Exam 1 - Nutrition Flashcards
1
Q
Nutrition
A
the integrated processes through which food is utilized to provide nutrients necessary to life
2
Q
Nutritionist
A
Scientist/professional focused on understanding or applying the process of nutrition
3
Q
Nutrition integrates…
A
biology, chemistry, anatomy and physiology, microbiology
4
Q
Factors affecting human nutrition and diet
A
Food preferences, religion, health, allergens, environment, socioeconomic status, physiology
5
Q
Differences between animal and human nutrition
A
digestive systems, nutrient composition, feed/food sources, dietary requirements, purpose and research
6
Q
Good animal nutrition…
A
Promotes health and wellbeing
Improves productivity and performance
Saves money and resources
Supports sustainability
7
Q
How does good nutrition promote health and wellbeing?
A
Reduces metabolic disorders
Minimizes hunger and suffering
Decreases infectious disease
Increases biosecurity - healthy gut biome = better immunity
8
Q
How does good nutrition improve productivity and performance?
A
Increases milk production
Enhances growth rates & feed-efficiency
Improves reproductive efficiency
9
Q
How does good nutrition save money and resources?
A
Decreases feeding costs
Reduces waste
Increases profits
Promotes sustainability
10
Q
How does good nutrition support sustainability?
A
Reduces environmental impacts
Minimizes the use of resources
Lessens environmental & health impacts
11
Q
Nutrient
A
chemical element or compound in the diet required for normal reproduction, growth, lactation, or maintenance
12
Q
Food
A
edible material that provides nutrients
13
Q
Feed (noun)
A
food designated for animal consumption
14
Q
Foodstuff or feedstuff
A
material made into or used as food/feed
15
Q
Diet
A
mixture of feedstuffs used to supply nutrients
16
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Ration
A
daily allocation of feed
17
Q
Ingestion
A
prehension, chewing, swallowing
18
Q
Digestion
A
mechanical and chemical (enzyme-catalyzed) reduction of complex nutrients to usable simple nutrients
19
Q
Absorption
A
active and passive transport of digested nutrients from the gut lumen to the blood or lymph
20
Q
Metabolism
A
chemical (enzyme-catalyzed) reactions in organisms to sustain life; may be catabolic or anabolic
21
Q
Nutrient requirements
A
nitrogen, fat, energy (from proteins, carbs, fats, etc.), minerals, vitamins
22
Q
What do nutrients do?
A
Provide energy
Give the body structure
Regulate chemical processes
23
Q
Classes of nutrients
A
fats (lipids)
carbohydrates
proteins
vitamins
minerals
water
24
Q
Macronutrients
A
Required in large quantities
Yield energy (except water)
Proteins, carbohydrates, lipids, water
25
Carbohydrates
“Hydrates of Carbon”
Composed of Carbon, Hydrogen & Oxygen in a 1:2:1 (Ex: glucose is C6H12O6)
Classified by:
Character of individual monomers
Degree of polymerization (DP)
Type of linkage (ab)
Function: major fuel source for all cells of the body
26
Lipids
Hydrophobic organic compounds
Three main types:
Phospholipids
Triglycerides
Sterols
Functions: energy storage, cell membrane structure, hormone production, insulation, vitamin absorption, protective cushioning
27
Proteins
Macromolecules composed of chains of amino acids
Provide building blocks for tissues and organs
Essential for growth, regeneration, and maintenance
Functions: serve as building blocks for tissues, provide structural support, facilitate chemical reactions, transport molecules, regulate bodily functions, aid in cellular communication, promote immune function
28
Water
One of the most vital nutrients
Composed of two hydrogens and one oxygen
Not energy-yielding
More than 60% of the body is water
Functions: transports nutrients to cells, regulates body temperature, lubricates joints, aids in digestion, removes waste products, maintains fluid balance
29
Micronutrients
Required in smaller amounts
Include all the essential minerals and vitamins
30
Minerals
inorganic elements classified according to how much the body requires (micro vs. macro)
31
Macrominerals are required in amounts of...
GREATER than 100 mg/day
sodium, chloride, potassium, calcium, phosphorus, magnesium, sulfur
32
Microminerals are required in amounts of...
