Eukaryotic cells evolved from symbiosis
Ø Anaerobic cell derived from an archaeon (primitive nucleus) à aerobic bacteria (containing
outer membrane and plasma membrane) à loss of membrane derived from archaeal cell à
early aerobic eukaryotic cell (containing nucleus with internal membranes, and mitochondria
with double membranes).
Ø Anaerobic cell engulfed an aerobic bacterium to become an aerobic eukaryotic cell.
Ø Mitochondria contain own DNA.
, Ø Early eukaryotic cell + photosynthetic bacterium à eukaryotic cell capable of photosynthesis
(containing chloroplasts).
Ø Aerobic eukaryotic cell engulfed photosynthetic bacterium to become eukaryotic
photosynthetic cell.
Ø Chloroplasts contain own DNA.
Model organisms
E. coli
Ø Anaerobic bacteria in colon of mammals
Ø Necessary for digestion
Ø E. coli is able to replicate fast in simple medium
Yeast (S. cerevisiae)
Ø Simple eukaryotic cell
Ø Fungi
Ø Used in genetic experiments
Thale cress (Arabidopsis thaliana)
Ø One plant can have thousands of off springs within 8-10 weeks
Ø Small genome: 125 Mb in 5 chromosomes which all have been mapped
Fruit fly (Drosophila melongaster)
Ø Key to vertebrate development
Caenorhabditis elegans
Ø Adult worm has exactly 959 cells
Ø 70% of human genes are equivalent in C. elegans
Zebrafish (Danio rerio) and frog (Xenopus Laevis)
Ø Vertebrate development
Mouse (Mus musculus)
Ø Almost every human gene has a comparable gene in mice.
Ø More than 95% of the mouse genome is comparable with the human genome
Plasma membrane
Ø Isolation of the cell
Ø Gives shape and strength (together with cytoskeleton)
Involved in:
Ø Intracellular communication
Ø Exchange of substances (import and export)
Ø Cell growth and mobility
Ø Phosphoglycerides and sphingolipids are the major phospholipids in cell membranes.
Sterols
Ø Cholesterol is the most common sterol.
Ø Polar head group, rigid steroid ring structure and a nonpolar hydrocarbon tail.
Ø Cholesterol: polar head group, cholesterol-stiffened region and more fluid bottom region.
Ø Cholesterol stabilizes and stiffens membrane
Lipid bilayer is a fluid
Ø Fluid bilayer
Ø Lateral diffusion possible
Ø Flip-flop occurs rarely (enzymatic).
Ø Fatty acid tails, lipid head groups and water molecules on the
outside.
Fluidity depends on its composition
Ø Unsaturated hydrocarbon chains with cis-double bonds have moving tails.
Ø Saturated hydrocarbon chains have stiff tails.
Ø Saturated hydrocarbon chains make the membrane less fluid.
Ø Membrane composition differs between various cells and organelles depending on which
cell, function or place within a cell
Membrane proteins
Ø Give properties to the cell membrane
Ø Proteins can associate in various ways with the membrane
Ø Amphiphilic
Ø Transmembrane proteins
Ø Membrane-associated proteins or peripheral membrane proteins.
, 1. Single a-helix (transmembrane/integral)
2. Multiple a-helix (transmembrane/integral)
3. b-barrel (transmembrane/integral)
4. Peripheral protein with a-helix attached (perifer)
5. Covalent bound lipid chain (perifer)
6. Covalent bound lipid chain (perifer)
7. Bound via other proteins (perifer)
8. Bound via other proteins (perifer)
Ø Amino acids are hydrophobic/hydrophilic?
Ø Most transmembrane proteins cross the lipid bilayer with a a-helix.
Ø No water present, so H-bonds are formed with each other à most possible with a-helix
Ø Transmembrane part is 20-30 amino acids long
Hydropathy plots predict membrane proteins
Ø Amino acids in the transmembrane region are mostly hydrophobic
Solubilizing membrane proteins
Ø Detergent: small amphiphilic molecules
Ø Soluble in water
Ø At low concentration: monomeric in solution
Ø High concentration: form micelles
Ø Used to lyse cells and solubilize membrane proteins
Ø Hydrophobic end bind to hydrophobic region of membrane proteins
Glycocalyx
Ø The glycocalyx, also known as the pericellular matrix, is a glycoprotein and glycolipid covering
that surrounds the cell membranes of some bacteria, epithelia and other cells.
Ø Contains a carbohydrate layer with glycoproteins/lipids with sugar units attached.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller brittcoenen. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.35. You're not tied to anything after your purchase.
