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06 FdSc Bioscience - Metabolism and Enzymology > Week 5 - fat metabolism and energy > Flashcards

Week 5 - fat metabolism and energy Flashcards

1
Q

How can lipids be divided into two broad categories?

A
  • Hydrolyzable lipids - are compounds with more than one hydrolyzable group (usually ester groups)
    • These include neutral fats, waxes, phospholipids and glycolipids
  • Non-hydrolyzble lipids - lack hydrolyzable groups
    • Include steroids
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2
Q

Describe how lipids act as barriers

A
  • They associate into nonpolar groups and act as barriers such as cell membrane and the barriers between and within cells
    • Play a protective role surrounding the major organs
    • Act as a thermal barrier to maintain temperature in organisms for reactions
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3
Q

How is the hyrophobic region of lipids important and what does this allow lipids to act as?

A
  • Hydrophobic areas provide a region for reactions requiring hydrophobic conditions (i.e. certain reactions in photosynthesis and cellular respiration)
  • This is important for the uptake of lipid soluble vitamins (A, D, E & K)
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4
Q

Name three additional functions of lipids

A
  1. Important energy source
  2. Involved in regulating cellular activities
  3. Associate with other biomolecules such as proteins and carbohydrates and play structural and recognition/receptor roles within the cell
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5
Q

What are the major classes of lipid?

A
  1. Neutral fats / lipids - fats & oils, involved in energy storage (90% of body fat)
  2. Phospholipids - major component of cell membranes (5% of body fat)
  3. Steroids - hormones that regulate cellular activity and are involved in membrane structure (5% of body fat)
  4. Waxes - protective coverings on cells
  5. Glycolipids - components of the cell membrane, involved in recognition/receptor functions
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6
Q

Where are neutral lipids found, why are they called this and what are their properties?

A
  • Neutral lipids are commonly found as storage fats and oils
  • Called “neutral” because at cell pH they have no charged groups and are neutral
  • Completely nonpolar and have no affinity for water
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7
Q

What are neutral lipids constructed from?

A
  • Composed of fatty acid and glycerol monomers
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8
Q

What are fatty acids?

Describe their properties

A
  • Long unbranched chains of carbon with hydrogen / other groups attached
  • There is -COOH group at one end which gives molecule acidic properties
  • C chain length varies from 4-24C
    • Generally it is 16 or 18 Cs and usually contains an even number of Cs
  • -COOH is polar meaning fatty acids are soluble in water although the longer the chain length (nonpolar) the less soluble the molecule is
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9
Q

Give two examples of fatty acids and their condensed formula

A
  • Stearate - CH3(CH2)COOH
  • Oleate - CH3(CH2)7CH=CH(CH2)7COOH
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10
Q

What effect does C=C have on the naming of fatty acids?

A
  • There may be C=C at some point in the chain (e.g. oleate)
  • If there are no C=C the fatty acids is said to be unsaturated (-H at all possible valency sites)
  • If there are C=C the fatty acid is said to be unsaturated
    • If there are multiple C=C the fatty acids is said to be polyunsaturated
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11
Q

What are the properties of saturated chains and where can they be found in nature?

A
  • Saturated chains are straight chains with a high melting point
    • Animal fats
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12
Q

What are the properties of unsaturated chains?

What are they two types and describe their properties

A
  • Unsaturated chains have kinks in the chain due to C=C which lowers their melting point
  • Cis C=C bonds cause 30o angle which trans C=C keep the chain straight
  • Unsaturated fatty acids in cells are generally in the cis form
    • Cis C=C makes chain more fluid and disordered
  • Trans fatty acids may be associated with disease
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13
Q

What is glycerol? Give the molecular formula and properties

A
  • Glycerol (C6H8O3) is a polar molecule since it contains three hydroxyl (-OH) functional groups
  • It is soluble in water
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14
Q

Outline the formation of neutral fats

A
  • Formed from fatty acid and glycerol
  • Formation occurs due to a condensation of dehydration synthesis reaction in which the fatty acid -COOH is linked to the glycerol -OH group
    • Linkage is called ester bond
  • All three -OH on glycerol can be linked to a fatty acid by ester linkages
  • A glycerol attached to three fatty acids is called a triglyceride
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15
Q

What allows the variation in neutral fats / lipids?

A
  • The fatty acid chains linked to glycerol may not be the same since there are many different fatty acids
  • Fish have ~20 fatty acids giving rise to 1500 possible triglycerides
  • The triglycerides produced varies with the diet
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16
Q

How do fatty acids affect the properties of triglycerides?

A
  • Triglycerides containing unsaturated fatty acid chains melt at a lower temperautre than those with saturated fatty acd chains
  • Triglycerides become less fluid as the chain length of the fatty acid increases
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17
Q

Where are phospholipds found and what are they also referred to as?

