Cellular Metabolism Flashcards
What are the main objectives of metabolism?
Breakdown of foods to use as energy
▫ We mainly use carbohydrates and lipids as energy substrates –
glucose, fatty acids etc.
* Breakdown of foods and cellular recycling for building new
proteins, nucleic acids, lipids and carbohydrates
▫ Formation of new molecules
* Processes that result in the elimination of cellular waste products
What are the two types of metabolism?
- Catabolism
- Anabolism
What is Catabolism?
▫ Catabolic processes break down complex molecules to simpler one
▫ Generally exergonic
They release more energy than they consume
What is Anabolism?
▫ Anabolic processes build larger structures from simpler one
▫ Endergonic
They consume energy
What is ATP?
- Cellular energy
- ATP provides most of the energy required for metabolic reactions in the cell.
- Each cell contains around 1 billion molecules of ATP.
- Each ATP molecules lasts less than 1 minute.
What is ATP used for?
- Powering Metabolic reactions in the cell
What is oxidation?
- result in a change to the original molecule or substance.
- Oxidation can occur in three ways:
▫ The addition of oxygen e.g. C + O2 → CO2
▫ Removal of electrons from an atom or molecule
▫ Removal of hydrogen - Usually exergonic - releases energy
What is reduction?
- result in a change to the original molecule or substance.
Reduction can also occur in three ways
▫ Removal of oxygen
▫ Addition of electrons to a molecule
These electrons are known as ‘high energy electrons’
▫ Addition of hydrogen - Usually endergonic – require and store energy
What is a endergonic reaction?
requires and stores energy.
What is an exergonic reaction?
Usually releases energy.
What is NAD?
- Nicotinamide adenine dinucleotide - NAD
▫ From Vit B3 – niacin
What is FAD?
- Flavin adenine dinucleotide – FAD
▫ From Vit B2 – riboflavin
What is a cofactor?
Non-protein chemical compound or metallic ion that is required for an enzyme’s role as a catalyst.
NAD redox states
- Oxidised NAD (NAD+) is reduced to NADH + H+
▫ NAD gains a hydride ion (H-)
Hydrogen atom with an additional electron
▫ 2 hydrogen ions (2H+) and 2 electrons (2e-)
▫ 1of the hydrogen ions is released
[NAD+ + 2H+ + 2e-] Oxidised & low energy <—->
[NADH + H+] Reduced & High energy
FAD redox states
Oxidised FAD is reduced to FADH2
* FAD gains:
▫ 2 hydrogen ions (2H+) and 2 electrons (2e-)
[FAD + 2H+ + 2e-] Oxidised & low energy <——>
[FADH2] Reduced & high energy.
What is the preferred energy substrate for ATP production?
Glucose
What are dietary carbohydrates hydrolysed to?
monosaccharides (mostly glucose 80%, also fructose and galactose, liver converts the galactose and most fructose to glucose)
How is glucose used in the body?
- Glucose can be oxidised to form ATP
- Additional metabolic pathways for glucose include:
▫ Formation of amino acids
▫ Formation of glycogen (glucose polysaccharide)
▫ Synthesis of triglycerides by the liver
Storage in adipocytes
How does glucose enter the cells?
- Entry via GluT molecules on most cells of the body – facilitated
diffusion
▫ GluT = Glucose Transporters
▫ Cell membrane proteins - Neurons and hepatocytes posses GluT 2 & 3 respectively
- Skeletal muscle and adipose cells produce and insert GluT 4
molecules in response to high insulin concentrations
▫ These two cell types make up a large portion of us as organisms
>60% in most individuals
How is glucose catabolised?
Glucose is phosphorylated once inside the cell
▫ Prevents glucose leaving the cell
* Glucose catabolism can then proceed
* Four distinct stages:
▫ Glycolysis
▫ Formation of acetyl coenzyme A
▫ Krebs cycle reactions
Krebs cycle AKA: citric acid cycle (CAC) or tricarboxylic cycle (TCA)
▫ Electron transport chain reactions
What is glycolysis?
- Pathway of 10 reactions in the cytosol of cells
- One molecule of glucose (C6H12O6) is oxidised to produce:
▫ 2 molecules of ATP
▫ 2 molecules of pyruvic acid
▫ 2 molecules of reduced NAD (NADH)
Contain energy - This process does is also used by anaerobic organisms
What is acetyl coenzyme A and how does it form?
- molecule that participates in many reactions in protein, carbohydrate and lipid metabolism.
- Intermediate stage that oxidises pyruvic acid
for entry into the Krebs cycle - In mitochondria, pyruvic acid produces:
▫ 1 molecule of CO2
▫ 1 molecule of reduced NADH + H+
Contains energy
▫ 1 molecule of acetyl coenzyme A
23
What is the Krebs cycle?
- Acetyl CoA is oxidised in the mitochondrial
matrix - Primary aim is to produce
▫ NADH
▫ FADH2
Used in the electron transport chain - Also produces:
▫ ATP (little)
▫ CO2
What is oxidative phosphorylation?
- Have you ever wondered why we need to breathe oxygen?
- O2 is involved in the final step of the electron transport chain
- Oxidative phosphorylation involves two connected processes:
▫ Passage of electrons along the electron transport chain
▫ Pumping of hydrogen ions - chemiosmosis
What is the electron transport chain?
- Series of electron carriers on the inner mitochondrial membrane
- 1000’s of transport chains per mitochondrion
▫ Due to folded inner membrane (cristae) increasing surface area - Carriers are systematically reduced and oxidised
▫ Exergonic reactions produce energy - Last electron acceptor is O2
- Electron carriers are proteins found in the inner mitochondrial
membrane - They are known as protein complexes I – IV
- Also contain two key additional factors:
▫ Coenzyme Q10
▫ Cytochrome C complex - Electrons are supplied by the two main products of the Krebs
cycle – high-energy electron carriers:
▫ NADH
▫ FADH2
How many protons does Complex 1 pump out?
4
How many protons does complex II pump out?
0
