Lipid Metabolism Flashcards
Lipids are not soluble in water, but they are soluble in…?
…non-polar organic solvents.
What is this the general formula for?:
CH3(CH2)nCOOH.
Fatty acids.
Fatty are a long ……………… chain with a terminal ………………. group.
Hydrocarbon, carboxyl (COOH).
Name some places where lipids are found in the body and in what forms.
Adipose tissue - triacylglycerol.
Membranes - phospholipids.
Plasma - free fatty acids / non-esterified fatty acids (NEFA).
Plasma - glycolipids.
Plasma - cholesterol esters.
Name some of the major biological roles of fatty acids.
Energy storage and production, protection, insulation, as components of biological membranes, as precursors to other biological molecules (e.g. eicosanoids, prostaglandins, prostacyclins, thromboxanes and leukotrienes).
What are the two most abundant lipids?
Triacylglycerol (TAG) and phospholipids (PL).
What is an ester?
Carbon double bonded to oxygen.
What is the name for carbon double bonded to oxygen?
An ester.
TAG molecules are formed from esters of haw many fatty acids, plus glycerol?
Three.
Phospholipids are formed from esters of how many fatty acids, plus glycerol?
Two.
Phospholipids are formed from two fatty acids, glycerol, and what else?
Phosphate and another alcohol (often including nitrogen).
What are the four ways in which fatty acids can differ?
- Chain length.
- Number of double bonds.
- Position of the double bonds(s) in the chain.
- Type of double bond (cis or trans).
In fatty acids, which is the most common type of double bond found in nature? Cis or trans?
A cis double bond, where the carbon atoms are on the same side.
Where are fatty acids with trans double bonds found?
In hydrogenated fats, e.g. in rumen and margarines.
What impact do cis/trans double bonds have on a membrane?
Membranes with fatty acids containing cis double bonds are more fluid and flexible. This is because the cis-bonded fatty acids cannot pack as closely together as trans-bonded fatty acids.
Which appears straight and which appears bent? Cis-bonded or trans-bonded fatty acids?
Cis-bonded fatty acids appear bent and trans-bonded fatty acids appear straight.
If a fatty acids has no double bonds, is it polyunsaturated, saturated or monounsaturated?
Saturated.
If a fatty acid has one double bond, is it saturated, polyunsaturated or monounsaturated?
Monounsaturated.
If a fatty acid has more than one double bond, is it monounsaturated, polyunsaturated or saturated?
Polyunsaturated.
How are ALL polyunsaturated fatty acids made?
Desaturating monounsaturated fatty acids.
Animals can only make polyunsaturated fatty acids based on which monounsaturated fatty acid?
Oleic acid.
How do animals make polyunsaturated fatty acids from monounsaturated fatty acids?
By inserting a double bond between the existing bond and the carboxyl group.
Animals cannot make which polyunsaturated fatty acids from oleic acid?
Linoleic acid and alpha-linolenic acid.
How do plants make polyunsaturated fatty acids from monounsaturated fatty acids?
They insert a double bond between the existing bond and the methyl group.
Where do plants add a double bond when they desaturate a monounsaturated fatty acid to a polyunsaturated fatty acid?
Between the existing bond and the methyl group.
Where do animals add a double bond when they desaturate a monounsaturated fatty acid to a polyunsaturated fatty acid?
Between the exisiting bond and the carboxyl group.
What is the name for fatty acids that can be made by plants, but not by animals?
Essential fatty acids.
Essential fatty acids can be made by ………………. , but not by ……………… .
Plants, animals.
What two functions are essential fatty acids vital for in the body?
Membrane function and as precursors of eicanosoids.
What are eicanosoids?
Local hormones which alter activity of the cells that they are produced in and those adjoining them.
They regulate a range of functions including inflammation, blood flow, blood clotting and ion transport across membranes.
Name some of the functions of eicanosoids, local hormones which are made from essential fatty acids.
They regulate a range of functions including inflammation, blood flow, blood clotting and ion transport across membranes.
Animal fats tend to be solid at room temperature, whereas plant fats tend to be liquid. Why is this, in terms of the double bonds in the fatty acids?
Animal fats tend to be saturated, having few double bonds in order to pack together tightly and store fat as efficiently as possible.
