IB SEHS Topic 3.2 -- Carbohydrates and Fat Metabolism

Role of Insulin in Glycogen formation and the accumulation of body fat

-After eating: -Glucose is absorbed by the blood, which causes the pancreas to release insulin -Insulin promotes: -Uptake of glucose by liver-converts glucose to glycogen (glycogenesis) -Glycolysis-converts glucose into pyruvate and acetyl CoA (further converts acetyl CoA in triglycerides and stored in adipose tissue) -Insulin: -Lowers blood glucose-signals energy availability -Increase glucose transport to liver -Inhibits glycogenolysis: conversion of glycogen to glucose -Inhibits lipolysis: breakdown of fatty acids -Inhibits gluconeogenesis: conversion of non-carbohydrates into glucose -Promotes glycogenesis: conversion of glucose into glycogen -Promotes glycolysis: synthesis of glucose into acetyl CoA

Lipolysis

-Breakdown of triglycerides from adipose -Fatty acids are released into blood stream and converted into acetyl CoA -Activated in the presence of glucagon when fasting

Carbohydrate metabolism

-Carbs are digested and broken down into monosaccharides: glucose, fructose, and galactose -Monosaccharides are absorbed in the blood and transported to the liver (galactose and fructose are converted to glucose and then transported to organs) -Glycogen-glucose that isn't immediately used (converted and stored by liver and muscle cells)

Catabolism

-Chemical reactions that break down complex organic compounds into simpler ones, with an energy release -Examples: Triglyceride to glycerol and fatty acid

Gluconeogenesis

-Conversion of fat or protein into glucose -Inhibited in the presence of insulin

Anabolism

-Energy-requiring reactions where small molecules are built up into larger ones -Examples: Glucose to glycogen

Functions of Glucagon and Adrenaline during fasting and exercise

-Glucagon is complementary to insulin and is also produced by pancreas -Decrease in blood glucose levels (caused by fasting) stimulates glycogenolysis to raise blood glucose levels -Adrenaline (also called epinephrine) is released to promote glycogenolysis -In a fasted state: -Promotes glycogenolysis: conversion of glycogen to glucose -Promotes gluconeogenesis: conversion of non-carbohydrates into glucose -Inhibits glycogenesis: conversion of glucose to glycogen

Glucose uptake during exercise

-Increased muscle contractions require increase amounts of glucose -Insulin levels fall; glucagon and adrenaline levels rise (less glucose is absorbed by the liver and increased glycogenolysis: releases more glucose into the blood)

Fat metabolism

-Kreb's cycle: series of chemical reactions (occurs in mitochondria and involves the oxidation of the coenzyme A (coA) to produce large ATP amounts) -Consuming more fat than required leads to fat stored as triglycerides in adipose tissue and skeletal muscles (adipose found under the skin and between organs) -Stored fat provides energy when energy supply is not immediately available from diet or glycogen pool

Metabolism

-Nutrients (such as fat) that can be stored are metabolized much slower than those that can't be stored (such as proteins) -All the biochemical reactions that occur within an organism, including catabolic and anabolic reactions

Glycolysis

-Occurs in the cytosol of cells-metabolism of glucose into pyruvate and production of energy in the form of ATP -When oxygen is available, pyruvate enters mitochondria where its oxidized into CO2 and H2O

Glycogenesis

-Occurs when more glucose is taken in than needed -Process of converting glucose into glycogen in order to store -Promoted by the presence of insulin

Glycogenolysis

-Stimulated by the presence of glucagon (when fasting) -Process of converting glycogen to glucose (glycogen stored in liver muscles is converted into glucose 1-phosphate and glucose 6-phosphate and controlled by glucagon (from pancreas) and epinephrine (from adrenal glands)