100 mg/day or less (trace minerals)
iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium, molybdenum
33
Vitamins
Essential, non-caloric, organic micronutrients required for many bodily functions
34
Water-soluble vitamins
dissolve in water, include vitamin C and all B vitamins
35
Fat-soluble vitamins
dissolve in fat, include vitamins A, D, E, and K
36
Energy-yielding nutrients
carbohydrates, protein, fat
Vitamins contain some energy, but bonds are unbreakable and therefore unable to be utilized by people and animals (also waste of resources: use more energy to break bonds than the vitamins actually contain)
37
Bomb calorimeter
Airtight chamber, burning and exploding feed sample
Amount of heat sample releases can be measured by the water bath around it
Water change of 1oC means 1 kcal is present
38
Organic nutrients
contain BOTH carbon and hydrogen
can be made by living organisms
carbohydrates, proteins lipids, vitamins
39
Inorganic nutrients
Nutrients that do not contain both carbon and hydrogen (can have one or the other, but not both)
Cannot be created or destroyed
Minerals, water
40
Nutrient analysis
Testing a feed sample in a laboratory to determine its nutrient content
Chemical methods used to directly measure quantities of compounds
Biologic and enzymatic methods indicate how animal will interact with its feed
41
Why is nutrient analysis important?
Ration formulation and feeding
Troubleshooting
Economics
42
Wet chemistry
Traditional laboratory methods of nutrient analysis
More accurate than NIRS
Used to calibrate NIRS instruments
Costly and time consuming, still considered the gold standard
43
Near-infrared spectroscopy (NIRS)
Uses light reflectance to measure nutrient content
Faster and cheaper than wet chemistry
More precise
Not as reliable/accurate
44
Proximate analysis
Chemical analysis, determines composition of animal feed in terms of its nutrients
Developed in the mid-19th century at the Weende Experiment Station in Germany by Henneberg & Stohmann
Comparative & predictive in nature
45
How to properly sample feed for analysis
1. Take multiple small samples from different locations
2. Mix all samples into a large composite sample
3. Collect a sum-sample from the composite
4. Maintain sample integrity
*Do not shake excess from your sample; small particles will be lost, reducing validity (small particles will be minerals and other fine nutrients)
46
What does proximate analysis measure?
Dry matter, crude protein, ether extract, ash, crude fiber, nitrogen-free extract
47
Dry matter (DM)
Most common procedure:
Dry feed material at 105oC overnight
Calculate: (dry weight/fresh weight) x 100 = % DM
48
Crude protein (CP)
Developed by a Danish chemist, Johan Kjeldahl, and is commonly known as the Kjeldahl procedure
Determines nitrogen content of the sample
To convert the measured N content of the test material to crude protein, a calculation factor of 6.25 (N x 6.25) is applied
49
Potential problems with the Kjeldahl procedure
Assumes all nitrogen is from protein (also comes from free amino acids, nitrates, nitrites, and others not freely available to be broken down)
Assumes all proteins are 16% nitrogen when they are not
50
Ether extract (EE)
Represents the fat content of a feed sample
1. Boil dried sample in diethyl ether for 4 hours
2. Ether separated and evaporated
3. Residue is weighed, residue = EE (crude fat)
51
Potential problems with ether extract procedure
Assumes all substances soluble in ether are fats (error is generally small)
52
Ash
Burning sample, all organic matter is burned leaving only inorganic residue
Measures inorganic compounds in feed
Provides an estimate of total inorganic component
High values indicate feed contamination
Method:
1. Weigh portion of dried feed sample
2. Heat sample in oven at 500-700oC for 2-4 hours
3. Reweigh sample
53
Potential problems with ash procedure
Some trace mineral may be lost to volatilization
Does not provide content of specific minerals
54
Crude fiber
Measures indigestible components of feed
Has little energy value but is important for gut health
Procedure:
1. Dried sample boiled in 1.25% H2SO4 and filtered
2. Residue boiled in 1.25% NaOH & filtered
3. Remaining residue dried and ashed
*Crude fiber = filtered dried sample – ash
55
Potential problems with crude fiber procedure
Underestimates true fiber in feed
Does not differentiate between fiber sources
56
Nitrogen-free extract (NFE)
NFE is a calculated value, not an analyzed value
% NFE = % DM - (% ether extract + % crude protein + % ash + % crude fiber)
57
Potential problems with NFE calculation
Accumulates error from all other analyses
Does not differentiate between carbohydrate sources
58
Van Soest fiber analysis
Improved methods of crude fiber analyses
Includes neutral detergent fiber (NDF) and acid detergent fiber (ADF)
Divides plant cells:
Contents (starch and sugars)
Walls
Method:
1. Boil feed sample for 1 hour in neutral detergent (SLS and EDTA) ; pH 7 (neutral)
2. Boil residual sample for 1 hour in acid detergent (H2SO4 and CTAB); pH ~4.9 (acidic)
59
What does the neutral detergent separate in Van Soest fiber analysis?
