Fundamentals of Metabolism I & II lectures

Question 1

What a cell does to exist?

What is necessary for it?

Answer 1

Cells continually build
up & break down molecules & expend cellular energy.

Existence depends on
CONTINUOUS PROVISION OF ENERGY …

FOR maintenance of
structure & function

Question 2

Cellular energy
enables:

Answer 2

• mechanical
• transport
• chemical

Run out of energy - cells die.

Question 3

In photosynthetic organisms…

Answer 3

1. light energy is used to synthesise carbohydrates from CO2.

2.Carbohydrates (& other
fuels) are metabolised
to CO2 & H2O providing
energy, for example as
ATP.

3. These metabolic
   pathways are very
   similar in bacteria & us!

Question 4

What is Metabolism?

Answer 4

For energy supply,
essentially it is the
conversion of food
into energy &/or
components required by cells, & thus the body, to
function

Question 5

2 TYPES OF METABOLISM?

REQUIRES?

Answer 5

1. Catabolism
2. Anabolism

Requires enzymes

Question 6

Basis of metabolic reactions…

Answer 6

Conversion of substrate(s) (reactants) into product(s).

Substrate (S) –> Product (P)

Question 7

Even the simplest reactions need enzymes…

Answer 7

— Hydration of carbon dioxide, spontaneous rate about 2-5 molecules per minute, add an enzyme…

CO2 + H2O —carbonic anhydrase –>H2CO3

1 molecule of carbonic anhydrase hydrates
100 000 CO2 every second (blood pH)

Question 8

Characteristics of Metabolic pathways = 4

Answer 8

1. multistep: Several reactions linked form a metabolic pathway

2.open systems…Product of each reaction becomes substrate for next, so reactions don’t reach equilibrium, & system is in
continual flux.

3 .Often, the product of one reaction can influence another reaction in the sequence

4. Enzyme activity controlled in numerous ways … – e.g.,
   feedback inhibition, protein shape altered by
   de/phosphorylation.

Question 8

Enzymes do not change the equilibrium of a reaction.

EXPLAIN

Answer 8

If a reaction ‘can’t’ take place, an enzyme ‘won’t’ make it happen,

but they do SPEED UP reaction rate…

Question 9

Fuels can be oxidised to CO2 & H2O explain…

Answer 9

1. Main fuels = carbohydrates, fats, proteins, (alcohol!)

2.Oxidise the carbons in fuels to CO2
C-H
C-C
C-N (amino acids)

“Reduced Bonds”: foundational meaning of oxidation…

Question 10

Metabolic pathways are

Answer 10

Complex network of reactions

Question 11

Examples of Macromolecules as Fuels..

Answer 11

1. Glucose
2. Stearic acid
3. Alanine

Question 12

Energy Generating Reactions: Glycogen + Triglyceride and Protein

Answer 12

OVERVIEW

Question 13

Oxidation of Fuels (Cellular Respiration)…

Answer 13

Fuels gradually broken down to CO2 & H2O, i.e., oxidising
the “reduced bonds” in fuels.

FOCUS ON GLUCOSE:

C6H12O6 (glucose) + 6O2 (OXYGEN) —> —> 6CO2 (CARBON DIOXIDE) = 6H20 (WATER)

Oxidation; Glucose loses electrons (and hydrogens)

Reduction: Oxygen gains electrons (and hydrogens)

Question 14

Energy in cells: how

Answer 14

1. OXIDATION of foods RELEASES ENERGY , which is stored in OTHER MOLECULES that are USED TO PERFOM WORK…
2. Examples of cellular “high energy” compounds

—– Activated carrier:
1. ATP
2. NADH, FADH2
3. Acetyl CoA

3. Energy can also be STORED as ION GRADIENTS & in other HIGH ENERGY BONDS TOO,

e.g., PPi (pyrophosphate)

4. Energy can be transferred between these

Question 15

Examples of cellular “high energy” compounds

Activated carrier: High-energy component

Answer 15

1. ATP = phosphoanhydride bond
2. NADH, FADH2 = electrons & hydrogens
3. Acetyl CoA = thioester bond

Question 16

Understanding Oxidation and reduction…

Answer 16

1. During catabolism, oxidation of fuels (loss of
   electrons) eventually produces CO2 & H2O.
2. This is oxidative metabolism – we need O2 to make enough ATP in our cells.

