Carbohydrates

Question 1

4 Functions of Carbohdrates

Answer 1

1. 1 degree source of energy for most cells and tissues
2. Storage form of energy
3. Source of Carbon for various metabolic processes
4. Structural elements on surface of cells

Question 2

1 . CHO as a source of energy

Answer 2

• Energy obtained via glycolysis and TCA/
Krebs cycle within cells;
• CHO provides 4 kcal/gram;
• Presence of -OH groups on sugars decreases
energy content, but increases solubility

• Bottom line: Fats store more energy but are less soluble and hence less rapidly accessible
(more readily available due to solubility)
Ex-sugar in water

Question 3

2. Energy Storage

Answer 3

Plant cells store energy as Starch
Animals store energy as Glycogen
They are the same thing; structurally nothing different

Question 4

3. CHO in Metabolic Pathways

Answer 4

-?
No ATP is produced!
(pathway is not active when
cellular ATP levels are low)

Question 5

4. CHO as structural components

Answer 5

Found on the surface of all animal cells;
Involved in…
• Cell trafficking
• Immune cell recognition of pathogens

Particular sugar on surface for different functions for animals
~Pig hearts and other organs can be used in humans

Question 6

Glucose vs. fructose

Answer 6

1. Both are simple sugars (monosaccharides) with
   identical chemical formulas (C6H12O6);
2. Both have the same energy content;
3. Glucose is an aldehyde, while fructose has a
   ketone group.
   Different how humans and animals digest them

Question 7

Sucrose

Answer 7

The intestinal enzyme Sucrase is needed to hydrolyze the covalent bond between glucose and fructose.
- 50/50 glucose and fructose
1. A disaccharide found in sugar cane and sugar beets;
2. Used to be the major sugar used for sweetening foods, soft drinks, etc.
3. When soft drink & food companies switched to
“high-fructose” corn syrup (largely from US & Europe) in 1980’s, there was a tremendous global impact on trade (& possibly OBESITY) in many countries.

Question 8

Lactose

Answer 8

Lactose = glucose + galactose
1. Found in milk from lactating mammals only;
2. Enzyme,lactase breaks apart the two sugars so they can be absorbed and metabolized separately;
3. All mammals produce lactase during the neonatal period, but most stop producing after weaning;
4. Feeding lactose to adults often leads to severe
intestinal cramping and diarrhea, because bacteria in gut now have access to an readily available energy source which they ferment, generating gaseous by-products.

Question 9

Nomenclature of Glucose

Answer 9

C_6 H_12 O_6

-ose&raquo_space; sugar and carbohdrate

Question 10

Carbohdrates associated with plantsynthesis and cellulose

Answer 10

The carbohydrates are the compounds which
provide energy to living cells.
• The carbohydrates we use as foods have their
origin in the photosynthesis of plants. (life on Earth)
• They take the form of sugars, starches, &
plant fibers (Cellulose, hemicellulose, lignin).
- Animals do not have enzymes to break down cellulose.

Question 11

Non-ruminants associated with Cellulose digestion

Answer 11

• Starches can be used as energy sources by non-ruminants, while cellulose can not.
• Non-ruminants are unable to digest cellulose because they can not digest the links between the glucose molecule

Question 12

Ruminants associated with Cellulose digestion

Answer 12

Some of the microbes in the rumen or lower GI tract are able to hydrolyze the linkages in cellulose, thus ruminants and hindgut fermentors can digest plant fibers such as cellulose.

Question 13

Comparison of Starch and Cellulose

Answer 13

1. Both Starch and Cellulose are carbohydrates which are classified as polysaccharides since they are composed of chains of simple sugar molecules.
2. While they are both chains of glucose molecules, starches can be used as energy sources by non-ruminants, while cellulose cannot.

Question 14

Cellulose

Answer 14

• It is the chief constituent of cell walls in most living
plants;
• Wood is mostly cellulose, making cellulose the most abundant type of organic compound on the Earth.

