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Cell biology summary course 5/term 2

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This summary consists of 28 pages. It is a summary of all the lectures given in course 5 of the study Life Sciences at HAN. The summary contains clear figures

Last document update: 3 year ago

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Lesson 1 Cells and organelles & membrane structure

Eukaryotic cell




Mitochondria and chloroplasts
An anaerobic bacterium once engulfed an aerobic bacterium, the
mitochondria
Ú Mitochondria has their own DNA, ribosomes, RNA and proteins
Ú Mitochondria has a double membrane

An early eukaryotic cell once engulfed a photosynthetic bacterium, the
chloroplasts
Ú Chloroplasts has their own DNA, ribosomes, RNA and proteins
Ú Chloroplasts has a double membrane

Plasma membrane
Ú Defines a cell
Ú Provides shape and strength (together with cytoskeleton)
Ú Important in facilitating:
o Intercellular communication
o Exchange of substances (import and export)
o Cell growth and mobility

Consists of:
Ú Lipids, proteins and sterols (cholesterol)
o Selective barrier
o Bilayer
o Non-covalent interactions
o Fluid bilayer




1

,Phosphoglycerides (phospholipids)
Ú Amphiphilic: hydrophilic head – hydrophobic tail
Ú 1 phosphate, 1 glycerol, 2 fatty acids (hydrocarbon tail)

Phospholipids and sphingolipids are the major phospholipids in
cell membranes
Ú Sphingolipids do not have a glycerol, but a sphingosine
Ú Sphingolipids have 1 fatty chain and 1 fatty acid tail

Sterols
Ú Cholesterol: most common sterol in plasma membrane
Ú 4 ring structure
Ú Cholesterol stabilizes and stiffens membrane
Ú Hydroxyl group is oriented towards the polar
head group

Membrane composition differs between various cells and organelles. Depending on which
cell and function of place within a cell, the membranes have various compositions

Free-energy costs is minimized in the following structures  self-organization




Lipid bilayer is a fluid
Ú Fluid bilayer
Ú Lateral diffusion possible
Ú Flip-flop occurs rarely (enzymatic)

Fluidity depends on its composition
Ú Saturated hydrocarbon chains make the membranes less fluid
Ú Unsaturated hydrocarbon chains make the membrane more fluid

Lipids rafts
Ú Enriched in cholesterol and sphingolipids and glycolipids
(sugar lipids)
Ú Facilitate protein-protein interactions

Membrane proteins
Ú Give properties to the cell membrane
Ú Proteins can associate in various ways with the membrane
Ú Amphiphilic
Ú Transmembrane proteins (stick out on 2 sides)


2

, Ú Membrane-associated protein of peripheral membrane proteins (only stick out on 1
side)
Types of membrane proteins
Transmembrane/integral membrane proteins
1 Single ⍺-helix


2 Multiple ⍺-helixes


3 β-barrel

Peripheral membrane proteins
4 Peripheral protein with ⍺-helix attached


5 Covalent bound lipid chain

6 Covalent bound lipid chain

7 Bound to other proteins


8 Bound via other proteins



Transmembrane protein
Ú Amino acids IN the membrane are hydrophobic
Ú Most transmembrane proteins cross the lipid bilayer with an ⍺-helix
o Why ⍺-helix formed?  no water present, so H-H bonds are
formed with each other since there is no water
Ú Transmembrane part is 20-30 amino acids long

Hydropathy plots predict membrane proteins
Amino acids in the transmembrane region are mostly hydrophobic,
since the transmembrane part is 20-30 AA long, and it is below the
0  hydrophilic (everything below 0 is hydrophilic)
Graph A: passes the membrane once (above the 0  hydrophobic),
so it is a transmembrane protein with a single ⍺-helix
Graph B: passes the membrane 7 times, so it is a
transmembrane protein with multiple (7) ⍺-helices

Transmembrane ⍺-helix interacts with each other for
proper structure and function



3

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