Nutrition Ch 9 - LOs

metabolism

the chemical processes and reactions involved in maintaining life

• enable us to release energy from carbs, fat, protein, and alcohol

  • permit us to synthesize new substances and excrete waste products

metabolic pathway

group of reactions that occur in a progression

anabolic pathway

use small compounds to build larger ones

• building blocks: glucose, fatty acids, cholesterol, and amino acids

• requires energy

• more prominent during growth

catabolic pathway

break down compounds

• ex. glycogen » glucose

• release of CO2, H2O, and ATP

• more prominent during weight loss or wasting disease

adenosine triphosphate (ATP)

energy source used to:

• synthesize new compounds

• contract muscles

• conduct nerve impulses

• pump ions across membranes

how does ATP generate energy?

high energy bonds between phosphates are broken during hydrolysis

add phosphate(s) back to AMP and ADP

how ATP is regenerated and recycled by cells

oxidized

loses electrons/H

gains O

reduced

gains electrons/H

loses O

derivatives of niacin and riboflavin

transfer hydrogens and energy yielding compounds to oxygen in metabolic pathways

niacin (vitamin B-3)

component of nicotinamide adenine dinucleotide

NAD+

what is the oxidized form of niacin?

NADH

what is the reduced form of niacin?

riboflavin (vitamin B-2)

component of flavin adenine dinucleotide

FAD

what is the oxidized form of riboflavin?

FADH2

what is the reduced form of riboflavin?

pantothenic acid (vitamin B-5)

precursor to coenzyme A (CoA)

pyruvate»lactate

what is being reduced (gain H) in this reaction?

NADH»NAD+

what is being oxidized (lose H) in this reaction?

aerobic cellular respiration

• molecules from food are oxidized to form ATP with O2 as final electron acceptor

• 30-32 ATP yield

anaerobic metabolism

• insufficient O2 present

• incomplete breakdown of glucose

• creates 2 ATP per glucose

glycolysis

INPUT: 1 glucose
OUTPUT: 2 pyruvate, 2 NADH & H+, 2 ATP

• occurs in cytosol

• role is to break down carbs to create energy and create building blocks for anabolic pathways

• doesn’t need oxygen

transition reaction

INPUT: 2 pyruvate
OUTPUT: 2 Acetyl-CoA, NADH & H+, CO2

• occurs in mitochondria

• requires oxygen

  • irreversible rxn

citric acid cycle

INPUT: 2 Acetyl-CoA
OUTPUT: 6 NADH & H+, 2 FADH2, 2 GTP (to make ATP), CO2

electron transport chain

INPUT: NADH & H+, FADH2
OUTPUT: ATP, water, NAD+

oxidative phosphorylation (O2 final acceptor) » combine with protons to form water, regenerates NAD+
- carried by NADH+ & H+, and FADH2 to form ATP
- needs Cu and Fe

fermentation

pyruvate is produced during glycolysis and converted to lactate » meant to regenerate NAD+ to keep glycolysis going (slow generation of ATP)

less glycolysis

what occurs when there is less NAD+?

cori cycle

generates lactic acid back into glucose in muscle fibers

steps of fatty acid metabolism

1. lipolysis

2. fatty acid oxidation

3. carnitine shuttle

4. beta oxidation/fatty acid breakdown

5. TCA cycle

6. ETC

lipolysis

breakdown of triglycerides into free fatty acids and glycerol

fatty acid oxidation

• breakdown of fatty acids for energy production

• fatty acids broken down with O2 as electron acceptor

• occurs in the mitochondria

carnitine shuttle

fatty acids are taken up by cells and shuttled into mitochondria from cytosol

hormone sensitive lipase

during fasting, triglycerides from adipose tissue are broken down into fatty acids

• activity is increased by glucagon, growth hormone and epinephrine

• activity is decreased by insulin

oxaloacetate

combines with acetyl-CoA to create citrate in TCA

beta oxidation

fatty acid carbons are cleaved off in pairs » produce NADH and FADH2

• cleaved carbons make acetyl-CoA, which enters TCA

TCA

fatty acids have more carbons than glucose:

• Glucose: 2 turns of TCA

• Fatty acids: 1 turn per carbon pair (2-26 pairs per acid)

Fatty acids store more chemical energy than glucose (less oxygen)

Fats yield more energy than carbs (9 vs. 4 kcal)

• some TCA compounds are used for other purposes

• cells that use glucose-derived pyruvate replenish oxaloacetate (keeps TCA for fatty acids running)

• there is no pathway to make carbs from fatty acids

how do carbs aid fat metabolism?

