P Y R U V A T EO X I D A T I O N
a n d t h e K R E B SC Y C L E
A f t e r g l y c o l y s i s ,f o r a e r o b i c r e s p i r a t i o nt o c o n t i n u e ,t h e 2 p y r u v a t e
m o l e c u l e sm u s t m o v e f r o m t h e
and enterthe
, w h e r e t h e s e c o n da n d t h i r d s t a q e s o f c e l l
r e s p i r a t i oonc c u r .
D r a wa n d L a b e lt h e S t r u c t u r e
of theMitochondrion:
- o u t e rm e m b r a n e
- i n n e rm e m b r a n e
- matrix
- i n t e r m e r n b r a nsep a c e
- cnstae
P y r u v a t eO x i d a t i o n
. T h i s i s t h e s e c o n ds t a q ei n
.
P y r u v a t em o l e c u l e se n t e rt h e
help of a
o f t h e m i t o c h o n d r i owni t h t h e
(two words) to
p a s s t h r o u g ht h e o u t e ra n d i n n e rm i t o c h o n d r im
a le m b r a n e s
. C o e n z v m e - Aa t t a c h e st o t h e
m o l e c u l ew
, h i c h e n a b l e si t t o b e
r e d u c e da n d b e c o m e s
. The remainino
group of the pyruvate
is
, while
g r o u pi s r e m o v e da s w a s t ei n t h e f o r m o f
. The resultinq
o r o d u c its
. W h e n t h e r ei s
C y c l et o c o n t i n u e
n e e d e dt,h i sa c e t v l - C o A
e n t e r st h e K r e b s
(aerobic/a
naerobic) respiration
Krebs Cycle
s t a g ei n c e l l u l a r e s p i r a t i o nt h, e K r e b sC y c l ei s a
Definition the
c y c l i c a ls e r i e s o f _ r e a c t i o n si n o r d e r t o t r a n s f e r
f r o n ro r g a n r cr n o l e c u ! eisn t ou s e a b l ef o r m sf o r t h e c e l l ,s u c h a s
while at the same time
and
C O za s a w a s t eP r o d u c t .
F o r e v e r yg l u c o s em o l e c u l et h a te n t e r sg l y c o l y s i s_, c y c l e so f K r e b s
OCCUT.
o f t h e m i t o c h o n d r i oann d ,a s
T h e K r e b sC y c l eo c c u r si n t h e
i n g l y c o l y s i se, a c h r e a c t i o ni s c a t a l y z e db y a s p e c i f i c
f o r t h a tr e a c t i o n .
1.
/)
Z.
a
t+.
5
f r o mp y r u v a t eo x i d a t i o n
T h e K r e b sC y c l eb e g i n sw i t h
(which already exisfs in the
r e a c t i n gw i t h
The CoA is removed.
matrix\to form
Citrate undergoes an
to
form
to Decome
T h r o u g ha r e d o xr e a c t i o ni,s o c i t r a ties
a n d a n N A D ' i o n f r o mt h e m a t r i x
, gaining electronsto form an energy
IS
coenzyme,
A l p h a - k e t o g l u t a r aftoer m s
a n d b e i n go x i d i z e db Y
is removed.
b y b i n d i n gw i t h C o A
, while
w h i c h i s r e d u c e dt o
. but not before
S u c c i n v l - C o lAo s e si t ' s C o A t o b e c o m e
s k e p l a c e . A p h o s p h a t ef r o m t h e m a t r t x
s o r n e p h o s p h o r y l a t i o nt a
d i s p l a c e st h e C o A , g u a n o s i n ed i p h o s p h a t(eG D P )i s p h o s p h o r y l a t e d
to become
, t h e n t h e p h o s p h a t eg r o u pi s t r a n s f e r r e tdo
to create
6
A n o t h e ri o n f r o mt h e m a t r i x_, , _ , o x i d e ss u c c i n a t et,o f o r ma n o t h e r
T h i s r e s u l t s s u c c i n a t eb e c o m i n g
energy coenzyme,
to fornr
is addedto fumar-ate
7
B.
