Biochemistry Flashcards
Metabolism Pathways
- Catabolic pathways
Break down complex molecules to simpler molecules
Produces energy - Anabolic pathways
Synthesize complex molecules from simpler precursors
Requires energy - Amphibolic pathways
Involve both catabolic and anabolic reactions
example is Kreb’s cycle
Central Pathway
Carbohydrate/glucose pathways are central to most other pathways
Carbohydrate Metabolism
Glycolysis- supplies little ATP
Citric acid cycle- supplies more ATP
Oxidative phosphorylation- supplies most ATP
Pentose phosphate pathway: NADPH, ribose 5-phosphate
Carbon skeletons for amino acids and precursors for fat and cholesterol synthesis
Gluconeogenesis: from lactate, glycerol, amino acids
Glycogenesis/glycogenolysis: storage form is glycogen
Key Intermediate for Pathways
Acetyl – CoA is a key intermediate for many pathways
Protein Metabolism
Protein synthesis (storage)
Transamination
Citric acid cycle
Oxidative phosphorylation
Gluconeogenesis
Ketogenesis
Lipid Metabolism
β-Oxidation- FAs to acetyl-CoA for CAC
Citric acid cycle
Oxidative phosphorylation
Lipogenesis - acetyl-CoA to FAs
Cholesterologenesis
Ketogenesis
Esterification/lipolysis: storage form is triacylglycerol (fat)
Subcellular Compartmentalization
Cytosol: glycolysis, glycogenesis, glycogenolysis, lipogenesis, pentose phosphate pathway
Ribosomes: protein synthesis
Mitochondrion: citric acid cycle, oxidative phosphorylation, β-oxidation, ketogenesis
Endoplasmic reticulum membrane: triacylglycerol synthesis
Key Points for Metabolism
- Dietary nutrients provide building blocks and energy
- Interconversion of molecules occurs via metabolic pathways; e.g. protein → glucose or fat
- Common metabolic intermediate is acetyl Co-A
- Subcellular compartmentation helps regulate metabolic pathways
- Store and retrieve ATP and glucose
ATP
Formation of energy and captures it in phosphate bonds
Two main sources:
- Respiratory chain: fueled by CAC and occurs in mitochondria and the final acceptor is O2; sets up gradient to make ATP
- Glycolysis: not much ATP produced, and doesn’t require O2; occurs in cytosol
Glucose
Major fuel: if around it is the top fuel choice
RBC: lack respiratory chain or CAC so energy is from GLYCOLYSIS ONLY
Brain requires glucose and during terms of fasting and starvation utilize ketone bodies
Can be used for synthesis of FAs and fat/triglycerides
Glycogen
There is only so much glucose we can store and so glycogen is used quickly
Muscle is a hog; uses glycogen and uses glucose for itself once broken down because lacks glucose 6 phosphatase
Stored by liver and kidney for later distribution
Fat
Long term storage in unlimited amounts
REQUIRES O2 (respiratory chain and CAC) to make ATP
Can supply glucose and ketone bodies to the body
Protein
Last resort energy once glucose, glycogen, and ketone bodies are gone
Can be converted to ketone bodies via ketogenesis
Gly and Leu are strictly ketogenic (make ketones), but the rest are glucogenic or both
Major storage is in muscle and some in the liver
Insulin vs. Glucagon
Insulin:
Beta cells take up glucose and if high amounts then releases insulin
Stimulates storage of glycogen, fat, and protein and inhibits breakdown of glycogen, fat, and protein
GLUT4 transports glucose in adipose tissue
Glucagon:
Signal for low glucose levels and released for alpha cells to breakdown glycogen for glucose to supply energy to body
No direct effect in skeletal muscle
Metabolic Responses: Fed, Fasting, and Starvation States
Well fed: store glucose, fat and protein
↑ insulin, ↓ glucagon
Synthesize glycogen, fat, and protein
Fasting: retrieve glucose and energy
↓ insulin, ↑ glucagon
Break down glycogen and fat (and protein)
Starvation: retrieve glucose and energy
↓ insulin, ↑ glucagon
Break down fat and protein
Liver
Key organ in energy distribution
Hepatic portal vein and chylomicron supplies
Liver is INDEPENDENT of insulin and uses GLUT2 for glucose uptake
Well fed: stores and distributes energy
Fasting: makes glucose and export it, breakdown FAs to make acetyl-CoA, makes ketone bodies
Muscle
Takes up glucose and insulin DEPENDENT
Makes glycogen, synthesis of protein, and beta oxidation
Cannot make glucose itself and cannot transport it out either to other organs
Uses ketone bodies and fatty acids
Releases AA to travel to other places
Kidney and RBCs
Kidney: can synthesize and breakdown glycogen like the liver to give to other places
RBC: no mitochondria and only uses glycolysis; also PPP
Fasting vs. Starving: Fuels Used
When fasting, starting to conserve glucose use for brain and red blood cells:
Liver burns FA; exports glucose and some ketone bodies
Adipose exports FA and glycerol
Muscle burns glucose (from its glycogen stores), FA and ketone bodies
When starving, need to make glucose:
Liver burns FA; exports glucose and ketone bodies
Adipose exports FA and glycerol
Muscle releases amino acids and imports and burns ketone bodies, FA and glucose
Brain adapts and burns ketone bodies
