The Cell – Label me!
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Learning Objectives
1.
Describe the fluid mosaic model of membrane structure and
explain the underlying reasons for this structure.
2.
Outline the roles of phospholipids, cholesterol, glycolipids, proteins
and glycoproteins in membranes.
3.
Outline the roles of the plasma membrane, and the roles of
membranes within cells.
Key words you should know
Glycoproteins
Glycolipids
Cholesterol
Proteins
Transport proteins
Receptor molecules
• Phospholipids
• Polar
• Hydrophilic
• Hydrophobic
• Micelles
• Phospholipid bilayer
• Fluid mosaic model
Cell membrane
• All living things are surrounded by a membrane.
A cell membrane is also known as plasma membrane.
Controls exchange of materials such as nutrients and waste
between cells and their environment.
Has other important functions for example to enable cells to
receive hormones.
To understand the function of anything in biology, you must
study the structure first!
Cell Membranes from Opposing Neurons
(TEM x436,740).
Nerve cell
Cell membrane {
Gap between cells
}
cell membrane
7nm wide
Nerve cell
Cell membranes are made of
PHOSPHOLIPIDs
• HYDROPHILIC heads (water
liking)
-Attracted to the water
• called POLAR
• HYDROPHOBIC tails (water
fearing)
-Not attracted to the water
• called NON-POLAR
A Phospholipid
A Phospholipid Bilayer
Phospholipids can form:
BILAYERS
-2 layers of phospholipids
with
hydrophobic tails protected
inside by the hydrophilic
heads.
The PHOSPHOLIPID
BILAYER is the basic
structure of membranes.
Structure of the cell membrane
Phospholipids
Cell membranes are made mainly of
phospholipids. They have:
HYDROPHILIC heads (water liking)
-Attracted to the water POLAR
HYDROPHOBIC tails (water fearing)
-Not attracted to the water NON-POLAR
Phospholipids can form BILAYERS
-2 layers of phospholipids with
hydrophobic tails protected
inside by the hydrophilic
heads.
The PHOSPHOLIPID BILAYER is
the basic structure of membranes.
Diagram representing the cell membrane
Remember the membrane is 7nm wide
Fluid mosaic model
Cell membranes also contain proteins within the phospholipid bilayer.
This ‘model’ for the structure of the membrane is called the:
FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins can move around freely within
the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when
the membrane is viewed from above.
Diagram of a cell membrane
Cell Membranes from Opposing Neurons
(TEM x436,740).
} Phospholipid Bilayer
7nm wide
STARTER: Features of the fluid mosaic model
•
Double layer – ……………………….of phospholipids which can move about by
………………………… in their own ……………………….
•
Phospholipid tails point inwards forming a …….………. and………………………… interior. The
phospholipid heads point outwards facing the aqueous (water containing) medium
surrounding the membrane.
•
Most protein molecules …………………. like icebergs in the layers, some are fixed to
………………………. inside the cell and don’t float.
•
Some proteins are embedded in the outer layer, some in the inner layer and some
………………… the two layers.
•
Hydrophobic and hydrophilic parts of the protein molecules sit next to the
…………………………… and ………………………….. portions of the ……………………………… of the
membrane. This ensures the proteins stay in the membrane.
•
The membrane is ……nm thick on average.
•
•
•
•
STRUCTURES
HYDROPHOBIC
NON-POLAR
FLOAT
•
•
•
•
•
PHOSPHOLIPIDS
7nm
MONOLAYER
BILAYER
DIFFUSION
• SPAN
• HYDROPHILIC
• HYDROPHOBIC
Features of the fluid mosaic model
•
Double layer – BILAYER of phospholipids which can move about by DIFFUSION in their own
MONOLAYER
•
Phospholipid tails point inwards forming a NON-POLAR HYDROPHOBIC interior. The
phospholipid heads point outwards facing the aqueous (water containing) medium
surrounding the membrane.
•
Most protein molecules float like icebergs in the layers, some are fixed to STRUCTURES
inside the cell and don’t float.
•
Some proteins are embedded in the outer layer, some in the inner layer and some SPAN the
two layers.
•
Hydrophobic and Hydrophilic parts of the protein molecules sit next to the HYDROPHOBIC
AND HYDROPHILIC portions of the PHOSPHOLIPIDS of the membrane. This ensures the
proteins stay in the membrane.
•
The membrane is 7nm thick on average.
Chemical nature of the plasma
membrane
water
acid
ethanol
water
acid
• Since bleeding occurs in the tubes containing _____________
,
water
at
70°C
ethanol
_____________
and _____________ the cell membranes must have been
destroyed in each of these tubes. _____________
and _____________
Acid
water at 70°C
denaturing
destroy the membrane by _____________
the protein molecules
Ethanol
embedded in the plasma membrane. _____________
dissolves the
phospholipid component of the membrane.
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Summary
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