Separates fiber from other carbohydrates and nutrients
Neutral detergent solubles (NDS) are dissolved (cell contents - soluble carbs, proteins, lipids, minerals, and vitamins)
Neutral detergent fiber (NDF) are left over (cell wall - insoluble fiber and fiber-bound compounds)
60
What does the acid detergent separate in Van Soest fiber analysis?
Separates neutral detergent fibers (hemicellulose) from acid detergent fibers (cellulose and lignin)
61
Process of nutrition
1. Ingestion - consumption of feed; act of taking feed into the body
2. Mastication - process of chewing
3. Digestion - processes involved in breaking down feed into substances that can be absorbed and utilized
4. Absorption - movement of nutrients from the digestive tract into the blood and/or lymph system
5. Metabolism - all chemical processes involved in the maintenance of life
6. Excretion - removal of waste products
62
Animals occupy _______ ecological niches and have devolved _______________
virtually all; specialized feeding strategies
63
Why is monogastric a misnomer?
Ruminants are technically also monogastric, as they have one stomach divided into four chambers, not four distinct stomachs
64
Autoenzymatic digesters
digestive processes carried out by enzymes that the animal secretes (pigs, people, chickens)
65
Alloenzymatic digesters
digestion accomplished by enzymes produced by microbes (ruminants, horses, foregut and hindgut fermenters, colonic fermenters, caeco-colonic fermenters)
66
Stomach
Functions - storage, mixing, secretion, digestion, absorption
Consists of four zones:
Cardiac
Fundus - gastric secretions
Body
Pyloric - gastric secretions
Gastric secretions - mucus, HCl, pepsin
67
Gastric ulcers
Sore or erosion that develops on the lining of the stomach
Causes include helicobacter pylori (H. pylori) bacteria, NSAIDs, corticosteroids
68
Steps of digestion in the stomach
1. Muscular contraction of stomach walls mechanically digests food (peristalsis)
2. Gastric juice contains hydrochloric acid (HCl) that activates pepsinogen, converting it to pepsin that digest proteins
69
Helicobacter pylori (H. pylori)
Able to survive in stomach acid
Secrete urease - converts urea to CO2 and ammonia, neutralizes HCl
70
Gastric ulcers in pigs
Known as gastroesophageal ulceration
Can form in the stomach and/or esophagus
Cause: excessive carbohydrate fermentation by bacteria (don’t slug feed)
Significant cause of death in commercial pig operations
71
How do hormones control gastric secretions?
1. Perception of food stimulates vagus nerve, resulting in Gastrin release
2. Gastrin regulates Histamine release from gastric mucosal cells
3. Histamine attaches to membrane receptors, activates cAMP
4. cAMP carbonic anhydrase, producing H+ ions & ATPase
5. H+ & ATPase cause Cl- secretion in exchange for K+
*Inhibited by Gastric Inhibitory Polypeptides (GIP)
72
Gastric secretions in young animals
Less HCl (pH 3-5) -> permits bacterial colonization to stimulate gut health, may cause enteric disease
Young animals secrete chymosin (rennin) which clots milk, this:
- Slows passage to increase digestion and absorption
-Prevents immature intestine from being overloaded
- May have a survival/protective role for prey species (broken down slowly = satisfied for longer when mom leaves baby to keep the smell away from them)
73
How is gastric mobility regulated?
