Organelles

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Organelles

• Control
• Nucleus (plant and animal)
• Centrosome (plant and animal)
• Assembly, Transport, and Storage
• Endoplasmic reticulum (plant and animal)
• Ribosomes (plant and animal)
• Golgi apparatus (plant and animal)
• Vacuoles (plant -1 large, and animal -
  many)
• Lysosomes (animal)
• Leucoplasts (plant only)
• Energy transformations
• Chloroplasts and chromoplasts (plant only)
• mitochondria (plant and animal)

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Figure 7.7 Overview of an animal cell
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Figure 7.8 Overview of a plant cell
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Nucleus

• Contains most of eukaryotic cells genetic
  library (mitochondria and chloroplasts contain
  their own DNA)
• Largest organelle
• Enclosed by nuclear envelope or membrane, which
  is a double membrane each of which is a lipid
  bilayer!!!
• Nuclear envelope has pores in it
• Nuclear lamina lines nuclear side of envelope a
  net-like array of protein filaments that maintain
  nuclear shape. May also be a nuclear matrix that
  extends into the entire nucleus
• Contains inactive DNA chromatin
• When gets ready to divide, chromatin condenses
  into chromosomes
• Directs protein synthesis by synthesizing mRNA
  and sending to ribosomes in the cytoplasm
• DNA ? mRNA ? protein (transcription and
  translation)

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Figure 7.9 The nucleus and its envelope 
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Nucleolus

• Prominent structure in non-dividing nucleus
• Ribosomal RNA and ribosomal subunits are made here

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Ribosomes

• Sites of protein synthesis
• Are made of rRNA and protein
• Made of two subunits one acts as attachment
  point for beginning of translation, other acts as
  cap to prevent mRNA from moving until tRNA has
  brought in appropriate amino acid
• Cells with high rates of protein synthesis have
  MANY ribosomes (human pancreas cell has MILLIONS
  of ribosomes)
• Are free ribosomes in cytosol that make
  proteins for the cell that they are inside of
• Ribosomes that are attached to endoplasmic
  reticulum (bound) are making proteins for
  packaging and export

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Figure 7.10 Ribosomes
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Endomembrane system

• Membranes in cell are not identical in structure
  or function (modifications are present according
  to job)
• Includes nuclear envelope, e.r., Golgi apparatus,
  lysosomes, vacuoles, plasma membrane

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Figure 7.16 Review relationships among
organelles of the endomembrane system 
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Endoplasmic reticulum

• EXTENSIVE accounts for more than half the total
  membrane system in eukaryotic cells
• Name means little net within the cytoplasm
• Smooth and rough e.r. are actually connected, not
  distinct, separate sections

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Figure 7.11 Endoplasmic reticulum (ER)
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Smooth e.r.

• Functions in synthesis of lipids, metabolism of
  carbs, detoxification of drugs and poisons
• Lipids oils, phospholipids, steroids
• (sex hormones and adrenal hormones)
• Liver cells glycogen gets converted to glucose
  phosphate which cannot leave cell, so e.r. makes
  enzyme that converts this to glucose
• Detox liver adds hydroxyl groups to drugs,
  makes them soluble and able to be flushed out of
  body

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Rough e.r.

• Makes secretory proteins
• (ex. Insulin made by pancreatic cells)
• Most are glycoproteins (proteins covalently bound
  to carbs)
• Once formed, e.r. membrane keeps the secretory
  proteins separate from the other proteins, and
  the secretory proteins will be wrapped in
  transport vesicles for outside transport
• Rough e.r. is also a membrane factory grows by
  adding proteins and phospholipids parts can be
  taken from here and added to other membrane
  systems using the vesicles for transport

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Golgi apparatus

• Finishes, sorts, ships cell products
• Has cis (entrance) side and trans (exit) side
• Golgi will modify products as needed gives more
  variety by removing some monomers and
  substituting others
• Knows what to do by using molecular
  identification tags (like phosphate groups) even
  adds molecules on their membranes that may
  recognize docking sites on organelle surfaces
  or on the cell membranes of other cells

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Figure 7.12 The Golgi apparatus
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Lysosomes

• Membrane-bounded sac of hydrolytic enzymes
• Different lysosomes break down each of the major
  classes of macromolecules proteins,
  polysaccharides, fats, nucleic acids
• Work best at pH of 5
• Using active transport to maintain this pumps
  hydrogen ions from cytosol into itself
• Used in autophagy recycle the cells own
  organic material for use
• Can also be used in programmed destruction of
  cells by lysosomal enzymes ex. Tadpole loses
  tail
• Related diseases Pompes and Tay-Sachs (pg. 122)

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Figure 7.13 Lysosomes
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Figure 7.14 The formation and functions of
lysosomes (Layer 1)
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Figure 7.14 The formation and functions of
lysosomes (Layer 2)
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Figure 7.14 The formation and functions of
lysosomes (Layer 3)
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Mitochondria and Chloroplasts

• Mitochondria cellular respiration
• Chloroplasts photosynthesis
• we will go over these in DETAIL with the next
  unit!!!

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Figure 7.17 The mitochondrion, site of cellular
respiration
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Figure 7.18 The chloroplast, site of
photosynthesis
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Peroxisomes

• Job is to generate and degrade hydrogen
  peroxidecontain enzymes that transfer hydrogen
  from various substrates and make H2O2 as a
  by-product
• Bounded by single membrane
• H2O2 is toxic, but peroxisomes contain enzymes
  that convert it to water.
• glyoxysomes in plants are specialized
  peroxisomes that convert fatty acids to sugar in
  seedlings (below soil level) until they can
  photosynthesize

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Figure 7.19 Peroxisomes