“fats burn in a carbohydrate flame”

fats are more efficiently utilized than carbohydrates

production of ketoacids

results in metabolic acidosis (depletion of bicarbonate)

fasting ketosis

• acidosis is mild

• self limiting: ketosis increases insulin sensitivity results in decreased fatty acids release and increased glucose uptake

diabetic ketoacidosis

• more serious metabolic acidosis

• seen in type 1 diabetics with insulin deficiency

glucogenic amino acids

use carbons from carbon skeleton to form glucose

ketogenic amino acids

use carbons from acetyl-CoA

amino acids being used for fuel must first be deaminated

• require vitamin B

• results in carbon skeleton entering TCA, creates acetyl-CoA OR pyruvate

gluconeogenesis

• allows body to create glucose from breakdown products of carbs, fats, or proteins

• WHERE: mainly in the liver, partly in the kidneys

• STARTING: glycerol, glucogenic AA, lactate » pyruvate (cori cycle), oxaloacetate

• VITAMINS: B

glycolysis and the transition reaction create acetyl-CoA which enters the TCA

how do carbs convert into energy?

lipolysis breaks down fatty acids » pyruvate » acetyl-CoA » TCA

how do fats convert into energy?

deamination breaks down proteins to AA » carbon skeletons of AA are converted into Acetyl-CoA or into other intermediates (oxaloacetate, fumarate) that enter the TCA

how do proteins convert into energy?

alcohol dehydrogenase converts ethanol to acetaldehyde » acetate » add CoA » Acetyl-CoA, which enters TCA

how does alcohol convert into energy?

carbon skeletons, amino acids, proteins, ammonia & urea

what can amino acids convert to?

stored body fat and glucose

what can glycerol convert to?

glucose

what can glycogen and glucose convert to?

stored body fat, cholesterol, and VLDL

what can fatty acids convert to?

stored body fat

what can alcohol convert to?

liver

what organ plays a major role in metabolic pathways

1. ATP concentrations

2. enzymes

3. hormones

what does regulation involve?

• gluconeogenesis

• protein breakdown

• lipolysis

low levels of insulin promote

• glycogen

• fat

• protein

increased insulin promotes synthesis of

absorptive state

what is another term for feasted state?

post-absorptive state

what is another term for fasted state?

fasting

• energy sources vary depending on length

• depletion of lean mass to 50% is fatal

  • approx. 7-10 weeks

• depletion of electrolytes due to diuretic effects of ketones

• buildup of urea due to protein catabolism

feasting

• excess energy intake from any source that results in fat storage

• excess dietary fat can be stored with minimal processing

• excess carbs

  • maximize glycogen as energy

  • convert to fat, spare fat from lipolysis

• excess protein

  • mostly convert to glucose

  • small amount of storage

  • increased muscle protein synthesis if combined with intense exercise

0-6 hrs after eating (postprandial fasting)

energy utilization:

1. carbs

2. proteins

3. fats

3-5 days after eating (short term fasting)

energy utilization:

1. protein

2. fats

5-7 days after eating (long term fasting)

energy utilization:

1. fats

2. proteins

phenylketonuria

• insufficient phenylalanine hydroxylase activity

  • cannot convert phenylalanine to tyrosine

  • form toxic metabolites

management of phenylketonuria

• special formula at birth

• low phenylalanine diet for life

• fruits, vegetables, and breads generally can be eaten

• dairy, eggs, meats, nuts, and aspartame must be avoided

galactosemia

• cannot convert galactose to glucose

• must use soy formula in infancy

• throughout life must avoid dairy products, butter, organ meats, and some fruits/vegetables

glycogen storage disease

• liver cannot convert glycogen to glucose

• leads to:

  • poor physical health

  • low blood glucose levels

  • liver enlargement

management of glycogen storage disease

must consume frequent meals and cornstarch between meals