Plant fats have more double bonds so they take up more space and are more liquid.
Why do animals synthesise fatty acids?
So that they have fat reserves that can be used for energy in bad times - when it is cold, or there is less food available, for example.
What does this show?:
Acetyl CoA - Malonyl CoA - Palmitic Acid - Stearic Acid - Oleic Acid.
The synthesis of fatty acids in animals.
Fill in the blanks:
C 2:0 - ?
? - Malonyl CoA
C 16:0 - Palmitic Acid
? - Stearic Acid
C 18:0 - ?
What does this represent?
Acetyl CoA
C 3:0
C 18:0
Oleic Acid.
Fatty acid synthesis in animals.
Do biologocally relevant fatty acids have ODD or EVEN numbers of carbons?
Even.
Where in the cell are fatty acids made?
In the cytosol.
What is the first step of fatty acid synthesis in animals?
Acetyl CoA (C 2:0) to Malonyl CoA (C 3:0).
What is the main difference between fatty acid synthesis in prokaryotes and eukaryotes?
In prokaryotes, fatty acids are synthesised by the action of a series of separate enzymes.
In eukaryotes, fatty acids are synthesised by the action of a multifunctional enzyme complex.
What does ACP stand for? What is its role in fatty acids synthesis?
Acyl Carrier Protein.
The intermediates in fatty acid synthesis are linked to ACP, which is different in eukaryotes and prokaryotes.
True or false? The Acyl Carrier Protein (ACP) is the same in prokaryotes and eukaryotes.
False.
In prokaryotes the ACP is a 77 amino acid protein joined to a phosphopantetheine group.
In eukaryotes it is part of the fatty acid synthase complex.
Complete these reactions:
Acetyl CoA + ACP =
Malonyl CoA + ACP =
What are these reactions called?
= Acetyl ACP + CoA
= Malonyl ACP + CoA.
The Acetyl and Malonyl Transacrylase reactions.
Which fatty acids are synthesised by the fatty acid synthase system?
Long chain saturated fatty acids.
In prokaryotes, the fatty acid synthase system for making long chain saturated fatty acids contains four separate enzymes. What are the substrates?
HINT: there are only three substrates!
Acetyl ACP, Malonyl ACP and NADPH.
What does the thioesterase enzyme do in fatty acid synthesis?
It releases the carbon chain (termination) when it reaches C 16:0 (palmitic acid).
Sometimes shorter chains are made, e.g. in the mammary glands.
Why does the non-polar nature of fatty acids mean that they are good for storing energy?
They do not need to be surrounded by water (unlike sugars), which increases efficiency of space water usage in the body.
What are the main steps of fatty acid synthesis?
HINT: there are only two!
- Formation of malonyl CoA.
- Synthesis of palmitate.
Complete the reaction for the formation of malonyl CoA, the first step in fatty acid synthesis:
7 Acetyl CoA + 7CO2 + 7ATP =
= 7 Malonyl CoA + 7ADP + 7Pi + 7H+.
Complete the reaction for the formation of palmitate from malonyl CoA, the second step in fatty acid synthesis:
Acetyl CoA + 7 Malonyl CoA + 14 NADPH + 7H+ =
= Palmitate + 7CO2 + 14NADP+ + 8CoA + 6H2O.
Complete the reaction for the overall synthesis of fatty acids (palmitate):
8 Acetyl CoA + 7ATP + 14NADPH =
= Palmitate + 14NADP+ + 8CoA + 6H2O + 7ADP + 7Pi.
Which is the main fatty acid synthesised in animals?
Palmitic acid / palmitate. C 16:0.
How many carbons does palmitic acid have? How many double bonds? Is it saturated or unsaturated?
It has 16 carbons, 0 double bonds and is saturated.
C 16:0.
60% of fatty acids in human adipose tissue have how many carbon atoms? What does this show?
60% of fatty acids in human adipose tissue have 18 carbon atoms.
As humans synthesise palmitic acid, these 18 carbon fatty acids must come from dietary sources or further metabolism of palmitic acid.
When palmitic acid has been formed, it is transported from the ……………. to the ……………….. ………………… where two carbon atoms are added to form ………………. ………………. (C 18:0).
Cytoplasm, endoplasmic reticulum, stearic acid.