Eukaryotic cell structure

• what is a cell


  the basic unit of all living things
• what are prokaryotic cells

  single celled organisms with a simple structure of just a single undivided internal area called the cytoplasm which is composed of cytosol
• what's cytosol composed of?

  water, salts and organic molecules
• what are eukaryotic cells?

  cells that contain a membrane bound nucleus (nucleoplasm) and cytoplasm, which contain many membrane-bound cellular components
• Eukaryotic cells make up multicellular organisms like plants, animals and fungi
• what's the ultrastructure of a cell?

  features that can be seen using an electron microscope
• metabolism 


  involves both the synthesis (building up) and the breaking down of molecules
• membranes 


  selectively permeable and control the movement of substances into and out of the cell and organelles but they're fragile
• features common to all eukaryotic cells:

  cell surface membrane, cytosol, ribosomes, centriole, cytoskeleton, mitochondria, nucleus, nucleolus, Rough Endoplasmic Reticulum, Smooth Endoplasmic Reticulum, microtubule network, vesicles, secretory vesicles, golgi apparatus
• nucleus


  contains coded genetic information in the form of DNA molecules
• DNA directs the synthesis of all proteins required by the cell (though it happens outside the nucleus). This way, the DNA controls the metabolic activities of the cell, as many of these proteins are the enzymes required for metabolism to occur
• DNA is contained within a double membrane called a

  nuclear envelope to protect it from damage in the cytoplasm
• the nuclear envelope contain nuclear pores which allow molecules to move into and out of the nucleus
• what is dna transcribed into and why?

  DNA is too large to leave the nucleus to the site of protein synthesis in the cytoplasm and is therefore transcribed into RNA which are exported via the nuclear pores
• DNA associate with proteins called histones to form a complex called chromatin
• what do chromatin coil and condense to form?

  Chromosomes
• nucleolus


  an area found within the nucleus responsible for producing ribosomes
• What is the nucleolus composed of?

  Proteins and RNA. The RNA is used to produce ribosonal RNA (rRNA) which then combines with proteins to form the ribsomes needed for protein synthesis
• Mitochondria


  the site of the final stages of cellular respiration, where the energy stored in the bonds of complex, organic molecules are made available for the cell to use by the production of the molecule ATP.
• the number of mitochondria in a cell usually reflects the amount of energy used by the cell, so very active cells will have more mitochondria
• Mitochondria


  • Have a double membrane
  • Inner membrane is highly folded to form structures called cristae
  • Fluid interior is called the matrix
  • Membrane forming the cristae contains the enzymes used in aerobic respiration
  • Contain a small amount of DNA, called mitochondrial (mt)DNA
  • Can produce their own enzymes
  • Can reproduce themselves
• vesicles


  membranous sacs that have storage and transport roles. they consist simply of a single membrane with fluid inside. Vesicles are used to transport materials inside the cell.
• lysosomes


  speciallised forms of vesicles that contain hydrolytic enzymes. They're responsible for breaking down waste materials in cells, including old organelles.
• lysosomes play an important role in the immune system as they're responsible for breaking down pathogens ingested by the phagocytic cells
• Cytoskeleton


  A network of fibres necessary for the shape and stability of a cell, present throughout the cytoplasm of all eukaryotic cells
• Cytoskeleton


  • Holds organelles in place
  • Controls cell movement and the movement of organelles within cells
• Components of the cytoskeleton

  • Microfilaments
  • Microtubules
  • Intermediate fibres
• Microfilaments


  Contractile fibres formed from the protein actin, responsible for cell movement and cell contraction during cytokinesis
• Microtubules


  Globular tubulin proteins that polymerise to form tubes, used to form a scaffold-like structure that determines the shape of a cell, act as tracks for the movement of organelles, including vesicles, around the cell, and compose spindle fibres which have a role in the physical segregation of chromosomes in cell division
• Intermediate fibres


  Give mechanical strength to cells and help maintain their integrity
• centrioles


  centrioles are a component of the cytoskeleton composed of microtubules. 2 associated centrioles form a centromere, which is involved in the assembly and oragnisation of spindle fibres during cell division
• flagella 


  (whip like) extentions to a cell. Enable cell motility. In some cells, they are used as a sensory organelle detecting chemical changes in the cells environment
• cillia


  (hair like)- smaller than flagella but there are usually larger numbers. Can be mobile OR stationary. Stationary cillia have an important function in sensory organs such as the nose. Mobile cillia beat in a rhythmic manner causing fluids/liquids to move. E.g. in the trachea to move mucus away from the lungs
• endoplasmic reticulum 


  network of membranes enclosing flattened sacs called cristernae. Connected to the outer membrane of the nucleus
• Smooth Endoplasmic Reticulum


  Responsible for lipid and carbohydrate synthesis and storage
• Rough Endoplasmic Reticulum


  Responsible for sythesis and transport of protein
• Ribosomes 


  Site of protein synthesis
• Golgi Apparatus 


  Responsible for modifying and 'packaging' proteins into vesicles. Secretory vesicles leave the cell whereas lysosomes stay
• Protein synthesis


  1. Proteins are synthesised on the ribosomes bound to the endoplasmic reticulum

  2. They then pass into its cisternae and are packaged into transport vesicles

  3. Vesicles containing the newly synthesised proteins move towards the Golgi apparatus via the transport function of the cytoskeleton

  4. The vesicles fuse with the cis face of the Golgi apparatus and the proteins enter

  5. The proteins are structurally modified before leaving the Golgi apparatus in vesicles from its trans face
• Secretory vesicles


  Carry proteins that are to be released from the cell