars contained in tonoplasts