AS OCR Biology - Chapter 1 - Cell Structure

Notes on first chapter of AS OCR Biology.

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  • Created by: Alice
  • Created on: 14-05-11 13:30

Cell Organelles - Nucleus

Nucleus -

  • Only a few eukaryotes without nucleus; RBC's, phloem, etc.
  • Contains chromosomes - form tangle known as chromatin.
  • DNA carries code that instrucs cells about making proteins.

Nuclear Envelope - pair of membranes with gaps inbetween - gaps in envelope are nuclear pores.

Nucleolus - contains DNA being used to make ribsomes.

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Cell Organelles - Endoplasmic Reticulum

Smooth Endoplasmic Reticulum -

  • no ribosomes
  • not joined to nuclear envelope

Rough Endoplasmic Reticulum -

  • coverered in ribsomes
  • usually joined to nuclear envelope

Cisternae - enclosed spaces formed by membranes.

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Cell Organelles - Golgi Apparatus

Golgi Apparatus -

  • Not stable, always moving and changing.
  • Sacs join and break away all the time.
  • Used in protein synthesis.

Protein Synthesis Overview -

  • Protein made by ribosomes of RER.
  • Vesicles carry protein and join to Golgi.
  • Protein modified in Golgi, e.g. sugars added.
  • Vesicles carry modified proteins.
  • Secretion from cell by exocytosis.
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Cell Organelles - Lysosomes

Lysosomes -

  • Tiny bags of digestive enzymes.
  • 0.5 micrometre diameter.
  • Used for digestion - by fusion with bacteria, old/worn out organelles etc.
  • Enzymes in lysosome break down large molecules into soluble substances.
  • Substances disperse into the cytoplasm.
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Cell Organelles - Mitochondia

Mitochondria -

  • Site of aerobic respiration.
  • ATP made in them.
  • Lots of mitochondria in places where lots of energy is needed, e.g. muscle cells.
  • Each cell makes its' own ATP as it has to provide own energy.
  • Double membrane - inner membrane folded to form cristae.
  • Matrix is background material.
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Cell Organelles - Plasma (Cell Surface) Membrane

Plasma (Cell Surface) Membrane -

  • Thin layer of phospholipid molecules.

Phospholipids -

  • Hydrophobic tails (water-hating).
  • Hydrophilic heads (water-loving).
  • Tails closest together, heads on outside.
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Cell Organelles - Centrioles

Centrioles -

  • Make and organise microtubules made of tubulin.
  • Microtubules form spindle to move chromosomes in cell division.
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Cell Organelles - Cytoskeleton

Cytoskeleton -

  • Network of microfilaments.
  • Gives cell mechanical strength.
  • Provides 'tracks' for organelles to move along.
  • ATP needed, because energy needed to pull organelles.
  • Can help whole cell to move.
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Prokaryotic Cells

Prokaryotic Cells -

  • Always contain -
    • Circular DNA (no nucleus) - sometimes referred to as chromosome.
    • Peptidoglycan cell wall - crosslinked peptidoglycan.
    • ~20nm ribsomes - smaller than eukaryotic ribsomes.
    • Cytoplasm.
    • Plasma membrane.
  • Sometimes contain -
    • Pili - attachment to other cells or surfaces.
    • Plasmid of DNA - several may be present.
    • Capsule - additional protection.
    • Mesosome - associated with DNA during cell division.
    • Infolded plasma membrane - photosynthetic membrane.
    • Flagellum - movement of cell.
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Microscopes

Light -

  • 1400 x mag.
  • Use glass lenses to refract light rays.
  • Living specimens.
  • Cheap.
  • Unable to show objects smaller than 200nm across.

Electron -

  • TEM - pass electrons through thin specimen.
  • Very thin specimens, and stained.
  • 300,000 x mag.
  • Much finer detail - better resolution.
  • Dead specimens.

MAGNIFICATION = IMAGE SIZE / ACTUAL SIZE

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Comments

Tim

Detailed enough for an end of unit test.

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