Eukaryotic cell structure

• Mitochondria:

  • Double membrane organelle, have their own ribosomes and DNA.
  • Contain a phospholipid bilayer embedded with proteins (inner layer = cristae and outer layer = mitochondrial matrix with enzymes for respiration).
  • Make ATP (adenosine triphosphate) via aerobic respiration.
  • 2-5um long.
• Centrioles:

  • Made up from parallel microtubules that surround a central cavity, making them cylindrical.
  • They are found as pairs at a right angle in most eukaryotic cells.
  • Only found alone when in basal regions of flagella and cilia.
  • These help to organise the mitotic spindles during cell division. These are also a key component of the cytoskeleton.
• Cell wall:

  • Plant cell walls are made of cellulose, over the cell membrane.
  • It provides structure to the cell whilst still allowing substances to pass in and out due to the permeability (plasmodesmata).
  • It acts as a defence mechanism, preventing pathogens from entering.
  • made of chitin in fungi
• Endoplasmic Reticulum:

  • A series of interconnected membranous sacs and tubules.
  • Rough ER = contains ribosomes on the surface, processes and folds proteins.
  • Smooth ER = contains no ribosomes, processes and folds lipids.
  • This is the largest organelle of most eukaryotic cells.
• Nuclear envelope:

  • double-membrane structure that has a number of pores. 
  • Both the inner and outer membranes are phospholipid bilayers
  • pores control the passage of ions, molecules and RNA between the nucleoplasm and cytoplasm.
• Nucleus

  • nucleoplasm = semi solid fluid containing chromatin and the nucleolus
  • contains linear chromosomes that are made up of DNA
  • controls the actions of the cell
  • ribosomal RNA is joined together with associated proteins in the nucleolus to assemble ribosomal subunits
• Nucleolus

  • largest substructure in the nucleus
  • made of proteins, RNA and DNA
  • where ribosomes are synthesised
  • immobilises proteins and forms signal recognition particles
• Chloroplasts

  • only found in plant and algal cells
  • have their own DNA, ribosomes and inner/outer membranes
  • The space enclosed by the inner membrane contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids.
  • Each stack of thylakoids is called a granum (plural = grana).
  • Lamellae are flat, thin parts of thylakoid membrane.
  • The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.
  • Grana are linked by lamellae.
  • site of photosynthesis
• Golgi Apparatus

  • series of flattened membranous sacs
  • transport vesicles empty proteins and lipids into the lumen of the golgi
  • proteins and lipids are then sorted and packaged to their specific areas
• Golgi vesicles

  • membrane bound fluid like vesicles located in cytoplasm
  • in high density near the edges of Golgi sacs
  • eg lysosomes
  • store and transport modified proteins and lipids out of golgi to specific cells
• Ribosomes

  • made up of protein subunits - not covered by a membrane
  • can be free floating or attached to ER
  • site of protein synthesis
• Plasma membrane

  • partially permeable barrier between inner cell and surroundings
  • fluid mosaic model - made up of phospholipids, cholesterol, proteins
  • phospholipid bilayer prevents polar substances from entering - hydrophobic facing inwards and hydrophilic outwards ( they are amphipathic)
  • protect the cells and allow certain molecules to enter and leave because they are semi permeable
  • part of cell signalling
• Cell walls

  • rigid covering that protects the cell
  • plant and algal - made from cellulose
  • fungal - made of chitin
  • provides structure and gives cell its shape
• Flagella

  • hair like structures
  • contain 9 pairs of microtubules surrounding a central pair
  • generate movement by moving in a propeller like way
• Cilia

  • have a central core called the axoneme
  • primary - nine plus zero arrangement
  • motile - nine plus two arrangement
  • can help to move substances internally in organisms by beating synchronised
• Lysosomes

  • contain digestive enzymes
  • break down dead organelles
• Cytoskeleton

  • maintains shape of cell
  • holds the organelles into position
  • allows cytoplasm and vesicles to move
  • enables cells in multicellular organisms to move
  • microfilaments - thicken the cortex around the inner edge of a cell and resist tension
  • intermediate filaments - hold organelles in place
  • microtubules - maintain cell shape by resisting compressive forces
• Microtubules

  • widest part of the cytoskeleton (25nm diameter)
  • Small hollow tubes made from 2 globular proteins
  • can disassemble and reform quickly
  • help cell resist compression
  • pull chromosomes to opposite ends during mitosis
  • help vesicles move through cell