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L01 : The function of cellular organellesEdit

Cellular structures:Edit

Cell L01






Other structures:Edit

  • ===Extracellular matrix: Network of macromolecules such as proteins and polysaccharides. Acts as scaffold and stabilises the cell===
  • ===Centrozome : Produces microtubules and contains centrioles===
  • ===Peroxisome : Enclosed in a single membrane, filled with enzymes and buds off from the endoplasmic reticulum. Contains hydrogen peroxide, a reactive chemical which breaks down lipids, pathogens and toxic susbtances via oxidation===
  • ===Vesicles : Involved in transport of material between one membrane-enclosed organelle and another===
  • ===Cytosol : Site of many vital cellular activities. Contains ribosomes which carry out protein synthesis===
  • ===Golgi apparatus : Synthesises, packages and modifies molecules destined to be secreted from cell. Also involved in routing newly synthesised proteins to correct cellular compartment===



Exchange within a cell

  • Continual exchange of materials takes place between the ER, the golgi apparatus, the lysosomes and the outside of the cell.
  •  This is mediated by vesicles which pinch off from the membrane of one organelle and fuse with another.

Endocytosis

  • Animals can engulf large particles/cells through this process
  • This can result in fusing with lysosomes as to digest the material

Pinocytosis

Eukaryotic cells ingest bits of their plasma membrane in the form of small pinocytic vesicles

  • This is a type of endocytosis and involves the ingestion of soluble substances
  • This comes from the ECM

Exocytosis

  • This is where vesicles in the cell fuse with the plasma membrane
  • This causes the release of their contents into the external medium
  • This includes hormones, neurotransmitters and other signalling molecules

Protein transport into organelles

This is done by 3 mechanisms:

  1. Through nuclear pores
  2. Via protein translocation
  3. Via transport vesicles

Nuclear pores

  • These allow for the movement of substances into and out of the nucleus
  • This includes RNA, proteins and ribosomes

Protein translocation

The transported protein must unfold in order to get through the membrane

  • This occurs in the mitochondria, ER and peroxisomes
  • Proteins enter the ER whilst being synthesised

Transport vesicles

These allow for the transport of substances between organelles

Role of endoplasmic reticulum

This serves as an entry point for proteins destined for other organelles (as well as the ER)

  • This includes proteins destined for the golgi apparatus, endosomes (endocytic vesicles) , lysosomes and cell surface
  • The proteins enter the ER from the cytosol
  • They are then ferried by transport vesicles from organelle to organelle

Types of proteins

  • Water soluble proteins are completely translocated across the ER membrane and are released into the ER lumen
  • Prospective transmembrane proteins only partially translocate across the ER membrane and become embedded

Transport within a cell

The cytosol is crisscrossed by long, fine filaments of protein

  • These can be anchored at one end of the plasma membrane or radiate from a central site next to the nucleus
  • This system of filaments is known as the cytoskeleton

The cytoskeleton can use energy from ATP to propel organelles and vesicles along the filaments

Types of filament

  • Actin filaments (thinnest) generates contractile forces and are present in large numbers in muscle cells. Form a meshwork beneath plasma membrane and strengthen it
  • Microtubules (thickest) pull duplicated chromosomes and distribute them equally between daughter cells
  • Intermediate filaments serve to strengthen the cell mechanically

These filaments work together to give the cell its strength, shape and drives and guides its movements

Compartments

  • Organelles are enclosed in their own membranes
  • This allows for sets of enzymes to operate without interference from other reactions