Biochem lecture 2 glycolysis

Seite 1

glucose fate goes through glycolysis then becomes pyruvate.

from pyruvate, it can go oxidation or fermentation

glucose glycolysis occurs in 2 stages

1) trapping of glucose and preparation

2) ATP is harvested

glucose transporters glucose transporters :

1) GLUT 1 to GLUT 5

-a single poly peptide chain ~500 residues

each has 12-transmembrane-helix structure https://o.quizlet.com/8EXXuo0X0VxIkT-paWHpFw_m.jpg

in stage 1 3 steps take place

1) phosphrylation

2) isomerizaiton

3) 2nd phosphorylation

conversion of glucose to F 1,6 BP occurs in 3 steps

beginning of glycolysis hexokinase traps glucose and begins glycolysis

-G6P does not pass through membrane because it is not a suitable glucose transporter

-addition of phophoryl group destabilizes glucose, further facilitating it to metabolism

ENZYME used : hexokinase

next step - isomerization of g6p to fructose 6 phospahte F6P -g6p ring is opened

-isomerization-> convert aldose into a ketose

-then reforms to become F6P, a 5 membered ring

ENzyme used : isomerase

next step, 2nd phosphorylation F6p is phosphorylated

ENzyme used : PFK

ATP is used for the reaction

cleavage of six-carbon sugar to 2 three carbon frag 2 three carbon fragments are DHAP or GAP (G3P)

reversible by adolase (enzyme used)

conversion of DHAP to GAP Using triose phosphate isomerase,

DHAP can be converted to GAP

summary of glycolysis stage 1 -2 molecules of GAP are generated from 1 molecule of glucose

-no energy is yet to be extracted

-2 ATP molecules are invested

2nd stage of GLycolysis stage 2 harvests some of the energy in G3P as ATP

conversion of glyceraldehyde 3- phosphate into 1,3-bisphosphoglycerate (1,3-BPG) using G3P dehydrogenase, and NAD+ w/P inorganic,

-aldehyde is oxidized

generation of ATP by phosphoryl transfer from 1,3-BPG phosphglycerate kinase is used to transfer phosphate from 1,3-BPG to ADP to yield--> 3PG + ATP

pyruvate formation from 3PG, there is 1) rearrangement (phosphoglycerate mutase) 2) creating an enol (enolse) 3) phophoryl-transfer (pyruvate kinase)

energy consideration the energy released in the anaerobic conversion fo glucose in to two molecule of pyruvate is -23 kcal/mol

NAD+ must be regenerated in fermentation

fermentation is an ATP generating process in which organic compounds ct both as the donor and as the acceptor of electrons-ethanol or lactate fermentation

conversion of pyruvate to ethanol 1) in yeast and several other microorganism

2) decarboxylation of pyruvate by pyruvate decarboxylase

3) reduction acetaldhyde to ethanol by alcohol dehydrogenase

result of alcoholic fermemtation 2 NADH generated but 2 NADH was used for generation of 2 NAD+

lactic acid fermentation in oxygen limiting conditions

-pyruvate is converted to lactate using lactate dehydrogenase

-2 NADH generated but 2 NADH used to generated 2 NAD+

Streptococcus mutan and dental carriess 1) anaerobc bacterium (gram positive)

2) lactic acid: main fermentation product

3) mineral slat in teeh is broken down by fermentation leading to development of carries in dentin and enamel

slide 25-28 skipped here but do read in the slide if have time

-Fructose can enter glycolysis after being converted into DHAP and become G3P

-Galactose can enter glycolysis after being converted into G6P then undergoe the process

lactase deficiency and milk intolerance -some adults have lactase deficiency and are unable to metabolize milk sugars

-lactic acid is generated and methane and hydrogen gas

- lactate osmotically active and draws water into intestin causing gastrointestinal disturbance

galactosemia disorder that interferes with galactose metabolism

glycolytic pathway is tightly controlled 3 irreversible site of control

1) hexokinase

2) phosphofructokinase

3) pyruvate kinase

control of glycolysis in muscle ATP shuts down PFK and pyruvate kinase at rest when there is abundant energy

when energy is needed low ATP and high AMP stimulates PFK to convert more of F 1,6 BP which stimulates pyruvate kinase for conversion of PEP to pyruvate https://o.quizlet.com/4ojLYG0F3RpVo8oLTaAGuQ_m.png

control of glycolysis in liver Hexokinase:

-Not inhibited by glucose 6-phosphate.

-Phosphorylates glucose when glucose is abundant

(Affinity for glucose ~50-fold lower than that of hexokinase)

-Provides glucose 6-phosphate for the synthesis of glycogen and for the formation of fatty acids.

-The low affinity of for glucose in the liver

gives the brain and muscles first call on glucose

when its supply is limited,

-glucose is not wasted when it is abundant

control of glycolysis Phosphofructokinase

More blood-glucose ->

More fructose 6-phosphate ->

More synthesis of F-2,6-BP ->

Increased affinity of phosphofructokinase for fructose 6-phosphate ->

Reduced inhibitory effect of ATP ->

Glycolysis accelerated

Feed-forward stimulation

control of pyruvate kinase in liver https://o.quizlet.com/eAJDgKX1BVnowBC8uf671Q_m.jpg

tumors and glycolysis -tumors display enhance rate of glucose uptake and glycolysis

-rapid growing tumor cell can use glucose to undergoe lactate ferm. even in presence of oxygen

glycolysis summary 1) two steps are involved: trapping and preparation/ energy havest

2) from 1 glucose, 2 ATP and 2 NADH are generated

3 Fermentation can produce ethanol or lactate

4) fructose and galactose are converted into glycolytic intermediates

5) glycolysis tightly controlled by 3 irreversible steps

6) tumors display aerobic glycolysis