Energy production (Carbs 1) Flashcards
Name the 3 properties of carbohydrates
(CH2O)n, contain an aldehyde or keto group and multiple hydroxyl groups, exist as mono, di, polysaccharides
How are carbs stored in the body?
glycogen (around 300g) and as a component of of cellular polymers like nucleic acids/glycolipids/glycoproteins
What happens when glycogen stores are full?
excess carbs are converted to triacylglycerols for storage in adipose tissue
What are the natural stereoisomers of monosaccharides?
D-forms
What are the 2 key features of sugar?
hydrophilic, partially oxidised so needs less oxygen than fatty acids for complete oxidation
When is a disaccharide non-reducing?
if the aldehyde or ketone groups of the two sugars are both involved in forming the glycosidic bond
Where is glycogen synthesised and how is it stored?
in the liver and skeletal muscle and stored as granules
Why is cellulose a major part of dietry fibre?
human GI tract doesn’t produce enzymes that are able to hydrolyse the beta 1-4 linkages
What are starch and glycogen hydrolysed by?
hydrolase enzymes
Where does the digestion of maltose, dextrins, and dietary disaccharides occur?
duodenum and jejunum
What are the major glycosidase enzymes?
lactase, glycoamylase, sucrase/isomaltase
Explain lactose intolerance
low levels of lactase enzyme, so lactose will continue into the colon where bacteria can break it down. the presence of lactose in the colon increases the osmotic pressure of the contents and draws water into the lumen, causing diarrhoea
What are GLUT 1 - GLUT 5 and what do they do?
they are a family of glucose transport proteins that are involved in facilitated diffusion/transport from cells into blood and blood into tissues
What happens when there is a high presence of insulin in skeletal muscle/adipose tissue?
increased uptake of glucose into these tissues by increasing number of glucose transport proteins in the plasma membrane
What is the major site of fructose and galactose metabolism?
the liver
What is the minimum amount of glucose required by a healthy adult on a normal diet?
around 180g a day
What are the different ways that glucose can enter?
glycolysis, pentose phosphate pathway, conversion to glycogen for storage
Why is glycolysis important?
generates
-ATP for cell function
-NADH from NAD+
-building block molecules for anabolism
-useful intermediates for specific cell functions
What is the overall reaction for the 10 steps of glycolysis?
glucose + 2Pi + 2ADP + 2NAD+ –> 2pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
What is the first step in glycolysis?
irreversible conversion of glucose to glucose-6-phosphate, requiring ATP and the enzyme hexokinase
In the liver and pancreas, apart from hexokinase what is the first stage of glycolysis catalysed by?
glucokinase
Why is the phosphorylation of glucose important?
-makes sugar anionic (negative charge) so it cannot cross the plasma membrane
-increases the reactivity of the sugar so it can be metabolised
-allows formation of compounds with high-phosphoryl-group transfer potential that can transfer their phosphate group to ADP (substrate level phosphorylation)
In the first stage of glycolysis how many moles of ATP are used per mole?
2 moles of ATP per mole of glucose
What are the starting material, end-products, and intermediates for glycolysis?
C6 or C3
Is there a loss of CO2 in glycolysis?
no
What are some of the C3 intermediates used by the cell for?
specific functions
What happens to glucose and NAD+ in glycolysis?
glucose is oxidised into pyruvate and NAD+ is reduced into NADH
What type of reaction is glycolysis?
exergonic with a negative delta G value
What is the net yield of ATP in glycolysis?
2
What is required for the synthesis of triacylglycerols in liver and adipose tissue?
glycerol phosphate
What is glycerol phosphate produced from?
dihydroxyacetone phosphate in adipose tissue
Why is the liver less dependent on glycerol phosphate produced by glycolysis?
it can phosphorylate glycerol directly using glycerol kinase and ATP
What does 2,3-biphosphoglycerate do?
it is an important regulator of the oxygen affinity of haemoglobin
What is one of the major functions of glycolysis?
to generate ATP from ADP by substrate level phosphorylation
What does myokinase do?
enables the high energy of hydrolysis phosphate bond in ADP to be used to drive ATP synthesis - 2ADP
<-> ATP + AMP
What is a high-energy signal?
an elevated concentration in the cell indicates high energy levels (like ATP)
What is the most important rate-limiting step in glycolysis?
step 3 - catalysed by phosphofructosekinase (PFK)
Name 2 ways that PFK can be regulated
-allosteric regulation (muscle) - inhibited by high ATP conc and stimulated by high AMP conc
-hormonal regulation (liver) - insulin stimulates and glucagon inhibits
When is pyruvate reduced to lactate?
when there isn’t enough oxygen / in cells without mitochondria
What enzyme reduces pyruvate to lactate?
lactate dehydrogenase
What is the equation for the reduction of pyruvate?
2 pyruvate + 2NADH + 2H+ –> 2 lactate + 2NAD+
What is the overall equation for anaerobic glycolysis?
glucose + 2pi + 2ADP –> 2 lactate + 2ATP + 2H2O
What is a significant increase in plasma lactate and why?
anything greater than 5 mmol/L because that exceeds the renal threshold for lactate - lactic acidosis
When may there be an increase in plasma lactate?
strenuous exercise, hearty eating, shock, congestive heart disease
