Lecture notes
Cells
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- Queen Mary, University Of London (QMUL)
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Fatty Acid Synthesis→ A 2 carbon fatty acid (acetate) is
attached to an acyl carrier protein
(ACP).ACP acts as a carrier of the
growing fatty acid and swings it around
the enzyme activities of the enzyme
complex to complete synthesis of the fatty
acid.
→ A 3 carbon fatty acid (malonate) is also
attached to second ACP. This is going to
be used to extend the fatty acid chain.
1.The first enzyme activity in the complex
is a ketosynthase which joins the malonate
to the acetyl-ACP with the loss of CO2
and release of the ACP (HS-ACP).
→ In the first round of extension thus produces a 4 carbon chain with two carbonyl groups
(where 0 has a double bond). They are going to be reduced.
2. 2. Ketoreductase activity uses a hydrogen from NADPH to reduce the carbonyl group to a
hydroxyl (OH).
3. Dehyrdase removes water to generate a beta-enoyl group.
4. Enoyl reductase activity reduces this carbon to carbon double bond by adding back two
hydrogens (supplied by NADPH) thus, fully reducing the growing acyl chain.
6 further rounds adding 2 carbons each time to make palmitate (16 carbon chain), then a
thioesterase cleaves the fatty acid from the S-ACP.
2 hydrogen for 1 carbon= fully saturated. Fatty acid synthesis:
2 carbon+3 carbon unit= 4 carbon product+CO2
• Palmitic Acid: 16 carbon chain. Fully saturated acyl chain, common fat.
• Stearic Acid: 18 carbons, has all single bond.
• Oleic Acid: 18 carbons, has 1 double bond, we have to desaturase stearic acid to make it.
Polysaturated has more than one carbon to carbon double bond
Monounstarurated fatty acids has only one carbon to carbon double bond.
1
, o Oleic Acid- monounsaturated (1 double bond)
o Linoleic Acid- polysaturated (2 double carbon bond)
o Alpha-linoleic Acid- polysaturated (3 double carbon
bond)
Omega-6FA (linoelic acid)
Omega-3F (alpha-linoelic acid)
We do not have the desaturase
to remove the hydrogens from w3 or w6 carbons. These are
essential fatty acids, via diet.
Lipids
Stored primarily as triglycerides (triacylglcerols)
Made in Smooth Endoplasmic Reticulum.
2
, Cholesterol Ester
TAG from Smooth ER, is glycerol +Fatty Acids. This structure is used in the mitochondrion.
(Glycerol+FA-→ FA-CoA)-→ H2O+ATP
Amino Acids
• mRNA is translated into protein by ribosomes. The code is read in
triplets (codon)
Condensation Reaction:
It occurs in the ribosome.
Carbonyl bond (Carbon to Oxygen
double bond) is able to accept H-
bonds.
Nitrogen to Hydrogen bond group
of the secondary amide is able to
donate Hydrogen bonds.
3
, • Non-polar R groups: Amino acids are relatively unreactive
side chains. There are no Hydrogen bonding but weak Van der
Waal forces. They have hydrophobic side chains (often buried internally or in lipid phase).
Aromatic rings can interact with each with each other (π- π stacking). Aromatic ring can interact
weakly with polar groups.
(In Proline, amino group is a 2nd amide. Rings structure contains flexibility of peptide bond.)
• Polar R groups: Have reactive side chains. They have hydrophilic side chains and they
accept/donate Hydrogen bonds.
(In Cysteine, mildly, polar, often buried in the protein Has S-S-Cys bonds which is a disulfide
bridge. It stabilizes the protein fold. But can only form in an oxidizing environment.)
• Charged R groups:
Aspartic acid negatively charged
Glutamic acid acidic
These groups can
form salt bridges.
Lysine
They can form
Arginine positive/ basic
Hydrogen bonds.
Histidine
Delocalized electrons generate weak charge in aromatic side chains.
Delocalized electrons are available for electrostatic interactions with;
Other aromatic as π- π stacking
Cations (side chains of Lys, Arg, His, ions and ligands)
Levels of Protein Structure
Primary (10 )
Secondary (20 ) organizes folding within a single polypeptide
Tertiary (30 )
Quaternary (40 ) interaction between two or more polypeptides
4
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