Download Cell Structure and Function

Cell Structure and Function
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The biological universe consists of two
types of cells:
1. Prokaryotic cells
2. Eukaryotic cells
Prokaryotic Cells:
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Single celled organisms
 Simple internal organization
 Lack a defined nucleus
 Less than 1 micrometer in diameter
A Prokaryotic Cell
Cell Wall:
 Offers protection for the cell.
 Composed of carbohydrateprotein complex called
Peptidoglycan.
Plasma Membrane:
 Found on inside of cell wall.
 Responsible for the passing of
various nutrients across the
membrane.
Capsule:
 Cell may have additional
carbohydrate layer that disables
it from interacting with various
surfaces
Pili:
 Extensions that are longer than
Cilia
 Mainly used for Sexual
reproduction with other
bacteria.
 DNA is exchanged via pili.
 Not all bacteria have pili
Cilia:
 May contain cilia. Used to
swipe molecules towards the
cell for endocytosis.
Flagella:
 May Contain Flagella.
 Longer than Pili
 Used for motility
Ribosomes:
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Most ribosomes
(protein synthesizing
particles) are found in
the DNA free region
of the cell.
 Site of Protein
Synthesis
 Appear Granular on
images
Nucleoid Region
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The Genetic material (DNA) is
found in a single circular DNA
molecule that is folded back on
itself many times in the central
region of the cell. It appears as
a dark dense mass in the center
of the cell.
It may contain small circular,
independent units of DNA
called Plasmids.
– May contribute in ability to
adapt to rare environments.
– Used in biotechnology (See
genetics – Topic 4)
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Mesosome
– Infolding of the plasma
membrane to assist in
compartmentalization
(ex. Enzymes can be
found here)
Most prokaryotes studied in
laboratories are bacteria.
I.e.
– Escherichia Coli (E.
Coli) found in animal
intestine
Cyanobacteria
(Previously known as
Blue-green Algae)
Binary Fission
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Bacteria go through binary
fission as a method of
reproduction (Asexual
Reproduction)
Steps involved:
 DNA is copied
 Separation of DNA
molecules toward two ends
of cell
 Elongation of cell
 Division of cytoplasm and
plasma membrane
 Microtubules help separate
DNA. It is a protein called
FtsZ
Eukaryotic Cells:
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Includes all members of plant and animal
kingdoms
 Surrounded by a plasma membrane that separates
it from the external environment
 Range from 5-100 micrometers
 Internal membranes enclose specific
compartments, organelles and separates them from
the rest of the cytoplasm (Region of cell lying
outside the nucleus.)
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Largest organelle in Eukaryotic cell is the
nucleus. It is a membrane bound organelle
and holds most of the cellular DNA.
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Other organelles present in nearly all
eukaryotic cells:
 1. Mitochondria – responsible for cells
energy metabolism
 2. Rough and smooth endoplasmic
reticulum – network of membranes in which
certain proteins and lipids are synthesized.
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3. Golgi Vesicles – Direct membrane components
to appropriate places in the cell.
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4. Peroxisomes – Fatty acids and amino acids are
degraded.
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5. Lysosomes
- Animal cells, not plant cells
- Degrade worn-out cell constituents and foreign
materials taken in by the cell
6. Chloroplasts – Plant cells and certain
single celled organisms
 7. Vacuoles
- plant and some single celled eukaryotes
- large fluid filled organelles
- store nutrients and waste compounds
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8. DNA in nucleus – packaged into linear
structures called chromosomes
The Cell Membrane and The
Fluid Mosaic Membrane
Model
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A phospholipid
molecule contains:
1. 2 fatty acid chains
 2. Glycerol backbone.
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The head of the molecule
is Polar and Hydrophilic
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The tail of the molecule is
non-polar and
hydrophobic.
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A molecule that is both
hydrophilic and
hydrophobic is called
AMPHIPATHIC.
What happens when phospholipids
are put in water…
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Attraction and repulsion
of polar head group and
non-polar tail group,
respectively.
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Forming a spontaneous
spherical bilayer –
Hydrophilic heads
facing the outside
Hydrophobic tails
facing eachother
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The Cell Membrane
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The cell membrane is composed of a
phospholipid bilayer.
 There are also other components within the
bilayer:
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Proteins
Glycoproteins
Glycolipids
Cholesterol
The Fluid-Mosaic Membrane
Model
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Phospholipid molecules and proteins that
are embedded in the membrane tend to drift
sideways. This supports the idea of the cell
membrane having a Fluid Consistency.
In the cell membrane we find:
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Proteins
 Carbohydrates
 Cholesterol
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Why do we need these components in the
cell membrane?
Proteins
There are two types of membrane proteins:
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1. Peripheral or Extrinsic Proteins
They do not interact with hydrophobic core
of phospholipid bilayer.
 Bound to polar head of the phospholipid or
 Bound to the integral or intrinsic proteins
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2. Integral or Intrinsic Proteins
Embedded in the phospholipid bilayer
They can be :
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Transmembrane (Span the entire phopholipid
bilayer)
Lipid-anchored (Anchored to one of the
phospholipid layers)
Function:
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On the Extracellular
surface
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1. Cell-cell signaling
2. Cell surface receptors
(I.e. Hormones use these
receptors to transmit
messages into the cell)
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Within the Membrane
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1. Proteins form
channels and pores to
move molecules
across the membrane
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On the Cytosolic Face
of membrane
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1. Proteins anchor
cytoskeletal proteins
that support the
membrane and send
signals to various parts
of the cell.
Carbohydrates
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Are found bound to either
Proteins – called glycoproteins
 Lipids – called glycolipids
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Purpose:
1. They help increase hydrophilic character
of lipids and proteins
 2. Stabilize conformation (or shape) of
many membrane proteins.
Cholesterol
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Generally, the cell membrane is
– Fluid-like
– And has drastic changes in physical properties
over a very narrow temperature range:
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High temperature – Very Fluid
Low temperature – Gel-like
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This steroid sits
between the
phospholipid tails of
the bilayer.
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Cholesterol maintains
the favored fluid-like
consistency.
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How does cholesterol
maintain the fluid-like
consistency?
1. At higher temperatures, cholesterol
makes the membranes less fluid by making
the fatty acid chains less mobile
 2. At lower temperatures, cholesterol keeps
membranes fluid by preventing the fatty
acid chains of the phospholipid from
binding to one another.
Recap of New terms:
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1. Peripheral or Extrinsic Proteins
 2. Integral or Intrinsic Proteins
– Transmembrane
– Lipid-anchored
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3. Extracellular surface
4. Cytosolic Face
5. Glycoproteins
6. Glycolipids
7. Fluid-like
8. Gel-like