ch18 - respiratory substrates

When an organism respires what substrate is used majority of the time?

Glucose (a carbohydrate)

What are the other two alternative respiratory substrates?

Proteins and Lipids 

How can lipids be used as a respiratory substrate?

1. Lipids such as triglycerides are hydrolysed which digests the ester bonds releasing individual glycerol and fatty acid molecules

2. Glycerol enters glycolysis as TP to be converted into pyruvate - (because glycerol and pyruvate both contain 3C)

3. Fatty acids molecules are broken down into 2C units to be converted into acetyl CoA

How can proteins be used as respiratory substrates?

1. Proteins are hydrolysed into amino acids during digestion

2. Amine group is removed from from amino acids by deamination in the liver leaving the 3C part to be converted into pyruvate

What is the respiratory quotient (RQ) and what does it tell us

ratio of volume of CO2 produced : to volume of O2 used (during respiration)

> it tells us the substrate being primarily used for respiration

What is the (RQ) formula

What is the RQ values for the 3 respiratory substrates

carbohydrates = 1.0

proteins = 0.9

lipids = 0.7

what does an RQ bigger than 1 suggest

that anaerobic respiration is taking place

how much quantity of ATP does carbohydrates release and what is their unique role in cellular respiration

energy yield = least amount

role = primary choice for energy as they are easily accessible

how much quantity of ATP does proteins release and what is their unique role in cellular respiration

energy yield = moderate amount 

role = only used for respiration when other sources are limited

how much quantity of ATP does lipids release and what is their unique role in cellular respiration

energy yield = highest amount (x2 ATP compared to carbohydrates due to high amount of CH bonds)

role = ideal for long term energy storage 

what can be used to measure oxygen consumption by organisms and how does it work

a respirometer

> if oxygen is absorbed the pressure will decrease so coloured fluid in apparatus will move CLOSER towards organism

> distance moved by fluid = volume of oxygen consumed