Flashcards in 23 - Pentose Phosphate Pathway and Introduction to Lipids Deck (76):
What is the pentose phosphate pathway?
A reductive pathway that uses glucose-6-phosphate to produce ribose-5-phosphate and NADPH in cytosol
What is NADPH needed for? (2)
- Reductive biosynthesis
- Regeneration of glutathione
What is the main source for NADPH in the cytosol?
Pentose Phosphate pathway
What is ribose-5-phosphate needed for and what pathway is it produced in?
Needed for nucleotide synthesis and produced in the pentose phosphate pathway
What stoichiometrically goes into the pentose phosphate pathway?
What stoichiometrically comes out of the pentose phosphate pathway?
2 Fructose-6-phosphate or 2 ribose-5-phosphate
Which two products of the pentose phosphate pathway feed into glycolysis?
Fructose-6-phosphate and GAP
What product of the pentose phosphate pathway is used for fatty acid and cholesterol synthesis as well as regeneration of antioxidant glutatione?
How do the products of the pentose phosphate pathway change depending on the needs of the cell?
Depending on the needs of the cell, ribose-5-phosphate or fructose-6-phosphate may be made
What are the three steps of the oxidative stage (first stage) of the pentose phosphate pathway?
1. G6P is converted to 6-phosphoglucono-δ-lactone with glucose-6-phosphate dehydrogenase (NADP+ to NADPH)
2. 6-phosphoglucono-δ-lactone is converted to 6-phosphogluconate with 6-phosphogluconolactonase (H2O to H+)
3. 6-phosphogluconate is converted to ribulose 5-phosphate (Ru5P) with 6-phosphogluconate dehydrogenase (NADP+ to NADPH)
What goes in and out of te oxidative stage (First stage) of the pentose phosphate pathway?
- 3 glucose-6-phosphate
- 6 NADP+
- 3 H2O
- 3 ribulose-5-phosphate (Ru5P)
- 6 NADPH
- 3 CO2
What is the first stage of the pentose phosphate pathway?
The oxidative stage, where glucose-6-phosphate is converted to ribulose-5-phosphate (Ru5P)
Produces 6 NADPH in the process
What is the second stage of the pentose phosphate pathway?
Isomerization and epimerization, where ribulose-5-phosphate is converted to ribose-5-phosphate and xylulose-5-phosphate
What isomerizes ribulose-5-phosphate in the pentose phosphate pathway? What does this produce?
ribulose-5-phosphate isomerase isomerizes Ru5P to make ribose-5-phosphate (R5P)
What epimerizes ribulose-5-phosphate? What does this make?
ribulose-5-phosphate epimerase epimerizes Ru5P to make xylulose-5-phosphate (Xu5P)
What can ribose-5-phosphate and xylulose-5-phosphate be used for?
(eg. making ribonucleotides or deoxyribonucleotides)
What goes in and out of the isomerization/epimerization stage of the pentose phosphate pathway?
- 3 ribulose-5-phosphate (Ru5P)
Out (3 pentoses)
- 1 Ribose-5-phosphate (R5P)
- 2 Xylulose-5-phosphate (Xu5P)
When cells don't require a lot of pentoses, but rather ATP energy, what products of the pentose phosphate pathway are converted into glycolytic intermediates?
Ribose-5-phosphate and xylulose-5-phosphate
1 Ribose-5-phosphate and 2 xylulose-5-phosphates (3 pentoses - 5C sugars) can be converted to what two glycolytic intermediates?
2 hexoses (6C sugar) and 1 triose (3C sugar)
1 glyceraldehyde-3-phosphate (GAP)
These enter glycolysis at different stages
How much ATP does the pentose phosphate pathway use up? (from 3 glucose)
How much ATP does the pentose phosphate pathway produce? (from 3 glucose)
10 ATP from pathway, 50 - 60 ATP from the 5 pyruvate produced (which makes ATP through TCA cycle and/of oxidative phosphorylation)
What produces more ATP, the pentose phosphate pathway or glycolysis?
Glycolysis does, but the pentose phosphate pathway oxidizes part of the glucose without producing ATP to yield useful metabolites
What are sources of free radicals that can cause oxidative stress? (3)
- Electron transport chain
- Oxidizing enzymes
What are free radicals?
Highly reactive oxygen species with unpaired electrons that can do damage to lipids, proteins and DNA (oxidative stress)
They are highly reactive because of unpaired electrons.
What are antioxidants?
They react with free radicals to pair up electrons. Ascorbic acid (Vitamin C), tocopherols (vitamin E), peptides with thiol groups (glutathione) and some enzymes are examples of antioxidants.
What is glutathione? What is needed ro regenerate it?
A peptide with thiol groups, can act as an antioxidant.
NADPH is needed to regenerate it.
It is a tripepetide of glutamate, cysteine and glycine
What enzyme oxidizes glutathione so that it can neutralize a free radical?
What enzyme reduces glutathione to regenerate it? What is required?
GLutathione reductase reduces glutathione and oxidizes NADPH (which is required)
What is the first committed step of the pentose phosphate pathway?
glucose-6-phosphate dehydrogenases conversion of G6P to 6-phosphoglucono-δ-lactone
What happens if there is a deficiency in GPPD (glucose-6-phosphate dehydrogenase)?
What is resulting condition called?
It is a genetic disorder that leads to low resistance to oxidative stress, due to the cell's inability to produce enough NADPH.
It is especially bad in red blood cells where there is no nucleus, meaning there is no protein or membrane turnover to combat oxidative stress imposed by free radicals.
This causes the breakdown of erythrocytes leading to hemolytic anemia
What three things do lipids do?
