Flashcards in Carbohydrates Deck (56):
Which two monosaccharides make up lactose?
Glucose and galactose
Which two monosaccharides make up sucrose?
Fructose and glucose
Which monosaccharides make up maltose?
Glucose and glucose
What is the bond between monomers of polysaccharides?
What is the general formula of carbohydrates?
What two things does starch contain?
Amylose and amylopectin
What type of enzymes hydrolyse starch and glycogen and which two specific enzymes do this?
-salivary amylase and pancreatic amylase
How does a lactase deficiency cause diarrhoea?
No lactase to break down lactose.
Lactose is therefore present in the colon.
This increases osmotic pressure drawing water into the lumen.
Why is cellulose not digested in the GI tract?
Glucose units are joined by beta-1,4 linkages.
Human GI tract does not possess enzymes able to hydrolyse these bonds.
What is the minimum glucose requirement for a healthy adult?
Give the two main products produced from glycolysis.
What is the first step of glycolysis and what enzymes are needed?
Glucose ➡️ Glucose-6-P
Hexokinase is the enzyme. Is some tissues (eg liver) glucokinase is used
What is the significance of the phosphorylation of glucose in glycolysis?
Makes glucose negatively charged so it cannot pass back across cell membrane
Increases reactivity of the sugar so it can be metabolised by different pathways
Allows for substrate level phosphorylation
What is produced after steps 2 and 3 in glycolysis?
How is NAD+ regenerated for glycolysis to continue?
By the electron transport chain
In anaerobic conditions or in cells lacking mitochondria, it is done in the lactate dehydrogenase reaction.
What is the net yield of ATP from glycolysis?
2 moles of ATP
What is the most important rate limiting step in glycolysis and which enzyme is involved?
Subject to allosteric regulation in muscle and hormonal regulation in the liver.
How is lactate removed?
-Released into circulation and transported to liver, heart and kidneys.
-In heart muscle it is converted back to pyruvate and oxidised to CO2
-In the liver and kidneys it is converted to glucose
What can galactose be used for?
Synthesis of glycoproteins and glycolipids
Where is galactose largely metabolised?
In the liver
Which two enzymes can be deficient and lead to galactosaemia?
Galactose-1-phosphate uridyl transferase
In galactosaemia, a deficiency of which enzyme is most serious?
The transferase enzyme
What happens to galactose when it accumulates in tissues and what are the consequences of this?
-Reduced to galactitol
-Depletes NADPH stores
-Damages lens structure in the eye due to cross-linking of proteins and can cause non-enzymatic glycosylation of lens proteins - both lead to cataracts
-Accumulation can cause glaucoma and blindness
-Accumulation of galactose 1P can cause liver, brain and kidney damage
What is the pentose phosphate pathway important for?
-Produces the 5C sugar ribose, important for nucleotides in DNA and RNA
What is NADPH important for?
-Provides reducing power for anabolic processes such as lipid synthesis
-In RBCs, it is important for maintaining free -SH groups on cysteine residues
-Involved in various detoxification methods that protect cells against toxic chemicals
Which two enzymes are involved in phase 1 of the pentose phosphate pathway?
-Glucose 6-phosphate dehydrogenase
What does the pentose phosphate pathway produce?
-5C sugar-phosphate (ribose)
How is the pentose phosphate pathway regulated?
Controls activity of glucose 6-P dehydrogenase.
NADPH inhibits it.
NADP+ activates it.
What does a G6PD deficiency lead to?
Low NADPH causing -SH groups to form sulphide bridges in proteins.
Haemoglobin and other proteins become cross-linked by disulphides bonds to form Heinz bodies.
Premature destruction of RBCs and haemolysis.
What does glutathione do?
Converts NADP+ to NADPH
Which enzyme converts pyruvate to acetyl CoA?
What type of regulation regulates phosphofructokinase?
Is the TCA cycle oxidative or reductive?
List the functions of the TCA cycle
Break the C-C bond in acetyl CoA (acetate) and oxidise the C atoms to carbon dioxide.
Use intermediates in the cycle to produce non-essential amino acids
Use intermediates for synthesis of haem and glucose
Use intermediates for the synthesis of fatty acids
Why are there no known genetic defects in the TCA cycle?
It would be fatal
How many molecules of ATP are there per molecule of glucose produced by the TCA cycle?
What components does the TCA cycle require?
NAD and FAD
How is the TCA cycle regulated?
Isocitrate dehydrogenase is allosterically regulated.
-NADPH inhibits it (a high energy signal)
-ADP activates it
List the products of the TCA cycle
CO2, CoA, NADH, H+, FAD2H, GTP
Which enzyme is commonly used for the replacement of intermediates of the TCA cycle?
What type of phosphorylation is done in the electron transport chain?
How many protein complexes are involved in the TCA?
What provides the electrons for the ETC and which gives the most energy?
NADH and FAD2H
NADH gives the most energy because it has more protons
What do three of the complexes act as in the electron transport chain?
Proton translocating complexes
How do proton translocation complexes transport proteins to the outer membrane space?
Use the free energy derived from electron transport
What is the proton motive force?
-Concentration of protons increase in the outer mitochondrial membrane space.
-The proton translocating complexes therefore transform the chemical bond energy of the electrons into an electro-chemical potential difference of protons.
What increases the pmf?
The greater the chemical bond energy of the electrons, the more protons that can be translocated so the greater the pmf.
Across which complex are protons passed back into the inner mitochondrial membrane during the ETC?
The ATP synthase complex
Compare oxidative phosphorylation to substrate phosphorylation.
-requires membrane associated complexes.
-energy coupling occurs indirectly through generation and subsequent utilisation of a proton gradient.
-cannot occur in absence of oxygen
-major process for ATP synthesis
-requires soluble enzymes.
-coupling directly through formation of a high energy hydrolysis bond.
-can occur in absence of oxygen.
-minor process for ATP synthesis.
How is the coupling of the ETC and ATP synthesis regulated?
By ATP concentration.
-when [ATP] is high, [ADP] is low, so ATP synthase stops due to lack of substrate
-prevents transport of protons back into mitochondria
-[H+] increases so more protons are not pumped out
-proton pumping steps
How are the ETC and ATP production uncoupled?
Increasing the permeability of the inner mitochondrial membrane. Protons can re-enter the ETC without driving ATP synthesis.
What are the uncoupling proteins called?
What is released by the sympathetic nervous system in response to cold and what does this do?
Noradrenaline. This causes an increase of lipolysis in brown adipose tissue. Produces fatty acids for beta oxidation. This causes an increase in NADH and FAD2H which causes an increase in the ETC and pmf.
Noradrenaline also activates UCP 1
What inhibits the ETC and how?
Poisons such as cyanide
NADH and FAD2H cannot be oxidised by ETC. Therefore no energy to drive proton pumping and no pmf is created. ATP is not synthesised and no heat generated.
What can galactose be synthesised from in the body?
Glucose 6 phosphate