Item11Item 11The main provider of energy for the brain and nervous system isMultiple Choicelactose.glucose.galactose.sucrose.

Nervous system cells burn mostly ________ for energy.Multiple Choicefructoseglucoselactosefiber

BRAIN METABOLISM➢ Fuels used by brain:1- Glucose. 2-Ketone bodies. 3-Amino acid• Nervous system closely depends on the availability of glucose, the lack ofwhich quickly results in death.• Glucose is brought to the brain by blood flowing through a special network ofarteries and is quickly catabolized by the glycolytic and tricarboxylic acidcycle pathways to synthesize energy.• It is also used in the synthesis of amino acids, nucleotides and NADPH (HMPpathway).• Glucose can be converted into glycogen in the brain.• The nerve tissue is capable of synthesizing glucose-6-phosphate in thegluconeogenic pathway• Brain carbohydrate metabolism is thus in many ways similar to livercarbohydrate metabolism.• The astrocyte constitutes the main cell implicated in this metabolism.➢ Brain Energy Metabolism• Brain is one of the most metabolically active organs in the body.• The brain stores little energy as glycogen and relies almost entirely oncirculating glucose for fuel.BIOCHEMISTRYNEUROSCIENCE-2023 2• Inside neurons, glucose is metabolized by cytoplasm & mitochondria in anumber of steps (glycolysis & Kreb’s cycle) to produce cellular energy, asATP.➢ Role of Oxygen to Brain• Having enough oxygen in the brain is crucial to brain function, and therefore,to the body as a whole.• The brain requires a constant supply of both oxygen and glucose.• Some brain cells start dying less than 5 minutes after their oxygen supplydisappears.• Without enough oxygen or with low blood-oxygen levels, lead to brain death.➢ Importance of Glucose1. Major source of energy for RBC and CNS.2. The only source of energy for skeletal muscle during exercise.3. Lipogenesis formation.4. Kreb’s cycle.➢ Fuel of brainA-General: use glucoseB-During Starvation: utilize ketone bodies➢ Amino Acid Content In Cerebral TissueBIOCHEMISTRYNEUROSCIENCE-2023 3• The three amino acids with the highest levels in brain tissues areGLUTAMIC ACID, GLUTAMINE, and ASPARTIC ACID.• Metabolism of glutamic acid and related substances plays a role in regulatingbrain functions➢ Fed Starvation CycleFate of glucose in Fed StateFate of glucose in liver:A- Make Glycolysis then Kreb’s CycleB-Excess glucose: stored in liver as Glycogen which used to maintain blood glucosebetween mealC-More excess glucose: converted to TriAcylGlycerol (TAG) synthesisFate of glucose in other tissues• Brain: make Glycolysis then Kreb’s Cycle• RBC: make Anaerobic Glycolysis end by lactic acid• Muscle:1- Make Glycolysis then Kreb’s Cycle2- Excess glucose: stored in muscle as Glycogen

Which item is used to supply some of the fuel needed by the brain only after the body has been fasting for a while?Group of answer choicesGlycerolFatty acidsProteinKetonesAmino acids

Protein can serve as an energy substrate ifGroup of answer choicescertain amino acids are presentit is utilized by the brainit is phosphorylated firstit is first converted to glucose

Where is this energy stored in glucose?