Metabolism Flashcards by Ira Advani

Stage I to III of metabolic pathway of carbohydrates

Carbohydrates –> monosaccharides –> acetyl CoA –> TCA cycle

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catabolic pathway

break down molecules

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anabolic pathway

build up molcules

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energy yield of carbs, proteins, and lipids

carbs –> glucose –> 4 calories

protein –> amino acids –> 4 calories

lipids fats –> 9 calories

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carbohydrate break down: simple vs complex

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maltose, lactose, and sucrose monosaccarides

maltose - glucose + glucose

lactose - glucose + galactose

sucrose - glucose + fructose

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high fructose syrup vs sucrose

sucrose = “real sugar” – 50% glucose and 50% fructose

high fructose syrup = “corn syrup” –mix of ratios of monosaccharides

→ ex: 40% glucose to 55% fructose

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absorption of carbohydrates?

______________monosaccharides (glucose, galactose, fructose) is what is eventually absorbed in the end

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absorption vs digestion

absorption = monosaccharides

digestion = break down of disaccharides

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lactose intolerance

what is the enzyme deficiency
symptoms?

lactase = breaks down lactose into glucose + galactose

if lactase deficiency than lactose enters large intestine/ colon and is broken down by bacteria that releases carbon dioxide, hydrogen gas, etc.

symptoms:

this leads to bloating, diarrhea, and dehydration

monosaccharide absorption into intestinal mucosal cells

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name the 2 transporters and if they require energy/ cofactors?

if so what?

GLUT-5 transports fructose –> energy and sodium (Na+) independent transport

SGLT-1 (sodium-glucose cotransporter-1): transports glucose and galactose.

it is energy and Na+ dependent

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monosaccharide absorption at basal membrane

which transporter

after monosaccharides are in the mucosal cell they are transported across the basal membrane to circulation/ portal vein via GLUT-2

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circulation order of carbohydrates/ glucose

small intestine –> portal vein –> liver –> circulation as blood glucose in muscle, fat, RBC, and CNS

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Location/ Description of the 5 GLUT Transporters

GLUT1

RBC, blood brain barrier, retinal barrier, placental barrier, testis barrier

–> all through blood circulation

–> high-affinity glucose transport system

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Location/ Description of the 5 GLUT Transporters

GLUT2

GLUT2 - liver, kidney, pancreatic B-cells, Serosal surface of intestinal mucosa

high capacity, low affinity transporter
helps monsaccharides through the basal membrane

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Location/ Description of the 5 GLUT Transporters

GLUT3

brain (neurons)

main transporter in CNS, high-affinity

Location/ Description of the 5 GLUT Transporters

GLUT4

adipose, skeletal muscle, heart muscle

insulin sensitive transporter = in presence of insulin, the #of transporters increases
high affinity system

Location/ Description of the 5 GLUT Transporters

GLUT5

intestinal epithelium, spermatozoa

fructose transporter to mucosal cells

GLUT transporters summary

liver removes how much glucose

typically 20 to 30%

3 ways to test blood glucose - diabetes

fasting blood glucose (10-12 hour fast)
glycation of hemoglobin
Oral Glucose Tolerance Test (2-3 hours)

diabetes, normal, and prediabetes

normal - less than 100 mg/dl

prediabetes - 100 to 125

diabetes - 126 or higher

HbA1C_

hemoglobin’s N terminal can be glycosylated = HbA1C

how can Hb1AC be used to diagnose diabetes?

HbA1C count is expressed as a percentage of hemoglobin

normal - less than 5.7%

prediabetes - 5.7 to 6.4%

diabetes - 6.5% or higher

Oral Glucose Tolerance Test

subject fasts for 10-12 hours (blood drawn) given flavored drink with 75g glucose 2 hours after glucose load = additional samples drawn

normal, prediabetes, and diabetes OGTT result

OGTT chart

**Subject #1:** Normal response, blood glucose rises and then falls, within 90 minutes **Subject #2:** A normal fasting plasma glucose, has impaired glucose tolerance, a 2- hour reading \>140 mg/dL and pre-diabetic **Subject #3:** Diabetic

Impaired fasting glucose (IFG):

blood glucose of 100-125mg/dL (pre-diabetic)

Impaired glucose tolerance(IGT):

blood glucose of 140-199mg/dL 2-hours after a glucose load (prediabetic)

Diabetes

- hyperglycemia, impaired - insulin secretion AND ultimately loss of b-cell function

glucose entry into muscle and adipose during fasting - which transporter

at fasting - there are low levels of insulin -- few GLUT4 at the cell membrane – GLUT4 = insulin sensitive

what traps glucose in a cell

phosphorylation – once glucose enters a cell = it is phosphorylated to G6P and now committed to further metabolism

hexokinase vs glucokinase

**hexokinase** = phosphorylates glucose in most tissues **glucokinase** = liver, pancreatic b-cells

Fate of Glucose

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_1. glycogen 2. pentose phosphate pathway 3. glycolysis 4. lipogenesis 5. energy metabolism: anaerobic & aerobic

glycogen primarily in which two regions?

liver muscle

glycogen in liver maintains blood glucose for

maintains blood glucose for up to 24 hours - 100g

glycogen in muscle

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_fuel reserve for muscle contraction --\> glucose can't be released for use by other tissues - 400g

gluconeogenesis vs glycolysis vs glycogen synthesis located in the liver only!

**gluconeogenesis**: pyruvate --\> glucose **gycolysis**: glucose --\> pyruvate **glycogen synthesis** --\> G1P to glycogen

glucose 6 phosphatase - where is it located

can convert G6P to Glucose -- allows glucose to no longer be trapped in the cell ONLY IN THE LIVER!