A
  • Primary lipids found in biological membranes
  • Phosphate-containing molecules structurally related to the triglycerides and are often referred to as phosphoglycerides
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18
Q

What is the structure of phospholipids and what may they contain?

A
  • Have a glycerol backbone attached to two fatty acid residues by ester linkages on C1 and C2 of glycerol
  • A phosphate group is attached to C3 of glycerol
  • Phosphate group may also be attached to an organic group such as an amino acid (serine and threonine), sugar (inositol, glycerol) or nitrogen based (choline, ethanolamine) group
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19
Q

What are the special characteristics of phospholipids ?

A
  • Phosphate group is polar meaning the phospholipid has polar characteristics in the C3 area
    • This area is often referred to as the polar head
  • The two fatty acid chains are referred to as the tail sections and they are nonpolar
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20
Q

What happens to phospholipids in water and why?

What is the use of this in nature?

A
  • When in water phospholipids form a bilayer which is found in cell membranes
  • The nonpolar fatty acid tails point to the interior of the lipid bilayer with the polar heads on the outside of the bilayer
  • Hydrophobic interactions of the fatty acid tails holds the molecules and layers together forming the cell boundary and boundaries within the cytoplasm of eukaryotic cells
  • Phospholipid bilayer is selectively permeable and allows small nonpolar molecules to pass through into the cell and separates the cell from the external environment
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21
Q

What are steroids, what are they made of and how can they vary?

A
  • Steroids are a class of lipids based on a framework of interconnected carbon rings
  • Consist of 3 x 6C rings and 1 x 5C ring
  • Different steroids vary in the functional groups attached to the rings and the number of double bonds and their position
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22
Q

What is the most abundant group of steroids?

What is their structure and what are their properties?

A
  • Most abundant group of steroids is the sterols which have an -OH at one end and a complex nonpolar carbon chain at the other
  • Generally very hydrophobic molecules but the -OH group may confer slight polarity to an area
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23
Q

How do lipids arrange in solution?

A
  • Lipids arrange in solution / location to suit the polar / nonpolar characteristics
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24
Q

Name six common types of steroids

A
  1. Cholesterol
  2. Oestradiol
  3. Testosterone
  4. Progesterone
  5. Vitamin B3
  6. Adrenocortical hormone
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25
Q

Give an overview of the steroid cholesterol

A
  • Unsaturated steroid
  • Component of eukarytic membranes (25% membrane weight)
  • Sits parallel to phospholipids in the membrane and stops phospolipids from packing together
  • Stabilised membrane at high temperatures
  • Precursor in the production of sex hormone
  • Used in the production of bile which is secreted into the intestinal tract
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26
Q

Give an overview of the steroid oestradiol

A
  • Female sex hormone
  • Regulates the development of female sex characteristics and organs
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27
Q

Give an overview of the steroid testosterone

A
  • Male sex hormone
  • Regulates development of male sex organs and characteristics
28
Q

Give an overview of the steroid progesterone

A
  • Human pregnancy hormone
29
Q

Give an overview of the steroid vitamin D3

A
  • A vitamin derived from cholesterol
30
Q

Give an overview of the steroid adrenocortical hormone

A
  • Secreted by the adrenal gland
  • Regulates cell growth and activity
  • Examples of adrenocortical hormone include aldosterone and cortisol
31
Q

What effect can the steroid cholesterol have on health?

A
  • Deposits of cholsterol form a major part of the material that accumulates inside arteries in atheroschlerosis resulting in the hardening of the arteries
  • Diet high in lipid and cholesterol can lead to reduced blood flow caused by deposit of lipid material on lining of blood vessels ​
32
Q

What are glycolipids?

A
  • Glycolipids are amphipathic (possessing both hydrophobic and hydropillic properties) lipids with 1/more carbohydrate group attached to the -COOH group
  • Carbohydrate chain may be mono/disaccharide or a complex polysaccharide (30 sugar units) that branches and contains a variety of ccarbohydrate monomers
33
Q

Where are glycolipids present at a cellular level and at a body level?

What is their function?

A
  • Glycolipids are present in the plasma membranes of prokaryotic and eukaryotic cells and in the thylakoid membrane of chloroplasts
    • % content varies depending on cell type
  • Brain & intestinal linings have high % of glycolipids
  • Involved in reducing permeability of membrane to certain ions
  • Hydrophillic nature of carbohydrate chain enables glycolipid to form H bonds and stabilise the membrane
34
Q

Give a specific example of where glycolipids stabilise the plasma membrane

A
  • They stabilise the intestinal lining against bile salts which would normally disrupt the membrane due to the detergent effect
35
Q

What in the blood is significantly impacted by glycolipids and how?

