Transcript Spotlight on Metabolism

What Is Metabolism?
• Catabolism
– Reactions that break down compounds into
small units
What Is Metabolism?
• Anabolism
– Reactions that build complex molecules
from smaller ones
What Is Metabolism?
• ATP is the body’s energy
currency
– ATP = adenosine
triphosphate
Breakdown and Release of Energy
– Anaerobic
• Partial breakdown glucose
• Do not req oxygen
• Lactic acid is main end-product little ATP
– Aerobic
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•
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•
•
Complete breakdown glucose, fat, and protein
Occurs in mitochondria
Releases most energy
CO2 , H2O, ATP and heat
Req oxygen
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Breakdown and Release of Energy
• Extracting energy from carbs
– Glycolysis
• Splits glucose into two
pyruvates
• Produces some ATP
– Pyruvate to acetyl CoA
• Releases CO2
• Enters TCA cycle if
O2 is present
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Breakdown and Release of Energy
• Lipolysis
– Triglycerides broken down into fatty acids and glycerol
• Extracting energy from fat
– Promoted by glucagon, growth hormone, epinephrine
– Takes place in mitochondria
– Beta-oxidation
• Breaks fatty acids into acetyl CoA
– Fat burns in a flame of carbohydrate
• Ketogenesis
– Ketone bodies formed by incomplete fatty acid oxidation
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Breakdown and Release of Energy
• Extracting energy from
protein
– Split protein into amino
acids
– Split off amino group
• Converted to urea for
excretion
– Carbon skeleton enters
breakdown pathways
– End products
• ATP, H2O, CO2, urea
Protein Metabolism
• Gluconeogenesis
– Forming glucose from glucogenic amino
acids and other compounds
– Typical fatty acids cannot be converted to
glucose, although glycerol can
• Disposal of Excess Amino Groups
– Converted to ammonia; then urea cycle
– Urea excreted in the urine
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Breakdown
and Release
of Energy
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Biosynthesis and Storage
• Making carbs
– Gluconeogenesis
• Uses pyruvate, lactate, glycerol, certain AA
• Storing carbohydrate (glucose  glycogen)
– Liver and muscle make glycogen from glucose
• Making fat (fatty acids)
– Lipogenesis
• Uses acetyl CoA from fat, amino acids, and
glucose
• Storing fat (triglyceride)
– Stored in adipose tissue
Biosynthesis and Storage
• Making ketone bodies (ketogenesis)
– From acetyl CoA
• When inadequate glucose in cells
• Making protein (amino acids)
– Amino acid pool supplied from
• Diet, protein breakdown, and cell
synthesis
– Biosynthesis
• Different pathways used to build amino
acids from carbon skeletons
Fasting and Feasting
• Fasting encourages:
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Glycogen breakdown
Body fat and protein breakdown
Gluconeogenesis
Ketogenesis
Urea synthesis
• Feasting encourages:
– Glycogen synthesis
– Body fat synthesis (lipogenesis)
– Protein synthesis
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Special States
• Feasting
– Excess energy intake
from carbs, fat, protein
• Promotes storage
– Fat  adipose
– AA  protein synthesis
– Carbohydrate 
adipose
Special States
• Fasting
– Inadequate
energy intake
• Promotes
breakdown
– Prolonged
fasting
• Protects body
protein as
long as
possible
Special States
• Fasting
– Survival priorities and potential energy sources
• Preserve glucose-dependent tissue
–RBC, brain cells, central nervous system
• Maintain muscle mass
– The prolonged fast: In the beginning
• Blood glucose drops, liver breaks down
glycogen to glucose
• Gluconeogenesis
• Fat and protein are primary fuel
Special States
• Fasting
– The early weeks
• Several energy-conservation strategies
– Several weeks of fasting
• Rely on stored body fat
– The end is near
• Muscle atrophy and emaciation
• Sacrificed muscle tissue in attempt to
preserve brain tissue
Box 1: DSM IV-TR Criteria for Anorexia Nervosa
Criteria
•Refusal to maintain body wt at or above a min wt for age/ height:
• Body weight less than 85% of that expected.
•Intense fear of wt gain or becoming fat, even though under wt.
•Disturbance in the way one's body shape are experienced,
•Denial of the seriousness of the current low body weight.
•Amenorrhea (at least three consecutive cycles) in postmenarchal
girls and women. Amenorrhea is defined as periods occurring
only following hormone (e.g., estrogen) administration.
Type
•Restricting type: During current episode the person has not
regularly engaged in binge-eating or purging behavior (selfinduced vomiting or misuse of laxatives, diuretics, or enemas).
•Binge-eating–purging type: During the current episode the
person has regularly engaged in binge-eating or purging behavior
(self-induced vomiting or the misuse of laxatives, diuretics, or
enemas).
Box 2: DSM IV-TR Criteria for Bulimia Nervosa
Criteria
•Recurrent episodes of binge eating characterized by both:
• Eating, in a discrete period of time (within a 2-hr period), an
amount of food definitely larger than most people would eat
during a similar period of time under similar circumstances
• A sense of lack of control over eating during the episode
•Recurrent inappropriate compensatory behavior to prevent wt gain
• Self-induced vomiting
• Misuse of laxatives, diuretics, enemas, or other medications
• Fasting
• Excessive exercise
•The inappropriate behavior at least twice a week for 3 months.
•Self evaluation is unduly influenced by body shape and weight.
Type
•Purging type: Regularly engaged in self-induced vomiting or the
misuse of laxatives, diuretics, or enemas.
•Nonpurging type: Used inappropriate behavior but not engaged in
self-induced vomiting,misused laxatives, diuretics, or enemas.
Weight Management
• Adopting a healthy weightmanagement lifestyle
• Diet and eating habits
– Total calories
– Crash diets don’t work
– Balancing energy
sources: fat,
carbohydrate, and
protein
– Eating habits
– Physical activity
Thrifty Gene and weight loss
What happens to metabolism when
calorie intake is severely restricted?
WHY?
In general, when non-athletes loss wt:
- loss 50 % adipose & 50% lean tissue
- wt gain 75% adipose & 25% lean tissue
One definition of yo-yo dieting:
restricted eating –loss 10 lbs or so, plateau
(doesn’t seem to loss any more wt), gets
frustrated – go off “diet” and regain the
weight.
Scenario:
1. Steve weights 200 lbs and wants to
loss wt..
Over the course of 6 months, he goes
on 3 yo-yo diets. At the end of the 6
months he still weights 200 lbs
– did anything change?
Explain what happened to his body
composition over the 6 months.
2. From the previous scenario, how
could the amount of muscle mass
lost be altered?
This time Steve decides to exercise
& restrict calories. Over the course
of a month, Steve losses 10 lbs. but
then plateaus out. What might be
happening?