Carbohydrates and the Carbon Cycle
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Questions and Answers

What is the main component of sucrose?

  • Glucose and Maltose
  • Fructose and Lactose
  • Glucose and Fructose (correct)
  • Glucose and Galactose

    • Which of the following statements is true regarding heterotrophs?

  • They can synthesize their own sugars.
  • They evolved to derive energy from plant-derived sugars. (correct)
  • They primarily synthesize glucose.
  • They rely solely on animal-derived sugars.

    • What role does fructose play in the body despite being present in low levels?

  • It serves as the primary energy source for tissues.
  • It is the main sugar stored in the liver.
  • It acts as a signal of the ingested dietary sugar. (correct)
  • It is converted primarily to starch.

    • How is sucrose digested in the body?

    <p>It requires cleavage into glucose and fructose.</p> Signup and view all the answers

    What metabolic pathways are linked to fructose consumption?

    <p>Converted to fatty acids and stored as triglycerides.</p> Signup and view all the answers

    What is a major consequence of high consumption of sugars in certain populations?

    <p>Increased prevalence of overweight and obesity.</p> Signup and view all the answers

    Which compound primarily circulates in animals as an energy source?

    <p>Glucose</p> Signup and view all the answers

    Loss of ChREBP is associated with what type of dysfunction?

    <p>Increased metabolic dysfunction.</p> Signup and view all the answers

    What percentage of all caloric sweeteners did HFCS represent in the United States by 2000?

    <p>42.0%</p> Signup and view all the answers

    Which of these foods is most likely to contain high-fructose corn syrup (HFCS)?

    <p>Most baked goods</p> Signup and view all the answers

    What is the fructose content percentage of high-fructose corn syrup compared to table sugar?

    <p>HFCS has 55% fructose, while table sugar has 50%</p> Signup and view all the answers

    According to the 2017-2018 NHANES data, what percentage of daily calories do Americans consume from added sugars?

    <p>22%</p> Signup and view all the answers

    What is a key feature of the ChREBPβ isoform?

    <p>It generates a shorter protein missing specific domains.</p> Signup and view all the answers

    What is the glycemic index comparison between agave and sucrose?

    <p>Agave has a lower glycemic index than sucrose.</p> Signup and view all the answers

    How does condensed chromatin affect gene expression?

    <p>It prevents RNA polymerase II from accessing genes.</p> Signup and view all the answers

    What percentage of calories do Americans derive from ultra-processed foods according to a 2016 study?

    <p>58%</p> Signup and view all the answers

    What role does ChREBP play in metabolic syndrome?

    <p>It enhances lipogenesis in insulin-resistant conditions.</p> Signup and view all the answers

    Which receptors are activated by monosaccharides such as glucose and fructose?

    <p>Tas1R2 and Tas1R3</p> Signup and view all the answers

    What is the average daily caloric intake for an American adult based on 2017-2018 NHANES data?

    <p>2100 calories</p> Signup and view all the answers

    What is known about the binding of ChREBP isoforms to ChoRE?

    <p>It is currently unknown if both isoforms bind.</p> Signup and view all the answers

    What is the primary function of transcription factors in gene expression?

    <p>To guide RNA polymerase II to promoter regions.</p> Signup and view all the answers

    What percentage of total liver lipids does de novo lipogenesis contribute in patients with non-alcoholic fatty liver disease?

    <p>25%</p> Signup and view all the answers

    What occurs in mice lacking ChREBP?

    <p>They show impaired glucose tolerance.</p> Signup and view all the answers

    Which component is involved in the transcription initiation complex?

    <p>Mediator</p> Signup and view all the answers

    What is the effect of ChREBP deficiency on lipogenesis?

    <p>It reduces lipogenesis.</p> Signup and view all the answers

    How does ChREBP deficiency affect plasma glucose levels in mice?

    <p>It increases plasma glucose levels.</p> Signup and view all the answers

    In mice deficient in ChREBP, what happens to liver glycogen levels?

    <p>They decrease significantly.</p> Signup and view all the answers

    What was the percent change in liver weight of ChREBP deficient mice compared to wild type on a high-starch diet?

    <p>It was significantly higher.</p> Signup and view all the answers

    Which parameter showed a significant increase in ChREBP deficient mice when given a standard rodent chow diet?

