Lecture Nutrition & Metabolism PART 1

A nutrient is a substance in food that promotes normal growth, maintenance, and repair

• Major:
• Carbohydrates, lipids, and protiens

• Other:
• Vitamins and minerals (also water)

*essential nutrients are 45-50 moleculres that cannot be made fast enough by the body to meet the body's need and must be provide by the diet

• DIETARY SOURCES:
• -Starch (complex carbs) in grains and vegetables
• -Sugars in fruits, sugarcane, sugar beets, honey, and milk
• -Insoluable fiber: cellulose in vegetables; provides roughage
• -Soluable fiber: pectin in apples and citrus fruits; reduces blood cholesteral levels

• USES:
• Glucose is fuel used by cells to make ATP
• -neurons and RBCs rely almost entirely upon glucose
• -excess glucose is converted to glycogen or fat and stored

• DIETARY REQUIREMENTS:
• -Minimum of 100g/day to maintain adequate blood glucose levels
• -recommended minimum is 130g/day (based on amount needed to fuel the brain)
• -recommended intake: 45-65% of total caloric intake should be mostly complex carbs

• DIETARY SOURCES:
• Triglycerides
• -saturated fats in meat, dairy food, and tropical oils
• -unsaturated fats in seeds, nutes, olive oil, and most vegetable oils
• Cholesteral in egg yolk, meats, organ meats, shellfish, and milk products

• ESSENTIAL FATTY ACIDS
• Linoleic and linolenic acid, found in most vegetables (must be ingested)

• ESSENTAL USES OF LIPIDS
• -Helps absorb fat-soluable vitamins (A,D,E,K)
• -major fuel of hepatocytes and skeletal muscle
• -Phospholipids are essential in myelin sheaths and all cell membranes

1. protective cushions around body organs

2. insulating layer beneath the skin

3. concentrated source of energy

• PROSTAGLANDINS (lipid)
• -smooth muscle contractions
• -control of blood pressure
• -inflammation

• CHOLESTERAL
• -stabilizes plasma membranes
• -precursor of bile salt and steroid hormone formation

Fats should represent 30% or less of total caloric intake

Saturated fats should be limited to 10% or less of total fat intake

daily cholesteral intake should be no more than 300 mg (1 egg yolk)

• DIETARY SOURCES: 
• -eggs, milk, dish and most meats contain complete proteins that meet all hte body's amino acids needs
• -legumes, nuts, and cereals contain incomplete proteins that lack some essential amino acids

• USES:
• Structural materials: kertain, collafen, elastin, muscle proteins
• Most functional molecules: enzymes, some hormones

• DIETARY REQUIREMENTS:
• Rule of thumb: daily intake of .8g per KG body weight

• ALL OR NOTHING RULE:
• all amino acids needed must be present for protein synthesis to occue

• ADEQUACY ON CALORIC INTAKE:
• protein will be used as fuel if there is insufficient carbohydrate or fat available

• NITROGEN BALANCE:
• (homeostatic state in healthy adults)
• -state where the rate of protein synthesis equals the rate of breakdown and loss
• -positive if synthesis exceeds breakdown (normal in children and tissue repair)
• -negative if breakdown exceeds synthesis (stress, buyrns, infection, injury, or starvation)

• HORMONAL CONTROLS:
• anabolic hormones (growth hormones and sex hormones) accelerate protein synthesis and growth

ORGANIC COMPOUNDS

• they are not used as energy or as building blocks, but are crucial in helping the body use nutrients
• -most function as coenzymes

Vitamins D, some B, and K are synthesized in the body

There are two types based on soluability

• 1. Water-soluable vitamins
• -B complex and C are absorbed with water
• -B₁₂ absorption required intrinic factor from the stomach (Definiency of B₁₂ leads to pernicious anemia)
• -these are not stored in the body (those not used within the hour are excreted in urine)

