overview of carbs, proteins, and lipid metabolism Flashcards
what are the components of carbs
- carbs are major component of plant tissue
- makes up 60-90% DM
- major source of energy in diet
- different types of carbs deposited in plant tissue
what are the functions of carbs
- metabolized to glucose and glycogen - major source of energy
- protein sparing effect
- CHO stored as glycogen
- CHO help to oxidize proteins and fats
- aid in absorption of Ca and P
- maintain glucose level of plasma
- aid in peristaltic movements of food
how are CHO classified
- monosaccharides
- oligosaccharides
- polysaccharides
what are monosaccharides
simple sugars that cannot be hydrolyzed into simpler compounds
how are monosaccharides further classified
triose, tetrose, pentose, hexoses - based on number of carbon atoms
what are the common monosaccharides in animal tissue
pentoses and hexoses
what does glucose contain
an aldehyde stucture
what does fructose contain
a ketone group
what are the three important hexoses
glucose, fructose and galactose
how do you tell the difference between an alpha glucose and beta glucose
based on the position of the OH, alpha is facing down and beta is up
what are disaccharides
formed when monosaccharides are bonded together by a glycosidic (covalent) bond
what type of glycosidic linkage is easier to digest
alpha linkage
what are oligosacchardies
- 3 to 15 monosaccharides are bonded together
- prebiotics to promote bacteria and gut health
what are polysaccharides
large polymers of simple sugars
how are polysaccharides stored
- in plant cells a - starch in grains
- animal cells - glycogen
what type of CHO is the main source in monogastrics
starch
what type of polysaccharides do ruminants use
cellulose and hemicellulose
where is the primary site of CHO digestion
lumen of SI
what does pancreatic amylase digest
amylose
where are disaccharides digested
on the intestinal border enzymes to monosacchardies which are absorbed by enterocytes
how are simple sugars absorbed
directly in the intestinal epithelium
what is absorption
simple diffusion and/or ATP depended active transport
what is the first priority of absorbed glucose
to convert glucose to glycogen in the liver and muscle (glycogenesis)
what is the second priority of absorbed glucose
glucose oxidation for energy and fatty acid synthesis
how does glucose oxidation occur
via glycolysis and the tricarboxylic acids (krebs cycle or citric acid cycle)
where does glycolysis
cytosol
where does the TCA cycle occur
mitochondria
how many ATP molecules does anerobic oxidation of a glucose molecule produce
2
how many ATP molecules does aerobic oxidation of a glucose molecule produce
8
what is the TCA cycle
the central pathyway for CHO, protein, and fat metabolism
how many ATP molecules does the TCA cycle yield
30
how many ATP molecules does glycolysis and the TCA cycle yield
38
what is glycogenesis
- initiated from different monosaccharides
- in liver and muscle
- consumes 2 ATP
- higher glucose levels lead to glycigenesis regulated by insulin
what is glycigenolysis
- occurs in the cytosol
- occurs during exercise, fasting and between meals
- reverse of glycogenesis and regulared by glucagon and adrenaline
what is gluconeogenesis
when glucose levels deplete, glucose can be synthesized from non-carbohydrate sources such as lactate, glycerol, propionate, and amino acids
what percent of AA are gluconeogenic
60%
in ruminants, what happens to CHO
they are fermented by microbes to volatile fatty acids
how are VFA absorbed
through the ruminal wall and metabolized to energy in the liver and utilized by host
what are the three VFA
acetic, propionic, and butyric acids
what type of epithelium does the rumen have
squamous epithelium which funciton similarly to the columnar epithelium in the small gut
acetate
fatty acid synthesis and converts to acetyl CoA
propionate
gluconeogenic - glucose synthesis
butyrate
rumen epithelial cells convert to ketone
what are lipids
- organic compounds and esters of fatty acids and glycerol
- insoluble in water and soluble in organic solvents - ether
- plant derived lipids are vegetable oils
- presented as simple lipids or complex lipids
- dietary are fats and oils
what are the functions of lipids
- energy
- carrier of fatty acids and fat-soluble vitamins
- structure (cholesterol)
- heat regulation
- protection
what is the main constituent for lipids
fatty acids
what do fatty acids include
hydrophilic carboxyl group and hyrophobic methyl group
saturated fats
all bonds are saturated - solids
unsaturated fats
mono and polyunsaturated fats based on number of double bonds
what are PUFAs
- fatty acids contain more than 2 double bonds
- structure can fold due to presence of double bonds
- term omega to denote the position of double bonds
what are the two types of PUFAs
omega 6 and omega 3
what are essential fatty acids
FA that cannot be sunthesized in the body and must be supplemented in the diet
what are the 3 essential FA
