lecture 22 - energy budgets and metabolism

Question 1

What are catabolic and anabolic metabolism?

Answer 1

In an exergonic reaction, energy is released to the surroundings. The bonds being formed are stronger than the bonds being broken.

In an endergonic reaction, energy is absorbed from the surroundings. The bonds being formed are weaker than the bonds being broken.

Two types of metabolic reactions take place in the cell: ‘building up’ (anabolism) and ‘breaking down’ (catabolism).

Anabolic reactions use up energy. They are endergonic. In an anabolic reaction small molecules join to make larger ones. For example, the following condensation reactions that occur in cells are anabolic:

amino acids join together to make dipeptides and the process continues as large protein molecules are built up

small sugar molecules join together to make dissacharides

Catabolic reactions give out energy. They are exergonic. In a catabolic reaction large molecules are broken down into smaller ones.

The conversion of glucose during respiration to produce carbon dioxide and water is a common example:

C6H12O6 + 6O2 –> 6CO2 + 6H2O

Question 2

Describe how energy intake is used

Answer 2

Catabolism - Release energy for:

Muscle contraction
Transport
Secretion

Anabolism

Tissue function
Growth repair
Storage molecules

Question 3

What is metabolic rate?

Answer 3

Break down nutrients, release energy as heat or uses it to perform work

The amount of energy expended per unit time is the body’s metabolic rate

Influenced by muscular activity, age, gender, body surface area and environmental temp

Basal metabolic rate (BMR): psychologically and physically rested, post-absorptive state and thermo-neutral

Question 4

What factors affect BMR?

Answer 4

Average adult human BMR: 20-25 kcal/Kg/day

Body weight
Lean body Mass
   Age
   Sex
   Diet 
   Pregnancy
Males tend to have higher BMR

Question 5

How do you measure BMR?

Answer 5

Measure heat produced (direct calorimetry)

Difficult to measure small heat changes
Body stores heat

Measure oxygen consumed (indirect calorimetry/ respirometry)

Depends on macromolecule being oxidised

Question 6

What is respiratory quotient?

Answer 6

RQ = CO2 produced
O2 consumed

Carbohydrate = 1
Protein = 0.8
Fats = 0.7

Question 7

Describe the relationship between metabolic rate and size

Answer 7

as mass increases, resting metabolic rate increases - not a linear relationship as does not increase to the same extent - to the 0.75
0.75 (or ¾) law is called Kleiber’s law

Larger animals have less surface area to volume (less heat loss)… 2/3 law??

Fractal branching to distribute nutrients - vessels branch

Evolutionary drive to get bigger

Question 8

Describe the relationship between metabolic rate and activity

Answer 8

Immediate energy (vertebrates)

     Phosphocreatine (PCr) + ADP -> ATP + Creatine (Cr)

Glycolysis (anaerobic ATP production)

Aerobic respiration produces the most ATP

Glucose used preferentially during exercise from glycogen breakdown (glycogenolysis)

Metabolic rate increases with activity due to increased aerobic ATP production

Question 9

Describe how the cost of running varies with size

Answer 9

larger animals more efficient than small

Energy consumption increases with distance travelled (not speed)

Running consumes more energy in small animals