Unit 1: Biochemistry (2.1)

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Unit 1 Biochemistry (2.1)

• Structures and Functions in Eukaryotic Cells

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Eukaryotic Cells

• Animals, plants, fungi and protists are composed
  of eukaryotic cells.
• All eukaryotic cells have the following in
  common
• ? DNA contained within a membrane-bound nucleus
• ? a cell membrane comprised of a phospholipid
  bilayer
• ? jelly-like cytoplasm

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Animal Cell
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Plant Cell
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Nucleus

• Control centre of the cell
• contains DNA/genes/chromosomes, which stores and
  replicates the genetic information
• usually uncoiled (chromatin ? a mixture of DNA
  and proteins)? and are only visible in dividing
  cells
• The number of chromosomes varies from species to
  species

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Nucleus contd

• May contain an area called nucleolus containing
  RNA and proteins
• Surrounded by the nuclear envelope a dbl
  membrane to separate nucleus from the rest of the
  cell. The space btw the 2 membranes is called
  the lumen.
• The membrane contains nuclear pore complexes
  which allow water and ions to pass freely, but
  regulate the passage of macromolecules and RNA
• The nucleus directs cell division

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_________________________
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Endoplasmic Reticulum

• The nuclear envelope is connected to and part of
  a complex of membrane-bound tubules and sacs
  called the endoplasmic reticulum (ER).
• Made up of 2 parts the rough ER and the smooth
  ER
• Regions of the ER which synthesize proteins have
  ribosomes on their surface, hence the name RER.
• It is here that proteins which are a part of
  membranes or intended for export from the cell
  are assembled (whereas proteins that function in
  the cytosol are made by ribosomes suspended there)

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Smooth Endoplasmic Reticulum

• Regions of the ER which do not have bound
  ribosomes are called smooth endoplasmic
  reticulum.
• The SER synthesizes lipids and lipid-containing
  molecules such as phospholipids that make up
  membranes.
• The SER also performs other functions depending
  on the type of cell. For example, the SER in
  liver cells help detoxify drugs and alcohol.

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Endoplasmic Reticulum
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______________
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Ribosomes

• Tiny organelles found in cytoplasm and attached
  to the endoplasmic reticulum
• Composed of two subunits made of protein and RNA
• No membrane
• Function makes RNA into protein
• Found in both plant and animal cells
• Eukaryotic ribosomes are different in structure
  compared to those of prokaryotes.

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The Golgi Apparatus

• A stack of curved membrane sacs that packages,
  processes, sorts and distributes proteins,
  lipids, and other substances within the cell
• Acts like a post office for the cell

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The Endomembrane System

• The endomembrane system consists of the nuclear
  envelope, the ER, the Golgi apparatus and
  vesicles.
• This system synthesizes, modifies and transports
  proteins and other cell products.
• This system also isolates individual parts of the
  cell so that particular functions are restricted
  to specific regions.
• The organelles that make up the endomembrane
  system are connected to one another either
  directly or by transport vesicles.

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Functions of the Endomembrane System

• On the surface of the RER, polypeptides are
  produced by bound ribosomes and extruded into the
  lumen, rather than being released into the
  cytosol
• These polypeptides travel through the lumen to
  the SER, where they are stored and processed.
  When they are ready for transport, pieces of
  smooth ER pinch off to form vesicles containing
  the protein.

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Functions of the Endomembrane System

• Vesicles from the smooth ER travel across the
  cell to the cis face (entry face) of the Golgi
  apparatus. There, the vesicles merge with the
  membrane of the Golgi and release their contents
  into the interior. In the Golgi, some proteins
  are stored and others are modified further.
• When modified proteins are ready for transport,
  pieces of the Golgi apparatus pinch off from the
  trans face (exit face) to form vesicles. These
  vesicles transport the proteins to the cell
  membrane, or to other destinations within the
  cell.

