glycolysis and the krebs cycle

8/18/2019 Glycolysis and the Krebs Cycle

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Glycolysis and the Krebs cycle

Quick revise

Both processes produce ATP from substrates but the Krebs cycle produces many more ATP

molecules than glycolysis! Every stage in each process is catalysed by a specific enzyme

n aerobic respiration both glycolysis and the Krebs cycle are involved "hereas in anaerobic

respiration only glycolysis takes place

The flo" diagram sho"s that every time a stage produces t"o hydrogen atoms# in the

presence of o$ygen# three ATP molecules are produced The role of these hydrogen atoms

is sho"n in the electron carrier system

Electron carrier system

The main feature of the electron carrier or electron transport system is that three ATPs are

produced every time %& atoms are transported t takes place in the mitochondria

Glycolysis – summary

A'' T&E (EA)T*+, + -'.)*'.,, TAKE P'A)E + T&E )E'' ).T*P'A,/

0*1T,2E T&E /T*)&*+2(*+3

•-lucose is a stable molecule containing 4 )arbon atoms

http://revisionworld.com/quick-revise/7633




•-lucose contains many )5& bonds and contains significant energy

•2uring -'.)*'.,, one glucose molecule is split into t"o P.(16ATE molecules

•Each P.(16ATE molecule contains three carbon atoms

• As glucose is a stable molecule it must first be made into a less stable 7(1)T*,E

B,P&*,P&ATE molecule before it can be broken do"n This re8uires the input

of energy

•0% $ ATP3

•7(1)T*,E B,P&*,P&ATE is split into t"o T(*,E P&*,P&ATE molecules



•The t"o T(*,E P&*,P&ATE molecules are converted into t"o -P molecules#

releasing energy 0% $ ATP3# and &ydrogen &ydrogen is picked up by +A2 to form

reduced +A2 0red+A23 The &ydrogen is taken to the mitochochondria "here is is

used to generate

• ATP by *92AT6E P&*,P&*(.'AT*+

•%-Ps are converted into t"o P.(16ATE molecules releasing energy 0% $ ATP3

Thus at the end of GLYCOLYSIS, one glucose mocule has generated

•% pyruvate molecules 0to the '+K (EA)T*+3

•% ATP molecules 0% input# : output3

•% red +A2 molecules 0to *92AT6E P&*,P&*(.'AT*+3

•+* )*% is produced by glycolysis

The LIK !E"CTIO

O#er#ie$

•Pyruvate from glycolysis is converted to "cetyl Coen%yme " 0acetyl )oA3"hich

enters the Krebs )ycle

•o ATP is generated

•& is released producing reduced "& for *$idative Phosphorylation

•CO' is released

The LIK !E"CTIO ste( by ste(

•)yru#ate09%3 is produced in the cytoplasm by glycolysis

•t is moved by acti#e trans(ort into the mitochondrial matri*

•

A series of chemical changes occur;

o decarbo*ylation 0)*% removed3 by pyruvate decarbo$ylase

o &ehydrogenation 0& removed3 by pyruvate dehydrogenase

o An "cetyl group 0%)3 is produced "hich reacts "ith )oenzyme A to

form "cetyl Co"

•"cetyl Co" is the end product of the 'ink (eaction and is needed for the ne$t stage

of cell respiration; Krebs cycle0also called the Citric "cid cycle3



•note that the )oenzyme A is not used up in the Krebs )ycle but is recycled back to

the link reaction to make another Acetyl )oA molecule 5 thus )oenzyme A acts as

a carrier for the acetyl molecule

The Yield of the Lin+ !eaction

•

o *ne )*% molecule per pyruvate 0"aste product3

•

o *ne 0% carbon3 Acetyl group per pyruvate for Krebs )ycle

•

o *ne reduced +A2 molecule per pyruvate for *$idative Phosphorylation

"cetyl Coen%yme "

)oenzyme A is made up of vitamin B< 0pantothenic acid3# Adenine and (ibose

)oA carries the acetyl group 0as Acetyl )oA3 from glycolysis to Krebs cycle and is

repeatedly recycled

/ost molecules used by living organisms for energy are converted into Acetyl )oA



!es(iration of ats

7ats = 7atty acids and glycerol

-lycerol = triose phosphate for glycolysis

7atty acids = %) chunks = acetyl )oA to Krebs )ycle

n reverse 5 e$cess )arbohydrate can be converted into fats via acetyl )oA

Krebs Cycle O#er#ie$

• Also kno"n as the )itric Acid cycle# it "as discovered in >?@ by &ans Krebs

•Krebs )ycel is a series of ? enzyme controlled reactions that breakdo"n Acetyl )oA

into )*%

•Krebs )ycle occurs in the mitochondrial matri$

•The %) Acetyl molecule is broken do"n into;

o % $ )*% molecules 0"aste product3

o releasing energy to build up %ATP molecules#

o releasing & carried by +A2 0red +A23 and 7A2 0red 7A23 to generate

more ATP via o$idative phosphorylation

Krebs Cycle Ste( by Ste(

•The 0%)3 acetyl group from Acetyl)oA combines "ith 0:)3 o$aloacetate to make

04)3 citrate

•)itrate is decarbo$ylated 0removal of )*%3 and dehydrogenated 0removal of

&ydrogen3 to give a <) compound# )*% and reduced +A2

•7urther decarbo$ylation and dehydrogenation gives the :)arbon compound

o$aloacetate# )*%# reduced +A2# reduced 7A2 and ATP

•The :) o$aloacetate combines "ith a ne" molecule of acetyl )oA and the cycle

starts again hydrogen carriers take & to the electron transport chain

Energy and "T)

Quick revise





Cithout maintenance a building becomes derelict All things become disordered Energy

input is needed to maintain order

S(ecifically, energy is needed for-

•,ynthesis of comple$ molecules eg proteins from amino acids

• Active transport 0c <D of ATP used for this in resting mammal3

•/echanical "ork eg muscle contraction# movement of microtubules# cilia# flagella#

movement "ithin cells

•Bioluminescence and electrical discharge# eg fireflies# electric eel

•/aintenance of F"armG body temperature

The Im(ortance of )hotosynthesis

The source of almost all energy on earth is sunlight

'iving organsisms;

•)onvert light energy to 0stored3 chemical energy

•Build up inorganic )arbon 0)*%3 into organic molecules 0containing )arbon and

&ydrogen3

".TOT!O)/S can use inorganic )arbon to build up molecules# those "hich must use

organic ) sources are /ETE!OT!O)/S

!es(iration

(espiration is the reverse of photosynthesis 5 it is the breakdo"n of organic molecules to

release the stored chemical energy for the cellHs specific needs

Energy is stored organically in the form of glucose 0)4&>%*43 during photosynthesis and

released during respiration



(espiration takes place as a series of small steps for % reasons;

•this allo"s precise control via feedback mechanisms

•it also avoids a sudden release of a lot of energy "hich "ould be difficult to harness

-lucose is a stable compound and the high activation energy must be lo"ered by enzymes

and by raising the energy level of glucose by phosphorylation 0adding phosphate groups3

glycolysis and the krebs cycle

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