Presence of unabsorbed lipid in the small intestine influences gastric emptying
Mediated through cholecystokinin (CCK)
Presence of chyme in the small intestine causes CCK and secretin to be released, CCK causes the gallbladder/liver to release bile and the pancreas to release enzymes, while secretin causes the pancreas to release bicarbonate (HCO3-)
74
How and where are carbohydrates broken down, and what are they broken down into?
Carbohydrates are broken down into simple sugars (eg glucose) by amylase (made in the salivary glands, pancreas, small intestine) in the mouth and small intestine
75
How and where are proteins broken down, and what are they broken down into?
Proteins are broken down into peptides and amino acids by protease (made in the stomach and small intestine) in the stomach and small intestine
76
How and where are lipids broken down, and what are they broken down into?
Lipids are broken down into fatty acids and glycerol by lipase (made in the pancreas and small intestine) in the small intestine
77
How and where are minerals and vitamins broken down, and what are they broken down into?
Minerals and vitamins are not broken down, they are absorbed intact
78
Avian digestive system
Autoenzymatic digestion with modifications
Two-compartment stomach:
Proventriculus = gastric
Ventriculus (gizzard) = grinding (because they don’t chew)
Crop - diverticulum of the esophagus; functions as food storage area
Small intestine contains 3 sections as mammals (duodenum, jejunum, ileum), segments are less distinct than mammals, proportionally smaller than mammals to maintain low density for flight
79
Crop "milk"
Milky substance produced in the crop of some birds
Comprised of lipid-rich epithelial cells plus ingested feed
Regurgitated into the crop of young - helps provide them with nutrients they can’t obtain on their own in a way their immature system can handle
80
Small intestine
absorptive area of 250 square meters
Major site of digestion and absorption
81
Reverse peristalsis in avians
digestive system can move forwards and backwards
Allows them to get more nutrients from food, so they don’t have to eat as much or as often
Gastric reflux: gizzard to proventriculus
Upper intestinal reflux: jejunum to gizzard
Lower intestinal reflux: colon to ceca
82
Anaerobic foregut fermenters (ruminants)
Have a large compartmentalized stomach with chambers
Rumen → reticulum → omasum → abomasum
Characterized by one chamber devoted to anaerobic fermentation (anaerobic respiration)
83
Microbes live in the ______ of ruminants and are responsible for breaking down most of the feed into ______
rumen; volatile fatty acids (VFAs)
Rumen has papillae to increase surface area, allowing VFAs to cross over and get absorbed into the bloodstream
Cellulase production by rumen microbes enables cellulose digestion
84
What additional nutrients (besides VFAs) does rumen microbial fermentation yield that benefit the host animal?
Amino acids
Water-soluble vitamins
Vitamin K (fat-soluble)
85
Reticulum
continuous with the rumen; often considered together (reticulo-rumen)
Lined with honeycomb shaped projections
Plays a role in particle separation and digestion
86
Omasum
small compartment containing membranous divisions called omasal leaves
Functions as a sieve, retaining material in the rumen until it has been degraded into small particle sizes
87
Abomasum
true gastric stomach (secretes pepsinogen and HCl)
Contains large spiral folds in the fundus region
Microbes attached to small particle are digested as a protein source along with their metabolites and fermentation products
88
Young ruminant digestive tract
Rumen and reticulum not functional in young
Esophageal groove shunts milk to the abomasum
Stimulated by suckling
89
Browsers (classification of ruminants)
Consume less lignified (more soluble fiber)
Deer, moose, giraffes
90
Intermediate feeders (classification of ruminants)
Share feeding and digestive strategies of both browsers and grazers
Sheep, goats, reindeer
91
Grazers (classification of ruminants)
Utilize high-fiber feeds
Cattle, buffalo, wildebeest
92
Other ruminants (classification of ruminants)
Camelids are ruminants, but have different stomach anatomy
3 compartment stomach: C1 (roughly comparable to the rumen), C2 (omasum), C3 (abomasum)
93
Ruminant microbe population consists of:
1. Bacteria - starch digesters (amylolytic) and cellulose digesters (cellulolytic)
2. Protozoa
3. Fungi
4. Yeast
*Rumen microbes are similar among different species and between wild and domestic animals
94
Describe the 4 main processes microbes do for ruminants
1. Synthesis of essential amino acids
2. Protein production from non-protein nitrogen
3. Synthesis of B-vitamins
4. Break-down of cellulose
95
Hindgut fermenters
Hindgut enlarged with microbial population performing many of the same functions as rumen microbe
