lecture quiz 2: carbs Flashcards
1
Q
primary source of CHO in livestock feeds
A
forages & grains
2
Q
carbohydrates are composed of…
A
C, H, & O in a 1:2:1 ratio (makes up ~3/4 of plant dry weight)
3
Q
main purpose of carbs
A
energy
4
Q
carbs formed by
A
plant photosynthesis
5
Q
origin of carbs
A
majority from plant origin (glycogen & lactose = exceptions ➞ don’t play a significant role in energy)
6
Q
carb classifications
A
- monosaccharides: composed of 1 sugar mol
- disaccharides: composed of 2 monosaccharides
- polysaccharides: sugar polymers
7
Q
monosaccharides
A
- composed of 1 sugar mol
- characterized by how many C
- pentose = 5 C
- ribose (most important)
- arabinose
- xylose
- hexose = 6 C
- glucose (most important)
- fructose (common in fruits & semen)
- galactose
- mannose
7
Q
ribose
A
- most important pentose in nutrition (monosaccharide)
- found in every living cell
- do not need to consume in diet ➞ can convert from glucose via pentose phosphate pathway
- structural component for compounds involved in metabolism:
- ATP/ADP (energy transfer)
- riboflavin (vit B2)
- DNA (genetic coding)
- RNA (protein synthesis)
8
Q
sucrose
A
glucose + fructose
- disaccharide
- table sugar
8
Q
glucose
A
- most important hexose in nutrition (monosaccharide)
- primary form of sugar used for energy at a cellular level
- most complex carbs contain or are made of glucose
- major end-product of carb digestion for non-ruminants (ruminants & hind-gut fermenters carb digestion end-product is volatile fatty acids - VFAs)
9
Q
lactose
A
galactose + glucose
- disaccharide
- milk sugar
10
Q
maltose
A
glucose + glucose
- disaccharide
- “beer sugar”
- intermediate during digestion of starches for non-ruminants
- sprouting grains (during germination) break down starches → ↑ level of maltose = malting in beer industry
11
Q
4 important polysaccharides important for animal nutrition
A
- starch
- β-glucans
- cellulose
- hemicellulose
11
Q
starch
A
- polysaccharide
- most abundant polysaccharide in many feeds
- made of repeating units of glucose connected by ⍺-bonds
- digestible by non-ruminants & ruminants
12
Q
components of starch
A
- amylose
- unbranched helical chain
- ⍺-1,4 linkage only
- 14-30% of total plant starch
- soluble in water
- amylopectin
- ⍺-1,4 linkage w/ ⍺-1,6 linkage at each branch point
- branched chain w/ more open ends
- 70-85% of total plant starch
- not soluble in water (usually forms gel)
- more digestible than amylose ➞ many open ends for amylase to act on
- genetically made grains have higher levels of amylopectin so easier to digest (e.g. waxy corn)
13
Q
β-glucans
A
- polysaccharide
- chains of glucose w/ β-1,4 & β-1,3 linkages
- branched structure
- found in plant cell walls of cereal grains, high levels in barley & oats
- affinity for water: absorbs water & forms a gel in intestine ➞ reduces absorption of other nutrients
- reduces passageway & rate of passage through GI tract (&↓feed consumption)
- reduces absorption & digestibility of other nutrients (& ∴ energy)
- may cause sticky or wet feces in pigs & poultry
- do not have high energy value for non-ruminants ➞ cannot break down β bonds
- ruminants & hind-gut fermenters can digest normally
14
Q
β-glucan effects on non-ruminants
A
tendency to absorb water and form gel in intestines that:
- reduces passageway & rate of passage through GI tract (also reducing feed consumption)
- reduces absorption & digestibility of other nutrients (& subsequent energy)
- may cause sticky or wet feces in pigs & poultry
15
Q
cellulose
A
- polysaccharide
- made of repeating units of glucose connected by β bonds
- most abundant biochemical on earth
- found in plant cell walls
- comprises 25-30% of fibrous plants (high in cell walls)
- no enzymes to digest in mamals or avians
- microbes in ruminants & hind-gut fermenters can break down β-bonds
16
Q
difference btwn starch & cellulose
A
starch is glucose connected by ⍺-bonds ➞ all glucose mol are in the same orientation
cellulose is glucose connected by β-bonds ➞ every glucose mol is upside down compared to neighbor
17
Q
hemicellulose
A
- polysaccharide
- complex mix of glucose, xylose, mannose, arabinose, & galactose w/ β-linkages
- principal component of plant cell walls
- degraded only by microbial enzymes in ruminants & hind-gut fermenters
18
Q
majority of carbs found in forages & roughages
A
hemicellulose & cellulose
(some in grains b/c of plant seed coat)
19
Q
glycogen
A
- animal starch
- similar structure to amylopectin: branched w/ protein center
- 5-6% of animal liver weight
- 1-2% of animal muscle weight
- only found in animal tissues
- quick source of energy for animals but not an important or significant source of energy/carbs
20
Q
β-bonds in carbs
A
cannot be broken down by mammalian or avian enzymes, only microbial ones of ruminants & hind-gut fermenters
- diff in structure = reason enzyme cannot break down
- found in cellulose, β-Glucans, & hemicellulose
21
Q
lignin
A
- not a carb, polyphenolic compound
- glue keeping fibers of cellulose & hemicellulose together in plant cell wall
- structure & rigidity: encases cellulose & hemicellulose
- as plants mature, they become woody due to lignification
- reduces digestibility by acting as a barrier to plant carbs
- indigestible ➞ no animal or bacterial enzymes can break down lignin
- 2nd most abundant biomaterial on planet (after cellulose)
- comprises 15-20% of dry weight of woody plants
22
plant cell walls
- made of carbs cellulose & hemicellulose + lignin
- "fiber" = plant cell wall components
- mature plants = ↑ cell wall content = ↓ digestibility
- even though ruminants can digest fiber, it has a lower digestibility than starches
- any cellulose & hemicellulose associated w/ the lignin is also not digested well & excreted in feces
23
sources of carbs for animals
- most feeds contain carbs b/c they are the main component of most plants
- there will always be some fiber in plant materials (not in animal carb sources)
- carbs in grains = mainly starch (corn, barley, wheat) for non-ruminants & in pet foods
- carbs in forages = mainly cellulose & hemicellulose for ruminants & hind-gut fermenters