A
  • Carbohydrate variation in the chain is important in the ABO blood grouping system
  • Different blood groups are characterised by differences in the carbohydrate chain
36
Q

How does temperature affect the physical properties of lipids?

A
  • Fats are solid at biological temperatures because they contain saturated chains (e.g. butter)
  • Oils are liquids at biological temperatures because they contain unsaturated chains (e.g. vegetable oil)
37
Q

How can unsaturated fats be converted to saturated fats?

A
  • Hydrogenation can be performed which adds -H synthetically to make the oil into a fat and therfore from liquid to solid
38
Q

How have animals living in cold climates adapted with regards fats?

A
  • Animals living in extremely low temperatures have triglycerides with unsaturated chains that prevent the triglycerides freezing in the cold
  • Different organisms have a range of triglycerides
39
Q

What is the difference between storing energy as fats compared to as carbohydrates?

A
  • Major function of fats is as energy storage
  • 1g of fat stores twice as much energy as 1g of carbohydrate
    • Fat 9 Kcal /g compared to carbohydrtae 4Kcal/g
  • Gram for gram fat stores 6x as much energy as glycogen since fat doesnt contain water
40
Q

What is the difference in body fat between males and females humans?

A
  • Body fat in human males is ~15%
  • Body fat in human females is ~25%
41
Q

Describe the amount of energy stored as fat and glycogen in an average human male

A
  • An average human male (70kg) stores 40,000 kcal in fat and 2,000 kcal as glycogen
42
Q

What is the difference between fat and glycogen as energy storage and where is fat found in the body?

A
  • Fat is long-term storage whilst glycogen provides short-term energy reserves
  • Humans and animals store fat in adipose tissues which swell and shrink as fat is deposited and removed
43
Q

How is energy stored differenty between different types of organism?

A
  • For mobile organisms fat as an energy storage reserve is more efficient than glycogen storage
  • Plant cells are relatively immobile and store starch as long-term energy reserves even though gram for gram fat stores more energy than starch
  • Vegetable oils are found in plants but are obtained from the seeds where compact, efficient storage is required
44
Q

Besides energy storage, what other functions does adipose tissue have?

A
  • Adipose tissues cushion and protect vital organs such as heart, liver, kidneys and brain
  • This is essential fat and is not used as an energy supply
  • Subcutaneous fats act as an insulator, especially in marine / arctic and antarctic animals
45
Q

What may dietary fats act as?

A
  • Dietary fats act as carriers for fat soluble vitamins such as A, D, E & K
46
Q

What is lipolysis and what does it produce?

A
  • Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by degradation into acyl units by beta oxidation
  • It produces ketones which can be used by the body for energy
47
Q

What can the excessive production of ketones by lipolysis cause?

A
  • Production of ketones in large quantities can cause ketosis
48
Q

Briefly describe what happens to triglycerides in lipolysis

A
  1. Triglycerides are transported through the blood to appropriate tissues (adipose and muscle) pakcaged into VLDL (very low density lipoproteins)
  2. Triglycerides present on VLDL undergo lipolysis by cellular lipases of the target tissue to yield glycerol and free fatty acids
  3. Free fatty acids are then released into the blood and are available for cellular uptake
49
Q

Briefly describe what happens to the free fatty acids after lipolysis

A
  • Free fatty acids not immediately taken up by cells may bind to albumin for transport to surrounding tissues requiring energy
50
Q

What is the major carrier of free fatty acids in the blood?

A
  • Serum albumin is a major carrier is free fatty acids in the blood
51
Q

Briefly describe what happens to the glycerol after lipolysis

A
  • Glycerol also enters the bloodstream and is absorbed by the liver or kidneys where it is converted into glycerol-3-phosphate by the enzyme glycerol kinase
  • Hepatic glycerol-3-phosphate is mostly converted to dihyroxyacetonephosphate (DHAP) and then to glyceraldehyde-3-phosphat (G3P)
  • As G3P it then enters either the glycolytic or gluconeogenic pathways
52
Q

Compare lipolysis to esterification

A
  • Lipolysis is triglyceride hydrolysis and esterification is the process by which triglycerides are formed
  • They are essentially reversals of one another
53
Q

What is beta-oxidation?

A
  • Beta-oxidation is the process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-CoA (which enters the citric acid cycle) and NADH, FADH2 to be used the the electron transport chain
54
Q

What stages can fatty acid catabolism be divided into?

A
  • Fatty acid catabolism involves three stages:
  1. Beta-oxidation
  2. Oxidation of acetyl-CoA to CO2
  3. Electron transfer from electron carriers (NADH, FADH2) to the electron transport chain
55
Q

What is the Carnitine Shuttle?