• 2. Fat soluable vitamins
• -A, D, E, K are absorbed with lipid digestions products
• - all stored in the body except for vitamin K
• -Vitamins A, C, and E acts as antioxidents to neutralize tissue damaging free radicals from metabolidm

• The 7 required minerals are:
• Calcium, phospherus, potassium, sulfure, sodium, chloride, and magnesium

*others are required in trace amounts

• they work with nutrients to ensure proper body functioning
• *uptake and excretion must be balace to prevent toxic overload

• EXAMPLES:
• -Calcium, phosphorus, and magn esium salts harden bone
• -iron is essential for oxygen binding to hemoglobin
• -Iodine is necessart for thyroid hormone synthesis
• -Sodium and chloride are major electrolytes in food

Metabolism: biochemical reactions inside cells involving nutrients

Anabolism: synthesis of large molecules from small ones (building)

Catabolism: hydrolusis of complex structures to simpler ones (breaking down)

Cellular respiration: catabolism of food fuels and capture of energy to form ATP in cells

• Phosphorylation: enzymes shift high-energy phosphate groups of ATP to other molecules
• -phosphorylated molecules are activated to perform cellular functions (they do the work!)

1. Digestion, absorption, and transport to tissues

• 2. Cellular processing (in cytoplasm of tissue cells)
• -synthesis od lipids, proteins, and glycogen, or
• -Catabolism (glycolysis) into intermediates(pyruvic acid or acetyl CoA)

• 3. Oxidative (mitochondrial) breakdown of intermediates into CO₂, H₂O, and ATP
• 

Oxidation: gain of oxygen or loss of hydrogen

• Redox reactions:
• -oxidized substances lose electrons and energy 
• -reduced substances gain the lost electrons and energy from the oxidized substance
• *this is a couples reaction

• Coenzymes act as hydrogen or electron acceptors (become reduced during oxidation)
• -Nicotinamide adenine dinucleotide (NAD⁺) (based on Niacin)
• -Flavin adenin dinucleotie (FAD) (derived from riboflavin)

• 1. Substrate-level phosphorylation
• -high energy phosphate groups directly transferred from phosphorylated substrates to ADP
• -occurs in glycolysis (in cytosol) and the Kreb's cycle (in mitochondria)
• 

• 2. Oxidative phosphorylation
• *release the most energy
• -Chemiosmotic process that couples movement of substance s across a membrane to chemical reactions
• -IN THE MITOCHONDRIA....
• *carried out by electron transport proteins
• *nutrient energy is used to create H⁺ gradient across mitochondiral membrane
• *H⁺ flows through ATP synthase
• *Energy is captured and attaches phosphate groups to ADP
• 

• Oxidation of glucose:
• 

• Glucose is metabolized in 3 pathways:
• 1. Glycolysis
• 2. Kreb's Cycle
• 3. Electron transport chain and oxidative phophorylation

• A 10 step anaerobic pathway that occurs in the cytosol of the cell
• *glucose will yield 2 pyruvic acid molecules

• 3 major phases:
• 1. Sugar Activation (energy investment stage)
• -glucose is phophorylated by 2 ATP to form fructose-1, 6-biphosphate

• 2. Sugar Cleavage
• -the Fructose-1, 6-biphosphate is split into 3-carbon sugars
• *dihydroxyacetone phosphate
• *glyceraldehyde 3-phosphate

• 3. Sugar oxidation and ATP formation
• - 3-carbon sugars are oxidized (reducing NAD⁺)
• -inorganic phosphate groups (P_i) are attached to each oxidized fragment
• * 4 ATP are formed by substrate level-phosphorylation

• 1. 2 pyruvic acid (C₃H₄O₃)
• -converted to lactic acid if O₂ not readily available
• -Enter aerobic pathway if O₂ is readily available

2. 2 NADH + H⁺ (reduced NAD+)