M a l a t eu n d e r g o e so n e m o r e r e d o xr e a c t i o nw i t h N A D - t o p r o d u c e
, r e a d Yf o r t h e c Y c l et o
NADH ano
b e g t na g a i n .
ln Summary:
p y r u v a t eO x i d a t i o np r o d u c e s_
contribution.
m o l e c u l eo f N A D H f o r i t s e n e r g ) /
FADH2
ATP and
N A D H ,_
T h e K r e b s c y c l e p r o d u c e s_
m o l e c u l e s f o r e a c h m o l e c u l eo f g l u c o s e t h a t e n t e r s c e l l u l a r
respiratton.
Student Worksheet
LSM 2.2-3
The Krebs Cycle
F i l l i n t h e m o l e c u l e s c r e a t e d o r r e l e a s e dd u r i n g t h e K r e b s c y c l e .F i l l i n t h e b l a n k s o f t h e s u m m a l e s .
Pyruvate Oxidation
entersthe mitochondrion
from the cytoplasm.
One -
atom is removedvia ___
and
ts removeoustnq _
becomesattachedto the remaintng__
creatrng
atoms,
Krebs Cycle
which then enlersthe Krebscycle
entersthe cycleand then combines
wrth -'-
to makethe six-carboncompound
Duringrhe eightstepsof the Krebscycle,
oo€
undergoesa nurnberof reactrons,
releasing
and _
_
i n a n u m b e ro f s t e p s ._
eventually
corrverledinlo -'.
o€
.-
ts
so i1can be
u s e da g a i nd u r i n gt h e K r e b sc y c l e .
C o A -S H
o€€ooo
o+o€
o+€30€
----ll
r-.--l*-'/
\F=*fl
u --?,
+t-f
oo€
c o AS H
o
oo€o
CoA- SH
-
oo€oo
Nn
k-
ooo€
\- oo0o
Products of the Krebs Cycle
l. _,._
?. __
rs releasedas waste
and __
m o v e l o l h e n e x l s t a g e o f c e l l u l a rr e s p i r a l r o |
3 . E r r e r q yt s r e l e a s e di n t h e l o r r n o l - .
r r l o l e c t l l e os f , , , , ^ r . , , i , . t ^ - , . t ^
A g l u c o s e n t o l e c u l ep r o d u c e s -
b e c a L t s et w o n r o l e c u l e so f -
a r e c r e a t e or r o n r
^ t
C o p y r i g h t@ 2 0 0 1 N e l s o n
( 1t.i1,11
I 1 ( cllular lle\JltJirrtur J5
The
Kreb's
Cycle*
(*oko the Citric Acid Cvclt nnd the Triinrboxvlic
A c i c lC v c l c )
a)
The pyrur''ate produced bv glvcolysis in the cytoplasm is transported into the
mitochondrion h'here it immediatelv undergoesoxidative delarboxvlation
a s i t i s t r a n f o r m e d i n t o a c e t r , l - C o A . D e t a i l s r . v h a th a p p e n s i n t h i s
p r e l i m i n a n ' s t a g eb e f o r et h e K C a c t u a l l r b
. egins.
b)
W h a t d o e s o . t i d o t i i ' Ld' e c n r b o x t l l n t i om
n e a n ? W h a t a r e t l r e c o - e n z v m e so f
t h i s i n i t i a l r e a c t i o n w ' i t h r n t h e m i t o c h o n d r i o n ? W h a t ' s s o s p e c r a la b o u t
acetyl-CoA?
)
How many carbons were in the originai substateof glycoll,sis _ i.e. glucose?...in
the glycolysis products - i.e. pv.r.'ite?...in the oxidijed product of the reactron
; u s t p r e c e d i n g t h e K C - i . e . a c e t v i - C o A ? A t t h i s p o i n t h o w m a n y c a r b o n sh a v e
been "lost" since the very frrst itep with the glucose molecule?...Wn"r. did
they
8o?
a
.).
