9- Metabolism 1 - glycolysis

Question 1

what is anabolism?

Answer 1

assimilation of molecules & complex structures from the building blocks of life
= requires energy

Question 2

what is catabolism?

Answer 2

breakdown of molecules to obtain the anabolic “building blocks” of life and substrates for energy
= breakdown of molecules to yield energy

Question 3

what is metabolism a balance between?

Answer 3

anabolism & catabolism

Question 4

is anabolism
a) endergonic or exergonic?
b) reductive or oxidative?

Answer 4

a) endergonic
b) reductive

Question 5

is catabolism
a) endergonic or exergonic?
b) reductive or oxidative?

Answer 5

a) exergonic
b) oxidative

Question 6

what happens in anabolism?

Answer 6

it takes oxidised precursors (products of catabolism) and with NADPH and H+ assembles them together to make biosynthetic products and NADP+ which can be used in catabolism

= anabolism is essential for process of growth & storage

Question 7

what happens in catabolism?

Answer 7

reduced fuel is broken down into oxidised products and NADH and H+ is used for oxidative phosphorylation of O2 to H2O which helps make energy

Question 8

what does metabolism always require?

Answer 8

• precursor→product
• reducing equivalent (that either accepts or donates electrons) to drive process forward

Question 9

what glucose molecules are in plants & animals?

Answer 9

plants = starch & cellulose
animals = glycogen

Question 10

what cells require glucose as an energy source?

Answer 10

• erythrocytes
• retina
• renal medulla
• brain (the brain accounts of about 20% of the oxygen requirement in a resting person even though only 2% of body weight of an individual - highly oxidative organ)
• all cancer cells

Question 11

what is structure of glucose?

Answer 11

6 carbon carbohydrate
- not naturally in linear form, usually circular

oxygen at top right corner - can think that it holds it in shape and holds likke spring so if you remove that O and do in controlled way you can release energy (glycolysis = breaking of glucose)

Question 12

what are disaccharides?

Answer 12

2 glucose that join together very easily, in lots of different orientations making a family

lactose, maltose, sucrose, cellabiose

Question 13

why is lactose so good for newborns?

Answer 13

it’s very easily broken down so good for supporting metabolism in newborn baby

Question 14

what are polysaccharides?

Answer 14

lots of glucose joined together

cellulose = glucose molecules linked in carbon 1-4 orientation

glycogen = glucose linked together, can make branches which means you can pack together so have ready source of glucose that can be tapped into in times of starvation

Question 15

if oxygen starved - what happens to pyruvate?

Answer 15

pyruvate converted to lactate

Question 16

what are the 3 different pathways of glucose?

Answer 16

1. converted to PYRUVATE by oxidation through aerobic glycolysis
2. converted to LACTATE by fermentation by anaerobic glycolysis
3. converted to RIBOSE-5-PHOSPHATE by oxidation through the pentose phosphate pathway

Question 17

what is ribose-5-phosphate?

Answer 17

precursor for nucleotide synthesis & DNA repair = essential for growth (ties into warburg effect of cancer cells = glucose use for cancerous tumours is double whammy; for providing energy & for precursor of growth

Question 18

how is glucose transported into cell?

Answer 18

via Na+/glucose symporters

Question 19

what are examples of glucose symports?

Answer 19

GLUT 1 = in brain, low Km
GLUT 2 = in liver and B cells, high Km & insulin dependant
GLUT 3 = in brain, low Km
GLUT 4 = in muscle and adipose tissue, insulin dependant
GLUT 5 = in gut, fructose transport

Question 20

what is process of GLUT 1 transporter?

Answer 20

• binding of glucose to the outside triggers conformational change
• binding site faces inwards
• glucose can be released in the inside
• Conformational change regenerates the binding site on the outside

Question 21

what is process of stage 1 of glycolysis?