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Additional Functions of the Endomembrane System

• Recall that the smooth ER is responsible for the
  creation and metabolism of lipids, including
  steroids and phospholipids that make up cell
  membranes and organelle membranes. The Golgi
  sorts, packages and distributes these lipids as
  well as proteins.
• The Golgi also manufactures macromolecules, such
  as carbohydrates, like pectin, a polysaccharide
  found in cell walls.
• In animal cells, the Golgi also produces
  lysosomes, which are membrane-bound sacs
  containing digestive enzymes.

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LYSOSOMES
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Lysosomes

• Lysosomes contain more than 40 enzymes that break
  down macromolecules into smaller ones that can be
  reused by the cell.
• They also break down parts of the cell that are
  old or no longer needed as well as bacteria and
  foreign particles that have been ingested by the
  cell.

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Peroxisomes

• Like lysosomes, but they are formed by breaking
  off of the ER. They break down excess fatty
  acids and hydrogen peroxide and participate in
  the creation of bile acids and cholesterol.
• They contain different types of enzymes than
  lysosomes (which catalyze hydrolysis rxns).
• The enzymes in peroxisomes break down many
  biological molecules and some toxic ones too.
  For example, the peroxisomes in liver cells
  oxidize and break down alcohol molecules.

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Vesicles and Vacuoles

• Vesicles are membrane-bound sacs used for the
  transport and storage of substances in the cell.
  They form by pinching off of cell and organelle
  membranes. They then fuse with cell and
  organelle membranes to release their contents. An
  animal cell typically contains many small
  vesicles however, plant cells contain a single,
  large central vesicle called a vacuole.
• This stores water, ions, sugars, amino acids,
  macromolecules and enzymes that break them down.
  The amount of water in the vacuole determines the
  turgor pressure of the plant cell, which causes
  the plant cell to be rigid.

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Plant Cell
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Cell Structures Animation Review

• http//www.youtube.com/watch?vLP7xAr2FDFUfeature
  related

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Chloroplasts

• The cells of eukaryotic organisms that carry out
  photosynthesis typically have one to several
  hundred chloroplasts
• These organelles contain the photosynthetic
  pigment chlorophyll, which absorbs light energy
  to convert CO2 and H2O into energy-rich glucose.
• Chloroplasts are filled with grana, which are
  stacks of chlorophyll-containing thylakoids. it
  is here that the suns energy is captured.

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Mitochondria

• All of the functions that a cell must perform
  need to be fuelled by an energy source. In
  eukaryotic cells, the mitochondria break down
  high-energy organic molecules (glucose) to
  convert stored energy into usable energy.
• Mitochondria have a smooth outer membrane and a
  folded inner membrane, called cristae. The
  fluid-filled space of the inner membrane is
  called the matrix.
• Both the mitochondria and chloroplasts contain
  some of their own DNA, which encodes some, but
  not all, of their own proteins.

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Cell Wall

• Cells of plants, fungi and some protists have a
  cell wall to protect and support the cell.
• It is generally made up of a combination of
  polysaccharides, glycoproteins, or both.
• Plant cell walls are made up of cellulose and
  pectins whereas fungal cell walls are made of
  chitin.

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Cytoskeleton

• An internal network of protein fibres in all
  cells. The fibres of the cytoskeleton extend
  through the cytoplasm, providing structure and
  anchoring the cell membrane and organelles in
  place.
• Vesicles and other organelles move along these
  fibres, which act like tracks.
• Refer to Table 2.1 on p. 66 to learn about the
  different protein fibres that make up the
  cytoskeleton.

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Centrioles

• Found in animal cells and are generally absent in
  plant cells.
• They are cylindrical structures that are composed
  of groupings of microtubules arranged in a 93
  pattern.
• They organize the assembly of microtubules during
  cell division.
• They replicate during the interphase stage.

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Centrioles contd
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Cilia and Flagella

• Are appendages that develop on the outside of
  some eukaryotic cells. If there are just 1 or 2
  appendages, they are called flagella. If many
  shorter appendages are present, they are called
  cilia.
• These structures are composed of an internal
  shaft of microtubules, covered with an outer
  membrane which is a continuation of the cell
  membrane.

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