3.In “original” terminology, “reduced bonds” (C-C, C-H) in
the fuels eventually share electrons with oxygen (C=O)
to become “oxidised bonds”

Question 17

Redox Reactions
Often Catalysed by…INVOLVES…

Answer 17

1. Often Catalysed by Dehydrogenases
2. In cells often involves transfer of H (atom has electron)
3. Hydride ions, H- (2 electrons) are being transferred

Question 18

Explain NADH…

Answer 18

1. NADH = (nicotinamide adenine dinucleotide)
2. Electron carrier
3. Cellular currency of REDUCTIVE POTENTIAL ENERGY produced during RESPIRATION

Question 19

Explain NADH process…

Answer 19

1. NADH = 2 high-energy electrons from sugar oxidation
2. ELECTRON DONATION

– unstable isomer

3. BOND REARRANGEMENT
4. NAD+

• hydride ion

3. 2 Electrons to electron-transport chain in membrane
   ETC.

Question 20

ATP Energy….

Answer 20

1. ATP
   = (PHOSPHATE = phosphoanhydride bonds, phospoanhydride bond + ribose, adenine)
2. ADP + Phosphate
   = NEW BOND, ENERGY RELEASED

Question 21

What is ATP? HOW DOES IT WORK

Answer 21

1. ATP = adenosine triphosphate, contains two “high energy” phosphate group bonds.
2. When a phosphate group is cleaved from ATP, ADP (adenosine diphosphate) is formed,
3. the energy released can be used to drive reactions in the cell.

Question 22

When does Reactions occur in cells?

Answer 22

1. Reactions occur all the time in cells, generating ATP
   when foods are catabolised, & hydrolysing ATP to ADP
   (or AMP) when energy is required by the cell.

2.Cells produce ATP & continually break it down &
reform it, as required.

3. Each ATP equivalent recycled 500-750 times a day
4. Energy: from food catabolism
   —> ATP hydrolysis yields = approx 30kj/mol energy

Energy: e.g, for anabolism

5.Cells produce ATP & continually break it down &
reform it, as required.

— Each ATP equivalent recycled 500-750 times a day

Question 23

ADP TO ATP

Answer 23

ADP+P —-> PHOSPHORYLATION —> ATP

AND

ATP —–> HYDROLYSIS —-> ADP+ P

Question 24

UNDERSTANDING Cellular Work

Answer 24

1. Sufficient ATP levels (1 - 10 mM) must be maintained,
2. or the
   cell quickly loses its ability to function - this is what happens when cells are deprived of oxygen.
3. Energy coupling is a key feature of how cells manage their energy resources.
4. ATP powers cellular work by coupling energy-generating reactions to energy-requiring reactions.
5. This energy can be used to drive other reactions, such as formation of new bonds & molecules… this is metabolism & it
   occurs in multiple reactions in various cellular compartments

Question 25

Organised & Disorganised Energy Release…

Answer 25

A. STEPWISE OXIDATION OF SUGAR IN CELLS

1. Sugar + O2
2. Small activation energies overcome at body temperature owing to the presence of enzymes
3. CO2 +H2O
4. Activated carrier molecules store energy (NADH)

B. DIRECT BURING OF SUGAR
1. SUGAR + O2
2. Large activation energy overcome by the heat from a fire
3. all free energy is released as heat; none is stored
4. CO2 + H2O

Question 26

Integration of Metabolism: 6

Answer 26

1. Metabolic processes are coordinated
2. Opposing pathways cannot operate simultaneously
3. Cell must respond to constant changes

—- ‘External conditions e.g., availability of nutrients’

—- ‘Internal conditions e.g., genetics’

4. In multi-cellular organisms, cells must communicate & cooperate, simplified by “division of labour” between tissues & cells
5. Different pathways operate in different tissues &
   cellular compartments
6. Consider glucose catabolism as an example…