A
  • The fatty acd must be primed for oxidation:
    • Known as the Carnitine shuttle
  1. Fatty acid activated in the cytosol by fatty acyl CoA synthetase
  2. Activated fatty acid are conjugated to carnitine by carnitine acyltransferase I
  3. Transport of activated fatty acid into mitochondria by translocase
  4. Release of fatty acid into mitochondrial matrix by fatty acyl transferase II
56
Q

Once the activated fatty acid is inside the mitochondrial matrix what happens and how many stages are there?

A
  • Once fatty acid inside mitochondrial matrix beta-oxidation can begin
  • There are four steps to beta-oxidation
    • Each covered separately on different flashcards
57
Q

Describe the first step of beta-oxidation

A
  • Step 1:
    • Long chain fatty acid dehydrogenated to create trans C=C betwen C2 & C3
    • Catalysed by acyl CoA dehydrogenase
    • Produces trans-delta 2-enoyl CoA
    • FAD is the electron receptor and it is reduced to FADH2
58
Q

Describe the second step of beta-oxidation

A
  • Step 2:
    • Trans-delta 2-enoyl CoA is hydrated at C2=C3 to produce L-B-hydroxyacyl CoA
    • Catalysed by enoyl CoA hydratase
59
Q

Describe the third step of beta-oxidation

A
  • Step 3:
    • L-B-hydroxyacyl CoA is dehydrogenated to produce B-ketoacyl CoA
    • Catalysed by B-hydroxyacyl CoA dehydrogenase
    • Uses NAD as an e- acceptor
60
Q

Describe the fourth step of beta-oxidation

A
  • Step 4:
    • Thiolysis occurs between C2 & C3 (alpha and beta carbons) of B-ketoacyl CoA
    • New molecule of CoA breaks the bond by nucleophilic attack on C2, this releaes the forst two C units, as acetyl-CoA, and a fatty acid CoA (without 1st 2 Cs)
    • Process continues until all of the C in the fatty acid are turned into acetyl CoA
    • Catalysed by thiolase enzyme
61
Q

Which tissues in the body do not use fatty acids for their energy requirements?

What do they use instead?

A
  • Fatty acids are oxidised by most of the tissues in the body
  • Some tissues, such as the adrenal medulla, do not use fatty acids for their energy requirements and use carbohydrates instead
62
Q

How oes the beta-oxidation cycle repeat?

A
  • Shortened fatty acyl-CoA that was the product of the last reaction goes through another beta-oxidation cycle
  • The cycle repeats unil we are left with two molecules of acetyl-CoA left in the final step
  • This acetyl-CoA is available to be further metabolised in the TCA cycle or can be used as a substrate for amino acid synthesis
  • The acetyl-CoA cannot be used as a substrate for gluconeogenesis
63
Q

How are fatty acids with an odd number of carbon atoms metabolised?

A
  • Fatty acids with an odd # Cs are common in plants and marine life
  • Humans and other animals that include these in their diets metabolise them in the beta-oxidation pathway as normal however then end product is propionyl-CoA instead of acetyl-CoA
    • Three carbons as opposed to 2 in acetly-CoA
  • Propionyl-CoA is converted to succinyl-CoA to enter the TCA cycle
64
Q

Outline the beta-oxidation of unsaturated fatty acids

A
  • They are still catabolised by beta-oxidation but they require two additional enzymes to handle the cis-double bonds
    • enoyl-CoA isomerase
    • 2,4-dienoyl-CoA reductase (for polyunsaturated fatty acids
65
Q

Describe the beta-oxidation of monounsaturated fatty acids

A
  • For monounsaturated fatty acids they go through beta-oxidation for as many times as possible before coming to the C=C, enoyl-CoA isomerase converts the cis C=C to a trans C=C and moves it over by one C
  • Product continues through the beta-oxidation pathway
66
Q

Describe the beta-oxidation of polyunsaturated fatty acids

A
  • Polyunsaturated fatty acids have more than one cis double bond and they go through the same process as for monounsaturated fatty acids but with one more round of beta-oxidation because you get a fatty acid with a trans and a cis C=C
  • For this 2,4-dienoyl-CoA reductase produces a trans-3-enoyl product which is converted by enoyl-CoA isomerase to a trans-2-enoyl-CoA which then goes through the normal pathway
67
Q

How is beta-oxidation regulated?

A
  • Malonyl-CoA can act to prevent fatty acyl-CoA derivatives from entering the mitochondria by inhibition carnitine acyltransferase that is respondible for the transport - thus inhibiton beta-oxidation
    • When fatty acyl-CoA levels rise beta-oxidation is stimulated
  • Increased citrate levels inhibit beta-oxidation because it indicates an abundance of acetyl-CoA

06 FdSc Bioscience - Metabolism and Enzymology (8 decks)

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