AS BIOLOGY The ultrastructure of the cell

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AS BIOLOGY The ultrastructure of the cell

• LEARNING OBJECTIVES
• By the end of this section you should be able
  to-
• Recognise the following organelles from a diagram
  of the eukaryotic animal and plant cell (rough
  and smooth endoplasmic reticulum, Golgi
  apparatus, mitochondria, ribosomes, lysosomes,
  chloroplasts, plasma (cell surface) membrane,
  nuclear envelope, centrioles, nucleus, nucleolus
  and cilia).
• Outline the functions of the following
  structures-rough and smooth endoplasmic
  reticulum, Golgi apparatus, mitochondria,
  ribosomes, lysosomes, chloroplasts, plasma (cell
  surface) membrane, nuclear envelope, centrioles,
  nucleus, nucleolus and cilia.

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The Eukaryotic Cell

• The Beginnings
• Robert Hooke was the first person to observe
  cells in 1665.
• He looked at thin slices of cork under a very
  simple microscope.
• The cork appeared as little boxes which he called
  cells.
• In 1883 MathiasSchleiden and Theodor Schwann
  proposed that all plants and animals were
  composed of cells which were the basic building
  blocks of life.
• In 1855 Rudolf Virchow stated that new cells
  arise from the division of pre-existing cells and
  that chemical reactions needed for life occurred
  inside the cell.
• All this work led to the formation of the cell
  theory (click to complete exercise on cell
  theory)
• For more information click on link below
• http//fig.cox.miami.edu/cmallery/150/unity/cell.
  text.htm

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Eukaryotic Animal Cell

• Eukaryotic means true nucleus
• Eukaryotic cells have a nucleus which contains
  the DNA.
• Eukaryotic animal cells are surrounded by a cell
  membrane.
• Inside is the jelly like substance called
  cytoplasm.
• Contained in the cytoplasm is the nucleus and
  other organelles (copy the glossary file into
  your area and continue to add words and meanings)
• The other cell organelles include the endoplasmic
  reticulum,(rough smooth) mitochondria, Golgi
  apparatus, ribosomes, lysosomes, centrioles,
  cilia, nucleolus.

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Endoplasmic Reticulum

• STRUCTURE
• Complex system of sheet like double membranes
  continuous with the nuclear membrane
• Fluid filled spaces/sacs between the membranes
  called CISTERNAE which allow materials to be
  transported through cell
• Two types of ER
• smooth has no ribosomes attached (RER)
• rough has ribosomes attached (SER)

• FUNCTION
• Forms an extensive transport system
• Site of protein synthesis (Rough ER)
• Site of lipid, steroid and carbohydrate synthesis
  (smooth ER)
• Stores and transports these materials
• SEE DIAGRAM

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Mitochondria

• STRUCTURE
• Relatively large organelle
• Rod/sausage shaped 1um 5um
• Have a double membrane
• The outer controls the entry exit of materials
• Inner has many folds called cristae
• Surface of each crista is covered with stalked
  particles where ATP is made
• Mitochondria are filled with a jelly like matrix
• The matrix contains proteins, lipids, ribosomes
  and loops of DNA
• Mitochondria can replicate themselves when the
  cell divides

• FUNCTION
• Site of aerobic respiration (Krebs cycle
  oxidative phosphorylation)
• Responsible for the production of energy rich ATP
  molecules
• The numbers of mitochondria reflect the metabolic
  activity of the cell so large numbers are found
  in muscle and liver cells
• SEE DIAGRAM

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Golgi apparatus

• STRUCTURE
• Formed from small pieces of rough ER which form
  small vesicles which join to make a Golgi body
• Chemicals made in the ER collect in the Golgi
  body where they are modified
• Small vesicles can then be pinched off the
  Golgi body carrying new chemicals away which are
  secreted when the vesicle reaches the cell
  membrane
• Some of the vesicles become lysosomes

• FUNCTION
• Assembling glycoproteins (such as mucin) by
  combining carbohydrate and protein
• Transporting and storing lipids
• Formation of lysosomes
• Producing digestive enzymes
• Secretes carbohydrates which are used in the
  formation of plant cell walls and in insect
  cuticles
• SEE DIAGRAM

