B 2.2 - ORGANELLES AND COMPARTMENTALIZATION

• What are organelles?

  discrete structures in cells that are adapted to preform one or more vital functions
• why are organelles efficient

  they are specialized for a limited range of functions
• which organelles have no membranes

  ribosomes, centrioles, microtubules, proteasomes, nucleoli
• which organelles have a single membrane

  vesicles, vacuoles, rER, sER, golgi apparatus, lysosomes
• which organelles have a double membrane

  nuclei, mitochondria, chloroplasts, amyloplasts, chromoplasts
• which structures are not considered to be organelles

  cell wall, cytoskeleton and cytoplasm
• why is a cell wall not considered an organelle

  outside plasma membrane so are extracellular structures rather than organelles
• why is a cytoskeleton not considered to be an organelle

  consists of narrow protein filaments spread through much of the cell so are not discrete enough to be an organelle
• why is cytoplasm not considered to be an organelle

  not a discrete structure as it includes many different structures and preforms many functions
• why do prokaryotes have fewer organelles than eukaryotes

  cells are smaller and they concentrate on a more limited range of functions
• what is an advantage of having DNA in a nucleus (eukaryotes)

  safeguards the DNA and thus keeps it from being damaged
• what is the benefit in prokaryotic cells of not having the DNA in a nucleus

  translation can occur faster/ immediately because DNA and ribosomes are together in cytoplasm
• what is the disadvantage in eukaryotic cells of having the DNA in a nucleus

  translation does not happen instantly and has to leave nucleus through nuclear pores, thus mRNA can be changed/modified after transcription
• how is cytoplasm in eukaryotic cells arranged

  divided into compartments by membrane-bound organelles
• advantages of compartmentalisation - enzymes

  enzymes and substrates can be much more concentrated than if they were spread throughout the cytoplasm
• advantages of compartmentalisation - damage

  substances that could damage the cell can be kept inside the membrane of an organelle (e.g. digestive enzymes can kill a cell but is in lysosomes thus are contained)
• advantages of compartmentalisation - conditions


  conditions such as pH and temperature can be maintained at an ideal level for a particular process, which may be different to other processes
• advantages of compartmentalisation - movement

  organelles with their contents can be moved around within the cell
• advantages of compartmentalisation - area

  larger area of membrane available for processes that happen within or across membranes
• What does the mitochondria do?

  produce ATP via aerobic cell respiration
• how is mitochondria adapted for its function

  structure
• mitochondria structure helps its function - outer membrane


  outer membrane separates contents of the mitochondrion from the rest of the cell, thus creating a compartment specialised for the biochemical reactions of aerobic respiration
• mitochondria structure helps its function - inner membrane

  site of oxidative phosphorylation - conations electron transport chains and ATP synthase which together generate proton gradient and use it to produce ATP
• What are cristae?

  projections of the inner membrane that increase the SA available for oxidative phosphorylation
• mitochondria structure helps its function - intermembrane space


  between inner and outer membrnae where there are high concentrations of protons is generated by electron transport chains - volume is small so concentration gradient builds up quicker
• mitochondria structure helps its function - matrix


  contains all enzymes and substrates for the Krebs cycle and link reaction. By concentrating enzymes and substrates in the small volume of the matrix, the reactions of these 2 parts of aerobic respiration can be preformed more rapidly than if they were dispersed in cytoplasm
• What is the matrix?

  fluid filling the compartment inside the inner mitochondrial membrane
• adaptions of chloroplast for photosynthesis

  double membrane, thylakoids, fluid inside thylakoid, fluid around thylakoid
• adaptions of chloroplast for photosynthesis - double membrane

  forming outer chloroplast envelope
• adaptions of chloroplast for photosynthesis - thylakoids


  internal membrane which are an intense green colour due to chlorophyl and have fluid inside and out of it which contain enzymes
• What do chloroplasts do?

  absorb light ; produce ATP by photophosphorylation ; carry out chemical reactions of Calvin process
• chloroplasts - light absorption


  pigment molecules (in photosystems in thylakoid membrane) absorb light
• how does the thylakoid membrane help with chloroplast absorption

  large area of thylakoid membranes ensure that chloroplasts has a large light absorbing capacity
• how are thylakoids usually structured

  generally arranged in stacks called grana; more thylakoid = more light absorbed
• chloroplasts - ATP


  proton gradient needed between inside and out of thylakoid, thus allowing ATP synthesis to begin
• where is the calvin cycle preformed in the chloroplast

  stroma is where enzymes needed for Calvin process are kept
• what speeds up Calvin Cycle

  enzymes and substrate concentration
• what is needed in the Calvin cycle

  ATP and reduced NADP which are easily accessible because thylakoids produce them and are distributed through stroma
• What is the Calvin Cycle?


  The cycle that uses chemical energy to store chemical energy as sugars and incorporate CO2.
• why are proteins needed in the nucleus

  proteins synthesised by ribosomes in cytoplasm are needed to form part of the structure of chromosomes