Question 15

Key Structural diffrenece between Starch vs. Cellulose

Answer 15

Starch- alpha(break in the structure)-1,4 linkages

Cellulose- beta(linear structure)-1,4 linkages

Question 16

**Digestion of Starch vs. Cellulose

Answer 16

1.   Amylase is the enzyme produced by all animals (cows, pigs, chickens, dogs, cats) that digest starches.
2.   They are somewhat like keys which will fit the geometry of the bonds found in starch, but not those of the cellulose bonds.
3.  ** Some of the microbes in the rumen or lower GI tract are able to hydrolyze the linkages in cellulose, thus ruminants and hind-gut fermentors can digest plant fibers, such as cellulose.

Question 17

Amylase

Answer 17

• The enzyme produced by all animals (cows, pigs, chickens, dogs, cats) that digest starches.
• Animals rely on amylase as a critical enzyme to hydrolyze carbon
• From the pancreas

Question 18

**Glucose metabolism in ruminants

Answer 18

1.  Dietary CHO is digested & metabolized by
rumen microbes;
2.  Glucose is convert to Pyruvate via
microbial glycolytic pathway;
3.  Absence of O2 (anaerobic conditions in the
rumen) leads to fermentation;
4.  Pyruvate is converted to volatile fatty acids
(VFA)
- They don’t just digest they metabolize until reaches anaerobic condition» leads to fermentation

Question 19

Volatile Fatty Acids (VFA)

Answer 19

1.  Volatile fatty acids (VFAs) are fatty acids
with a carbon chain of six carbons or fewer.
Sometimes referred to as short-chain fatty acid (SCFA)
2.  VFA are absorbed through rumen wall, reach the liver via portal vein; easily absorbed»diffused
3.  Propionate is converted to glucose; (gluconeogenesis)
4.  Acetate & butyrate can be used for milk fat synthesis.

Majority of smells come from VFA’s

Question 20

Low GLUCOSE Availability in RUMINANTS

Answer 20

1.   Blood glucose levels in ruminants are ~1/2 those found in monogastrics.
2.   WHY? Very little glucose makes it past the rumen to be absorbed in the intestine of the ruminant.
3.   Around half of the glucose in the circulation of ruminants is synthesized from propionate and glucogenic amino acids in the liver by a process called gluconeogenesis. (other half comes from the diet)

Question 21

Fates of absorbed carbohydrates

Answer 21

1.   Oxidized to provide energy;
2.   Stored in liver and muscle for future energy needs; form of glycogen in skeletal muscles
3.   Converted into fat and stored in adipose tissue.

Question 22

How do cells derive energy from glucose?

Answer 22

1.   Glycolysis (first stage)
2.   TCA (Krebs) cycle (2nd)
3.   Respiratory (electron transport) chain (3rd)
   * *Need all 3 to extract max glucose

Question 23

Which carbohydrates are readily absorbed in the small intestine?

Answer 23

Glucose and lactose

Question 24

Glycolysis

Answer 24

a)   Occurs in Cytosol of all tissues;
b)   Can occur in the absence of Oxygen;
c)   Provides important metabolic intermediate
d)   Lactate (lactic acid) is the end-product when O2 is limiting.

Question 25

Energetics of Glycolysis

Answer 25

have to use 2 ATP and get 4 ATP out

Question 26

Pyruvate dehydrogenase (PDH)

Answer 26

1.   Links glycolysis with TCA Cycle
2.   Converts pyruvate into acetyl CoA
3.   Provides 2 NADH per glucose
4.   CO2 is formed
5.   Highly regulated step… mostly via feedback inhibition by end-product (acetyl CoA) or by high concentration of ATP or NADH

Question 27

TCA (tricarboxylic acid) cycle

Answer 27

1.  Occurs in the Mitochondria;
2.  Recovers much more energy from glucose than glycolysis;
3.  Provides various metabolic intermediates for anabolic processes…
•  fatty acid biosynthesis
•  amino acid biosynthesis
•  gluconeogenesis
4.  Conversion of acetyl CoA to …
(2) CO2 + (3) NADH + FADH2 + ATP
5.  Common pathway for oxidation of C-skeleton of CHO, Fats, and Proteins

Question 28

• *Electron transport chain

a. k.a. respiratory chain or oxidative phosphorlation

Answer 28

1. Uses a series of cytochrome coenzymes for oxidation-reduction reactions;
2. Occurs on the mitochondrial membrane
3. It is how we obtain energy from NADH and
   FADH 2;
4. O2 serves as the final e-
5. Metabolic H2O is formed