3. Net gain of 2 ATP (4 produced, but 2 used during phase 1)

It occurs in the mitochondrial matrix

It is fueled by pyruvic acid and fatty acids

*pyruvic acid enters mitochiran by active transport by help of transport protein

• Transitional Phase: Each pyrucic Acid is converted into acetyl CoA
• 1. Decarboxylation: removal of 1 C to produce acetic acid and CO₂
• 2. Oxidation: H+ is removed from acetic acid and picked up by NAD⁺
• 3. Acetic acid + coenzyme A forms acetyl coA

Coenzyme A shuttles acetic acid to an enzyme of the Krebs cycle

• Each acetic acid is decarboxylated and oxidized generating:
• -3 NADH + H⁺
• -1 FADH₂
• -2 CO₂
• -1 ATP

• *the Krebs cycle does not directly use O2
• *breakdown products of fats and proteins can also enter the cycle
• *cycle intermediates may be used as building materals for anabolic reactions

The part of metabolism that directly uses O₂

Chain of proteins bound to metal atoms (cofactors) on inner mitochondrial membrane

substrates NADH + H⁺ and FADH₂ deliver hydrogen atoms

• 
• Hydrogen atoms are split into H⁺ and electrons

electrons are shuttled along the inner mitochondrial membrane, losing energy at each step

released energy is used to pump H⁺ into the intermembrane space

Respiratory enzyme complexes I, II, and IV pump H⁺ into the intermembrane space

H⁺ diffuses back to the matrix via ATP synthase

ATP synthase uses released energy to make ATP

• Electrons are delivered to O, forming O^-, which attracts H⁺ to form H₂O
• 

Transfer of energy from NADH + H⁺ and FADH₂ to ozygen releases large amounts of energy

This energy is released in a stepwise manner through the electron transport chain

the only major part of the membrane that is H+ permeable (this is important for the electron transport chain and oxidative phosphorylation!)

Works like an ion pump in reverse!

• Two major parts connected by a rod:
• 1. Rotor in the inner mitochondrial membrane
• 2. Knob in the matrix

• Glycogenesis:
• glycogen formation when glucose supplies excees need for ATP synthesis (mostly in the liver and skeletal muscles)

• Glycogenolysis:
• Glycogen breakdown in response to low blood sugar (mostly in the liver)
• 

Glucose formation from noncarbohydrate (glyceral and amino acid) molecules

mainly in the liver

protects against damaging effects of hypoglycemia, especially on the nervous system

* lipids are the body's most concentrated form of energy

Fat catabolism yiels 9kcal per gram (vs. 4 kcal per gram of carb or protien)

most products of fat digestion are transported as chylomicrons and are hydrolyzed by endotheial enzymes into fatty acids and glycerol

Only triglycerides are routinely oxidized for energy

• two building blocks are oxidized separately
• -glycerol pathway
• -fatty acid pathway

• Glycerol is conerted to glyceraldehyde phosphate
• -enters the kreb cycle
• -equivilent to 1/2 glucose

• Fatty acids undergo beta exidation in mitochondria which produces:
• 1. two carbon acetic acid fragments, which enter the krebs cycle
• 2. reduces coenzymes, which enter the electron transport chain
• 

• Triglyceride synthesis occurs when cellular ATP and glucose levels are high
• *when sugar is high this is the major activity in the adipose and an important function of the liver

• glucose is easily converted into fat because acetyl CoA is
• -an intermeduate in glucose catabolism
• -a starting point for fatty acid synthesis

• The reverse of lipgensis
• Oxaloacetic acid is necessary for complete oxidation of fat
• -without it, acetyl CoA is concerted by keogenesis in the liver to ketone bodies and released into the blood
• 

Phospholipids for cells membranes and myelin

cholestol for cell memebranes and steroid hormone synthesis

• in the liver:
• -synthesis of transport lipoprotiens for cholesterol and fats
• -synthesis of cholesterol from acetyl CoA
• -use of cholesterol to form bile salts