M C A T P r e p . E x a m PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor Insert figure 6.1 here 1 Lecture 2 Enzymes
Feb 25, 2016
MC
AT
Prep. Exam
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Insert figure 6.1 here
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Lecture 2
Enzymes
Cells break down organic molecules to generate energy (ATP)
Energy is used for: growth, cell division, contraction, secretion, and other functions
Metabolism is all the chemical reactions that occur in an organism
Chemical reactions provide energy and maintain homeostasis:
metabolic turnover growth and cell division special processes, such as secretion, contraction, and
action potential propagation
Metabolism
Metabolic reactions could be either catabolic (catabolism) or anabolic (anabolism)
AnabolismAnabolism is the formation of new chemical
bonds to produce new organic moleculesNew Organic molecules are needed for/to:
Performance of structural maintenance and repairsSupport of growth Production of secretionsBuilding of nutrient reserves
Metabolism
CatabolismCatabolism is the metabolic reactions that
breaks down organic substrates in order to release energy
Catabolic reactions occur in series of stepsCatabolic reactions generate energy by breaking
down large molecules to small moleculeSmall molecules enter Mitochondria to release more
energy
Metabolism
Cells provide small organic molecules for their mitochondria
Mitochondria produce ATP that is used by the cell to perform cellular functions i.e. cells feed mitochondria nutrient and in return mitochondria provide the cells with energy (ATP).
Mitochondria accept only specific organic molecules e.g. Pyruvic Acid, acetyl coenzyme A
Large organic nutrients (e.g. Glucose) are broken down into smaller fragments (e.g. Pyruvic Acid) in the cytoplasm, before they could enter mitochondria
Cells and Mitochondria
Mitochondria breaks down the molecules to carbon dioxide, water, and generates more energy (ATP) via two pathways: 1. TCA cycle 2. Electron transport system (ETS)
Cells and Mitochondria
Glycolysis is the process of breakdown of glucose into pyruvic acid
Glycolysis occur in the cytoplasm and it requires: One molecule of glucose + 2 ATP + 4ADP + 2NAD +
inorganic phosphate + cytoplasmic enzymes Glycolysis generates:
Two pryruvic acid + 4ATP +2ADP + 2NADH The net gain of ATP of glycolysis is 2ATP (it produces 4ATP
but two of the ATP are used)
Carbohydrate Metabolism
Aerobic metabolism (cellular respiration) Pyruvic acid will enter mitochondria and generate more ATP via
TCA cycle and ETS Two pyruvates = 34 ATP• The chemical formula for this process is
C6H12O6 + 6 O2 6 CO2 + 6 H2O
• Anaerobic metabolism (fermentation)• In the absence of oxygen pyruvic acid will not enter mitochondria• Pyruvic acid will go through the process of anaerobic respiration
and will be converted into Lactic acid• This process dose not generate any ATP
Carbohydrate Metabolism
Glycolysis: Steps in Glycolysis1) Glucose (a 6 carbon molecule) enters
the cell
2) As soon as glucose is inside the cell, a
phosphate is added to carbon number
6, and the new molecule is called
glucose 6 phosphate. This reaction is
called phosphorylation and it requires
one ATP, enzyme called hexokinase.
3) Glucose 6 phosphate goes through
the second phosphorylation reaction
and a phosphate is added to carbone
number 1. The new molecule produced
as a result is called Fructose 1,6
Bisphosphate
4) The Fructose 1,6 bisphosphate (6
carbon molecule with phosphates
attached to carbon 1 and carbon 6) will
split into two 3 carbon molecule:
1) Glyceraldehyde 3 phosphate
2) Dihydroxyacetone
5) Each 3 carbon molecule will become a
pyruvic acid through number of steps
(see the diagram on the left)
The two pyruvic acid molecules will enter mitochondria In the mitochondria pyruvic acid will join
Coenzyme A (CoA) to form acetyl CoA before entering the TCA cycle.