Hindgut fermenters (such as horses) tend to be more athletic/mobile than ruminants (such as cattle), so they adapted to eat small meals throughout the day rather than large meals that are carried around in the rumen all day
96
Nutritional disadvantages to hindgut fermentation
Soluble nutrients absorbed in small intestine, so material is less favorable to maximal microbial growth
Less efficient area for nutrient absorption
More rapid passage rate, lower efficiency of fiber digestion
97
Horse digestion
Relatively small stomach for their size (eat many small meals)
Modifications of colon and cecum permit forage utilization:
1. Expanded length of large intestines
2. Forward and backward flow of ingesta
98
Rabbit digestion
Hindgut functions to selectively excrete fiber and retain non-fiber components for fermentation
Contractions expel fibrous fecal pellets
Cecal contents squeezed into the proximal colon
Goblet cells secrete mucin creating cecotropes (soft feces)
Cecotropes are consumed directly from the anus, providing more digestible products (microbial protein and B vitamins)
99
Physical state of lipids
liquids or non-crystalline solids at room temperature
100
Sensory characteristics of lipids
colorless, odorless, and tasteless
101
Lipid energy storage
energy-rich organic molecules, serving as fuel for the body
102
Solubility of lipids
insoluble in water (hydrophobic), but soluble in organic solvents
103
Lipid electrical charge
lack ionic charges
104
Lipid structure
Primarily composed of carbon, hydrogen, and oxygen
Non-polymeric (lack repeating monomeric units)
105
Function of lipids
Source of energy
Membrane structure
Signaling molecules
Insulation and organ protection
106
Simple lipids
Made of fatty acids and alcohols
Fats, oils, and waxes
107
Fatty acids
"precursor lipids"
Carboxylic acids with hydrophilic head and long hydrophobic tail
108
Fatty acid structure
methyl end (CH3) = omega end
Carboxyl terminal end (-COOH) = acid end = alpha end
109
Hydrocarbon chains may be _________ or ___________
saturated; unsaturated
110
Saturated fatty acids
all carbon-carbon bonds are single
Straight in shape - unbranched linear CH2 groups linked together by carbon-carbon single bonds
simplest form of fats
'saturated' indicates that the maximum number of hydrogen atoms are bonded to each carbon atom
general formula is CH3(CH2)nCOOH
111
Unsaturated fatty acids
one or more carbon-carbon double bonds are present
bent chain groups linked together by one or more carbon-carbon double bonds
more complex molecules
May have "cis" or "trans" formation
112
Mono- vs. poly-unsaturated fatty acids
Monounsaturated = one double bond
Polyunsaturated = multiple double bonds
113
Cis vs. trans unsaturated fat isomers
cis = hydrogen atoms on the same side of the double bond
trans = hydrogen atoms on opposite sides of the double bond
114
Essential fatty acids
not synthesized in vivo due to lack of delta-12 and delta-15 desaturase enzymes
MUST be obtained from diet
115
Triacylglycerol (TAG)
Main form of lipids in the body and food
Comprised of one glycerol and three fatty acids
Serve as energy storage molecules
116
Phospholipids
complex lipids
amphiphilic - water loving and fearing
make up cell membranes
act as emulsifiers
117
Glycolipids
complex lipids
118
TAG vs. phospholipid
TAG = three fatty acids coming out of glycerol
phospholipid = phosphate and something else replacing one of the fatty acids
119
Sterols
derived lipids
have a characteristic four-ring structure
crucial for cell membranes
serve as precursors for other molecules
120
Eicosanoids
derived lipids
compounds derived from 20 carbon and 22 carbon FA
signaling molecules:
prostaglandins
prostacyclins
thromboxanes
leukotrienes
121
Terpenes
derived lipids
122
Cholesterol
produced by the liver or obtained from diet
important metabolite for:
steroid hormone synthesis
vitamin D precursor
bile salt formation
component of cell membrane
123
Lipid digestion: non-ruminants
accomplished by emulsification (break down of fat by dispersing the molecules)
involves lipases and bile salts
124
Lingual lipase
mouth
secreted from glands at the back of the tongue
targets short- or medium-chain TAGs
125
Gastric lipase
secreted by chief cells of gastric mucosa
targets some TAGs
126
Processing dietary lipid in the stomach
digestion begins in the stomach
catalyzed by acid-stable lipases
critical processes occurs in the duodenum, purpose is to increase surface area
accomplished by bile salts and mechanical mixing
127
Bile salts
made in liver and stored/released from gallbladder
derivatives of cholesterol
amphipathic - hydrophilic and phobic
128
synthesis of bile acids
1. Hydroxyl groups are inserted at specific positions on the steroid structure
2. Double bonds of the cholesterol B ring are reduced
3. Hydrocarbon chain is shortened by 3 carbons
4. Carboxyl group introduced at the end
129
How and why are bile acids converted to bile salts?
