CH 5 - MICROBIAL METABOLISM
Stephanie Lanoue
Learning Objectives
5-1
Define metabolism, and describe the
fundamental differences between anabolism
and catabolism.
5-2
Identify the role of ATP as an intermediate
between catabolism and anabolism.
OPENING DISCUSSION
WHAT IS METABOLISM?
Take a moment to formulate your response. You may use google
but answer in your own words.
These chemical reactions provide ________ and create substances
that sustain life.
There are 2 types of chemical reactions that sustain metabolism:
catabolic and anabolic.
CATABOLIC VERSUS ANABOLIC REACTIONS
1.
Catabolism refers to the ______ _______ of complex molecules into
simpler substances. These type reactions usually release energy.
2. Anabolism refers to reactions in which simpler substances are
___________ to form more complex molecules. These type
reactions usually require energy.
CATABOLIC AND ANABOLIC REACTIONS CONTINUED
Metabolism (and metabolic pathways) are determined by _________.
Question - What are enzymes?
Take a minute to google. Try to
formulate a definition in your own
words. Be prepared to share.
ENZYMES
Learning Objectives continued
5-3 Identify the components of an enzyme.
5-4 Describe the mechanism of enzymatic action.
5-5 List the factors that influence enzymatic
activity.
ENZYMES CONTINUED

Chemical reactions ______ enzymes.
Enzymes act as:
Biological catalysts
_________ the rate of reaction
Naming of Enzymes
Enzymes are substrate specific, adding “ase” to the
substance. For example:
Lipases, Lipids
Sucrases, Sucrose
Ureases, Urea
Proteases, Proteins
Dnases, DNA
Dehydrogenase, remove a hydrogen
Phosphatase, remove a phosphate
HOW DO ENZYMES WORK IN CHEMICAL REACTIONS
Steps (see image below)
1 – 2. Substrate contacts the enzyme's _____ site to
form an enzyme-substrate complex
3- 4. _______ is transformed and rearranged into
products, which are released from the enzyme
5. Enzyme is unchanged and can react with other
substrates
Question: What is
a substrate?
Substrate
A – any substance
an enzyme reacts
with
Active site
Enzyme–substrate
complex
Products
ENZYME SPECIFICITY AND EFFICIENCY

Enzymes have ________ for particular substrates
Substrate
Enzyme
Substrate
Figure 5.3b The mechanism of enzymatic action.
COENZYMES AND COFACTORS
Most enzymes consist of two molecular components:
1. A holoenzyme consisting of a ________ portion (or
apoenzyme)
2. And a ___-protein portion (or cofactor). The cofactor can
be an inorganic (or non-carbon based) component. Example:
Iron, zinc, etc.

Or an organic component (also known as a co-enzyme). Example:
 B12
Substrate
Coenzyme
Apoenzy
me
(protein
portion),
inactive
Cofactor
(nonprote
in
portion),
activator
Holoenzy
me
(whole
enzyme),
active
ENZYME ACTIVITY
Factors Influencing Enzyme Activity:
1. ________________
2. pH
Discussion Question – What is pH?
Answer – The measure of a substances
acidity or alkalinity in a solution
ENZYME ACTIVITY

High temperature (40 C) ____________ proteins
Question – What does denaturing mean?
ENZYME ACTIVITY (CONT’D)

pH

H+ concentration (pH) changes protein threedimensional structure (enzyme denaturation)
ENZYME ACTIVITY (CONT’D)

Generally, at _____
temperatures, enzymes
undergo denaturation and loose
their catalytic properties.
And, at low
temperatures,
reaction rates
decrease/ ________.
A NEW DISCOVERY: RIBOZYMES

Prior to 1982, it was believed that only protein
molecules had enzymatic activity.
But researchers working on microbes discovered a
unique type of ____ called a ribozyme.
Ribozymes are ___ protein enzymes in most ways
- they can function as catalysts
- they have active sites that _____ to substrates
- and they are not used up in chemical reactions
But they also:
- cut and splice RNA
- and are involved in protein synthesis at ribosomes
REVIEW QUESTIONS
1. What is special about ribozymes versus regular protein
enzymes?
2. What is an enzyme?
3. What is a catalyst?
ENERGY


Most microorganisms use ___________ (sugars and
starches) as their primary source of cellular
energy.
Sugar (and starch) can therefore be broken down
to produce __________. This is of great importance
in cell metabolism.
NOTE: microorganisms can also catabolize various lipids and
protein for energy production

