An introduction to metabolism (last year)

Question 1

what is metabolism

Answer 1

inter-conversion of molecules using chemical reactions

Question 2

name the catabolic (degradative) reactions

Answer 2

production of chemical energy (atp) and ion gradients
production of mechanical energy (muscle contraction)
production of reducing equivalents (nadh,nadph)
production of biosynthetic precursors

Question 3

name the anabolic (biosynthetic) reactions

Answer 3

storage of energy
production of macromolecules and cellular structures

Question 4

many reactions are endothermic and are often driven atp or hydrolysis( removal of products)

Answer 4

true

Question 5

what is glycolysis

Answer 5

A process in which glucose (sugar) is partially broken down by cells in enzyme reactions that do not need oxygen. Glycolysis is one method that cells use to produce energy.

Question 6

where does glycolysis occur?

Answer 6

in the cytosol

Question 7

explain stage 1 of glycolysis

Answer 7

activates glucose for metabolism ( energy is put in as ATP in two different steps( second step has phosphofructokinase 1) and rearrangement ( allows for 2 C3 sugars to form in stage 2)
double phosphorylation causes opening of sugar

Question 8

what is the produce of glycolysis stage 1?

Answer 8

fructose-1,6-bisphosphate

Question 9

(advanced) step by step mechanism of stage 1 glycolysis:

Answer 9

Glucose—(ATP to ADP)—>Glucose-6-phosphate—->Fructose-6-phosphate—(ATP to ADP + phosphofructokinase1)—>Fructose-1,6-bisphosphate

Question 10

explain stage 2(+ advanced) of glycolysis

Answer 10

Fructose-1,6-bisphosphate is converted into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (using aldolase). dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate ( via triose phosphate isomerase)

Question 11

explain stage 3 of glycolysis

Answer 11

2 Glyceraldehyde-3-phosphate in stage 2 are converted to two pyruvates, also producing 2NADH(from NAD) and 4 ATPs ( from ADP)(all in total)

Question 12

explain Anaerobic respiration

Answer 12

normally happens in muscle during anaerobic exercise
and in the absence of oxygen. Pyruvate is turned into R-lactate. This process oxidises NADH to NAD+ which allows glycolysis to continue. R-lactate can also be reoxidised to pyruvate using NAD+

Question 13

explain the Cori cycle

Answer 13

Recycling of R-lactate to glucose. Lactate is transported from muscle to the liver via blood. Using lactate dehydrogenase (in liver), lactate is converted to pyruvate. then pyruvate is converted into glucose by gluconeogenesis. This process requires 6ATPs
( glycolysis produces 2 ATPS

Question 14

what is Gluconeogenesis and where does it happen

Answer 14

conversion of R-lactate (to pyruvate and then) to glucose. It happens primarily in the liver cytosol.

Question 15

Explain the process of Gluconeogenesis

Answer 15

firstly 2 pyruvates are needed for one glucose
ATP+CO2+pyruvate make oxaloacetate (happens in mitochondria)
then oxaloacetate is exported to the cytosol and converted to phosphoenolpyruvate
2 ATP and one NADH also required
we need additional enzymes where some steps of glycolysis is irreversible
finally, phosphatase allows export of glucose to other tissues

Question 16

explain the structure of mitochondria and why it is important

Answer 16

it plays a key role in aerobic respiration and is
crucial for the degradation of glucose and fats. its matrix contains the enzymes for the tricarboxylic acid cycle. its membranes are needed for electron transport system. it plays a role in gluconeogenesis

Question 17

what is pyruvate dehydrogenase complex

Answer 17

The pyruvate dehydrogenase complex (PDHc) is a group of enzymes that converts pyruvate into acetyl-CoA, a molecule that enters the citric acid cycle to produce energy for cells.
PDHc controls pyruvates entry into the TCA cycle and has 3 types of subunits.
PDH (E1) which decarboxylates pyruvate( requires thiamine pyrophosphate ;TPP)
Dihydrolipoyl transferase ( E2) which makes CoA and requires lipoamide to do so.
Dihydrolipoyl dehydrogenase (E3) which converts reduced lipoamide to disulfide form and requires FAD.
mammals of 30 E1, 12 E2 and 12 E3

Question 18

Explain the formation of acetyl-CoA

Answer 18

1-TPP anion is added to pyruvate and CO2 is released ( E1 is used)
2-Lipoamide disulfide is added to acetyl group and a redox reaction occurs(E2 is used)
3-Disulfide exchange occurs to form acetyl-CoA and reduced lipoamide (using E2)
4- reduced lipoamide is oxidised to disulfied firn using FAD ( using E3)
5-FADH2 is oxidised by NADH, which is fed into the electron transport system