Post absorptive metabolism

Question 1

Can nutrients be converted from one form to another? Give an example.

Answer 1

yes -> fat can be synthesised from proteins or CHOs

Question 2

Energy needed quickly is stored as…?

Answer 2

CHOs & glycogen

Question 3

Potentially huge energy reserves stored as…? What quantities can it be stored?

Answer 3

fat (kg stores)

Question 4

What is stored in large (kg) quantities and is a vital energy source in life-threatening conditions?

Answer 4

protein

Question 5

A bit about ATP…

Answer 5

present in EVERY cell in body

3 phosphate bonds (2 high-energy)

Question 6

A bit about creatine phosphate (phosphocreatine)…

Answer 6

transfers P group -> ADP during muscle contraction

reformed during recovery, or when ATP in excess

Question 7

Body stores of ATP & phosphocreatine can provide energy needs for how long?

Answer 7

only a few seconds

Question 8

What are the 4 fates of glucose?

Answer 8

1. aerobic metabolism to generate energy (O2 available)
2. anaerobic metabolism generate energy (O2 limited)
3. Glycogen synthesis (short-term energy store)
4. Fat synthesis (long term storage)

Question 9

Describe the metabolic fate of glucose during aerobic metabolism…?

Answer 9

steps involved include (glycolysis; pyruvate->Acetyl CoA; TCA cycle, Ox phos)
glucose -> H2O + CO2 + energy (ATP) via Acetyl CoA
Feedback mechanisms:
1. insulin (cell uptake & glycogen synthesis)
2. ATP
3. citrate ions
4. Low ADP & AMP
Conditions favouring this pathway:
Generates energy for mod. to high energy demand (moderate exercise) when there is adequate O2 delivery to tissue.

Question 10

Describe the metabolic fate of glucose during anaerobic metabolism…?

Answer 10

Glucose -> pyruvate + absence of O2 -> lactate (lactic acid) -
Conditions favouring this pathway:
During intense/high exercise -> increased glucose & glycogen utilisation -> increased pyruvate accumulation due to large ATP usage -> cellular acidosis. Thus, pyruvate accepts 2 hydride anions -> lactate to buffer cellular acidosis. it can not be metabolised by skeletal muscle. Thus, lactate -> liver & converted -> pyruvate (when O2 returns) to repay ‘oxygen debt’ during vigorous exercise.

Question 11

Describe the metabolic fate of glucose during glycogen storage…?

Answer 11

Glucose uptake and storage into cells is limited due to high osmotic pressure, thus needs to be stored in another form - glycogen.
Biochemical process:
Glucose -> G-6-P -> G-1-P -> uridine diphoshphate glucose -> glycogen
All cells store glycogen, but most is stored in liver and muscle that can be accessed quickly (short-term energy store) Occurs when an animal has more glucose than is need to meet current energy requirements -> insulin released (pancreas) -> liver glucose -> glycogenesis. When animal is fasted and requires energy -> glucagon released (pancreas) -> glycogen breakdown (glycogenolysis) -> blood glucose -> energy for cellular metabolism. Also if adrenaline is released -> glycogenolysis

Question 12

Describe the metabolic fate of glucose during fat synthesis & storage…?

Answer 12

After liver & muscle glycogen stores are topped up & there is still excess glucose around, it gets converted to TAGs.
Process:
excess glucose -> Acetyl Co -> fatty acids -> triglycerides
This process requires energy which is supplied by the pentose phosphate pathway (liver & fat cells) 6 glucose molecules -> 5 glucose + CO2 & H (H is used in fat synthesis but can also be oxidised -> ATP)