bile acids are conjugated to glycine or taurine by adding an amide bond between carboxyl group of bile acid & amino group of added compound
bile salts are more effective detergents
130
What are the three steps of degradation of lipids by pancreatic enzymes?
1. Triacylglycerol (TAG) degradation
2. Cholesteryl ester (CE) degradation
3. Phospholipid degradation
131
Triacylglycerol (TAG) degradation
too large to be taken up by mucosal cells
acted upon by pancreatic lipase (removed fatty acids at carbons 1 and 3)
Lipase anchored by colipase
hydrolysis reaction results in 2-monoglycerol and free fatty acids (FFA) - now able to be absorbed
132
Cholesteryl ester (CE) degradation
most dietary cholesterol is nonesterified, 10-15% esterified
cholesteryl esters aid in storage and transport of cholesterol
cholesterol esterase hydrolyzes, yielding free cholesterol and fatty acid
133
Phospholipid degradation
pancreatic juice is rich in phospholipase A2:
1. activated by trypsin and requires bile salts
2. removes one fatty acid from carbon 2 of a phospholipid, leaving a lysophospholipid
example: phosphatidylcholine → lysphophatidylcholine (remaining fatty acid at carbon 1 can be removed by lysophospholipid)
some absorped, but most excreted
134
How is lipid digestion controlled?
mucosal cells produce CCK in response to lipids
CCK acts on the gallbladder and exocrine cells of pancreas
pancreas releases enzymes
decreases gastric motility
other intestinal cells secrete Secretin in response to low pH:
pancreas and liver release bicarbonate rich solution to help neutralize pH
too low a pH could denature enzymes (acid-stable, but optimum range is 4-6)
if fats are being broken down in the small intestine, more can’t be let in until what is already there gets broken down
135
How do the intestines absorb lipids?
primary products of degradation = free fatty acids, free cholesterol, and 2-monacylglycerol
products and bile salts form mixed micelles (disk-shaped cluster of amphipathic lipids; hydrophobic tails on the inside and hydrophilic heads on the outside)
brush border membrane separated from intestinal lumen by unstirred water layer
hydrophilic surface of micelle facilitates transport of lipids through water layer to membrane for absorption
short- & medium-chain do not require micelle transport
136
Resynthesis of TAG and cholesterol esters
absorbed lipids migrate to endoplasmic reticulum for biosynthesis
1. fatty acids converted to activated form by acyl coA synthetase
2. fatty acyl coA derivatives and 2-monoglycerols are converted to triacylglycerols by triacylglycerol synthase
3. lysophospholipids are recycled to form phospholipids by acyltransferases
4. cholesterol is esterified to a fatty acid by cholesterol acyltransferase
137
Exocrine pancreatic insufficiency
decreased production of digestive enzymes by the pancreas
reduces nutrient absorption
clinical signs include polyphagia, weight loss, and large volume of loose stools
138
Lipid digestion: ruminants
no emulsifying agents or gastric lipase
microbial lipase hydrolyze lipids; release glycerol and free fatty acids
glycerol metabolized by bacteria to form propionic acid (VFA absorbed across rumen wall)
hydrolysis is a prerequisite for the next step
139
Biohydrogenation
bacteria convert unsaturated fatty acids to saturated fatty acids
linoleic & linolenic acids are the primary substrates for biohydrogenation
two groups of bacteria: Group A & Group B
overall goal: alter double bond positions to make more stable compounds
stearic Acid (saturated)
140
Lipid absorption: ruminants
Same processes as non-ruminants
141
Why can't fats be directly absorbed into the bloodstream?
