A6 Phagocytosis of Extracellular Phagocytosis + A7. Endocellular Material in the Cell

Question 1

Phagocytosis of Extracellular Phagocytosis

Answer 1

• Part of the innate immune system, the 2nd line of defense.
• Process where phagocytes ingest/engulf other cells/ particles to get rid of pathogens which have made it through the 1st line of defense. The phagocyte may be a free-living one-celled organism, such as an amoeba, or a body cells, such as a WBC.
• Main phagocytes: monocytes, macrophages, neutrophils and dendritic cells.
• The phagocytes are equipped with intracellular compartments such as Lysosomes - which contain microbial substances such as lysozymes, nucleases, proteases, lipases, hydrogen peroxides
• Dendritic cells: special type of phagocytes ;they perform antigen processing and presentation in the adaptive immune system
• Neutrophils: highly specialized phagocytes - most numerous and lethal among phagocytes, because they contain 3 types of cytoplasmic granules; primary-, secondary- and tertiary granules, which contain microbial substances contributing to phagocytosis.
o After ingestion and killing of pathogens, they undergo apoptosis → short lived
o Dead neutrophils are phagocytosed by macrophages.

Question 2

Steps of phagocytosis:

Answer 2

1. Recognition of invading pathogen
   o PRR on plasma membrane of phagocytes recognize PAMPs – bind together
2. Ingestion and formation of phagosome o Plasma membrane of the phagocyte surrounds the bound pathogen, then pinches of and internalizes the pathogen forming a sac called phagosome or phagocytic vesicle
3. Formation of phagolysosome
   o Fusion of lysosome and phagosome, forming a larger structure called phagolysosome
4. Microbial Killing and formation of residual body
   o There is an acidic environment inside the phagolysosome, and together with the microbial substances of lysosomes, together they destruct and eternalizes the pathogen.
   o At last the only thing left of the pathogen is called residual body
5. Elimination or Exocytosis
   o The residual body moves to the cell border and discharges itself outside the cell.

Question 3

Nucleus and Nucleolus

Answer 3

• The nucleus, formed by a nuclear membrane around a fluid nucleoplasm, is the control center of the cell. Threads of chromatin in the nucleus contain DNA, the genetic material of the cell.
• The nucleolus is a dense region of RNA in the nucleus and is the site of ribosome formation.
• The nucleus determines how the cell will function, as well as the basic structure of that cell.

Question 4

Cytoplasm

Answer 4

• The cytoplasm is the gel-like fluid inside the cell. It is the medium for chemical reaction.
• It provides a platform upon which other organelles can operate within the cell.
• All of the functions for cell expansion, growth and replication are carried out in the cytoplasm of a cell.
• Within the cytoplasm, materials move by diffusion, a physical process that can work only for short distances.

Question 5

Cytoplasmic organelles

Answer 5

• Cytoplasmic organelles are “little organs” that are suspended in the cytoplasm of the cell.
• Each type of organelle has a definite structure and a specific role in the function of the cell.
• Examples of cytoplasmic organelles are mitochondrion, ribosomes, endoplasmic reticulum, golgi apparatus, and lysosomes.

Mitochondria: has a specialized double-membrane structure, generate ATP, a molecule that provides organisms with energy.

Ribosome: is a complex molecule made of ribosomal RNA molecules and proteins that form a factory for protein synthesis in cells.

Endoplasmic reticulum (ER): type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane.
• Important in protein synthesis, -folding, -modification and -transport
• Smooth and rough

Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, the Golgi apparatus packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination.

Peroxisomes: are single-membrane structures found in all eukaryotic cells. They are small, membrane-bound structures that use molecular oxygen to oxidize organic molecules. The structure is one of the major oxygen utilizing organelles, the other being the mitochondria. It contain oxidative enzymes and other enzymes that help produce and degrade hydrogen peroxide.