Cell Structure - Official

• Bacteria (singular bacterium) has a singular DNA as its genetic material, a cell wall, ribosomes, plasmids and may have one or more flagella. Some are pathogenic while others are non-pathogenic.
• A virus has a protein coat enclosing its genetic material, which is either DNA or RNA. Unlike living things, a virus does not have cellular structures, and does not grow, move, feed, respire or excrete. However, it can reproduce by entering a living cell, which acts like its host. This is because the host contains the necessary materials for reproduction, such as enzymes and organelles like ribosomes.
• • the cell is the fundamental building block of an organism
  • made out of nucleic acids, proteins, carbohydrates and lipids
  • all eukaryotic cells have a plasma membrane, cytoplasm and nucleus
• Prokaryotic cells:

  • smaller than eukaryotic cells
  • simpler internal structure
  • lack membrane-bound organelles
  • includes bacteria
• Eukaryotic cells:

  • occur in algae, protozoa, fungi, plants and animals
  • larger than prokaryotic cells
  • contain a distinct nucleus, have a cytoplasm and plasma membrane
  • have a compartmentalised internal cell structure and many membrane-bound organelles
• Plasma membrane:

  • Forms a physical boundary between the cytoplasm of the cell and the external environment
  • Separates the contents of the cell from its external environment. It is selectively permeable.
• Plant cells have cell walls that encloses the entire plant cell, surrounding the plasma membrane. Made out of cellulose, protects the cell from injury and gives the plant cell a fixed shape. Fully permeable.
• Cytoplasm:

  • the cytoplasm of a eukaryotic cell is the site where most cellular reactions occur
  • is an aqueous medium that contains many dissolved substances and enzymes
  • it also contains many organelles such as the rough endoplasmic reticulum, smooth endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria and chloroplasts
• Nucleus:

  • controls cell activities such as cell growth and the repair of worn-out parts
  • essential for cell division
  • bound by a double membrane
• Chromatin:

  • Is composed mainly of proteins and DNA
  • DNA contains all the genetic information that are essential to the survival of the cell
  • When the cell is dividing, chromatin condenses into more tightly coiled structures called chromosomes
• Mitochondria:

  • bound by a double membrane
  • site of aerobic respiration where energy is produced in the form of ATP
  • there are numerous mitochondria present in cells with high energy requirements
• Chloroplasts:

  • large double membrane-bound organelle
  • oval structures found in plant cells
  • contain a green pigment called chlorophyll and other photosynthetic pigments
  • chlorophyll is essential for photosynthesis
• Rough endoplasmic reticulum:

  • consists of a network of flattened spaces lined with a membrane
  • surface appears rough when viewed under the microscope as ribosomes are attached to the outer surface
  • ribosomes attached to the RER synthesise proteins that are transported out of the cell
  • outer surface of the RER is continuous with the nuclear membrane
  • transports proteins made by the ribosomes to the Golgi apparatus for secretion out of the cell
• Ribosomes:

  • Synthesise proteins in the cell
  • ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell
• Smooth endoplasmic reticulum:

  • synthesises substances such as fats and steroids
  • converts harmful substances into harmless substances through detoxification
• Golgi apparatus:

  • chemically modifies substances made by the ER
  • stores and packages these substances in vesicles for secretion out of the cell
• Golgi apparatus steps:

  1. Vesicles transport substances within the cell. Small vesicles containing substances made by the ER are pinched off
  2. The vesicles fuse with the Golgi body and release the contents into the Golgi body. Substances made by the ER may be modified inside the GA.
  3. Secretory vesicles containing the modified substances are pinched off from the GA. They move to the cell membrane.
  4. Secretory vesicles fuse with the cell membrane, contents are then released out of the cell
• Vacuoles:

  • fluid-filled space enclosed by a partially permeable membrane
  • store substances within the cell
  • vacuole is surrounded by a single membrane known as the tonoplast -> selectively permeable membrane
• vacuoles in plants vs animals:

  • plant cells have a large central vacuole which contains a liquid called cell sap, which contains dissolved substances such as sugars, mineral salts and amino acids
  • animal cells have many small vacuoles that contain water and food substances, which usually exist temporarily