Download Cell Energy Part 3 – Respiration

NOTES – Cell Energy Part 3
(Cellular Respiration)
Cell Energy Review
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Cell Energy Part 1 – ATP
 ATP is the “energy currency” of the cell
 Cells must regenerate ATP from ADP and P to keep
working
 A constant input of energy (food) is required to power
the ATP cycle
Cell Energy Part 2 – Photosynthesis
 The source of almost all food molecules
 Light energy is converted into chemical energy and
stored in the bonds of high-energy molecules
 These molecules are used to power the ATP cycle and
are used as skeletons to build other molecules
necessary for life
Metabolism – The Chemical
Reactions of an Organism

Metabolism – the set of chemical reactions
that happen in an organism to maintain life
 Allow organisms to grow/reproduce, maintain
structures, respond to environment
 Organized into pathways, where one chemical
is transformed through a series of steps into
another chemical
 Two categories: catabolism and anabolism
Metabolism – The Chemical
Reactions of an Organism
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Catabolism – metabolic reactions that release
energy by breaking down complex molecules into
simpler compounds
 Ex - Cells break down glucose to power the
ATP cycle (cell respiration)
Anabolism – metabolic reactions that store
energy by building simpler compounds into more
complex molecules
 Ex - Photosynthesis
Glucose-Glycogen Metabolism
How do cells use food molecules,
such as glucose, to produce ATP?
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Glycolysis – process where glucose is
broken down into 2 pyruvic acid molecules
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Takes place in cytoplasm of all cells
Requires glucose, 2 ATP, and NAD+
Produces 2 pyruvic acid, 4 ATP, and 2
NADH
Glucose + 2 ATP + NAD+  2 pyruvic acid +
4 ATP + 2 NADH
Net gain of 2 ATP molecules
Glycolysis – What happens?
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4 e- are removed from
glucose and transferred to
2 NAD+ which become 2
NADH
NAD+ must be present to
accept e- from glucose,
otherwise glycolysis cannot
take place
Small overall energy yield
(2 ATP), but extremely fast
process
After a few seconds, all of
a cell’s available NAD+ is
used up
What happens when there is no
more NAD+?
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Cells need a way to convert NADH back
into NAD+
How they do this depends on the amount
of oxygen present in the cell
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Insufficient oxygen = fermentation
Plentiful oxygen = aerobic respiration
Fermentation
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Fermentation – process where e- from
NADH are passed back to pyruvic acid
molecules, producing NAD+
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Keeps glycolysis going
Anaerobic process – does not require oxygen
Pyruvic acid molecules are changed into new
products
Most cells perform some type of fermentation
2 Common Types of Fermentation
1. Alcoholic Fermentation – process where
pyruvic acid accepts e- from NADH
producing ethyl alcohol, CO2, and NAD+
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pyruvic acid + NADH  ethyl alcohol + CO2 +
NAD+
Performed by yeast, plants, some bacteria
Used to produce alcohol in wine, beer, etc.
Used to make bread rise
Honey Wheat Sandwich Bread
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The holes in the bread are made by bubbles of CO2 in the dough
The alcohol produced by the yeast boils away in the oven
Rustic Bread
Italian Bread
French Bread
Ciabatta Bread
Plain and Sesame Bagels
Cinnamon Raisin Bagels
Marble Rye Bread
Casatiello Bread
Sourdough Bread
Pane Siciliano (Sicilian Bread)
Oatmeal Bread
Pizza
Pita Bread
Soft Pretzels
Bretzel (Bavarian Pretzel) Rolls
Hard Rolls (Kaiser Rolls)
2 Common Types of Fermentation
2. Lactic Acid Fermentation – process where
pyruvic acid accepts e- from NADH producing
lactic acid and NAD+
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pyruvic acid + NADH  lactic acid + NAD+
Performed by animals, some bacteria
Used to produce cheese, sour cream, yogurt
Responsible for quick bursts of energy in
animals (Ex. Sprinting)
Different Types of Fermentation
Lactic Acid Fermentation and Exercise
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Low oxygen = body converts pyruvic acid
into lactic acid = continued glycolysis
After 1 to 3 minutes, lactic acid
concentration in muscles is high
High lactic acid = burning sensation in
muscles & less glucose breakdown
You stop = muscle damage is prevented
Rest + oxygen = lactic acid  pyruvic acid
Remember…
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The goal of fermentation is to generate
NAD+ to keep glycolysis going in low
oxygen conditions
The e- from NADH are passed back to
pyruvic acid molecules, generating
different products and NAD+
If there is plenty of oxygen available, in
most cells a different process occurs
Cellular Respiration – Overview
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After glycolysis about 90% of the chemical
energy available in glucose is still unused
The energy is locked up in the pyruvic acid
molecules
In the presence of plentiful oxygen, most
cells can break down pyruvic acid
molecules further, generating much more
ATP
Cellular Respiration
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Cellular Respiration – process that
releases energy by breaking down food
molecules (glucose) in the presence of
oxygen
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6 O2 + C6H12O6  6 CO2 + 6 H2O + 36 ATP
Aerobic process – requires oxygen
In eukaryotic cells, respiration takes place in
mitochondria
In some prokaryotic cells, the entire cell
functions like a single mitochondrion, allowing
respiration to be carried out
Cell Respiration – What happens?
