4 - Energy and Cellular Metabolism

Energy is required for ______, _______, and ____________.

growth, renewal, reproduction

How do Animals gain energy

Through ingestion from food (either plants or other animals)

What is the key process for energy production (in both plants and animals)?

Respiration (consumes O₂ + produces CO₂)

What happens to the extra energy (calories) that isn’t used?

Gets stored in chemical bonds (such as triglycerides - lipids/adipose tissue)

• Glycogen and lipids are the main energy stores

• Available when an animal’s energy needs exceeds its food intake

Energy

The capacity to do work; consists of:

• Chemical work (making/breaking chemical bonds)

• Transport work (move ions, molecules, etc.)

• Mechanical work (movement)

Kinetic energy

Energy of motion

Potential energy

Stored energy

1st Law of Thermodynamics

Energy cannot be created nor destroyed, but can be converted to different forms

2nd Law of Thermodynamics

Natural spontaneous processes move from a state of order to a condition of randomness/disorder (entropy).

• Creating + maintaining order in an open system requires the input of energy

• Disorder occurs when open systems lose energy to their surroundings without regaining it

  • When this happens, we say that the entropy of the open system has increased

Purpose of chemical reactions in cells

To transfer energy from one molecule to another OR to use energy stored in reactant molecules (free energy) to do work

Generally, complex molecules have more chemical bonds and therefore higher free energies; T or F

True

Activation energy

The initial input of energy required to bring reactants into a position that allows them to react with one another

• Low activation energy = reaction is spontaneous

• High activation energy = reaction is very slow or doesn’t happen (not deemed useful)

Exergonic reaction

Releases energy

• Energy can be used by other molecules to do work or given off as heat

• E.g. ATP (when converted to ADP + P_i —> 34 kJ released)

Endergonic reaction

Requires input of energy

• Some energy stays trapped in the chemical bonds

• Often synthesis reactions (forming a new or complex molecule)

Reaction Coupling

Energy released from one reaction is used to drive another reaction

Enzymes

Proteins that speeds up the rate of chemical reactions (catalysts) without being used up within the reaction; allows for less activation energy to be utilized

• Can be active, inactive, or modulated

  • Some produced as inactive and activated on demand

  • Some require co factors (Ca²⁺, Mg²⁺, etc.) for activation

Characteristics of Enzymes

• Usually large proteins with 3D shapes

• Exhibit specificity, competition, and saturation

• Holds substrates in place so that they are in position to react with one another

• Reaction rate will depend on temp, amount of enzymes and amount of reactions

• Cells control enzyme concentration to control reaction rate

All chemical reactions that take place in an organ makes up metabolism; T or F

True

Catabolism

The break down of large biomolecules (energy released from high energy bonds)

• The breakdown of glucose for energy production

• (Cats destroy)

Anabolism

The creation of large biomolecules (transfer of energy into covalent bonds of macromolecules)

• (Anabolic steroids build)

Intermediate metabolic reactions

The productions of one reaction (anabolic) that becomes substrates of another (catabolism)

• E.g. krebs cycle

How cells regulate metabolism (5)

1. Controlling the enzyme concentration

2. Producing modulators that change reaction rates

   1. usually controlled by hormones or other signals from outside the cell —> inhibition feedback

3. Using two different enzymes to catalyze reversible reactions

4. Compartmentalizing enzymes within cellular organelles

   1. Digestive enzymes that could disrupt these processes are kept in separate lysosomes

5. Maintain an optimum ratio of ATP to ADP

   1. Indicator of cellular energy status; if ATP is high, ATP production decreases / if ATP is low, ATP production increases

What is the end goal for catabolic pathways?

ATP production

Glycogenolysis

Process where glycogen (readily available energy stored in the body) is broken down into glucose-1-phosphate to be used for energy production

• Lysis = break down

Glycolysis

The breakdown of glucose (either anaerobic [no O₂] or aerobic [O₂])

• Lysis = break down

Glycogenesis

The process where glycogen is synthesized from glucose to be stored in the liver/muscle.

• Genesis = building

Gluconeogenesis

The conversion of fats or protein into glucose

• Neo = new (never been a carbohydrate)

• Genesis = building

The Oxidative System

Uses O₂ to generate energy from metabolic fuels (aerobic)

• Oxidative ATP production takes place in the mitochondria

• Greater ATP production compared to anaerobic systems

O₂ provides the electron in the electron transport chain. Without O₂, the Krebs/Citric Acid cycle doesn’t operate.

Krebs Cycle (what we need to know)

For every individual acetyl-CoA that enters the krebs cycle, it produces:

• 1 ATP

• 3 NADH

• 1 FADH₂

  • Doubled

2 acetyl-CoAs enter the krebs cycle for every glucose molecule that is broken down

What happens when there isn’t enough O₂

Pyruvate starts to build up in the cytosol and undergoes fermentation to lactate

• E.g. in high intensity exercise

Gene

DNA region/segment containing info to make protein

Steps for Protein Synthesis

1. Gene Activation (nucleus)

   1. Most genes turn on/off as needed (“regulated”)

   2. Genes for proteins are almost always turned on

2. Transcription (nucleus)

   1. DNA used as a template to create a single strand of messenger RNA (mRNA)

3. mRNA Processing (nucleus)

   1. Non-coding segments removed

   2. mRNA can be activated or destroyed before a protein is created

4. Translation (cytoplasm)

   1. mRNA leaves the nucleus (pores) and finds ribosomes in the cytosol

   2. Ribosomes read the mRNA sequence and create the corresponding amino acid chain

5. Post-Translation Modifications (cytoplasm)

   1. Cleavage of the amino acid chain

   2. Addition of molecules/groups

   3. Cross-linkage formed

   4. Bottom line - secondary + teritary structure created