IMS1 TBL6 Glucose and Energy Metabolism (AKT REMAKE)

What is glycolysis

The cytosolic breakdown of one glucose into two pyruvate producing two ATP net and two NADH

Where does glycolysis occur

In the cytosol of all cells

Does glycolysis require oxygen

No it is anaerobic

What is the overall reaction of glycolysis

Glucose produces 2 pyruvate 2 ATP net and 2 NADH

How does glucose enter most cells

Through GLUT transporters by facilitated diffusion

Why is glucose phosphorylated immediately after entering the cell

To trap glucose inside the cell by preventing diffusion back out

Which enzyme catalyses formation of glucose 6 phosphate

Hexokinase

Which enzyme catalyses formation of fructose 1 6 bisphosphate

Phosphofructokinase 1

Which enzyme catalyses conversion of phosphoenolpyruvate to pyruvate

Pyruvate kinase

How many ATP are used during glycolysis

Two ATP are invested

How many ATP are produced during glycolysis

Four ATP are produced

What is the net ATP yield from glycolysis

Two ATP net

How many NADH are produced in glycolysis

Two NADH per glucose

What reducing equivalent is generated during oxidation step

NADH

What step produces NADH in glycolysis

Conversion of G3P to 1 3 bisphosphoglycerate

Which enzyme produces NADH in glycolysis

Glyceraldehyde 3 phosphate dehydrogenase

Which steps of glycolysis generate ATP

Conversion of 1 3 bisphosphoglycerate to 3 phosphoglycerate and conversion of phosphoenolpyruvate to pyruvate

