Definitions

• Nucleus?


  A double membrane (nuclear envelope) with nuclear pores. Contains chromatin (DNA and histone proteins) and a nucleolus. The nucleus stores genetic information (DNA) and controls cellular activities. The nucleolus is responsible for ribosome production.
• Ribosomes?


  Composed of ribosomal RNA (tRNA) and proteins; these can be free int he cytoplasm or bound the thr rough endoplasmic reticulum (RER). Ribosomes are the site of protein synthesis, translating mRNA into polypeptide chains.
• Rough endoplasmic reticulum?

  A series of flattened membrane-bound sacs which are joined at some pints in the nuclear envelope, and has ribosomes attached to its membrane (giving it the 'rough' name). Its function is to transport and store proteins (i.e. trasnports proteins to the Golgi body)
• Smooth endoplasmic reticulum?

  A series of flattened membrane-bound sacs which are joined at some points in the nuclear envelope, but has no ribosomes/proteins attached to its membrane. SER synthesises lipifd, metabolises carbohydrates and detoxifies drugs.
• Golgi apparatus/body?

  Stacks of flattened membrane-bound sacs (cisternae) with a cis (receiving) and trans (shipping) face. The golgi body modifies, sorts and packages proteins for secretion or use within the cell.
• Mitochondria?

  Double membrane with an outer membrane and a highly folded inner mebrane (cristae), enclosing a matrix (aqueous solution within the inner membrane). Mitochondria are the site of aerobic respiration producing ATP which is used in metabolic processes such as exocytosis, protein synthesis and transcription.
• Chloroplasts?

  Double membrane with internal thykaloids arranged in stacks forming grana, surrounded by a fluid-filled stroma. Chloroplasts are the site of photosynthesis, converting light energy into chemical energy (glucose). Thykaloids contain the pigment chlorphyll which is essential for trapping light in the proccess of photosynthesis.
• Cell wall?

  Composed of mainly cellulose (and sometimes pectin), forming a rigid outer layer. The cell wall provides structural support, protection and helps maintian cell shape; is also a permeable layer which allows for the transport of substances.
• Lysosomes?

  Membrane bound organelles which contain strong digestive enzymes. Lysosomes giest macromolecules, old organelles and pathogens; involved in cellular waste disposal.
• Cytoskeleton?

  A network of protein fillaments and tubules. Provide structural support, maintains cell shape and enables cell movement.
• Vesicles?

  Small, memrane-bound sacs which trasnport materials within the cell, between organelles or to the cell membrane for secretion.
• Centrioles (animal cells only)?

  Cylindrical structures made of microtubules arranged in specific patterns. They are involved in cell division, helping to organise the mitotic spindle.
• Nucleolus?

  A region of the nucleus which is darkly shaded and made from condensed chromatin. Responsible for the synthesis of ribsomal RNA and for the production of ribsomal units (so essenitally ribsosomes synthesis).
• Plasemodesmata (plant cells only)?

  Channels of cytoplasm that pass through one plant cell to another through cell walls. Allow substances to diffuse directly from one plant to another without having to cross membranes/cell walls.
• Vacuoles?

  Plant cells usually have large, permanent vacuoles which are fluid-filled sacs surrounded by a tonoplast membrane. Contains cell sap and stores water, becoming turgid when full and increasing turgor pressure.
• Mesosomes?

  Infolding of the plasma membrane. Increases the sirface area of the membrane, enabling higher rates of absorption of nutrients. Enzymes for respiration and photosynthesis attached to membranes.
• Nucleoids?

  Carry bacterial genetic code and is the main DNA molecule within prokayotic cells.
• Plasmids?

  Carry additional genes - antibiotic resistance genes for example which can be passed from one bacterium to another.