The breakdown (catabolism) of sugar happens in
different ways:
1.
2.
3.
Aerobic respiration (the Kreb’s Cycle)
Anaerobic respiration
Fermentation
CARBOHYDRATE CATABOLISM
Learning Objectives
5-6
Explain the steps of the Krebs cycle.
5-7
Compare and contrast aerobic and anaerobic
respiration.
5-8
Describe fermentation.
CATABOLISM
Carbohydrate catabolism:
 Microorganisms oxidize carbohydrates as their primary
source of _______
 Glucose – most _________ energy source
 Energy is produced by two processes
1. Cellular Respiration (also known as just Respiration)* - is either
aerobic (occurs in the presence of O2) or anaerobic (without O2)
2. Fermentation (does not require O2 but can happen in its
presence)
*not the same as breathing
OVERVIEW OF CELLULAR RESPIRATION
(RESPIRATION) INSIDE CELLS
The breakdown of carbohydrates to ________
energy
1.
2.
3.
Glycolysis - Intermediate step
Krebs cycle
Electron transport chain
RESPIRATION - STEP 1 GLYCOLYSIS
Happens in the ____________. Requires 2 molecules of ATP to get
started plus glucose (a 6 carbon-chain sugar). Glucose is split into
two, 3 carbon sugars which are then converted into pyruvic acid.
This splitting (oxidation) of glucose into pyruvic acid results in the
additional production of ____ and an energy-containing molecule
called NADH.
Question: What is
NADH ?
An coenzyme that
functions in the
transfer of hydrogen
ions (H-) and electrons
NOTE: Glycolysis is also known as the
Embden-Meyerhof pathway.
RESPIRATION - GLYCOLYSIS (CONT’D)
Pyruvic acid cannot enter the Kreb’s Cycle
___________.
 But it is important because pyruvic acid (thru a
series of steps), is turned into acetyl coenzyme A
(or acetyl coA) which is needed for the Kreb’s
Cycle

FIGURE 5.12 AN OUTLINE OF THE REACTIONS OF GLYCOLYSIS (EMBDEN-MEYERHOF PATHWAY).
RESPIRATION – STEP 2 THE KREB’S CYCLE
In eukaryotes, this happens in the _____________
(within the matrix).
NOTE: in prokaryotes, happens in the _____________.

Krebs cycle (most basic steps):
Pyruvic acid (from glycolysis) is oxidized and
decarboxylation (loss of CO2) occurs
 The resulting two-carbon compound attaches to
coenzyme A, forming acetyl CoA and NADH
 Oxidation of acetyl CoA produces NADH, FADH2, and
ATP, and liberates CO2 as waste

FIGURE 5.13 THE KREBS CYCLE.
Respiration – Step 3
The Electron Transport Chain

Electron transport chain (system)
Occurs in the ________ membrane of prokaryotes;
inner mitochondrial ___________ (cristae) of
eukaryotes
 Series of carrier molecules are oxidized and
reduced as electrons and are passed down the ”chain”

RESPIRATION
THE ELECTRON TRANSPORT CHAIN
These carrier molecules (mentioned from
previous screen) are classified into three main
categories:
1) flavoproteins
2) cytochromes
3) ubiquinones

Take a moment to look at page 123
in your textbook. Answer these
questions now:
1) What are flavoproteins derived
from?
2) Cytochromes are proteins that
contain what important chemical?
3) Ubiquinones are also commonly
referred to as this substance (sold
over-the-counter at drug stores)?
Answers:
1. Flavin (a coenzyme derived
from riboflavin); B2
2. Iron
3. Coenzyme Q
RESPIRATION
AN OVERVIEW OF CHEMIOSMOSIS

Energy released can be used to _________ ____ by
chemiosmosis
Question: What is chemiosmosis?
Electrons (from NADH) pass down the
electron transport chain while protons
(positively charged particles) are pumped
across the plasma membrane.
RESPIRATION – SUMMARY OF ALL 3 STEPS




The final electron acceptor in the electron transport chain
is molecular _________ (O2)
In aerobic prokaryotes, ___ ATP (from the entire process of
all 3 steps - glycolysis, Kreb’s and electron transport chain).
In eukaryotes, 36 ATP are produced.
By-products include ____ and H2O
Unnumbered Figure pg. 126