Glycolysis Flashcards
What is glycolysis?
The breakdown of glucose to smaller molecules, so producing ATP
Where does glycolysis take place?
In the cytoplasm
What is an aldehyde?
A compound containing a functional group with the structure R−CHO
What is a ketone?
A compound containing a functional group with the structure R1−CO−R2
What is a carboxylic acid?
An acid compound containing a functional group with the structure R−COOH
What suffix is used to denote a sugar?
“-ose”
Why is it important to be able to recognise sugars?
Sugars like glucose can often exist in different forms that are all in equilibrium
What is a triose?
a sugar with 3 carbons
What is a sugar with three carbons called?
a triose
What is a hexose and give an example?
a sugar with 6 carbons,
eg glucose
What is the structural difference between fructose and glucose?
While glucose tends to form a six-membered (pyranose) ring, fructose forms a 5- membered (furanose) ring
How are proteins formed from amino acids?
the amino group of one amino acid joins to the carboxyl group of its neighbour (a peptide bond)
What acids are common in metabolism?
Keto acids
What is glucose converted to in glycolysis?
pyruvate
What is the initial stage of glycolysis
Phosphorylation, which consumes ATP
What does the first phosphorylation do to the glucose undergoing glycolysis?
Traps glucose in the cell, because glucose-6-P is ionized and unable to cross the cell membrane as it no longer matches any transport proteins
What is the second step of glycolysis?
isomerization
What occurs to the Glucose-6-P in the isomerization stage of glycolysis?
Glucose-6-P converted to fructose-6-P
Both sugars = C6H1206
What is the third stage of glycolysis?
Another phosphorylation
What occurs to the fructose-6-P in the second phosphorylation stage of glycolysis?
CONSUMES ATP
Forms a hexose diphosphate that can be split into two phosphorylated 3-carbon compounds
What is the fourth stage of glycolysis?
Cleavage + isomerization
What occurs to the hexose diphosphate in cleavage + isomerization of the fourth stage of glycolysis?
Forms two phosphorylated 3 carbon compounds, then allows dihydroxyacetone-P (a triose) to be converted to glyceraldehyde-3-P which can be metabolized
What is the fifth stage of glycolysis?
Oxidative phosphorylation
What occurs to glyceraldehyde-3-P in oxidative phosphorylation in glycolysis?
Glyceraldehyde-3-P is simultaneously oxidized and phosphorylated
Hydrogen and electrons from glyceraldehyde-3-P are passed to nicotinamide adenine dinucleotide (NAD+)
What is Nicotinamide adenine dinucleotide (NAD+/NADH + H+) made up of?
1 Nicotinamide molecule containing the reactive site
1 Adenine molecule
2 Ribose molecules sandwiching the Adenine
What is the name for the adenine-ribose complex found in NAD+?
Adenosine
What is the difference between NAD+ and NADP?
In NAD, R = H, while in the related nicotinamide adenine dinucleotide phosphate (NADP), R = phosphate
What provides the nicotinamide part of the NAD+ molecule?
Vitamin B3 (niacin)
How is vitamin B3 (niacin) made by the body?
It isn’t, it has to be provided in the diet
What does lack of Vitamin B3 (niacin) cause?
pellagra - Sensitivity to sunlight, dermatitis, alopecia, glossitis, weakness, ataxia
What is the sixth stage of glycolysis?
The transfer of a phosphate to ADP and so the production of ATP
What is the ratio of ATP produced/glucose molecules consumed in glycolysis in the first ATP producing stage?
2 ATP per molecule of glucose
What is the seventh stage of glycolysis?
molecular rearrangement
What occurs in the molecular rearrangement phase of glycolysis?
Phosphate group moved from one position to another (isomerization)
What is the eighth stage of glycolysis?
Dehydration
Why does dehydration occur in glycolysis?
It favours the transfer of phosphate to ADP
What is the final stage of glycolysis?
The second transfer of phosphate to ADP and so ATP production occurs
What is the ratio of ATP produced/glucose molecules consumed in glycolysis in the second ATP producing stage?
2 ATP per molecule of glucose
How much ATP is produced per molecule of glucose consumed in glycolysis?
four
What are the stages of glycolysis
1st Phosphorylation Isomerization 2nd Phosphorylation Cleavage + isomerization Oxidative phosphorylation 1st Transfer of phosphate to ADP Molecular rearrangement Dehydration 2nd Transfer of phosphate to ADP
Discuss glycolysis in aerobic conditions
Under aerobic conditions NAD+ is regenerated because NADH passes the electrons and the hydrogen atoms which it receives from glyceraldehyde-3-P through a system known as the electron transfer chain which combines them with molecular oxygen to form water
-The electron transfer system also generates ATP
Discuss glycolysis in anaerobic conditions
In the absence of molecular oxygen (anaerobic conditions) NADH builds up because NAD+ cannot be regenerated
-If this situation persisted glycolysis would halt
How is NAD+ regenerated?
In humans, NADH is re-oxidized by reducing
pyruvate to lactate
What is a downside to the buildup of lactate as a result of regenerating NAD+?
It is this lactate that is responsible for muscle aches experienced after prolonged exercise!
How does yeast regenerate NAD+?
To regenerate NAD+ it converts pyruvate to ethanol
Hence beer🍺
What enzymes are key in how the rate of glycolysis is controlled?
- Hexokinase
- Phosphofructokinase
- Pyruvate kinase
What does hexokinase do?
Catalyses: glucose → glucose-6-P
What does phosphofructokinase do?
Catalyses: fructose-6-P → fructose-1,6-
bisphosphate
What does pyruvate kinase do?
Catalyses: phosphoenolpyruvate → pyruvate
What enzyme is the most important point at which glycolysis is regulated?
phosphofructokinase
How does phosphofructokinase regulate the rate of glycolysis?
- High [ATP] allosterically inhibits the enzyme
- Low pH inhibits the enzyme (lactate accumulation)
- High [citric acid] inhibits
- High [fructose-6-P] stimulates the enzyme
Why is the regulation of the rate of glycolysis important?
so that glucose stores are only drawn on when energy is required and when conditions will allow sugars to be broken down
What else may regulate the rate of glycolysis?
the concentration of certain hormones
How many types of amino acids are there in the body?
20
How many ketone bodies are keto acids?
2 Ketone bodies are keto acids, one is not
What are keto acids useful for?
Transamination
What enzyme converts glucose to glucose-6-P?
Hexokinase
How much ATP is used vs created in glycolysis?
2ATP used
4ATP created
Per glucose consumed
What causes lactate acidosis?
The protons released by ATP -> ADP