TCA cycle will break down pyruvic acid completely
Decarboxylation Hydrogen atoms passed to coenzymes
Oxidative phosphorylation
Mitochondrial ATP Production (cellular respiration)
The TCA Cycle Steps
1) Pyruvic acid combine with coenzyme A to
form acetyl coenzyme A. This reaction
releases NADH and carbon dioxide
2) Acetyl is a 2 carbon molecule. Acetyl-
coenzyme A will give the two carbon
molecule (acetyl) to the 4 carbon molecule
(oxaloacetic acid)
3) The 4 carbon molecule will become a 6
carbon molecule (citric acid)
4) Citric acid will go through number of steps
and will become back a 4 carbon molecule .
5) The TCA cycle will begin with formation of
citric acid and end with formation of
oxaloacetic acid.
6) The TCA cycle will run twice for one
molecule of glucose, because one molecule
of glucose produces two pyruvic acid and
each pyruvic acid turns once cycle
7) Each cycle of TCA will generate 3NADH, 1FADH2,
and 1GTP
8) NADH and FADH2 will enter the electron transport
system and generate ATP
9) One NADH = 3ATP and one FADH2 = 2ATP (see
ETS)
The TCA Cycle
• Pyruvic acid (a 3 carbon molecule) requires NAD and Coenzyme to form Acetyl coenzyme A
• This reaction will generate NADH, carbon dioxide and acetyl coenzyme A. Notice that pyruvic acid is a 3
carbon molecule , in this reaction one of the carbons was released as carbon dioxide is formed and two carbon
is left as a acetyl
• Acetyl coenzyme A will transfer the acetyl to oxaloacetic (a 4 carbon molecule) acid and
coenzyme A will becomee free. 4 carbon molecule from oxaloacetic acid and two carbon from
acetyl will generate a 6 carbon molecule (citric acid)
• The free coenzyme A will be reused by another pyruvic acid.
• Citric acid will go through number of steps (e.g. it will become isocetric acid then ketoglutaric acid and
so on)and eventually will become oxaloacetic acid
The TCA Cycle
• Citric acid will go through number of steps (e.g. it will become isocetric acid then ketoglutaric acid and so
on)and eventually will become oxaloacetic acid
Requires coenzymes and consumes oxygenKey reactions take place in the electron transport
system (ETS)Cytochromes of the ETS pass electrons to oxygen,
forming waterThe basic chemical reaction is:
2 H2 + O2 2 H2O
Oxidative phosphorylation and the ETS
Electron Transport System (ETS)
ETS is sequence of proteins called cytochromes
Each cytochrome has:A protein - embedded in the inner membrane of
a mitochondrion, A pigment
Electron Transport System (ETS)
STEP1: coenzyme strips a pair of hydrogen atoms from a substrate molecule.
STEP2: NADH and FADH2 deliver hydrogen atoms to coenzymes embedded in the inner membrane of a mitochondrion.
STEP3: Coenzyme Q accepts hydrogen atoms from FMNH2 and FADH2 and passes electrons to cytochrome b.
STEP4: Electrons are passed along the electron transport system, losing energy in a series of small steps. The sequence is cytochrome b to c to a to a3.
STEP5: At the end of the ETS, an oxygen atom accepts the electrons, creating an oxygen ion (O–). This ion has a very strong affinity for hydrogen ions (H+); water is produced.