The-acetvlpart of the acetvi-CoA bonds u,ith oxaloacetateto begin the Kreb's
Cvc.lepathway. How many carbons are there in the acetvl grotipZ...ln the
o x a l o a c e t a t em o l e c u l e ? . . . i nt h e p r o d u c t o f t h i s r e a c t i o n ,c i t r i c a c i d ?
4.
How many carbox)rlgroups are there in the citric acid molecule?
5. The first
s t e p s o f K C i n v o l v e i n t e r n a l b o n d i n g r e a r r a n g e m e n r sw i t h i n t h e
.two
c i t r i c a c i d m o l e c u l e . T h e i s o m e r t h a t r e s u l t si s c a l l e d i s o c i t r a t e . T h e n e x t t w o
s t e p s a f t e r t h a t i n v o l v e o x i d a t i v e d e c a r b o x l , l a t i o n .W h a t a r e t h e b t ' - p r o d u c t so f
t h e s e t r v o s t e p s ? H o n , r r l . 1 n 1c'a r b o n sa r e r e m a i n i n g r n t h e s r r c c i p r , l - b o A ?
6'
A T P i s p r o d u c e d r n t h e n e x t s t e p i n K C , a n e x o t h e r m i cr e a c t i o n f r o m r t , h i c h t h e
energv is initiallv removed by the co-enzvme CDP. How does this chemrcal
e n e r g ) ' g e t p a s s e do v e r t o A T p ?
S u c c i n a t ei s o x i d i z e d a n d t r a n s f o r m e di n t o f u m a r a t e i n t h e n e x t s t e p . B u t N A D + i s n o t t h e o x i d i z i n g c o - e n z y m et h r s t i m e . W h a t i s t h e m o l e c u l e
that
r e m o v e s t h e h v d r o g e n a t o m s ( w i t h t h e i r e x c r t e de l e c t r o n s ) ?
8 . A f t e r a n i n t e r m e d i a t es t e p i n w h i c h a n , a t e r m o l e c u l e i s a d d e d t o t h e f u m a r a t e
t o p r o d u c e m a l a t e , t h e l a s t s t e p r n t h e K C o c c u r s- a n o t h e r o x i d a t i o n
reaction.
where did the 2 eiectrons and protons (aka h-r'drogenatoms)
go this time?
What is the product of this reaction? Hon, -unr, Ja.bo.rs
doei it have? What
d o v o u n o t i c e a b o u t t h i s " f i n a l p r o d u c t " \ / e r s u si h e b e g i n n i n g
of KC?
9.
s t a r t i n g w i t h o n e p y r u v a t e a n d e n d i n g r t , i t h t h e o x a l o a c e t a t eh, o r . v
man'
c a r b o n sw e r e r e m o v e d ( a s c o 2 ) ? H o r r i m a n v A T p ' s \ \ , e r e
produced? H;*,man'
N A D H ' s ? H o w j m a n v F A D H 2 ? o ' e r a l l * , h a t i r a p p e n e dt o t h e
carbons,
h v c i r o g e n s ,a n d o x y g e n s o f t h e p y r u v a t e m o l e c u l e ?
1 0 C o r r s i d e r i n gt h a t t l - " . : \ \ / e r - e2 p v r u v a t e sp r o d u c e d b r 1 g l u c o s e ,n ' h a t
is the total
production of the Kreb s Cvcle pathrn,al.?
ll
w h a l h a p p e n s . t ] . 9 . * 't n t h e h i g h - e l " t g ) , e l e c t r o n st h a t . u v e r e, , c a p t u r e d ,
bi, NADH
a n d F A D H 2 ? ( W h e r e d t d t h e s ee l e c t r o n so r t g i n a t e ? )