Transcript Ch.24Pt.2_001

Regulatory mechanisms for glycolysis include
1. Allosteric regulation
2. Hormonal control (via enzyme phosphorylation)
3. Substrate level control
4. Covalent modification (phosphorylation via the
kinase cascade)
Key regulatory enzymes in the
glycolytic pathway include:
1. Hexokinase
substrate-level regulation by glucose-6-phosphate
2. Phosphofructokinase
allosteric regulation by AMP, ADP, ATP, citrate, and
fructose-2,6 bisphosphate
3. Pyruvate kinase
allosteric regulation by D-fructose1,6-bisphosphate,
ATP, acetyl-CoA, and phosphorylation
Three common fates of pyruvate
What happens to the end products of
Glycolysis if O2 is present for
the completion of cell respiration?
Formation
of acetyl CoA:
NADH forms,
is used at ETC,
then oxidized
back to NAD+
CO2 is formed
as a waste product
Formation of acetyl CoA
Catalyzed by an enzyme complex:
pyruvate dehydrogenase
• First the carboxyl group is split off of the 2
pyruvates as carbon dioxide
• Then remaining two-carbon acetyl fragment is
oxidized and electrons transferred to NAD+
making NADH
• Finally, the oxidized two-carbon acetyl group
is attached to coenzyme A
• Creates acetyl CoA
In the absence of O2
Glycolysis alone will
still produce some
ATP.
Lactic acid
(lactate)
fermentation
Different organisms
follow 1 of 2 different
metabolic pathways:
each will regenerate
NAD+
Ethanol
fermentation
Fermentation: Yeasts (single-celled eukaryotic fungi) and some bacteria can
also do a different type of anaerobic respiration when O2 isn’t readily
available.
Not very efficient: it’s just glycolysis with an extra bit
added to recycle the NADH back to NAD+.
Alcoholic fermentation
Yeast excretions! Yum! Yum!
Yeasts are facultative anaerobes:
they switch to fermentation when O2 levels are low.
• In alcoholic fermentation, 3 C pyruvic acid is
converted to CO2 and ethanol (C2H5OH)
– This recycles NAD+ to keep glycolysis working
2 Ethanol
2 Pyruvic
acid
Glucose
released
GLYCOLYSIS
Pyruvic acid
decarboxylated
forming CO2 and ethanol
NADH molecules oxidized
back into NAD+.
Ethanol is the
oxidizing agent
helping NADH
get oxidized
back to NAD+.
Alcoholic fermentation
Yeast is allowed to do anaerobic alcohol fermentation
to produce ethyl alcohol.
Above ~17% alcohol content the yeast die off.
• In lactic acid fermentation, pyruvic acid is
converted to lactic acid
– As in alcoholic fermentation, NADH is recycled
by oxidation back to NAD+
• Lactic acid fermentation is used to make cheese,
yogurt, kefir, sauerkraut, pickles, poi, & wine
Glucose
GLYCOLYSIS
2 Pyruvic
acid
2 Lactic acid
Our muscle cells do this if needed.
Skeletal muscle tissue is composed of
2 general types of muscle fibers:
fast-twitch and slow-twitch
•Slow -twitch muscle fibers used for:
- steady, low-intensity, repetitive contraction.
•Do not tire easily – used for endurance.
•Used for low-intensity, high-endurance activities:
- long distance running.
Fast-twitch muscle fibers used for:
- heavy work, strength and power.
Contract quickly, providing short bursts of energy.
High-intensity, low-endurance activities:
- sprinting, weightlifting, or shot-putting.
Fast-twitch muscle fibers become exhausted quickly.
White meat and dark meat?
Chicken or
turkey:
White meat is
fast twitch
muscle.
Dark meat is
slow twitch
muscle.
It is dark
because it
contains
myoglobin.
Slow twitch
muscles:
wing & leg - long
term endurance.
Breast is usually
fast twitch quick response.
Wild animals tend
to have more slow
twitch muscle.
Why do athletes breath heavily
before an event?
Strenuous bursts of muscle activity produce
high levels of lactic acid as glucose is broken
down for energy anaerobically.
Causes muscle cramp/fatigue.
To counteract this,
rapidly deep breathing for 30-40 seconds will
– introduce temporary alkaline condition
– helps to neutralize the acidity arising from
lactic acid.
Lactic acid fermentation
Running from danger, pushing beyond
body’s ability to provide O2 to muscles
– must switch to anaerobic fermentation
CH3CHOHCOOH
During Fast-twitch muscular exercise:
• Increase O2 supply by dilating blood vessels in muscles –
increases blood flow
• Running from danger pushes beyond bodies’ability to
provide O2
• Muscles kick over to anaerobic fermentation.
• Muscles continue to break down glucose to liberate some
energy for a short time
• This partial breakdown produces lactic acid
• When lactic acid reaches certain levels in the muscles and
blood - fatigue occurs
Oxygen debt: waste not, want not!
Why do you keep breathing hard after you
stop exercising?
Huffing & puffing after exercise helps repay
the “oxygen debt”
• Break down the lactic acid
– get the rest of the energy out of the molecules
• Once adequate O2 is available, lactic acid must be
catabolized
– Broken down into CO2 and H2O
• Pay back any oxygen that has been borrowed from
hemoglobin, myoglobin, air in the lungs, and body fluids
• Hard breathing and sufficient discomfort stops muscle
activity until homeostasis is restored
All 3 fates of pyruvate from glycolysis provide
for the regeneration of NAD+ from NADH.