Nutrition 251 Penn State Exam 3

Metabolism

the chemical and physical processes in maintaining life

Metabolism enables us to

- release energy from carbohydrate, fat, protein, and alcohol

- synthesize new substances

- excrete waste products

Anabolic Pathways

use small compounds to build larger ones

Anabolic Pathways characteristics

- Glucose, fatty acids, cholesterol, and amino acids are building blocks

- requires energy

- more prominent during growth

Catabolic Pathways

Break down compounds

Catabolic Pathway results

release CO2, H2O, and energy (ATP)

Anabolic ATP

is requires it

Catabolic ATP

it produces it

Three stages of Catabolism

1. digestion - breakdown of their complex molecules to their component building blocks

2. conversion of building blocks to acetyl-CoA

3. Metabolism of acetyl-CoA to CO2 and formation of ATP

Metabolic pathways convert food into energy

energy is captured in the bonds of ATP

Hydrolysis of Bonds

Release energy

cellular respiration

- how cells generate ATP

- Food molecules are oxidized to form ATP

- oxygen is the final electron acceptor

- may be aerobic or anerobic

Aerobic

- in the presence of oxygen

- more efficient

creates 30-32 molecules of ATP

Anaerobic

- without oxygen

- creates 2 molecules of ATP

Oxidation

lose electron

Reduction

Gain of electrons

Synthesis of ATP requires

Exchange of electrons

4 stages of metabolic fate of carbohydrate

1. glycolisis (going into the cytosol) (2pyruvate) (anaerobic metabolism)

2. transition reaction (acetyl-CoA into citric acid cycle)

3. Citric acid cycle

4. electron transport chain

Glycolysis

the anaerobic breakdown of glucose to pyruvic acid, which makes a small amount of energy available to cells in the form of ATP

Pyruvate

pyruvate to lactate in the cytosol

- when energy is needed quickly (sprinting)

- anaerobic

- occurs in the cytosol

reversible

Acetyl-CoA

Acetic acid with coenzyme

- when energy needed more slowly

- aerobic

-occurs in the mitochondria

irreversible

- pyruvate transition from cytosol to mitochondria is irreversible

electron transport chain

primary site of ATP production

where the majority of the energy is produced

- end products are water and ATP and a little carbon dioxide

- aerobic

going into mitochondria

shuttling of electrons

Anaerobic metabolism occurs when

- cells do not have mitochondria

- oxygen is not present

Glycolysis in cytosol

anaerobically converts glucose to pyruvate

In the absence of oxygen

pyruvate is converted to lactate

lactate transported from muscles

to liver for conversion to glucose

Lipolysis

Process by which triglycerides are broken down into fatty acids + glycerol

Break down by hormone sensitive lipase

- increased by glucagon, growth hormone, epinephrine

- decreased by insulin

Fatty Acid Oxidation

fatty acids are cleaved 2 carbons at a time, creating acetyl-CoA

- Acetyl-Coa enters TCA cycle

- more carbons than glucose = more ATP production than glucose

- More acetyl-CoA to enter TCA cycle

- NADH + H+ and FADH2, chemical energy storage

the citric acid cycle also produces compounds that enter biosynthetic pathways resulting in

slowing of the cycle, as not enough oxaloacetate is produced

cells can synthesize oxaloacetate from

pyruvate

Carbohydrates are needed to create _____________, as fatty acids create ______________.

Pyruvate

Acetyl-CoA

low carbohydrate consumption decreases _____________ production, slowing _______________.

Oxalocetate

TCA Cycle

Build up of acetyl-CoA

can be used to create ketone bodies (acetone, acetoacetate, and beta-hydroxybutyrate)

Ketones can form form

inadequate insulin production

Build up of ketone body (acetone) leaves the body via lungs

fruity smelling breath

Ketosis Steps

1. insufficient insulin production

2. large amounts of fatty acids released by adipose cells

3. fatty acids flood into the liver and are broken down into Acetyl-CoA

4. high production of acetyl-CoA from beta-oxidation slows citric acid cycle

5. high amounts of acetyl-CoA unite in pairs to from ketone bodies

If insulin is not present

- cells cannot use glucose

- rapid lipolysis occurs

- ketone bodies are produced in excess

- spill into urine with sodium and potassium, leading to ion imbalances

- blood becomes acidic because of acid groups on ketone bodies

- resulting in condition is diabetic ketosis

During semi-starvation what happens to glucose and insulin levels

they fall

Protein metabolism

begins with deamination (removal of an amino group)

- results in carbon skeleton

Glucogenic Amino Acid

a carbon skeleton used to form glucose

Gluconeogenesis

making glucose from non-glucose sources

Ketogenic amino acid

carbon skeleton used to form acetyl-CoA

Protein metabolism primarily occurs where

In the liver

where can branched chain amino acids be metabolized

in muscle

protein deamination that occurs during metabolism results in amino groups that are

- converted to ammonia

liver prepares amino groups for excretion with urea cycle

- 2 nitrogen groups + CO2 = urea + water

- urea excreted in urine

regulation of energy metabolism

liver

- the liver plays a major role in metabolic pathways

- most nutrients first pass through the liver after absorption

Key metabolic functions include

- conversions between forms of simple sugar

- fat synthesis

production of ketone bodies

- amino acid metabolism

- urea production

-alcohol metabolism

- nutrient storage

ATP Concentrations

high concentrations

- decrease energy-yielding reactions

- promote anabolic reactions

High ADP concentrations

Stimulate energy-yielding pathways

Enzymes (regulation of energy metabolism)

Presence and rate of activity are critical to chemical reactions

- synthesis controlled by cells and the products of reactions

Hormones

low blood levels of insulin promote

- gluconeogenesis

- protein breakdown

- Lipolysis

high blood levels of insulin promotes synthesis of

- glycogen

- fat

- protein

Alcohol Metabloisim

cannot be stored

- alcohol dehydrogenase pathway

Alcohol requires no

digestion, transporters, or receptors

the stomach absorbed _________ of alcohol

- the rest is absorbed in the

20%

Small intestine

Fasting: Postprandial

- during initial fasting, the body fuels itself with glucose from glycogen breakdown and fatty acids from triglyceride breakdown

- some energy may come from fat, which cannot be used to fuel nervous system or red blood cells

Fasting: short term

- remember, by this point glycogen stores have been depleted

- fats continue to be broken down and cannot be used to fuel nervous system or red blood cells

- body tissue its broken down to make glucose from gluconeogenic amino acids

fasting long term

- adaptations slow breakdown of lean tissue

- fatty acids cannot be used for gluconeogenisis

- body adapts to use less glucose and more ketone bodies

- sodium and potassium are depleted (lost in urine with ketone bodies)

- blood urea levels increase

Feasting

excess consumption beyond body's kcal requirements from any energy yielding nutrient will contribute to increases in total body fat