Lipids are hydrophobic on one side, and blood is an aqueous solution (fat and water don't mix
Therefore, lipoproteins are required to transport lipids
142
Plasma lipoproteins
Spherical macromolecular complexes of lipids and apolipoproteins
Differ in composition, size, and density
Function to keep component lipids soluble and provide transport mechanism
143
Composition of plasma lipoproteins
Neutral lipid core (TAG & CE)
Amphipathic shell (apolipoproteins, phospholipid, nonesterified cholesterol)
Polar (hydrophilic) portion exposed to the surface
144
Chylomicron
largest size plasma lipoprotein
lowest density, as they are more full of fat and have less protein molecules in their shell
Resynthesized TAG & CE packaged into chylomicron
Released by exocytosis from enterocytes into lymphatic system
Follow lymphatic system to thoracic duct; enter circulation (majority go to the liver)
145
Very low density lipoproteins (VLDL)
2nd largest plasma lipoprotein
more dense than chylomicrons
Produced in the liver
Composed of chylomicron
Carry lipid to peripheral tissues
146
Low density lipoproteins (LDL)
2nd smallest plasma lipoprotein
moderately dense
147
High density lipoprotein (HDL)
smallest size plasma lipoprotein
greatest density, as it has a high amount of protein in its shell and less fat
Heterogeneous family of lipoproteins
148
How is the TAG in chylomicrons used by tissues?
Most TAG in chylomicrons broken down in capillary beds of adipose tissue, skeletal & cardiac muscle
muscle cells & adipose tissue secrete lipoprotein lipase (LPL)
LPL degrades TAG to free fatty acids & glycerol
149
How is free fatty acid in chylomicrons used by tissues?
Free fatty acids enter adjacent muscle cells/adipocytes or transported in blood to other cells
move through membrane of adipocyte & bind to albumin; transported to tissues via albumin
Oxidized to produce energy
Adipocytes may re-esterify to produce TAG which are stored until needed
150
How is glycerol in chylomicrons used by tissues?
Glycerol taken up from blood
adipocytes lack glycerol kinase, cannot metabolize released glycerol
transported to the liver using aquaporin (carrier protein)
Phosphorylated by hepatic glycerol kinase to produce glycerol 3-phosphate or DHAP for use in glycolysis or gluconeogenesis
Used to make TAG in adipocytes
151
Chylomicron metabolism
1. LPL (lipoprotein lipase) action: TAG hydrolyzed within chylomicron
2. Chylomicron remnant formation: converted to remnant containing mostly cholesterol & other lipids
3. Hepatic uptake: remnants internalized; TAG hydrolyzed; CE stored or used for metabolic processes
152
What are the three possibilities for the fate of chylomicron remnants?
1. After TAG has been removed, chylomicron remnants are endocytosed in the liver
2. Intracellular remnants are hydrolyzed to component parts
3. Cholesterol & nitrogenous bases of phospholipids may be recycled
153
Lipoprotein interconversion
Chylomicrons are transported to the liver, where their remnants are converted to VLDL and LDL that is transported to adipose and other tissues
The VLDL and LDL are then converted in adipose and other tissues into HDL, which is transported back to the liver
154
How is VLDL converted to LDL?
LPL hydrolyzed TAG releasing free fatty acids and glycerol
VLDL decreases in size and increases in density as its triglycerides are broken down, forming LDL
LDL particles have higher concentration of cholesterol and cholesteryl esters
155
How are LDL particles internalized by cells?
receptor-mediated endocytosis -> LDL particles bind to receptors and are internalized
components are released
cholesterol used to make cell membrane or stored as CE
performed by cells that use cholesterol, especially liver, muscle, adrenal gland (steroid hormones), gonads (steroid hormones)
156
How are HDLs involved in reverse cholesterol transport (RCT)?