What type of phosphorylation generates ATP in glycolysis

Substrate level phosphorylation

What is the fate of fructose 1 6 bisphosphate in glycolysis

It is split into G3P and DHAP

Which enzyme cleaves fructose 1 6 bisphosphate

Aldolase

Which enzyme interconverts DHAP and G3P

Triose phosphate isomerase

From which point in glycolysis do reactions occur twice per glucose

After G3P is formed

Which enzyme is the main regulatory enzyme of glycolysis

Phosphofructokinase 1

How does ATP affect phosphofructokinase 1

High ATP inhibits phosphofructokinase 1

How does AMP affect phosphofructokinase 1

AMP activates phosphofructokinase 1

Which product inhibits hexokinase

Glucose 6 phosphate

Which metabolite activates pyruvate kinase

Fructose 1 6 bisphosphate

Why is hexokinase considered irreversible

Large negative free energy change and trapping of glucose

Why is phosphofructokinase 1 considered irreversible

Large negative free energy change and committed step in pathway

Why is pyruvate kinase considered irreversible

Large negative free energy change and ATP production stage

What is the oxidation step in glycolysis

Conversion of G3P to 1 3 bisphosphoglycerate

Which molecule first captures energy in glycolysis

NAD plus that becomes NADH

How does glycolysis supply energy for red blood cells

It provides ATP for membrane ion pumps since RBCs lack mitochondria

Why does brain rely heavily on glycolysis

Neurons rely mainly on glucose availability for ATP

What are the four main stages of glycolysis

Phosphorylation cleavage oxidation substrate level phosphorylation

Which two reactions use ATP

Formation of glucose 6 phosphate and formation of fructose 1 6 bisphosphate

Which two reactions produce ATP

Formation of 3 phosphoglycerate and formation of pyruvate

What is substrate level phosphorylation

Direct transfer of a phosphate group to ADP forming ATP

What is the high energy intermediate formed after oxidation

1 3 bisphosphoglycerate

Which high energy intermediate donates phosphate to ADP later

Phosphoenolpyruvate

What does phosphoglycerate kinase do

Transfers phosphate from 1 3 bisphosphoglycerate to ADP

What does pyruvate kinase do

Transfers phosphate from phosphoenolpyruvate to ADP

What stimulates glycolysis hormonally

Insulin

What inhibits glycolysis hormonally

Glucagon and glucocorticoids

How does insulin promote glycolysis

It increases activity of glycolytic enzymes indicating fuel abundance

How does glucagon inhibit glycolysis

It promotes gluconeogenesis and reduces glycolytic enzyme activity

What is the normal fasting glucose range

Four to five point nine millimoles per litre

What makes glycolysis a universal pathway

It occurs in every cell providing ATP regardless of oxygen availability

Where does oxidation in glycolysis produce its electrons

From oxidation of G3P

What metabolic state activates glycolysis

Low energy state indicated by high AMP

What metabolic state suppresses glycolysis

High energy state indicated by high ATP or high citrate

Why does citrate inhibit glycolysis

It signals abundant acetyl CoA and sufficient TCA cycle activity

What is the first committed step of glycolysis

Formation of fructose 1 6 bisphosphate

Why is phosphorylation essential at start of glycolysis

To activate glucose making it more reactive and trapping it intracellularly

Why is NADH production important

It transfers reducing equivalents to mitochondria for ATP production later

What happens if NAD plus runs out

Glycolysis slows because oxidation step cannot proceed

What is cytosolic location advantage of glycolysis

It allows rapid ATP generation without requiring organelles

What is produced per glucose in full glycolysis

Two pyruvate two NADH and two ATP net

Which step marks six carbon to three carbon conversion

Cleavage of fructose 1 6 bisphosphate into DHAP and G3P

What determines pyruvate fate after glycolysis

Availability of oxygen

What happens to pyruvate with oxygen present

It enters mitochondria and is fully oxidised to CO2 and H2O

What happens to pyruvate with limited oxygen

It remains in cytosol and is converted to lactate

What enzyme converts pyruvate to lactate

Lactate dehydrogenase

What reaction is catalysed by lactate dehydrogenase

Pyruvate plus NADH plus H plus forms lactate plus NAD plus

Why is lactate formation important

Regenerates NAD plus so glycolysis can continue

Where does anaerobic metabolism occur

In the cytosol

How much ATP is produced per glucose anaerobically

Two ATP net

Why is anaerobic yield low

No oxidative phosphorylation occurs

What is lactate transported to liver for

Conversion back to glucose via gluconeogenesis

What cycle links muscle lactate with liver glucose production

Cori cycle

Where does lactate form in Cori cycle

In anaerobic muscle

Where is lactate reconverted to glucose

In liver

Why is Cori cycle useful

Clears lactate and supplies glucose back to muscle

What is energetic cost of gluconeogenesis in liver

Uses ATP but supports muscle ATP demand indirectly

What happens to pyruvate aerobically

It is transported into mitochondria

Which process fully oxidises pyruvate aerobically

Krebs cycle followed by electron transport chain

What additional energy molecules are produced aerobically

NADH and FADH2

Where do NADH and FADH2 release electrons

Electron transport chain

What process synthesises ATP from electron transport

Oxidative phosphorylation

Why does aerobic metabolism generate more ATP

Complete oxidation of carbon to CO2 allows full electron extraction

Why can NADH not freely enter mitochondria

Inner mitochondrial membrane is impermeable to NADH

What must be transferred into mitochondria instead of NADH

Reducing equivalents or electrons

What are the names of NADH shuttle systems

Malate aspartate shuttle and glycerol 3 phosphate shuttle

Where is malate aspartate shuttle mainly found

Liver kidney and heart

Where is glycerol 3 phosphate shuttle found

Skeletal muscle and brain

What cytosolic molecule is reduced to malate

Oxaloacetate

What reduces oxaloacetate to malate

NADH

Why is malate suitable for transport

It has a specific mitochondrial carrier

What happens to malate once inside mitochondria

It is oxidised back to oxaloacetate generating mitochondrial NADH

How many ATP are generated per NADH transported via malate shuttle

About two point five ATP

What is oxaloacetate converted to when leaving mitochondria

Aspartate

Why is aspartate exported

To regenerate cytosolic oxaloacetate completing shuttle cycle

What does NADH reduce in glycerol 3 phosphate shuttle

Dihydroxyacetone phosphate

What product is formed when DHAP is reduced

Glycerol 3 phosphate

What does glycerol 3 phosphate form in mitochondria

FADH2

How many ATP per FADH2 from glycerol shuttle

About one point five ATP