BIO 105-03

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Bio 105 Lecture 2 Notes

Carbohydrates: Sugars, Starches and Fibers

A. Carbohydrate Facts

B. Types of Carbohydrates

1. Simple Sugars

a. Monosaccharides

b. Disaccharides

2. Complex Carbohydrates are Polysaccharides

  • Polysaccharide: many monosaccharides linked together
  • not sweet
  • they can accumulate without causing problems in the body, they can be stored
  • ex: starch, glycogen, cellulose
  1. Starch

  • starches are insoluble in water and thus can serve as storage depots of glucose
  • plants convert excess glucose into starch for storage (not an option in animals)
    • many glucose units hooked together
      • straight chain = amylose
      • branched chain = amylopectin

b. Glycogen

  • stores glucose in muscles and liver (never in plants)
  • richly branched
    • similar to amylopectin
    • branching permits rapid breakdown when needed (ie strenuous exercise)

3. Fiber/Types

  • stimulates saliva
  • delays gastric emptying
  • delays absorption of fats and carbs in small intestine
  • attracts water to soften stool in large intestine
  • fibers are fermented by bacteria

a. Soluble Fiber

  • dissolves in water
  • generally digested by bacteria in lg intestine
  • more viscous (like oatmeal)

– Soluble Fiber: Pectins

found in vegetables and fruits (citrus & apples)

– Soluble Fiber: Gums and Mucilages (added to food as stabilizer)

b. Insoluble Fiber

  • does not dissolve in water
  • generally not digested by bacteria
  • not viscous

– Insoluble Fiber: Lignin

  • very tough fiber (gives wood its stiffness)
  • we eat ffew foods containing lignin
  • occurs in woody parts of vegetables (carrots, small seed of fruits (strawberries)

– Insoluble Fiber: Cellulose

  • main structural component of plant cells (makes up most of cell wall)
  • second storage form of glucose in plants
  • insoluble and is an ideal structural component

C. Fiber and Health

1. Diverticulitis

  • diverticula are weak spots in the colon (large intestine) that bulge out
    • caused by long-term constipation
  • infection in these bulges = diverticulitis
    • symptoms: stomach pain, fever, nausea, vomiting, cramping & chills
  • found more often in countries where high-fiber diets are less common

2. How does fiber help your health?

  1. Insoluble fiber

    1. keeps things moving along – lees time for cancer-causing agents to absorb
    2. encourages healthy bacterial growth
  1. Soluble fiber

    1. slows down digestion in small intestine
    2. absorption of glucose slowed so less of sugar spike — improves sensitivity to insulin
    3. absorbs bile — bile excreted — body replaces bile with cholesterol from blood

D. Body’s Use of Carbs

  • body uses glucose for energy
    • only nutrient that the brain and nerves can use for energy

regulation of glucose

  • hormones: chemical messengers in body
  • two hormones involves: insulin, glucagon
  • insulin and glucagon are released by pancreas
  • regulate glucose feedback loop

1. Insulin

  • released when spike of glucose in blood
  • directs cells to take up glucose from blood
    • glucose is used
    • glucose is stored as glycogen in liver and muscle cells
      • glycogenesis: limited amount of storage possible
    • excess glucose is stored as fat (unlimited storage)
    • without insulin, glucose stays in blood
  • stops being released when glucose in blood in lowered
  • spikes about 45min after eating

2. Glucagon

  • directs cells to release glucose from glycogen stores when blood glucose dips (appx 4 hr. after last meal)
    • liver glycogen – glucose for body
    • muscle glycogen – glucose for muscles
    • glycogen breakdown = glycogenolysis
  • glucagon stops being released when glucose in blood is normal

3. Diet and Glycogen

  • Diet affects glycogen use
  • experimental research: 3 groups of runners fed different diet for several days, then maximum endurance time test
    • fat and protein diet = 57 min
    • normal mixed diet = 114 min
    • high carb diet = 167 min
  • carbo-loading

4. Fasting

  • long-term fasting (18 hours) use up glycogen stores
    • glucagon prompts protein to be made into glucose
      • gluconeogenesis
      • only done in liver & kidneys
    • glucagon also stimulates energy release from fat
  • very long-term fasting = starvation (days)
    • w/o carbs, fat breakdown incomplete
    • buildup of ketone bodies = ketosis
      • eventually brain/nerves need to use ketone bodies to help compensate for reduced glucose (50/50)

Clicker Questions

The main source of added sugars in the American diet is:

  1. Candy

  1. Cookies and cakes

  1. Juices and fruitades

  1. Soft drinks

Which of the following diseases is related to carbohydrates?

  1. Rickets

  1. Diabetes

  1. Phenylketonuria

  1. Anemia

Which one of the following sugars is a disaccharide?

  1. Fructose

  1. Galactose

  1. Glucose

  1. Sucrose

Which of the following is not a major source of starch in our diets?

  1. Wheat

  1. Fruit

  1. Rice

  1. Potatoes

Your blood cholesterol level is too high so you would like to eat additional viscous, soluble high-fiber foods to help lower it. A good choice would be…

  1. Broccoli

  1. Chocolate chip cookies

  1. Low-fat milk

  1. Oatmeal

_____ is the storage form of glucose in your body.

  1. Glucagon

  1. Glycogen

  1. Galactose

  1. Glucose

3 – 4 hours after a meal…

  1. Insulin levels are rising and glucagon levels are declining

  1. Glucagon levels are rising and insulin levels are declining

  1. Insulin and glucagon levels are holding steady

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