Nutrition and Metabolism

NUTRITION and METABOLISM

I. Metabolism

A. Anabolism - "building up"

B. Catabolism - "breaking down"

II. Metabolic Processes

A. Anabolism

1. Example - Dehydration synthesis reactions:

Glucose + Glucose --> Maltose + H₂O

Glycerol + 3 fatty acids --> Triglyceride + 3 H₂O

Amino acid + Amino acid --> Dipeptide + H₂O

B. Catabolism

1. Example - Hydrolysis reactions (reverse of dehydration synthesis):

Disaccharide + H₂O --> monosaccharide + monosaccharide

Triglyceride + 3 H₂O --> glycerol + 3 fatty acids

Dipeptide + H₂O --> amino acid + amino acid

C. Enzymes

1. Control rate of reactions

2. Coenzymes and cofactors activate enzymes

3. Are activated in a specific sequence in metabolic pathways

D. Oxidation

1. Cells "burn" (oxidize) glucose (C₆H₁₂O₆)

2. Energy released drives metabolic reactions (muscle contraction, nerve impulse conduction, etc...)

3. Preferred energy source of the cell = ATP (adenosine triphosphate)

Adenine – Ribose Sugar – P~P~P

4. One glucose molecule can yield up to 38 ATP!

E. Cellular Respiration

1. Defined: process by which energy (from phosphate bonds) is released from molecules (like glucose) and is transferred to other molecules:

ADP + P_i --> ATP

2. Anaerobic (glycolysis)

a. Occurs in the cytosol
b. Does not require oxygen
c. Net production of 2 ATP

3. Aerobic (Kreb’s Cycle)

a. Occurs in the mitochondria
b. Requires oxygen to complete the pathway
c. Production of 36 ATP (most from electron transport chain)

III. Carbohydrate Metabolic Pathways

Glycolysis

Intermediate Step No O₂

PYRUVIC ACID <----> LACTIC ACID (fatigue, pain)
3C
O₂ avail. CO₂ liberated and NAD⁺ combines with 2H --> NADH₂

ACETYL + COENZYME A (from pantothenic acid) --> ACETYL CoA --> Enters Kreb’s Cycle

Summary of Glycolysis:

-Series of 10 steps (some reversible, some not) with specific enzymes for each step
-Invested 2 ATP in the process, 4 ATP were produced (this is our "energy currency")
-Net gain is 2 ATP (glycolysis extracts only 10% of the total energy from the glucose molecule!)
-End product = 2 Pyruvic acid molecules
-Intermediate step: 2C acetyl condenses with Coenzyme A to form Acetyl CoA, which enters the Kreb’s cycle (provided oxygen is available)

Krebs Cycle (TCA cycle, Citric Acid cycle)

AEROBIC RESPIRATION

oxidation - losing an electron (or hydrogen atom)
reduction - gaining an electron (or hydrogen atom)

Summary of Kreb’s Cycle: Per pyruvic acid:

1. First step: Acetyl CoA (2C) condenses with oxaloacetic acid (4C) --> Citric Acid (6C)

2. Series of oxidation-reduction (redox) reactions occur:

3 NAD⁺ are reduced to form 3 NADH₂1 FAD⁺ is reduced to form 1 FADH₂

3. Two decarboxylations liberates 2 CO₂ molecules to regenerate oxaloacetic acid (4-C)

4. One ATP is formed by substrate-level phosphorylation

5. The 3 NADH₂ and 1 FADH₂ are shuffled off to the electron transport system and go through a process called oxidative phosphorylation (defined: way in which ATP is formed as electrons are transferred from NADH₂ or FADH₂ to oxygen by a series of electron carriers).

Summary of Electron Transport System:

NADH₂ or FADH₂ hold most of the energy from glucose. They are oxidized to NAD⁺ and FAD

"golden nuggets" of energy

NADH₂ --> NAD⁺ + H₂ (contains 2 electrons)

FADH₂ --> FAD⁺ + H₂ (contains 2 electrons)

The electrons are sent through a series of electron carriers, many of which are cytochromes (iron-containg protein enzymes)-- energy is released in the process...ATP, which traps this energy, is generated (by oxidative phosphorylation) in the process:

ATP Synthase

ADP + P_i --> --> ATP

-cytochrome oxidase - is the last electron carrier in the chain and it releases electrons to oxygen (thus oxygen is the final electron acceptor). Oxygen then combines with hydrogen ions to form metabolic water.

III. Carbohydrates

A. Sources and Types of Carbohydrates

1. Complex carbs:

a. Starch ( maltose, glucose)

b. Glycogen (polymer of glucose)

c. Cellulose (fiber)

2. Simple carbs:

a. Disaccharides and Monosaccharides

b. Examples

Sucrose = glucose + fructose

Maltose = glucose + glucose

Lactose = glucose + galactose

B. Fate of Carbohydrates

1. Glycolysis --> Kreb’s cycle --> Electron transport chain

2. Glycogenesis:

glucose + glucose.... --> --> -->glycogen

reverse = glycogenolysis

3. Excess glucose --> FAT (this is called lipogenesis)

4. Building blocks of carbs = 5 or 6 carbon sugars

5. Sole energy source for neurons (i.e. brain, etc...)

IV. Lipids

A. Sources and Types of Lipids

1. Fats (triglycerides)

a. Saturated fat

b. Unsaturated fat

2. Phospholipids (cell membrane component)

3. Cholesterol

a. Above 200 mg/100 mL of blood is bad

b. High levels linked to heart disease

B. Packaging and Transport of Lipids

1. HDL’s (should be >40 mg/100 mL)

a. Rich in proteins, low in phospholipids and cholesterol

b. HDL’s transport cholesterol from tissues to the liver to be broken down

c. Liver releases HDL’s minus cholesterol to blood

2. LDL’s (should be <100 mg/100 mL)

a. Cholesterol rich

b. Liver = source of VLDL’s

c. VLDL’s --> peripheral tissues --> LDL’s

3. Chylomicrons (from intestines - lowest density)

C. Fate of Lipids

1. Digestion --> Fatty acids + glycerol

a. Glycerol may be converted to glucose or enter the Kreb’s cycle

b. The liver may convert fatty acids to...

Triglycerides
other Fatty acids
Lipoproteins
Phospholipids
Cholesterol

2. Excess is stored (lipogenesis)

3. Beta Oxidation of Fatty Acids Acetyl CoA Kreb’s cycle ETC

4. Ketone bodies (keto-acidosis)

5. Essential fatty acids - linolenic and linoleic

V. Proteins

A. Sources of Proteins

1. Animal sources (meat, fish, poultry)

2. Plant sources (beans, peas)

3. Other sources (eggs, dairy, nuts)

B. Amino Acids

1. 21 total

2. Eight are essential

3. Essential amino acids cannot be stored

4. If missing even one amino acid, the protein cannot be made

C. Fate of Amino Acids

1. Structural proteins

2. Enzymes

3. Hormones

4. Plasma proteins

5. "Parts" used to make glucose (gluconeogenesis)

6. Excess stored as fat

7. How about that Atkins' Diet?

VI. Nucleic Acids

A. Sources

B. Functions

VII. Vitamins

A. Fat-soluble Vitamins (A, D, E, K)

B. Water-soluble Vitamins (B & C vitamins)

C. Antioxidants (beta carotene, Vit. C, Vit. E, sulfur and selenium)

VIII. Minerals

A. List some functions and sources of the following minerals:

calcium

potassium

phosphorus

sodium

VI. Trace Minerals

A. Minerals needed in very small amounts

B. List some functions and sources of the following minerals:

iron

fluorine

iodine

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Last Updated 06/08/07