Cellular Respiration

An Overview of

Cellular Respiration

• Cellular respiration is a set of

metabolic reactions and processes
that take place in cells that converts
nutrients to ATP and releases waste.

• Cells break down glucose (C6H12O6), or a

nutrient that has been converted to
glucose, into carbon dioxide (CO2) and
water (H2O)

• As the molecule breaks down, potential

energy that had been stored in its bonds
is released

• Energy released is transferred to the

high-energy bonds of ATP

• There are 3 pathways for this:

glycolysis, citric acid cycle (Krebs
cycle), and electron transport chain

• This happens in the cytoplasm and the

mitochondria

Step 1: Glycolysis

• Glycolysis literally

means “sugar
splitting”

• It is an anaerobic

process in the cytosol

• Anaerobic means

“without oxygen”

• This is a catabolic

process starting with
glucose (C6H12O6) and
ending with 2 Pyruvic
Acids, 2 NADH, and 2
ATP.

Fate of

Pyruvic Acid

• Pyruvic acid can take 1 of

2 pathways:

• If there is oxygen

available, it will take
the aerobic pathway

• Kreb’s Cycle and

Electron Transport
Chain

• If there is no oxygen

available, it will take
the anaerobic pathway

• Lactic Acid

Fermentation

Step 2: Aerobic

Pathway – KreB’s

Cycle

•

In the presence of
oxygen cells will enter
into the KREB’S
CYCLE – the 2nd
stage of cellular
respiration
•

Pyruvic Acid is
broken down to
form Acetyl CoA
in the inner
chamber of the
mitochondria
(inside the
cristae)

•

Products are 2
ATP, NADH
(energy carrier),
and CO2 as a
waste product.

•

These products will
then enter the next
stage (STEP 3):
Electron Transport
Chain

Step 3:
Aerobic

Pathway –

Electron
Transport

Chain

•

The final stage of cellular respiration is the
Electron Transport Chain

•

This is the goal for cellular respiration - it yields
the highest amount of ATP

•

Takes place across the inner membrane (cristae)

•

Energy carrying molecules NADH and FADH2
donate H+ ions
•

As the number of H+ ions build up it forms a
concentration gradient

•

H+ will then begin to move across the cristae

•

Energy from the ion flow will be transferred
to ATP

•

Products of electron transport are H2O, CO2,
and ~32-34 ATP

Anaerobic
Pathway –
Lactic Acid

Fermentation

•

If no oxygen is present,
cells will utilize the
LACTIC ACID
FERMENTATION
pathway
•

Happens in muscle
cells during
prolonged activity

•

Leads to muscle
soreness

•

Pyruvic Acid will get
broken down to form 2
ATP and NAD+

•

This cycle will continue
until oxygen is available

•

Yields very little energy
output