Carbohydrates, Glycolysis and Gluconeogenesis Flashcards
(41 cards)
Describe carbohydrates AND how they are used by the body (functions)!
- “hydrates of carbon”
- they all have the same basic formula (monosaccharides); isomers provide the variation from the simple formula
- two monosaccharides are connected through glycosidic bonds (ether bonds)
Functions:
- SOURCE of energy and STORE of energy
- glucose storage molecules; glycogen (mammals), starch (plants), cellulose
- component of mammal cell membranes (e.g ur blood type shows what carbs are present)
- cell wall component in bacteria,
- cellulose in plants
- insect exoskeleton
What is the structure of monosaccharides?
- CH2O
- can be aldoses or ketoses
What is the bond that joins monosaccharides to form larger molecules?
Glycosidic bonds (ether bond between the two sugar molecules)
Glycogen, starch and cellulose and what type of bond is present?
All glucose storage molecules
Glycogen in mammals. Starch in plants. Both have alpha-1,4 glycosidic bonds.
Cellulose has B-1,4 glycosidic bonds. We lack enzyme to break these thus fibre pass through undigested.
Describe the process of carbohydrate digestion.
Large ones must be broken down to be absorbed.
Starts in the mouth with salivary a-amylase which cuts up the 1,4-glycosidic bonds to make smaller molecules.
Then they go into the small intestine which has disaccharide specific brush border enzymes that are MADE by pancreatic a-amylase. These include maltase, lactase, and sucrase.
Does amylase from the pancreas digest disaccharides?
No. It makes the disaccharides that do!
What is disaccharide intolerance in digestion + an example?
Disaccharide intolerance arises when one of the enzymes is not active.
Example, lactose intolerance:
- due to lack of lactase brush border cells
- lactose travels through the small intestine to large intestine where it’s instead broken down by bacteria which is what results in the uncomfort for lactose intolerant ppl
Where does glycolysis occur, what does it produce and what is it used in?
Cytoplasm
Glucose -> pyruvate
Used in all cells to provide ATP and intermediates for other pathways (energy is released)
Why do red blood cells rely on glycolysis?
They depend on glycolysis for energy bc they don’t have mitochondria
Glycolysis is ___________ glucose to release energy:
a) reducing
b) oxidizing
oxidizing
What is the energy generation phase and what does it produce?
Final 5 steps of glycolysis
Generates 4 ATP, 2 NADH and 2 molecules of pyruvate
NADH and pyruvate both can go on to be further oxidized in TCA and ETC which produces more ATP.
What is the energy investment phase and what is consumed in this process?
First 5 rxns of glycolysis
2 molecules of ATP are invested (consumed)
Why is NAD+ super important?
It’s required for glycolysis to continue
Activated carrier of electrons
What does anaerobic glycolysis rely on to regenerate NAD+?
lactic acid fermentation
(strenous exercise produces lactate because you’re outgoing anaerobic glycolysis)
What is the energy yield of glycolysis? Aerobic and anaerobic
Aerobic:
Glucose + 2Pi + (2NAD+) + 2ADP –> 2 pyruvate + 2 ATP + 2 NADH + (2H+) + 2H2O
- Net gain 2 ATP per glucose
- requires oxidation of NADH by ETC producing 3 ATPs for each NADH entering the ETC
Anaerobic:
Glucose + 2Pi + 2ADP –> 2 lactate + 2ADP + 2H2O
- Net gain of 2 ATP per glucose
- NO net production or consumption of NADH
What is the net production/consumption of NADH in anaerobic glycolysis?
NO net production or consumption of NADH
Describe the process of glycolysis with emphasis on the 3 key regulatory enzymes and the net energy produced by the pathway.
Glycolysis plays two roles:
1. degrade glucose to generate ATP
2. provide building blocks for other pathways
The rate of glycolysis is tightly controlled by 3 regulatory enzymes:
1. Hexokinase (glucokinase in the liver):
- P from ATP added to glucose to form glucose-6-phosphate
- Traps glucose in the cell (once the glucose has a P it cannot be transported out of the cell)
- hexokinase is inhibited by it’s product G-6P
- PFK-1
- P from ATP is added to fructose 6-P by PFK to form fructose 1,6-bisphosphate
- committed step for glycolysis - Pyruvate kinase:
- transfers a P from PEP to ADP, which forms ATP and pyruvate
ALL ARE IRREVERSIBLE!!! (need another enzyme in order to be reversible)
Describe the regulation of glycolysis in muscles!
Since we moving theres increase in glycolysis (we need more energy!!)
The ratio of ATP/AMP indicates energy level in cells. If we have more ATP then less glycolysis is required cuz we good.
In muscles the primary role of glycolysis is to provide ATP
What does the ratio of ATP/AMP show?
The ratio of ATP/AMP indicates energy level in cells. If we have more ATP then less glycolysis is required cuz we good.
3 key regulatory enzymes in glycolysis inhibited by what? And what happens when they are?
PFK inhibited by high levels of ATP!!! Activated by AMP!!!
Hexokinase is inhibited by its product, G-6P. High concentrations of glucose 6-phosphate signal that the cell no longer requires glucose for energy, so no more glucose needs to be broken down. When PFK is inhibited, we have more AMP, therefore PFK inhibition also leads to hexokinase inhibition!
Pyruvate kinase is allosterically inhibited by ATP (lots of ATP = bye bye). It is activated by Fructose 1-6-bisphosphate (a product of PFK)
Describe the regulation of glycolysis in the liver.
Liver is a more biochemically diverse tissue: more complex tissue leads to more complex regulation
Liver maintains blood glucose concentrations
- Stores glucose as glycogen
- Synthesizes new glucose via gluconeogenesis
- Uses glucose to make building blocks for other molecules
PFK: Regulated by ATP like the muscle, however less ATP since the liver does not experience the sudden ATP needs that a contracting muscle does, so less significant regulation
Liver also produces carbon skeletons for biosynthesis, thus availability of these molecules regulates PFK
* Citrate – first intermediate of citric acid cycle – inhibits: In the liver, phosphofructokinase is inhibited by citrate, an early intermediate in the citric acid cycle. A high level of citrate in the cytoplasm means that biosynthetic precursors are abundant, so there is no need to degrade additional glucose for this purpose. In this way, citrate enhances the inhibitory effect of ATP on phosphofructokinase.
What are isozymes?
enzymes, encoded by the different genes, that catalyze the same reaction
Why does glucose uptake into the cell membrane require a glucose transporter?
Glucose is hydrophilic, so it can’t cross the membrane without a glucose transporter
IN MUSCLES
Enzyme, activated by, inhibited by?
Hexokinase, _________, ___________
PFK-1, ___________, ____________
Pyruvate kinase, __________, ___________
Hexokinase
Activated by:
Inhibited by: Its product (glucose 6-P)
PFK-1
Activated by: AMP
Inhibited by: high levels of ATP
Pyruvate kinase
Activated by: Fructose 1,6-bisphosphate (product of PFK)
Inhibited by: high levels of ATP
