Introduction to Metabolism

Question 1

Metabolic Pathways

Answer 1

Enzymatic reactions producing specific products; branched and interconnected

Question 2

Metabolites

Answer 2

Reactants, intermediates & products that vary by cell type, nutritional status and developmental stage

Question 3

Catabolism

Answer 3

Degradative metabolism

Question 4

Anabolism

Answer 4

Biosynthetic metabolism

Question 5

Which is the rate determining step of metabolic flux

Answer 5

The slowest step of a metabolic pathway with the largest -ve gibbs free energy value

They act as dams as they are the most one way reactions

REVISE THIS

Question 6

Why do many reactions have two different enzymes for the forward and reverse reaction

Answer 6

To allow more effective metabolic control and regulation

Question 7

Energy sources in humans and recommended percentage intake of calories

Answer 7

Carbohydrates 55%, fats/lipids 30% and protein 15%

Question 8

Energy yielded by carbohydrates, proteins and lipids per gram

Answer 8

Carbs and proteins (4kcal - 17kJ)

Lipids
9kcal - 37kJ

Question 9

How does body digest carbohydrates

Answer 9

Salivary amylase digests carbohydrates in mouth to oligosaccharides

Further digestion in small intestine by pancreatic enzymes until they become disaccharides (e.g. pancreatic amylase)

Final digestion into monosaccharides by mucosal cells

Glucose taken into cells along with Na+ by active transport

Question 10

Oligosaccharides

Answer 10

Simpler carbohydrates that have three to six units of sugars

Question 11

Glucose

Answer 11

C6H12O6

Question 12

Which enantiomer of glucose is used in metabolism

Answer 12

D Glucose

Question 13

How can glucose exist

Answer 13

Either linearly or as a hexagonal ring (In solution)

Question 14

Pyranose and Furanose

Answer 14

Pyranose - 6 Membered ring structure (e.g. glucose)

Furanose - 5 Membered ring structure (e.g. ribose)

Question 15

What concentration is glucose generally kept at in the blood

Answer 15

5mM

Question 16

How badly does the brain need/like glucose

Answer 16

Badly

Question 17

Why does anaerobic glycolysis lead to the formation of lactate

Answer 17

The reduction of pyruvate to lactate is needed to reoxidise NADH that is made in the conversion of glyceraldehyde 3-P into 1,3-Bisphosphoglycerate

Question 18

Na+ independent facilitated diffusion transport

Answer 18

One of two main methods for glucose to enter cells

Glucose moves via concentration gradient; binds to glucose transporter protein that allows it into the cell when bound

Various GLUT forms (GLUT 1-14) for the various tissue types
Respond to insulin

Question 19

ATP-Dependent Na+-monosaccharide transport system

Answer 19

One of two main methods for glucose to enter cells
Against concentration gradient

Co-transport system

Na+ pumped out of cell against gradient
When Na+ moves along gradient towards transporter; ion causes conformational change that allows it to bind to glucose and brings the sugar and Na+ into the cell

Found in Intestinal epithelial cell

Question 20

Two main stages in glycolysis

Answer 20

Energy investment reaction (First 5 reactions)
- Phosphorelates molecules using ATP

Energy Generation Phase

Question 21

How is glucose committed to glycolysis

Answer 21

It is phosphorylated to keep it in the cell ready for the reaction to occur

Question 22

Hexokinases

Answer 22

Regulatory enzymes of glycolysis
Different forms (I-III) found in different tissues

Inhibited allosterically by G6P

Low Km to permit efficient phosphorelation of low glucose levels

Low Vmax so no overabundance of G6P

Question 23

Glucokinase

Answer 23

Hexokinase IV
In liver parenchymal/β cells

Higher Km so only active after carb rich meal
High Vmax allowing glucose in liver to be maximally absorbed

Question 24

Phosphoglucose Isomerase

Answer 24

Reversible enzyme that catalyses the isomerisation of G6P to/from F6P

Question 25

Phosphofructokinase

Answer 25

PFK Irreversible *Rate limiting reaction* that phosphorylates: F6P --> F-1,6-BP High ATP causes inhibition, AMP activates it; Reaction Uses ATP Allosterically Inhbited by Citrate (TCA intermediate)

Question 26

Aldolase

Answer 26

Reversible enzyme catalysing the cleavage reaction of FBP into DiHydroxyAcetone Phosphate (DHAP) and GlycerAldehyde-3-Phosphate (GAP)

Question 27

Triose Phosphate Isomerase

Answer 27

Enzyme that reversibly converts DHAP (Dihydroxyacetone Phosphate) into GAP (Glyceraldehyde-3-Phosphate) since only GAP is used in glycolysis

Question 28

Glyceraldehyde-3-Phosphate Dehydrogenase

Answer 28

GAPDH Enzyme that oxidates GAP using NAD+ and Phosphate into 1,3-Bisphosphoglycerate (1,3-BPG) and NADH

Question 29

Phosphoglycerate Kinase

Answer 29

Reversible enzyme that synthesises 3-Phosphoglycerate from 1,3-BisphosPhoglycerate and produces ATP via substrate level phosphorelation 2 ATP (from lysis) to 'repay' previously used up ATP

Question 30

Phosphoglycerate Mutase

Answer 30

Enzyme that reversibly converts 3-phosphoglycerate to 2-phosphoglycerate (figure out what the reaction dumbass)

Question 31

Enolase

Answer 31

Reversible enzyme that Redistributes the energy within the molecule by Dehydration 2-Phosphoglycerate to PhosphoEnolPyruvate (high energy intermediate)

Question 32

Pyruvate Kinase

Answer 32

3rd Irreversible Enzyme of glycolysis Forms Pyruvate from Phosphoenolpyruvate through substrate level Phosphorelation (2 more ATP)

Question 33

Lactate Dehydrogenase

Answer 33

Reversible enzyme that converts Pyruvate into Lactate and uses up NADH (or NAD in reverse) Has different Isozymes

Question 34

Energy balance in glycolysis

Answer 34

Glucose - G6P (-ATP) F6P - F1,6bP (-ATP) 2 GAP - 2 1,3bPG (+2NADH) 2 1,3bPG - 3PG (+2ATP) 2 PEP - Pyruvate (+2ATP) Yields 2 ATP and 2 NADH (which means extra 6 ATP in mitochondria)

Question 35

Haemolytic Anaemia

Answer 35

Usually issue with pyruvate kinase Not generating full amount of ATP needed for blood cells to fuel ion pumps in their membrane that leads to incorrect osmotic flow; strains membrane and forms odd shapes Spleen sends phagocytes to attack them and thus haemolytic anaemia Often spleen is removed as treatment Regular transfusions needed