BLOCK 1 lecture 2

drinking like a fish

 

Goldfish can turn on a variant of an enzyme which converts pyruvate to acetadelyde and then to ethanol

Do this so that if the surface of the water freezes they can survive with little oxygen - there are also less plants producing oxugen because less light

So fish use the ability to make ethanol to export carbons that they are using (in glycolysis) to make ATP to generate NAD

Don’t make that much ethanol and it gets excreted thriugh gills so not too much of a problem with the by-products

overview of digestion

Stomach has some enzymes and the filling of the stomach sends things to the brain to activate the rest of the gut and the regulation of how much we need to eat (but this is poorly understood)

Gut flora - plays a role in digestion

absorption paths from the gut

transporters and nutrient absorption

fat absorption

Most villi have capillaries but some are modified to have a lacteal which is associated with lymph production

the fed state and macronutrient management

 

Glucose and fatty acids are our primary fuels

Proteins can be converted to fuels but not major - most used for synthesising proteins etc but any excess gets converted to wither glucose or acetyl coA(which is stored as fatty acids)

So wither way excess protein will probably be stored as fat

At rest muscles mainly use fatty acids, but when doing high intensity exercise hard to get enough energy from this, so starts to use glucose as well as fatty acids

But muscle glycogen is unable to maintain blood glucose levels

what can you do with glucose

glycogen synthesis

Glycogen is kind of just a PTM to a protein

Then can subsequently add other carbohydrates to that carbohydrate

Glycogen synthase adds glucose

branching

We thin we have branching because it increases the number of ends of the molecule - it is the ends that grow and shrink

glycogen synthase and phosphorylase

UDP-glucose

Don’t know why this is what we do but it is

glycogen synthesis - branching enzyme

Branching enzyme recognises 6-8 glucose monomers that are attached in a chain

Breaks a1-6 bond and makes an a1-4 bond

glycogen synthesis - debranching enzyme

Enzyme removes the end 3 monomers and breaks the a1-4 linkage of the branch and converts it to an alpha1-6 linkage on the main chain of the glycogen

The remaining (green) monomer is hydrolysed seperately

branching complexity

Each glycogen is unique and grows differently when used up

why is glycogen so branched

Formation of glycogen is costly - why? Seems to mostly be about osmotic stress

So it is stored as glycogen because of osmotic strength but because of this it is hard to access so that is why we have so many ends