- Provide structure (membranes)
- Act as energy stores (triacylglycerol)
- Have bioactivity (eg. bile acids, steroid hormones, lipophilic vitamins etc.)
What are the 6 subclasses of lipids?
1. Fatty acids and fatty acid derivatives
3. Wax esters
6. Isoprenoids and steroids
What two components do fatty acids have?
Hydrocarbon chain (hydrophobic) and carboxygroup (hydrophilic)
Which part of a fatty acid can be esterified? Esterified into what?
The carboxygroup can be esterified into fatty acid esters and other lipid classes
What is a free fatty acid?
An unesterified fatty acid ,the hydrocarbon chain can vary in length and saturation grade
What are eicosanoids?
A derivative of fatty acids with 20 carbon atoms
- Produced in the body from arachidonic or eicosapentaenoic acid
- Mediators of inflammation (anti-inflammatory)
- Prostaglandins and thromboxanes are examples
What are triacylglycerols?
Fat that serves as energy stores in the body and as dietary fat. TG are hydrophobic.
Not found in membranes but in lipid droplets, mostly stored in adipocytes
Where are triacylglycerols (TG) stored?
Mostly in adipocytes, fat cells that store energy as fat.
Do naturally occuring fatty acids have an odd or even number of carbon atoms?
How many double bonds do saturated fatty acids have?
How do you make a symbol for fatty acids?
X = number of carbon atoms
Y = Number of double bonds
What is the symbol and systemic name for for palmitic acid?
What is the structure of palmitic acid? (Symbol: 16:0)
What is the ω end of a fatty acid chain?
The methyl (CH3) terminal end
When naming fatty acids, carbons are counted away from this end
What is the symbol and systemic name for stearic acid?
What is the structure of stearic acid? (Octadecanoic acid)
What is a monounsaturated fatty acid?
A fatty acid with one double bond
Eg. Oleic acid
What is a polyunsaturated fatty acid?
A fatty acid with more than one double bond
eg. linoleic acid and α-linoleic acid
Double bonds in unsaturated fatty acids are usually in what type of configuration?
separated by one CH2 group
How do you make symbols for unsaturated fatty acids?
X = Number of carbon atoms
Y = number of double bonds
n = symbol (can also be ω)
c = The number of the first doible bonded carbon atom, counting from the ω methyl terminal end
What is the symbol and systemic name of linoleic acid?
What is the symbol and systemic name of oleic acid?
What is the symbol and systemic name of arachidonic acid?
What is the structure of oleic acid? (9-octadecenoic acid) 18:1n-9
What is the structure of linoleic acid? (18:2n-6)
What is the α carbon in fatty acids?
The carbon atom next to the carboxy-group atom (eg. second carbon atom on chain at end of carboxy group)
What is the omega (ω) carbon in fatty acids?
The carbon atom in the methyl group
IE. The last carbon atom in the chain
This is the carbon counted from when naming fatty acids.
What are the three components of fatty acids?
- Carboxy group end
- Hydrocarbon chain (with or without double bonds)
- Methyl group at end of the chain
What is the method of defining fatty acids chains using Δ?
X = # of carbon atoms
Y = # of double bonds
n = Positions of double bonds, in superscript, counting from the carboxy group carbon (alpha carbon is carbon 2)
Define the fatty acid below using the Δ method
What fatty acid is this?
How does length of fatty acid affect melting point?
Longer fatty acid = higher melting point
How does saturation of a fatty acid affect melting point?
More saturated fatty acid = higher melting point
(why desaturated fatty acids are usually oils)
How does the configuration of fatty acid double bonds affect melting point?
Fatty acids with cis double bonds have lower melting points than fatty acids with trans double bonds
(Just think about how trans-fatty acids would be more likely to be in a butter form than cis-fatty acids)
How does a double bond increase melting point of fatty acids?
A double bond creates a kink, which prevents the fatty acid from packing in as tightly as a straight one. This leads to a lower melting point (because of low ability to pack closely to other fatty acids)
How does double bond configuration in fatty acids affect melting temperature?
Double bonds with a cis-configuration causes a kink in the chain, which trans-configuration leaves the chain straight.
Are double bonds in fatty acids planar?
Yes, double bonds are always planar
What is the symbol for oleic acid that includes configuration? (Hint, it has 18 carbons with 1 double bond)
What property of fatty acids allows them to serve as detergents and soaps? What is the consequence of this for fatty acids in water?
They are amphiphillic, meaning they are hydrophilic (carboxy end) and hydrophobic (hydrocarbon chain). The hydrophobic parts allows them to be soluble in grease and dirt, but the hydrophilic end allows them to be washed away.
In water, fatty acids form micelles, which are droplets of fatty acids with chains sticking inwards and carboxy groups sticking outwards (interacting with water)
What are the components of phospholipids?
They are esters of glycerol phosphate
2 Fatty acids
There is a glycerol phosphate, which has a hydrophilic headgroup attached to the phosphate part, and 2 hydrophobic fatty acid chains attached to the glycerol part (alltogether called glycerophospholipid)
What are the six common classes of glycerophospholipids? (characterized by their differing phospholipid headgroups)
What are the names of the phospholipids formed from these?
- Phosphatidic acid
- Phosphatidylcholine (lecithin)
What are sphingolipids?
Membrane lipids that are amphiphilic, they contain sphingosine as backbone (instead of glycerol)
What is sphingosine?
A long chain amino alcohol, has a long saturated hydrocarbon chain. Used instead of glycerol for backbone in sphingolipids
What are the components of sphingolipids? (3)
One fatty acid amide
What is ceramide?
A sphingosine fatty acid amide
Has a sphingosine with a fatty acid chain
What is sphingomyelin and its components?
Fatty acid amide side chain
Choline as headgroup