Answer 21

2 ATP →2 ADP energy helps convert glucose to fructose-1,6-biphosphate

• 1 ATP used by hexokinase for glucose →glucose-6-phosphate and (phosphoglucose isomerase →fructose-6-phosphate)
• 1 ATP used by phosphofructokinase to make fructose-1,6-biphosphate

Question 22

what is the net gain of ATP in glycolysis?

Answer 22

2 ATP (2 used at start and then 4 made so 4-2 = 2)

Question 23

what happens in stage 2 of glycolysis?

Answer 23

fructose-1,6-biphosphate converted into two 3-carbon triose phosphates

= 2 interconvertible 3-carbon molecules, triose phosphates, are formed

Question 24

what happens in stage 3 of glycolysis?

Answer 24

triose phosphate then used 2 NAD →2 NADH + 2H+ and 4ADP →4 ATP to make 2 pyruvate

(both triose phosphate undergo reaction so reaction happens twice →2 pyruvate)

pyruvate kinase catalyses last step to pyruvate making final bit of ATP

Question 25

what are the 2 main cellular needs of glycolysis?

Answer 25

• production of ATP
• provision of building blocks for synthesis reactions

Question 26

what are the 3 control points in glycolysis?

Answer 26

1. hexokinase = takes 1 ATP and energises glucose (labels glucose for entry into glycolytic pathway) →phosphorylates glucose to glucose-6-phosphate = very 1st step
2. phosphofructokinase = control rate of flow of glucose-6-phosphate →fructose-1,6-bisphosphate, important in acting like energy sensor, also uses 1 ATP
3. pyruvate kinase = controls exit of pyruvate from glycolytic pathway (inhibited by high ATP concentration)

Question 27

what is reaction catalysed by pyruvate kinase?

Answer 27

phosphoenolpyruvate + ADP + H+ →pyruvate + ATP

Question 28

what is reaction catalysed by phosphofructokinase?

Answer 28

fructose-6-phosphate + ATP →fructose-1,6-phosphate + ADP + H+

Question 29

what is reaction catalysed by hexokinase?

Answer 29

glucose + ATP →glucose-6-phosphate + ADP + H+

Question 30

what is each control point of glycolysis inhibited by?

Answer 30

hexokinase = inhibited by glucose-6-phosphate

phosphofructokinase = inhibited by ATP

pyruvate kinase = inhibited by ATP

Question 31

what are some inhibitors of metabolism?

Answer 31

ATP = will slow glycolysis if energy abundant

citrate = TCA cycle intermediate, slows downstream pyruvate entry to TCA cycle if energy abundant

H+ = slows glycolysis if too much lactic acid being produced

Question 32

what are activators of glycolysis?

Answer 32

AMP and fructose-2,6-biphosphate →will increase glycolysis if energy is needed

Question 33

what is the ATP/AMP ratio, energy change?

Answer 33

it’s the idea that if all adenylate nucleotides are in ATP form then cell fully charged

if cell only contains AMP & Pi then discharged

Question 34

why is AMP not ADP positive regulator?

Answer 34

if ATP is rapidly used up …
ATP → ADP + Pi

= adenylate kinase can salvage some of the energy in ADP…
2 ADP → ATP + AMP

(so if lots of energy being used, low energy - then high AMP)

Question 35

where does the 2 NADH + 2H+ go from stage 3 of glycolysis?

Answer 35

to electron transport chain & ATP synthesis

Question 36

what is the warburg effect?

Answer 36

= up-regulation of anaerobic glycolysis in cancer cells

cancer cells rely on aerobic glycolysis as their primary energy-producing pathway even in presence of sufficient oxygen (contrast to normal cells where they typically generate energy through oxidative phosphorylation in mitochondria)

• cancer cells have low Km hexokinase

Question 37

what are the advantages to cancer cell’s way of energy production?

Answer 37

• Rapid energy production
• Supports other pathways for nucleotide synthesis (needed for growth)
• Supports rapid cell growth (proliferation)

Question 38

what are the disadvantages to cancer cell’s way of energy production?

Answer 38

• Produces H+and lactate as end products
• Very inefficient ATP synthesis
• High glucose consumption demand
• Cancer patients lose weight