    <p>Plasma insulin.</p> Signup and view all the answers

    What effect does ChREBP deficiency have on epididymal fat weight?

    <p>It decreases significantly.</p> Signup and view all the answers

    How is plasma free fatty acid (FFA) concentration affected in ChREBP deficient mice?

    <p>It decreases significantly.</p> Signup and view all the answers

    What was the effect of ChREBP deficiency on pyruvate levels in the wild-type mouse liver on a high-starch diet?

    <p>Lower than normal</p> Signup and view all the answers

    Which parameter showed the largest increase in ChREBP−/− mice compared to wild-type on a standard diet?

    <p>Glucose</p> Signup and view all the answers

    How did the deficiency of ChREBP affect lipogenesis?

    <p>Decreased lipogenesis</p> Signup and view all the answers

    What was a consequence of ChREBP deficiency in mice regarding metabolism?

    <p>Impaired glucose tolerance</p> Signup and view all the answers

    In ChREBP−/− mice on a high-starch diet, how did PEP levels compare to wild-type mice?

    <p>Lower</p> Signup and view all the answers

    Which metabolite is primarily responsible for the hypothermia observed in ChREBP−/− mice?

    <p>Fructose</p> Signup and view all the answers

    Which experiment indicated the role of ChREBP in glycolysis?

    <p>Feeding radioactive isotopes</p> Signup and view all the answers

    Study Notes

    Carbohydrate Contribution to the Carbon Cycle

    • Animals are heterotrophs, meaning they can't make their own carbohydrates and depend on plants for their supply.
    • Glucose is a primary fuel for most tissues in animals.
    • Fructose represents a small portion of circulating sugar in animals.
    • Fructose is rapidly processed by the intestines and liver, serving as a signal for dietary sugar intake.
    • Sucrose, the main circulating sugar in plants, is composed of equal parts glucose and fructose.
    • Fructose is converted for energy, transformed into glucose, or stored as a polymer (glycogen) or triglycerides.

    Fructose Consumption and Health

    • Fructose consumption has increased significantly in the United States, particularly due to the rising popularity of high-fructose corn syrup.
    • High-fructose corn syrup represents a substantial portion of sweeteners used in the US food industry.
    • Fructose is prevalent in many commercially processed foods.
    • Fructose intake is linked to weight gain and metabolic diseases.

    The Sweetness of Sugar

    • Animals have evolved mechanisms to seek out and consume sugars, primarily through taste receptors.
    • Sweetness triggers the release of neurotransmitters leading to a sense of pleasure and reward.
    • This evolutionary adaptation is a response to fluctuating food availability to ensure energy storage during times of scarcity.

    ChREBP Regulation of Metabolism

    • ChREBP is a transcription factor that regulates glucose and fructose metabolism in the liver.
    • ChREBP controls the expression of genes involved in glycolysis, lipogenesis, and other metabolic pathways.
    • Two isoforms of ChREBP are known: ChREBPα and ChREBPβ.
    • The presence of ChREBPβ might be regulated by ChREBPα.
    • ChREBPα regulates the expression of genes like pyruvate kinase, contributing to glucose utilization and fat synthesis.

    ChREBP Deficiency and Metabolic Dysfunction

    • ChREBP deficiency in mice leads to impaired glucose tolerance, inability to metabolize fructose, and hypothermia.
    • ChREBP deficiency in mice results in reduced lipogenesis and increased liver glycogen levels.
    • ChREBP deficient mice exhibit lower body temperatures and eventually die due to their inability to metabolize fructose, underlining the importance of ChREBP in sugar metabolism.

    Transcriptional Regulation

    • Transcriptional activation in cells is dependent on chromatin state and the binding of transcription factors.
    • Access to DNA for transcription depends on chromatin configuration.
    • Open chromatin allows transcription factors to bind to promoter and enhancer regions, initiating gene expression.
    • Condensed chromatin restricts access to DNA, inhibiting gene expression.
    • Transcription factors can guide RNA polymerase II to target genes or work together with other proteins for gene transcription initiation.

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    Week 2 Lecture 4 PDF

    Description

    This quiz explores the role of carbohydrates, specifically glucose and fructose, in the carbon cycle and their significance in animal physiology. It also discusses the implications of fructose consumption on health, particularly in relation to processed foods and high-fructose corn syrup. Test your knowledge on these essential concepts!

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