Topic 1 : Carbohydrate Biosynthesis and Metabolism Flashcards
Metabolism is the sum of these 2 processes
Catabolism (breakdown)
Anabolism (synthesis)
Energy release of ATP hydrolysis
γ-β bond - 30.5 kJ / mol
β-α bond - 32.8 kJ / mol
Function of glycolysis
energy production
function of gluconeogenesis
glucose resynthesis
function of citric acid cycle
building blocks and energy
function of pentose phosphate pathway
NADPH and pentose synthysis
Brain uses this in well - fed state
glucose
storage of glycogen in this organ
liver
methods of enzyme regulation (general)
enzyme activity modification (short term ie hours, minutes) enzyme concentration (long term ie days, hours)
WHAT ARE THE ADVANTAGES OF USING A SINGLE ENERGY CURRENCY?
Easy to distribute energy. Reduces the number of necessary pathways to use energy
Can stock up on ATP without having to worry about converting to other forms
WHY DO CELLS LIKE MYOCYTES & NEURONS USE PHOSPHOCREATINE AS WELL AS ATP FOR ENERGY?
Phosphocreatine allows rapid regeneration of ATP from ADP. Cells like myocytes and neurons have to rapidly fire, and benefit from speedy recovery
IF ENZYMATIC STEPS ARE REVERSIBLE: WHY USE TWO PATHWAYS TO SYNTHESIZE AND BREAKDOWN COMMON CELLULAR COMPONENTS?
It makes it easier to regulate.
There are some steps that are virtually irreversible, the regulation of which aid in preventing the pathway from gong in both directions.
Sugar isomer used by mammals
D-isomers
Common aldoses (3)
D-glucose
D-galactose
D-mannose
Aldose
contains multiple alcohol groups and one carbonyl as an aldehyde
Ketose
contains multiple alcohol groups with one carbonyl as a ketone
Common Ketoses (2)
Fructose
Ribulose
anomeric carbon
hemiketal / hemiacetal carbon in a sugar
can be OH down (α)
or OH up (β)
What is unusual about the linkage between glucose and fructose in sucrose ?
They are both attached on the reducing end Therefore: Fru(2β-α1)Glc is the same as Glc (2β-α1) Fru
Reducing end
Hemiketal or hemiacetal end of a sugar (carbon 1)
or sugar chain
bonds of glycogen and amylopectin
α 1-6 linkages to create branches
α 1-4 linkages within branches
bonds between cellulose sugars
β 1-4 linkages
forms straight chains
n-linked glycoproteins use what aa for linkage to sugar ?
Asn
ARE DIGESTIVE ENZYMES GENERAL OR SPECIFIC FOR CERTAIN POLYSACCHARIDES OR GLYCOSIDIC LINKAGES?
Specific.
Amylases in the mouth are general
WHY DO ERYTHROCYTES (RED-BLOOD CELLS) DEPEND HEAVILY ON GLUCOSE FOR THEIR ENERGY?
There are no organelles,
most energy producing processes take place in the mitochondria
WHY DO WE NEED GLYCOPROTEINS, PROTEOGLYCANS AND MUCOPOLYSACCHARIDES ?
Glycoproteins are used as cell markers
Proteoglycans are used for shock absorbing in cartilage
mucopolysaccharides are slippery (mucus)
3 main sources of sugars
Diet (plant / animal)
Glycogen storage
Individual sugars
1st step of glycolysis
Hexokinase is considered the first step, but is not always done
product of glycogen breakdown
glucose 1 phosphate (G1P)
later transformed into g6p
glucose transporter in liver
GLUT2
glucose transporter in muscle
GLUT4
insulin dependent glucose transporter
GLUT4
Difference between GLUT2 and GLUT4
GLUT2 (liver) has a high Km so it can absorb glucose when in excess
GLUT2(muscle) has lower Km, so it can take in glucose at physiological concentration
ATP producing steps of glycolysis
7 (phosphoglycerate kinase)
10 (pyruvate kinase)
Substrate level phosphorylation
Irreversible steps of glycolysis
1 (glucose -> G6P by hexokinase)
3 (fructose 6-phosphate -> fructose 1,6-biphosphate by phosphofurctokinase-1)
10 (phosphoenolpyruvate -> pyruvate by pyruvate kinase)
2 phases of glycolysis
preparatory
payoff
Purpose of lactate cycle
Remove pyruvate
and
revert NADH back to NAD+
WHY CAN’T HUMANS METABOLIZE CELLULOSE?
Do not have the proper enzymes to break linkages (β-1,4)
WHY DO WE NEED GLUTs?
Glucose does not diffuse fast enough through the membrane
WHAT HAPPENS TO EXCESS BLOOD GLUCOSE?
Insulin is released and it is absorbed into the tissues.
It is converted to glycogen in the liver
It may also be turned into fats
What is glucuconeogenesis ?
synthesis of glucose from non carbohydrate precursors
What non carbohydrate precursors can be used to make glucose ?
Lactate, glucogenic amino acids (alanine, etc), glycerol
Where does gluconeogenesis happen ?
Liver
Kidney (to a lesser extent)
Normal HbA1c ?
3.5 - 5.5 mM
What happens when HbA1c drops below normal ?
hypoglycaemic shock / coma