Cell Respiration is a 3-Step process:
1. Glycolysis – begins break down of glucose in
cytoplasm into pyruvic acid
2. Krebs Cycle – breaks down pyruvic acid into CO2,
releasing energy (in mitochondria)
3. Electron Transport Chain – generates ATP in
mitochondria using products from the Krebs Cycle
Step 1 - Glycolysis
Structure of Mitochondrion
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Outer membrane –
simple phospholipid
bilayer
Inner membrane –
highly folded
phospholipid bilayer,
site of electron
transport chain
Matrix – inner
portion of
mitochondrion, site of
Krebs Cycle
The Krebs Cycle (Citric Acid Cycle)
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2nd stage of cell respiration where pyruvic
acid molecules are broken down producing
CO2, NADH, FADH2, and ATP
2 pyruvic acid  6 CO2 + 8 NADH + 2 FADH2 +
2 ATP
NADH & FADH2 carry e- to the final stage of
cell respiration
CO2 is a waste product
Step 2 – Krebs Cycle
The Electron Transport Chain (ETC)
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3rd stage of cell respiration where e- from the
Krebs Cycle are used to convert ADP into ATP
e- are passed from NADH and FADH2 to a
series of carrier proteins that are embedded in
the inner membrane of a mitochondrion
As the e- pass from one protein to the next, H+
ions are pulled from the matrix into the
intermembrane space of the mitochondrion
e- flow back into the matrix through ATP
sythase proteins, which use the energy to
convert ADP into ATP
Using e- to make ATP
What happens to the electrons?
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As e- reach the end of the chain, they must go
somewhere, or else the chain cannot accept new
e- from the Krebs Cycle
Oxygen molecules accept the e-, and
immediately bond H+ ions, forming H2O
molecules
As long as there is plentiful oxygen, NADH is
continually converted to NAD+ by the ETC,
allowing glycolysis to continue
If oxygen is not brought in quickly enough, the
chain slows down, NAD+ is quickly used up, and
fermentation begins
Step 3 – Electron Transport Chain
How much energy does cellular
respiration provide?
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Overall ~ 36 ATP
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Glycolysis =
Krebs Cycle =
ETC
=
2 ATP
2 ATP
34 ATP
2 ATP are used up transporting pyruvic
acid into mitochondria
36 ATP represents about 40% of the
energy released from glucose, the other
60% is converted to heat energy
A variety of
molecules can
be used by
cells for cell
respiration
What is the relationship between
photosynthesis and cellular respiration?
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They are opposite processes
 Photosynthesis stores energy in glucose (it is
an endergonic anabolic reaction)
 Respiration releases energy by breaking down
glucose (it is an exergonic catabolic reaction)
 The products of photosynthesis are the
reactants of cell respiration
 The products of cell respiration (excluding the
ATP) can be recycled by photosynthesis
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Energy enters an
ecosystem as light
It is converted to
chemical energy
(glucose, then
ATP)
Energy leaves the
ecosystem as
heat, and must
continuously be
replaced
Cell Energy Review
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Cells use ATP for energy (ATP Cycle)
Cells generate ATP by releasing energy
from food molecules (glucose) during the
processes of cell respiration and
fermentation
Food molecules (glucose) are generated
during the process of photosynthesis