CELL ORGANELLES

• Plasma membrane- structure- proka and euka


  Phospholipid bilayer with proteins embedded in the bilayer. Carbohydrates on extracellular surface.
• FUNCTION OF PLASMA MEMBRANE

  Only in eukaryotes

  Selectively permeable barrier between internal and external environments of a cell.
• Cytoplasm- function and structure- proka and euka


  No set structure: mainly fluid (the cytosol) which contains dissolved substances and enzymes. Site of many cell reactions, e.g. anaerobic respiration.
• Mesosome- proka only


  Infolding of the plasma membrane. Increases surface area of membrane. Higher rate of absorption of nutrients / excretion of wastes. Enzymes for respiration, photosynthesis are attached to membranes.
• Nucleoid - proka only

  Circular DNA molecules free in cytoplasm.

  carries bacterial genetic code. The main DNA molecule in the cell.
• Peptidoglycan cell wall- structure


  Rigid layer composed of sugars with amino acid side chains.

  β bonding enables cross links to form between molecules of peptidoglycan to form microfibrils.

  Peptide bonds provide stronger links than hydrogen bonding in cellulose.
• Mitochondria- structure


  This organelle has a double membrane.

  The inner membrane is folded to form cristae. The folding increases the surface area for the attachment of enzymes that are used in aerobic respiration.

  The molecule of DNA and 70S ribosomes enables mitochondria to synthesise their own proteins and to self-replicate (make copies of themselves).
• Rough endoplasmic reticulum (RER)- structure

  RER is a series of flattened membrane-bound sacs which are joined at some points to the nuclear envelope.

  It is covered in ribosomes.
• Smooth endoplasmic reticulum (SER)- structure

  SER is a series of flattened membrane-bound sacs which may be joined at some points to the nuclear envelope.

  It can also be attached to RER. SER has no ribosomes attached.
• Ribosomes- structure


  Made of two sub-units each containing ribosomal RNA – rRNA and proteins.

  Ribosomes in prokaryotic cells are small, 70S, and are free in the cytoplasm.

  Ribosomes in eukaryotic cells are larger, 80S, and can be found free in the cytoplasm and attached to RER.
• Golgi body- structure- euka only


  These are series of flattened membrane-bound sacs called cisternae.

  The cisternae are formed by the fusion of transport vesicles from RER.
• Nucleus- structure


  An organelle with two membranes forming the nuclear envelope.

  Nuclear pores in the nuclear envelope enable communication between the nucleus and the cytoplasm.

  mRNA leaves the nucleus through nuclear pores.

  Chromatin is made from DNA and histone proteins.

  Each nucleus can contain one or more nucleolus.
• Nucleolus- euka only


  A region of the nucleus which is darkly stained. Made from condensed chromatin.

  The nucleolus is responsible for the synthesis of ribosomal RNA and the production of the ribosomal sub-units.

  In highly active cells there can be several nucleoli.
• Centrioles- animal cells - structure


  Each centriole is made from 9 sets of three microtubules.

  A pair of centrioles is called a centrosome.

  A centriole is identical to the basal body of a flagellum / cilium.
• Chloroplasts- structure


  A double membrane with membrane-bound sacs inside.

  The internal membranes form structures called thylakoids which are stacked to form grana.

  Starch grains may be present.

  Each chloroplast has a molecule of DNA and 70S ribosomes which enables it to synthesise its own proteins and to self-replicate (make copies of itself).
• Plasmodesmata- plant cell only 


  Plasmodesmata (one = plasmodesma) are channels of cytoplasm that pass from one plant cell to another through the cell walls. Plasmodesmata enable substances to diffuse directly from one plant cell to another without having to cross cell membranes or cell walls.
• Vacuoles


  Plant cells usually have a large, permanent vacuole, a fluid-filled sac- surrounded by a membrane called the tonoplast. The fluid inside a vacuole is called cell sap.

  The vacuole stores water, nutrients and wastes. When full / turgid, the vacuole pushes against the cell membrane which increases turgour pressure in the cell and gives shape to the cell.
• Cellulose cell wall- plants only


  All plant cells have a cell wall containing cellulose. Cellulose microfibrils are made from beta glucose and are laid down in layers in different directions. Other chemicals, e.g. pectin and some proteins, are also found in the cell wall.

  Provides a strong, permeable layer which supports and protects the cell. Cellulose makes the cell wall tough (due to the large number of hydrogen bonds between microfibrils) but flexible.
• plasmids- proka only


  carry additional genes, e.g. antibiotic resistance genes and can be passed from one bacterium to another.
• peptidoglycan cell wall- proka only


  Determines the shape of the bacterial cell. Protection from toxic compounds. Protection from osmotic effects.
• mitochondria - function- euka only 


  Mitochondria synthesise ATP during aerobic respiration and produce most of the ATP in a eukaryotic cell.
• RER - FUNCTION- euka only


  The RER transports polypeptides synthesised by the ribosomes to the Golgi body. The ends pinch off to form transport vesicles containing polypeptides which then fuse to form Golgi bodies.
• SER - FUNCTION- euka only


  SER is involved in the synthesis and transport of lipids in eukaryotic cells.
• ribosomes - function- euka only


  Ribosomes carry out the translation stage of protein synthesis. They translate the code carried by messenger RNA – mRNA into chains of amino acids – polypeptides. This is where amino acids get joined together by peptide bonds to form polypeptides.
• golgi body - function- euka only


  Polypeptides are modified and processed by the addition of carbohydrate – glycosylation and the tertiary / quaternary structure of the final protein forms.

  The proteins, e.g. enzymes, are then packaged into: secretory vesicles which release their contents to the outside of the cell, lysosomes which release their contents into vesicles inside the cell usually to digest the contents of those vesicles.
• nucleus - function- euka only


  DNA in the chromosomes carries the genetic code which codes for polypeptides.

  It is responsible for controlling cell activities through the synthesis of different types of RNA.
• centriole - function- animal cell only


  Centrioles are responsible for producing and organising the spindle fibres that control cell division in animals.

  Flagella are made from microtubules and are able to move a whole cell, e.g. the tail of a sperm cell.

  Cilia are shorter and large numbers of them are used to move liquids over the surface of the cell, e.g. ciliated epithelium moving mucus out of the lungs.
• chloroplast - function


  Photosynthesis to produce glucose for respiration and carbohydrates to use as the building block for all organic compounds in a plant. Photosynthesis involves transferring light energy to chemical energy in ATP and then transferring the energy in ATP into glucose.
• prokaryotic cells


  DNA not enclosed in a nuclear membrane

  unicellular - protoctista
• prokaryotic cell organelles

  pili

  ribosomes 70s

  circular DNA

  mesosome

  cytoplasm

  flagellum

  capsule

  plasma membrane

  peptidoglycan cell wall
• eukaryotic cells


  DNA enclosed in a nuclear membrane

  multicellular - plant animal fungi

  larger than proka - 10 to 100 nanometres
• euka cell organelles -plant

  RER

  GB

  cellulose cell wall

  plasmodesmata

  nucleus contain DNA in linear chromo

  chloroplast

  ribosomes 80s

  large permenant vacuole

  tonoplast

  cytoplasm

  mitochondria
• euka cell organelles - animal

  microvilli

  golgi vesicle

  GB

  microtubule radiating from centrosome

  ribosome 80s

  plasma membrane

  SER

  RER

  mitochondria

  lysosome

  centrosome with 2 centrioles close to nucleus and at right angles