Running head: Cell Biology - BIO2001 1
Cell Biology - BIO2001
Summary
Name
Institution
Course
Tutor
Date
,Cell Biology - BIO2001 2
BIO2001 – Cell Biology
,Cell Biology - BIO2001 3
Cell membranes
Cell membranes are crucial to a cell. They are a dynamic fluid structure
containing a lipid bilayer impermeable to water soluble molecules and
membrane proteins that mediate all other functions of the membrane: like
signalling and transportation.
Plasma membrane: encloses the cell, defines its boundaries and
maintains the essential differences between the cytosol and the
extracellular environment.
Organelle membrane: maintain the differences between the contents of
the organelle and the cytosol.
Lipids: (about 50% of the mass of a cell membrane) are
amphiphilic molecules meaning they have a
hydrophilic/polar head and a hydrophobic/nonpolar end. They can move within
their bilayer (fluid mosaic model). Lipid bilayers are asymmetric: the lipid
composition of the two separate monolayers is strikingly different. They often
differ in charge, which is very important in signalling (bringing extracellular
signals inside the cell).
Phospholipids: most abundant, their polar head contains a phosphate
group and their tale is made of two hydrocarbon tails (fatty acids). One
tail can have cis-double bonds, which makes it
unsaturated and creates a kink in the tail. The other
does not contain double bonds and is therefore
saturated. Difference in length and saturation
influences how the phospholipids are packed together.
This, as well as temperature, influences fluidity of the
membrane. (higher temperature means more
movement of lipids)
o Phosphoglycerides (animal cells) contain a glycerol, phosphate
group and another head group (like choline) and two long chain
fatty acids.
o Sphingolipids contain sphingosine instead of glycerol. Serves as a
cell receptor site.
, Cell Biology - BIO2001 4
Glycolipids: have sugars attached instead of a phosphate-linked head
group. Are found exclusively in the monolayer facing away from the
cytosol. Are important for extracellular interactions. Protects the cell and
prevents it from becoming sticky, giving it a hydrophobic coting.
Sterols:
o Cholesterol: a ring structure with one polar hydroxyl group and a
short nonpolar hydrocarbon chain. It decreases mobility and
tightest the packing of lipids, which makes the membrane less
deformable and less affected by temperature changes.
o Sterols from plants are up taken by the cell and not released in the
blood stream.
Membrane fluidity has to be carefully regulated, since it can influence transport
processes and enzyme activities when reaching a certain threshold level.
Membrane proteins: (25-75% of the mass of the cell membrane)
Vary wildly in structure and the way they are associated with the
membrane. They are, just like lipids, amphiphilic, with hydrophobic and
hydrophilic regions. They are also able to diffuse/move in the plane of the
membrane.
o Integral membrane proteins (intrinsic): their hydrophobic parts
pass through the membrane and their hydrophilic regions are
exposed on either side of the membrane. They are transmembrane
proteins.
Single pass transmembrane proteins: the polypeptide
chain crosses the membrane only once
Cell Biology - BIO2001
Summary
Name
Institution
Course
Tutor
Date
,Cell Biology - BIO2001 2
BIO2001 – Cell Biology
,Cell Biology - BIO2001 3
Cell membranes
Cell membranes are crucial to a cell. They are a dynamic fluid structure
containing a lipid bilayer impermeable to water soluble molecules and
membrane proteins that mediate all other functions of the membrane: like
signalling and transportation.
Plasma membrane: encloses the cell, defines its boundaries and
maintains the essential differences between the cytosol and the
extracellular environment.
Organelle membrane: maintain the differences between the contents of
the organelle and the cytosol.
Lipids: (about 50% of the mass of a cell membrane) are
amphiphilic molecules meaning they have a
hydrophilic/polar head and a hydrophobic/nonpolar end. They can move within
their bilayer (fluid mosaic model). Lipid bilayers are asymmetric: the lipid
composition of the two separate monolayers is strikingly different. They often
differ in charge, which is very important in signalling (bringing extracellular
signals inside the cell).
Phospholipids: most abundant, their polar head contains a phosphate
group and their tale is made of two hydrocarbon tails (fatty acids). One
tail can have cis-double bonds, which makes it
unsaturated and creates a kink in the tail. The other
does not contain double bonds and is therefore
saturated. Difference in length and saturation
influences how the phospholipids are packed together.
This, as well as temperature, influences fluidity of the
membrane. (higher temperature means more
movement of lipids)
o Phosphoglycerides (animal cells) contain a glycerol, phosphate
group and another head group (like choline) and two long chain
fatty acids.
o Sphingolipids contain sphingosine instead of glycerol. Serves as a
cell receptor site.
, Cell Biology - BIO2001 4
Glycolipids: have sugars attached instead of a phosphate-linked head
group. Are found exclusively in the monolayer facing away from the
cytosol. Are important for extracellular interactions. Protects the cell and
prevents it from becoming sticky, giving it a hydrophobic coting.
Sterols:
o Cholesterol: a ring structure with one polar hydroxyl group and a
short nonpolar hydrocarbon chain. It decreases mobility and
tightest the packing of lipids, which makes the membrane less
deformable and less affected by temperature changes.
o Sterols from plants are up taken by the cell and not released in the
blood stream.
Membrane fluidity has to be carefully regulated, since it can influence transport
processes and enzyme activities when reaching a certain threshold level.
Membrane proteins: (25-75% of the mass of the cell membrane)
Vary wildly in structure and the way they are associated with the
membrane. They are, just like lipids, amphiphilic, with hydrophobic and
hydrophilic regions. They are also able to diffuse/move in the plane of the
membrane.
o Integral membrane proteins (intrinsic): their hydrophobic parts
pass through the membrane and their hydrophilic regions are
exposed on either side of the membrane. They are transmembrane
proteins.
Single pass transmembrane proteins: the polypeptide
chain crosses the membrane only once
