Energy Balance and Metabolism II (Lecture 18)

Question 1

Describe the generation and function of ATP

Answer 1

• ATP is generated by the combustion of:
  
  • Carbohydrates
  • Fatty Acids
  • Proteins

Question 2

Explain how phosphocreatine functions as an accessory storage depot for energy and as an “ATP Buffer”

Answer 2

• Phosphocreatine cannot act as a direct coupling agent for energy transfer between the food and funcitonal cellular systems, but it can transfer energy intercahngeably with ATP
• Phosphocreatine has high energy in phosphate bonds (13,000 calories), this is more thant the amount present in ATP. It is also 3-8x more abundant than ATP. so when ATP is neeed phosphocreatine and ADP react to rapidly form new ATP. This effect keeps the concentration of ATP at an almost constant high level as long as any phosphocreatine remains.

Question 3

Differentiate between essential and nonessential amino acids

Answer 3

• Essential amino acid
  
  • Cannot be synthesized in sufficient quantities in the body and thus must be obtained already formed from food.
  • include:
    
    • Threonine
    • Lysine
    • Methionine
    • Arginine
    • Valine
    • Phenylalanine
    • Leucine
    • Tryptophan
    • Isoleucine
    • Histidine
    • (PVT TIM HALL)
• non-essential amino acid formation depends on alpha-keto acid precursors

Question 4

Describe a peptide linkage

Answer 4

• Holds amino acids together in the protein chain
• a hydroxyl radical (OH-) is removed from the COOH portion of the first amino acid and a hydrogen (H+) of the NH₂ portion of the other amino acid is removed.
  
  • These combine to form water,, and the two reactive sites left on the two successive amino acids bond with each other.

Question 5

Describe the pathway for the synthesis of alanine from pyruvic acid and define “transamination”

Answer 5

• Pyruvic acid is keto acid precursor of the amino acid alanine
• amino radical is transferred to the alpha-keto acid, and the keto oxygen is transferred to the donor of the amino radical.
• (promoted by aminotransferases, which ae derivatives of pyridoxine, B₆)
• (note amino radical is transferred to the pyruvic acid from another chemical that closely allied to the amino acids— glutamine. But can be transferred from asparagine, glutamic acid, and aspartic acid

Question 6

List/Describe the steps in the formation of a peptide bond

Answer 6

• amino acid + ATP → Amino Acid—AMP + 2Pi
• Amino acid—AMP + tRNA → Amino acid—tRNA + AMP
• Attachment of tRNA to mRNA via codon-anticodon pairing
• Formation of peptide bond with second amino acid using peptidyl transferase + GTP

Question 7

Be able to diagram the ornithine cycle

Answer 7

Question 8

Differentiate which parts of the ornithine (urea) cycle occur in the mitochondria and which parts occur in the cytoplasm

Answer 8

• In mitochondria
  
  • Ammonia + CO₂ → Carbamoyl phosphate
  • Carbamoyl phosphate + ornithine → citruline
• In cytoplasm
  
  • Citrulline + aspartate → Argininosuccinate
  • Argininosuccinate → arginine + fumarate
  • Arginine → urea + ornithine
  • Fumarate can enter citric acid cycle

Question 9

Describe the relationship between the rate of a chemical reaction and the concentration of substrate and enzymes

Answer 9

• Rate of overall chemical reaction is determined by:
  
  • Concentration of the enzyme
  • Concentration of the substrate
• When substate is high
  
  • Reaction rate is determined almost entirely by concentration of enzyme
• When enzyme concentration is high
  
  • Reaction rate becomes directly proportional to concentration of substrate and enzyme

Question 10

Give examples of reaction rates that are determined almost entrirely by concentration of enzyme

Answer 10

• Diabetes mellitus and glucose:
  
  • Large quantities of glucose enter renal tubules
  • Glucose (substrate) is in great excess in the tubules
  • Transport enzymes become saturated
  • Further increases in glucose levels in tubules have little effect on glucose reabsorption
  • Glucose reabsorption rate is limited by concentration of transport enzymes

Question 11

Define the rate-limiting step in a series of reactions

Answer 11

• Overall rate of a series of chemical reactions is determined by the rate of reaction of the slowest step in the series

Question 12

What is the major rate-limiting factor in almost all energy metabolism in the body

Answer 12

• ADP
  
  • cellular concentration of ADP are low
  • chemical reactions that depend on ADP as one of the substrates are very slow
  • Examples of the ADP substrate dependence
    
    • All oxidative metabolic pathways
    • Other pathways for the release fo energy
  • ATP is converted to ADP during cellular activity; therefore, ADP concentration increases during cellular activity
  • increased concentration of ADP increases reaction rates

Question 13

Describe factors that influence metabolic rate

Answer 13

• Arousal vs. Sleeping
• Skeletal muscle
• Age
• Thyroid activity
• Testosterone
• Growth hormone
• Fever
• Sleep
• Malnutrition

Question 14

* Define basal metabolic rate?

• How is it calculated?
• what is its relationship to age and gender?

Answer 14

• The minimum level of energy required to exist and accounts for 50-70% of the daily energy expenditure in most sedentary persons
• how is it calculated
  
  • skeletal muscle, even under resting conditions, accounts for 20-30 percent of the BMR. For this reason, BMR is usually correceted for differences in body size by expressing it as calories per hour per square meter of body surface area, calculated from height and weight.
• Declines with increasing age
  
  • this is probably due to loss of muscle mass and replacement with adipose tissue with a lower rate of metabolism
• is lower in females