Oxidative Phosphorylation
Per molecule of glucose entering these pathwaysGlycolysis – has a net yield of 2 ATP Electron transport system – yields approximately
28 molecules of ATPTCA cycle – yields 2 molecules of ATP
Energy yield of glycolysis and cellular respiration
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
The Energy Yield of Aerobic Metabolism
A Summary of the Energy Yield of Aerobic Metabolism
GluconeogenesisSynthesis of glucose from noncarbohydrate
precursors such as lactic acid, glycerol, amino acids Liver cells synthesis glucose when carbohydrates are
depleted
GlycogenesisFormation of glycogen
Glucose stored in liver and skeletal muscle as glycogen Important energy reserve
Synthesis of glucose and glycogen
Key Concepts
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Process Location Molecules produced
ATP NADH FADH CO2
Glycolysis cytoplasm 4 2 0 0
Fermentation/anaerobic respiration
cytoplasm 0 0 0 0
Transition/Intermediate steps (Pyruvate to Acetyl CoA)
Mitochondria 0 1 0 1
TCA Mitochondria 1 3 1 2
ETS Mitochondria (inner Mitochondrial Membrane
NADH = 3ATPFADH2 = 2ATP
0 0 0
Carbohydrate Breakdown and Synthesis
LipolysisLipids broken down into pieces that can be
converted into pyruvateFor example triglycerides are split into glycerol
and fatty acidsGlycerol enters glycolytic pathwaysFatty acids enter the mitochondrion
Lipid catabolism
Beta-oxidation Breakdown of fatty acid molecules into
2-carbon fragmentsLipids and energy production
Used when glucose reserves are limited
Lipid catabolism
Beta Oxidation• In beta oxidation long chain of fatty acids are broken down into fragments of two carbons.
• Say we have a fatty acid chain that is 18 carbon long. During beta oxidation fragments of two
carbon will be removed from the chain of fatty acid. So after the first round of reaction (as
shown in the figure) a fatty acid chain that is 16 carbon long will remain, after the second
round of reactions a fatty acid chain that 14 carbon long will remain
• For each round of reaction two carbon will be removed from the chain. As two carbons are
removed from the chain, NADH, FADH2 and Acetyl CoA will be generated.
• The steps in beta oxidation:
1) Coenzyme A bind to fatty acid. This step requires one ATP
2) This reaction will prepare fatty acid for beta oxidation and generate a fatty acid attached to
CoA
Beta Oxidation
3) The first round of beta oxidation will generate one NADH, one FADH2 and one Acetyl
CoA
4) Acetyl CoA will enter TCA cycle and generate 3NADH, 1FADH and 1GTP. 3NADH =
9ATP, 1FADH2 = 2ATP, and GTP = 1ATP.
Beta Oxidation5) NADH and FADH2 will enter the ETS and generate ATP
1NADH = 3ATP
1FADH2 = 2ATP
Summary :
one round of beta oxidation will generate :
NADH = 3ATP
FADH2 = 2ATP
Acetyl CoA = 12ATP
So if each round of beta oxidation produces 17ATP, then one molecule of fat will
produce a lot more ATP (energy) than one molecule of glucose. Remember that
glucose produced 2ATP in glycolysis and 34/36ATP via TCA and ETS
If other sources inadequate, mitochondria can break down amino acids TCA cycle
The first step in amino acid catabolism is the removal of the amino group (-NH2)
The amino group is removed by transamination or deamination Transamination – attaches removed amino group to a
keto acid Deamination – removes amino group generating NH4
+
Proteins are an impractical source of ATP production
Protein Metabolism
Amino acid catabolism
Oxidation, Reduction, and Energy Transfe
Enzymatic steps of oxidative phosphorylation involve oxidation and reduction
The loss of electrons is oxidation; the acceptance of electrons is reduction
Electron donor is oxidized (loss energy) and electron recipient reduced (gain energy)
Reduced molecule does not acquire all the energy released by oxidized molecule – thus some energy is released as heat, and formation of ATP
Coenzyme acts as intermediary that accepts electrons from one molecule and transfer it to another
In Kreb Cycle NAD and FAD remove hydrogen atoms from organic substrates
NADH and FADH2, the reduced forms of NAD and FAD, transfer their hydrogen to other coenzymes
Protons are released, and the electrons, which carry the chemical energy, enter a sequence of oxidation–reduction reactions
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