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Ribosomes

• STRUCTURE
• Small dense structures found in huge numbers.
• Can be attached to the rough ER of floating in
  the cytoplasm.
• Are about 20 25 nm in diameter in eukaryotic
  cells and slightly smaller in prokaryotic cells
• (80s type prokaryotic)
• (70s type eukaryotic)
• Made up from two sub units

• FUNCTION
• Synthesize proteins
• Synthesize enzymes
• SEE DIAGRAM

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Lysosomes

• STRUCTURE
• Small vacuoles formed when small pieces of Golgi
  body are pinched off
• Contain hydrolytic enzymes which digest materials
  in the cell
• SEE DIAGRAM

• FUNCTION
• Release enzymes which destroy worn out organelles
• Digest material taken into the cell (eg white
  blood cells which have engulfed a bacterium)
  phagocytosis
• Release enzymes to the outside of the cell which
  digest material around the cell exocytosis
• Completely break down cells after they have died
  autolysis

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Plasma (cell surface) membrane

• STRUCTURE
• This is the boundary between the cell cytoplasm
  the environment
• Is partially permeable
• Made up 45 protein 45 phospholipids with the
  remaining 10 cholesterol, glycoprotein
  glyolipids

• FUNCTION
• Controls movement of substances in out of the
  cell
• Forms a recognition site so that the bodys
  immune system can recognize its own cells
• Acts as a receptor site for the attachment of
  specific hormones and neurotransmitters.
• SEE DIAGRAM

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Nucleus, Nucleolus Nuclear envelope

• STRUCTURE
• Largest organelle in the cell (10um diameter)
• Surrounded by a nuclear membrane / envelope
• Double membrane outer is continuous with the ER
• Nuclear pores in the membrane allow the passage
  of large molecules in out (eg messengerRNA)
• Material inside the nucleus is called nucleoplasm
  this contains chromatin which makes up the DNA
  of the cell in non-dividing cells it is spread
  out and during cell division it condenses to form
  the chromosomes
• A spherical structure called the nucleolus is
  found in the nucleus this makes ribosomal RNA
  and assembles the ribosomes.

• FUNCTION
• Acts as the control centre of the cell through
  the production of mRNA and protein synthesis
• Retains the genetic material in the cell in the
  form of DNA / chromosomes
• Manufactures ribosomal RNA (rRNA) ribosomes
• Starts the process of cell division
• SEE DIAGRAM
• What have you learnt?
• Click here to complete the crossword

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Cilia

• STRUCTURE
• 3-10 um in length, 0.2um in diameter
• Made of rings of 9 pairs of microtubules
• Have basal body embedded in cytoplasm
• Rest extends from basal body
• Only a few types of cell possess cilia
• On cells which have cilia there are large numbers

• FUNCTION
• To move an entire organism (eg in paramecium it
  propels it through the water)
• To move material within an organism ( eg cilia in
  the lining of the respiratory tract)
• SEE DIAGRAM

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CENTRIOLES (not found in plant cells)

• Two short bundles of hollow cylinders
  (microtubules) positioned at right angles to each
  other
• Found just outside the nucleus in a clear area of
  cytoplasm called the centrosome
• Wall of each centriole is made of 9 triplets of
  tubes arranged at an angle
• During cell division they migrate to opposite
  poles to produce the spindle which helps to
  move the chromosomes during cell division
• SEE DIAGRAM

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Chloroplasts

• Found inside photosynthetic tissues of plants
  (abundant in palisade mesophyll cells of leaves)
• Flat discs 2-10 um in diameter 1um thick
• Have a double membrane called the chloroplast
  envelope
• Inner membrane folded into a series of lamellae
• Membrane controls the entry exit of substances
• Inside the membrane is a fluid stroma which
  contains the enzymes involved in photostnthesis
• Small amounts of DNA and oil are found in the
  stroma
• In stroma is a network of flattened sacs called
  thylakoids
• Grana (granum sing) are formed when many
  thylakoids are stacked together (like a pile of
  coins) (thylakoids also called lamella)
• Chlorophyll molecules are attached to the
  thylakoids
• Large starch grains are also present which act as
  a tempory store of charbohydrate made in
  photosynthesis
• SEE DIAGRAM
• Click here to label the eukaryotic animal cell

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Click here to play cell organelles catch phrase