1. Free cholesterol removed from peripheral cells
2. Free cholesterol is esterified by lecithin cholesterol acyltransferase; incorporated into HDL particle
3. CE transferred to apolipoprotein B-containing particles in exchange for TAG
4. CE from lipoproteins taken up by hepatocytes for degradation to bile acids
157
Good vs. bad cholesterol
LDL has more cholesterol contained in it than HDL, and is therefore considered "bad cholesterol"
The cholesterol in LDL can build up in the arteries as plaque, constricting blood flow and lead to heart issues
158
How are lipids stored?
Excess dietary lipid stored primarily as TAG in adipocytes (white adipose tissue)
Under hormone control
Synthesized in two ways: VLDL, derived from glucose
159
Insulin
Hormone that acts on liver, muscle, and adipose tissues
Encourages cells to take up lipids
High levels stimulate LPL
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Fatty acid synthesis (lipogenesis)
Occurs primarily in the cytosol of liver or adipose tissue
1. Citrate transported to cytoplasm via Citrate Shuttle
2. Citrate acted on by ATP citrate Lyase; Acetyl CoA produced
3. Acetyl CoA carboxylated to Malonyl-CoA by Acetyl CoA Carboxylase
4. Fatty Acid Synthase adds 2-C units until Palmitate is produced
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TAG formation
palmitate is esterified to form TAG for storage
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Lipid mobilization
Mobilization requires hydrolytic release of fatty acids & glycerol from TAG
Hormone-sensitive lipase (HSL) removes a fatty acid from carbon 1 or 3
Other lipases remove remaining fatty acids
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How is hormone-sensitive lipase (HSL) activated?
1. Epinephrine binds to receptor
2. ATP converted to cAMP via adenylate cyclase
3. cAMP activates protein kinase
4. Protein kinase phosphorylates HSL (active form)
5. Active HSL hydrolyzes TAG to release a fatty acid; leaves Diacylglycerol
6. Phophatase dephosphorylates HSL (inactive form)
7. Other lipases remove remaining fatty acids
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How do insulin and epinephrine impact hormone sensitive lipase?
High insulin causes HSL to be deactivated
High epinephrine causes HSL to be activated
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Fatty acid oxidation
Major pathway for fatty acid catabolism
occurs in the mitochondria
removal of 2-carbon fragments from the chain
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How and why are long-chain fatty acids (LCFA) transported into the mitochondria?
LCFA cannot enter mitochondria as is
Must be converted to its CoA derivative by long-chain fatty acyl CoA synthetase
Uses carnitine as a carrier in a process called the carnitine shuttle
SCFA and MCFA do not require carnitine
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Carnitine shuttle steps
1. Transfer of an acyl group from cytosolic coenzyme A to carnitine palmitoyl transferase 1 (CPT-1); forms acylcarnitine & regenerates free CoA
2. Carnitine palmitoyl transferase (CPT-2) transports acylcarnitine into the mitochondria; removes acyl group & regenerates free carnitine
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Inhibition of carnitine shuttle
malonyl CoA inhibits CPT-1 (recall: malonyl CoA produced by fatty acid synthesis
prevents newly made palmitate from entering mitochondria
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Where does carnitine come from?
Obtained from diet
synthesized from lysine and methionine
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Carnitine deficiencies
Decreased ability of tissues to use LCFA as fuel
Accumulation of toxic amounts of free fatty acids & branched-chain acyl groups in cells
Causes:
Liver disease
Malnutrition
Dietary restrictions
Increased carnitine requirements (pregnancy, trauma, burn)
Hemodialysis
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Beta-oxidation reactions
Four reactions that shorten fatty acid chain & produces energy:
1. Oxidation (produces FADH2)
2. Hydration
3. Oxidation (produces NADH)
4. Thiolytic cleavage (releases acetyl CoA)
*Produces one NADH & one FADH2 per acetyl CoA, which then go to TCA cycle
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Three examples of ketone bodies
Acetoacetate
3-hydroxybutyrate
acetone
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How are ketone bodies synthesized in the liver?
1. Thiolase converts two acetyl-CoA molecules into acetoacetyl-CoA
2. HMG-CoA synthase converts acetoacetyl-CoA to HMG-CoA
3. HMG-CoA lyase converts HMG-CoA into acetoacetate
4. Acetoacetate converts into acetone or 3-hydroxybutyrate