- linoleic
- linolenic
- arachidonic - essential in cats
what are sterols
then most abundant steroid in the human diet
what is cholesterol
best known steroid and is the precursor of many other substances such as VD, bile acids, sex hormones, and corticosteroid hormones
what is emulsification
process by which large lipid molecules to small lipid droplets
dietary lipids in ruminant diets constitute what percent
< 5%
does emulsification and digestion by lipase occur in the rumen
no
what do microbial lipases do
hydrolyze complex lipids to glycerol and FFA
glycerol is metabolized by the rumen bacteria to___
propionic acid
what is biohydrogenation
conversion of PUFA to saturated FA
where does fatty acid oxidation occur
in the mitochondria
what does fatty acid form
fatty acyl CoA in cytosol ready for transport into mitochondria
what does carnitine act as
a carrier
what happens in beta oxidation
2 carbonds are cleaved off at a time starting from carboxyl end
how are lipids stored
as TAG which are formed in the cytosol of hepatocytes or adipose tissue in ruminants
what do TAGs attach do and how are they mobilized
- attached to lipoproteins and deposited in the blood for transport
- lipoprotein complexes are recognized by lipoprotein lipase and the TAGs are removed and deposited as fat
when does mobilization of lipids occur
when lipoprotein lipase is activated during starvation, stess, or increases in energy usage
what hormones increase during mobolizationof lipids
- glucagon and epinephrine
- insulin is reduced and stimulated lipases
what happens in ruminants during the transition period
lipids
- fat mobilization is at its peak and may exceed the rate at which acetyl CoA enters the TCA cycle
- during this hepatic synthesis of ketone bodies occurs
what is the basic unit of lipids
Triacyl glycerol
lipids are transported as ____ and absorbed as ___
micelles; chylomicrons
what is good and bad cholesterol
HDL, LDL
what is the end product of B-oxidation
acetyl CoA
what are proteins
- organic compounds made up of amino acids joined by peptide bonds
- nitrogen makes proteins very unique in animal nutrition
dipeptide
two amino acids joined by one peptide bond
tripeptide
three amino acids joined by two peptide bonds
polypeptide
a peptide with more than ten amino acids
how is the structure of a protein determined
by the sequence of individual amino acids it has in the polypeptide chain - called the primary structure of a protein
what are the functions of proteins
- major structural component of animal tissues
- involved in biochemical, immunological, transportational and other regulatory activities
- can provide energy
how do ruminants get protein
microbes synthesize microbial protein from non protein sources
what are globular proteins and examples
- soluble in water or dilute acids, bases or alcohol
- albumin and globulin
what are fibrous proteins and examples
- insoluble in water and are resistant to digestive enzymes
- keratins and collagen
what are conjugated proteins and examples
- contain other nonprotein compounds in structure
- lipoproteins, hemoproteins, glycoproteins, nucleoproteins
what are amino acids
- bulding blocks of proteins
- composed of an amino group and carboxyl group
- 10 essentual AA that the animal body cannot synthesize and need to be supplemented in the diet
what do acidic amino acids contain more of
carboxyl groups
what do basic amino acids contain more of
amino groups
what are S-containing amino acids
methionine and cysteine
what are imino acids
contain an imino instead of an amino group - proline
what are essential amino acids
animal body cannot synthesize some AA or not in the amount that is needed for body requirements
why don’t ruminants need EAA
because they are synthesized by rumen microbes
how is protein digested in monogastrics
involves denaturationto expose peptide bonds and then hydrolysis to release free amino acids
protein digestion in ruminants
- protein breakdown and microbial protein synthesis
- to maximize rumen function, readily available CHO and RDP must be balanced
what is the fate of absorbed proteins
used for anabolic purposes such synthesis of nonessential AA, tissue protein synthesis, enzyme or hormone synthesis, deamination or transamination
where is the major site of AA metabolism
liver
transamination
- an amino group from AA is transferred to organic acid to synthesize a new amino acid
- mediated by VB6
deamination
removal of amino group
all amino acids exept which are glucogenic
leucine and lysine
what are leucine and lysine
stricky ketogenic amino acids and can provide acetyl CoA as an energy source
which amino acids are glucogenic and ketogenic
isoleucine, phenylalanine, tyrosine, tryptophan
what are amino acids used for
- energy
- glucose synthesis
- ketone body formation
- fat synthesis
where does conversion of ammonia to urea (urea cycle) occur
liver and kidney
what non protein amino acids are needed for the urea cycle
ornithine and citrulline
