Transcript The Cell Membrane

Unit 1: Biochemistry (2.1)
Structures and Functions in
Eukaryotic Cells
Eukaryotic Cells
 Animals, plants, fungi and protists are
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composed of eukaryotic cells.
All eukaryotic cells have the following
in common:
 DNA contained within a membranebound nucleus
 a cell membrane comprised of a
phospholipid bilayer
 jelly-like cytoplasm
Animal Cell
Plant Cell
Nucleus
 Control centre of the cell
 contains DNA/genes/chromosomes,
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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
Nucleus cont’d
 May contain an area called nucleolus
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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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Endoplasmic Reticulum
 The nuclear envelope is connected to and part
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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)
Smooth Endoplasmic Reticulum
 Regions of the ER which do not have bound
ribosomes are called smooth endoplasmic
reticulum.
 The SER synthesizes lipids and lipidcontaining 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.
Endoplasmic Reticulum
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Ribosomes
 Tiny organelles found in cytoplasm and
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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
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.
Functions of the Endomembrane System
 On the surface of the RER, polypeptides
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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.
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.
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.
LYSOSOMES
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.
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.
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.
Plant Cell
Cell Structures Animation – Review
 http://www.youtube.com/watch?v=LP7x
Ar2FDFU&feature=related
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 sun’s energy is captured.
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.
Cytoskeleton
 An internal network of protein fibres in all
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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.
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 9+3 pattern.
 They organize the assembly of
microtubules during cell division.
 They replicate during the interphase
stage.
Centrioles cont’d
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.