BIOCHEMISTRY carbohydrate metabolism

08-11-25

Mouth

Start of the digestion process is always the ?

Salivary α-amylase

hydrolysis of some α-glycosidic linkages;
an enzyme found in human saliva that plays a role in the digestion of carbohydrates, specifically breaking down starch into smaller sugar molecules

Gastric juice

no effect on digestion

Stomach

an organ that helps the conversion of solid food to liquid

Intestine

resumes the enzymatic degradation using the pancreatic digestive enzyme

Pancreatic digestive enzymes

hydrolysis of polysaccharides to disaccharides

Brush border of intestines

disaccharides reaches further hydrolysis when it reaches ?

Intestinal Lining (Villi)

Where products of monosaccharides get absorbed

Salivary enzyme α-amylase

An enzyme that catalyzes the hydrolysis of α-glycosidic linkages of starch and glycogen to produce smaller polysaccharides and disaccharide — maltose

Stomach

Part of the carbohydrate digestion where very little carboydrate is digested
No carbohydrate digestion enzymes present in ?
Salivary amylase gets inactivated because of ? acidity

Stomach acidity

In the stomach, Salivary amylase gets inactivated because of ?

Small intestine

The primary site for the carbohydrate digestion is within the ?
Where Pancreatic α-amylase breaks down polysacccharide chains into disaccharide — maltose

Outer membranes

The final step in carbohydrate digestion occurs on the ? of intestinal mucosal cells

Maltase

hydrolyses maltose to glucose

Sucrase

hydrolyses sucrose to glucose and fructose

Lactase

hydrolyses lactose to glucose and galactose

Bloodstream

Glucose, galactose, and fructose are absorbed into the ? through the intestinal wall

Liver

Galactose and Fructose are converted to products of glucose metabolism in the ?

Galactose and Fructose

are not actually used, usually gets converted to get used by the body

Oxidized to CO2 and H2O (ATP)
Converted to fat
Converted to muscle glycogen

The glucose in the tissues may be:

Blood-sugar level

The proper functions of the body are dependent on precise control of the glucose concentration in the blood.

Glucose concentration

In blood-sugar level, The proper functions of the body are dependent on precise control of the ? in the blood

70-90 mg/100 mL.

The normal fasting level of glucose in the blood is ?

Hypolgycemia

• condition resulting from a lower than the normal blood-sugar level (below 70 mg/100 ml)

• extreme hypoglycemia, usually due to the presence of excessive amounts of insulin, is characterized by general weakness, trembling, drowsiness, headache, profuse perspiration, rapid heart beat, lowered blood pressure and possible loss of consciousness.

• Loss of consciousness is most likely due to the lack of glucose in the brain tissue, which is dependent upon this sugar for its energy.

Hyperglycemia

• higher than the normal level (above 120 mg/100 mL); when the pancreas does not secrete enough insulin

• may temporarily exist as a result of eating a meal rich in carbohydrates.

• extreme hyperglycemia, the renal threshold (160-170 mg/100 mL) is reached and excess glucose is excreted in the urine

Hormones

Besides enzyme inhibition, carbohydrate metabolism may be regulated by ?

Insulin, Glucagon, Epinephrine

Three major hormones control carbohydrate metabolism:

Insulin

51 amino acid polypeptide secreted by the pancreas

Promotes utilization of glucose by cells

The release of insulin is triggered by high blood-glucose levels

Its function is to lower blood glucose levels by enhancing the formation of glycogen from glucose (glycogen synthesis)
Aids in glycogen synthesis

High blood-glucose levels

The release of insulin is triggered by ?

mom Insulin

involves insulin binding to proteins receptors on the outer surfaces of cells which facilitates entry of the glucose into the cells

Glucagon

29 amino acid peptide hormone produced in the pancreas

Released when blood glucose levels are low

Principal function is to increase blood-glucose concentration by speeding up the conversion of glycogen to glucose (glycogenolysis) in the liver

elicits the opposite effects of insulin

Epinephrine

also called adrenaline
Released by the adrenal glands in response to anger, fear, or excitement

Function is similar to glucagon, i.e., stimulates glycogenolysis

Primary target of epinephrine is muscle cells

Promotes energy generation for quick action

Glycogenesis, Glycogenolysis, Gluconeogenesis, Hexose Monophosphate Shunt, Glycolysis, Citric Acid Cycle

Six major metabolic pathways of glucose

Glycolysis

A series of reactions in the cytoplasm which converts glucose (C₆) to two molecules of pyruvate (a C₃ carboxylate), and ATP and NADH are produced.

Also called Embden-Meyerhof pathway, after the scientist who elucidated the pathway.

An anaerobic process; each step takes place without O₂; one of its advantages, the body can obtain energy from glycolysis quickly, without waiting for a supply of O₂ to be carried to the cells.

Occurs in cells lacking mitochondria, e.g., erythrocytes and in certain skeletal muscle cells during intense muscle activity.

Embden-Meyerhof pathway

Glycolysis is also called ?, after the scientist who elucidated the pathway

Phase 1 of Glycolysis

“energy investment phase”
Phosphorylation of glucose and conversion to 2 molecules of glyceraldehyde-3-phosphate; 2 ATP are used in these reactions

Phase 2 of Glycolysis

“energy payoff phase”
Conversion of glyceraldehyde-3-phosphate to pyruvate and coupled formation of 4 molecules of ATP.

Hexokinase

an enzyme that transfers phosphate group
an enzyme that catalyzes the phosphorylation of hexoses, particularly glucose, using ATP

Step 1 of Glycolysis

Formation of glucose-6-phosphate
Endothermic reaction catalyzed by hexokinase
Energy needed is derived from ATP hydrolysis

Step 2 of Glycolysis

Formation of Fructose-6-phosphate:
Enzyme: Phosphoglucoisomerase

Step 3 of Glycolysis

Formation of Fructose 1,6-bisphosphate Enzyme: phosphofructokinase

Step 4 of Glycolysis

Formation of Triose Phosphates

C6 species is split into two C3 species

Enzyme: Aldolase

Step 5 of Glycolysis

Isomerization of Triose Phosphates

DHAP is isomerized to glyceraldehyde 3-phosphate

Enzyme: Triosephosphate isomerase

Step 6 of Glycolysis

Formation of 1,3-bisphosphoglycerate

Glyceraldehyde 3-phosphate is oxidized and phosphorylated

Enzyme: Glyceraldehyde-3-phosphate dehydrogenase

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