Transcript Review of cells

Trends in Biomedical Science
Review of cells
Cell Theory
Cell Theory
1. All organisms are made of cells.
2. Cells are the smallest living things.
3. Cells are only made from parent cells.
All cells today come from the first living cells.
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Cell size is limited.
-As cell size increases, it takes longer
for material to diffuse from the cell
membrane to the inside of the cell.
Surface area-to-volume ratio: as a
cell increases in size, the volume
increases 10x faster than the surface
area
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Microscopes are needed to see cells.
Light microscopes can resolve
structures that are 200nm apart.
Electron microscopes can resolve
structures that are 0.2nm apart.
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All cells have certain structures in
common.
1. genetic material – in a nucleoid or
nucleus
2. cytoplasm – a semifluid matrix
3. plasma membrane – a phospholipid
bilayer
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Eukaryotic cells
-have a membrane-bound
nucleus
-separate many cellular functions
within organelles and the
endomembrane system
-have a cytoskeleton for support
and to maintain cellular structure
and transport within the cell
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Cells are not
just bags of
chemicals.
They are
crowded with
many
organelles
which interact
with each other.
Each color
represents a
structure with a
unique function and
composition
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Nucleus
-stores the genetic material of the cell
in the form of multiple, linear
chromosomes
-surrounded by a nuclear envelope
composed of 2 phospholipid bilayers
-in chromosomes – DNA is organized
with proteins to form chromatin
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The nucleus has a 3 dimensional (3D)
structure.
Special parts (compartments) of the nucleus
are where chromosomes are transcribed
and replicated.
Chromosomes seem have special areas
(chromosome territories).
Different parts of chromosomes are next to
other chromosomes in different tissues.
Gene-dense human chromosomes are
found in the center of the nucleus,
while gene-poor chromosomes are
found near the boundary of the
nucleus.
Nuclear organization is highly specific
and has functional relevance to the
cell. The organization gives proper
gene expression, replication and the
stability of the genome.
Nuclei are intricately structured, and nuclear
metabolism has an elaborate spatial
organization. The architecture of the nucleus
includes two overlapping and nucleic-acid
containing structures - chromatin and a nuclear
matrix.
The nuclear matrix is a ribonucleoprotein (RNP)
network.
The ultrastructure of the nuclear matrix is well
characterized and consists of a nuclear lamina
and an internal nuclear network of
subassemblies linked together by highly
structured fibers.
These complex fibers are built on an underlying
scaffolding of branched 10-nm filaments that
connect to the nuclear lamina.
The nuclear matrix is a nuclear skeletal
structure that is believed to be
involved in many nuclear functions
including DNA replication,
transcription, repair, and pre mRNA
processing/transport.
The nuclear matrix is now thought to be
dynamic.
This thinking is partly based on the
tracking of the intranuclear movement
of proteins tagged with
fluorochromes.
Representation of nuclear compartments.
Nuclear pore complexes allow the transport
of molecules across the nuclear envelope.
This transport includes RNA and ribosomal
proteins moving from nucleus to the
cytoplasm and proteins (such as DNA
polymerase and lamins), carbohydrates,
signaling molecules and lipids moving into
the nucleus.
The nuclear pore complex (NPC) can
actively conduct 1000 translocations per
complex per second.
Structure and function of the nuclear lamina.
http://en.wikipedia.org/wiki/File:Structure_and_function_of_the_nuclear_lamina.jpg
Creative Commons Attribution 2.0 Generic license
The nuclear lamina is a dense (~30 to 100 nm
thick) fibrillar network inside the nucleus of
a eukaryotic cell, on the inner surface of the
inner nuclear membrane (INM). It is composed
of intermediate filaments and membrane
associated proteins. Besides providing
mechanical support, the nuclear lamina
regulates important cellular events such as DNA
replication and cell division. It organizes
chromatin and binds nuclear pore complexes
(NPCs) and nuclear envelope proteins (purple)
and transcription factors (pink).
Ribosomes
-the site of protein synthesis in
the cell
-composed of ribosomal RNA
and proteins
-found within the cytosol of the
cytoplasm and attached to
internal membranes
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Endomembrane system
-a series of membranes throughout the
cytoplasm
-divides cell into compartments where
different cellular functions occur
1. endoplasmic reticulum
2. Golgi apparatus
3. lysosomes
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An insulinproducing
pancreas cell
contains
thousands of
membraneenclosed
compartments.
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Phospholipid membranes form a barrier that
most molecules cannot cross. But living cells
need to be able to interact with their
environment.
Membrane proteins that contact the spaces
on both sides of the membrane are gates
between cellular compartments. Each type
of compartment has a specific population of
membrane proteins that largely define its
function. On average, proteins make up
about half the mass of membranes.
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Nuclear pore complexes on the nuclear membranes of frog oocytes as
seen from the cytoplasm (left) and from inside the nucleus (right)
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Rough endoplasmic reticulum (RER)
-membranes that create a network of
channels throughout the cytoplasm
-attachment of ribosomes to the
membrane gives a rough appearance
-synthesis of proteins to be secreted,
sent to lysosomes or plasma
membrane
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Smooth endoplasmic reticulum (SER)
-relatively few ribosomes attached
-functions:
-synthesis of membrane lipids
-calcium storage
-detoxification of foreign
substances
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Golgi apparatus
-flattened stacks of
interconnected membranes
-packaging and distribution of
materials to different parts of the
cell
-synthesis of cell wall components
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Lysosomes
-membrane bound vesicles
containing digestive enzymes to
break down macromolecules
-destroy cells or foreign matter
that the cell has engulfed by
phagocytosis
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Microbodies
-membrane bound vesicles
-contain enzymes
-not part of the endomembrane system
-peroxisomes contain oxidative enzymes
and catalase
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Vacuoles
-membrane-bound structures with
various functions depending on the
cell type
There are different types of vacuoles:
-central vacuole in plant cells
-contractile vacuole of some protists
-vacuoles for storage
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Mitochondria
-organelles present in all types of
eukaryotic cells
-contain oxidative metabolism
enzymes for transferring the energy
within macromolecules to ATP
-found in all types of eukaryotic cells
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Mitochondria
-surrounded by 2 membranes
-smooth outer membrane
-folded inner membrane with layers
called cristae
-matrix is within the inner membrane
-intermembrane space is located
between the two membranes
-contain their own DNA
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Mitochondria
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Cytoskeleton
-network of protein fibers found in
all eukaryotic cells (probably all
cells)
-supports the shape of the cell
-keeps organelles in fixed
locations
-helps move materials within the
cell
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Cytoskeleton fibers include
-actin filaments – responsible for
cellular contractions, crawling,
“pinching”
-microtubules – provide organization
to the cell and move materials within
the cell
-intermediate filaments – provide
structural stability
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Actin filaments – light purple, microtubules – yellow, nuclei
– greenish blue
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Cell movement takes different
forms.
-Crawling is done using actin
filaments and the protein myosin.
(show Active membranes in fish skin
http://learn.genetics.utah.edu/content/begin/cells
/membranes/)
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Cytoskeleton is also connected to
proteins in the membranes of the
cell.
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Filaments attached to Membrane
Proteins.
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Other References
Inside the cell http://learn.genetics.utah.edu/content/b
egin/cells/insideacell/
MEMBRANES ORGANIZE CELLULAR COMPLEXITY
http://learn.genetics.utah.edu/content/be
gin/cells/membranes/
Inside the Cell
NIH Publication No. 05-1051
Revised September 2005
http://www.nigms.nih.gov
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