Metabolism Introduction

why is a well-regulated metabolism essential?

essential for health and for coping with disease

what happens if you have metabolic dysregulation?

can lead to diabetes, cancer, ageing, neurogeneration

involved with genetic diseases (understanding metabolism can help with diagnosis and treatment)

what is the definition of metabolism?

the sum of all the chemical processes necessary to make possible the characteristics of living cells/organisms

how does metabolism connect with characteristics of living organisms?

DNA codes for proteins

proteins control metabolism thorugh enzymes, transporters…

this determines our composition and characteristics

what are the three main things that organisms must do to survive?

maintain themselves, grow, reproduce

require chemical reactions to do this

what do chemical reactions require?

• energy

• carbon source

• ‘reducing power’

what are the four categories that describe where living organisms get their energy/carbon/reducing power from?

• autotrophs

• heterotrophs

• phototrophs

• chemotrophs

what do you call an organism that gets energy for a reaction from light (e.g. the sun)?

phototroph

what do you call an organism that gets their energy from chemical reactions?

chemotroph

what do you call an organism that uses inorganic carbon as their source of carbon?

autotroph

(reduces carbon itself)

what do you call an organism that uses organic carbon as their carbon source?

heterotroph

(ingesting reduced carbon)

what do you call an organism that uses inorganic sources of electrons?

autotroph

what do you call an organism that uses organic sources of electrons?

heterotroph

what are some examples of inorganic compounds for energy?

H₂, FeCO₃, NH₃

what is an inorganic source of carbon?

CO₂

what are inorganic sources of electrons?

H₂O, H₂S, H₂, FeCO₃, NH₃

what are organic compounds for energy?

glucose, fats

what are organic sources of carbon/organic sources of electrons?

isopropanol, lactate, glucose, fats

summary grid of autotrophs, heterotrophs, phototrophs and chemotrophs

what are higher plants?

photoautotrophs

• use light as their source of energy

• convert inorganic CO₂ into organic carbon

• use inorganic sources of electrons

what are sulfur/iron/hydrogen bacteria?

chemoautotrophs/chemolithotrophs

• bacteria with a compound attached to name are usually chemoautotrophs

• use chemical reactions as source of energy

• reduce inorganic carbon

higher animals

chemoheterotrophs

• use chemical reactions as source of energy

• obtain organic carbon from other organisms

what are the three major energy sources in human diets (chemoheterotrophs)?

• carbohydrates

• fats

• proteins

what are the options when metabolising these energy sources?

• break them down completely into CO₂, energy, electrons (+ urea for proteins)

• break them down partially into useful compounds and use those to make something else (require energy and reducing power)

what are the two main types of metabolic pathways?

catabolism

• fuel oxidation (breaking down)

• complex molecules —> simple molecules

anabolism

• biosynthesis

• simple molecules —> complex molecules

what is an example of a catabolic process?

respiration of glucose (breaking glucose down)

what is an example of an anabolic process?

DNA synthesis

what kinds of reactions does catabolism include?

oxidative reactions (electrons/hydrogens removed, oxygen added)

process releases energy (can occur spontaneously)

what kind of reactions does anabolism include?

reductive reactions (electrons and hydrogens added)

process requires energy (cannot occur spontaneously)

catabolism vs anabolism

what is the equilibrium constant, K_eq?

equilibrium constant quantifies the balance between reactants and products in a reversible chemical reaction at a specific temperature

what is the equation for K_eq?

if products are favoured, K_eq is larger

if reactants are favoured, K_eq is smaller

what is the equation for standard Gibbs free energy change of a reversible reaction?

if products are favoured, ΔG is negative

if reactants are favoured, ΔG is positive

what is standard gibbs free energy?

energy change associated with a reaction proceeding forwards (into products) if starting with equal concentrations of everything

what is the equation for gibbs free energy?

Q = reaction quotient (ratio of product concentrations to reactant concentrations)

what happens when you couple reactions?

if you couple a reaction that provides a lot of energy (exothermic, negative ΔG) to a reaction that requires some energy (endothermic, positive ΔG), the endothermic reaction can use energy from exothermic reaction to occur

overall ΔG is negative

process of catabolism —> anabolism

what form is the energy from catabolism in?

• high energy bonds e.g. ATP (coenzyme)

• reduced coenzymes e.g. NADH

• concentration gradients e.g. H+ gradient

how does ATP (adenosine triphosphate) release energy

releases energy when β-ɣ bond is broken

-ΔG

what type of coenzyme is NAD (nicotinamide adenine dinucleotide)?

redox coenzyme

how is NAD used?

• used to react with reduced substrates

• NAD gets reduced and the substrate gets oxidised

• involved in catabolism, as an oxidising agent

what type of coenzyme is NADPH?

redox coenzyme

similar to NAD but with extra phosphate

phosphate impacts what enzymes can bind to it

how is NADPH used?

• involved in anabolic pathways

• acts as reducing agent (itself oxidised)

what type of coenzyme is FAD?

redox coenzyme

always bound to its enzyme

how is FAD used?

• used in catabolic pathways as an oxidising agent (itself reduced)

cycling of coenzymes

how is metabolism regulated in unicellular organisms?

• take up chemicals they need even at low concentrations

• make chemicals that are not available

• dependent on environment

how do multicellular organisms regulate metabolism?

each individual cell has its needs

each cell’s actions must be coordinated with the rest of the body

what important needs must metabolic regulation meet?

• need adequate metabolic fuel

• receive fuel in the correct form (e.g. brain needs glucose)

• blood glucose must be kept within a set range

• excess fuel needs to be stored

• waste products need to be safely removed

role of brain in metabolism?

normally uses glucose as metabolic fuel

(can use ketone bodies during starvation)

role of skeletal muscle in metabolism?

when glucose is plentiful it stores glycogen for its own use

role of liver in metabolism?

when glucose is plentiful, stores excess as glycogen and makes fat

releases stored fuel during fasting and exercise

role of adipose tissue in metabolism?

when fat is plentiful, stores fat

released during fasting and exercise

what are the three main metabolic states?

• fed

• exercise

• fasting

what occurs during the fed state?

• liver uses excess fuel to make glycogen and fat

• tissues take up excess glucose

• adipose takes up and stores fat

what occurs during the fasting state?

• liver releases glucose

• liver releases ketone bodies

• adipose releases fatty acids

• most tissues switch to fat use

what happens during exercise state?

• muscle fuel use increases

• adipose releases fatty acids

• liver releases glucose