carbohydrates

CARBOHYDRATES

WEEK 3BIOCHEMISTRY

LECTURE

organic compounds composed of C, H & O

found primarily in plantsan excellent source of energy

CARBOHYDRATES

the sugar GLUCOSE is the most important CHO

it is as GLUCOSE that the bulk of dietary CHO is absorbed into the bloodstream and it is from GLUCOSE that all other CHO in the body are formed

CARBOHYDRATES

A.Monosaccharides building blocks of CHO are CHO that cannot be hydrolyzed or

broken into simpler CHO composed of single CHO unit ex. glucose, fructose, galactose

CLASSIFICATION

B. Disaccharidesyield two molecules of monosaccharides when hydrolyzedex. sucrose (glucose+fructose); lactose (glucose+galactose); maltose (glucose+glucose)

CLASSIFICATION

C. Polysaccharidesconsist of many units of monosaccharides ex. starch and fiber – food sources; glycogen--storage form in the liver and muscles

CLASSIFICATION

provide energy, fiber and naturally occurring sweeteners

protein-sparing effect—if enough CHO is provided to meet the energy need of the body, CHON can be spared or saved to use for specific protein functions

ketones or ketone bodies—intermediate products of metabolism of fats

ketoacidosis—increase levels of ketones in the body that affects the pH balance of the body

FUNCTIONS

the gastrointestinal tract has the role of digesting CHO into monosaccharides for easy absorption

digestion: mouth—salivary amylase/ptyalin (enzyme)

ex. starch------- dextrin, maltase small intestine—brush border

cells secrete enzymes(maltase,sucrase) monosaccharides are then absorbed in the small

intestine

DIGESTION & ABSORPTION

Glycogenesis- the process of converting glucose to glycogen

Glycogenolysis- the process of converting glycogen back to glucose

Gluconeogenesis- the process of producing glucose from fats and proteins

METABOLISM

blood glucose is a source of energy to all cells

glucose is essential for normal brain function and cell formation

N value= 70-120 mg/dl

BLOOD GLUCOSE REGULATION

controlled by a sophisticated hormonal system: INSULIN- lowers blood glucose level by

glycogenesis GLUCAGON- increases blood glucose level by

glycogenolysis SOMATOSTATIN- inhibits the functions of

insulin & glucagon

BLOOD GLUCOSE REGULATION

many meanings: simple CHO, sucrose, white table sugar

3 issues: focus sources: nutritive sweeteners: refined white

sugar, brown sugar, dextrose, honey, sugar alcohols (sorbitol, mannitol)

consumption levels

SUGAR- A Special Disaccharide

health effectso nutrient displacement- occurs when whole foods,

which are minimally processed, are not eaten and are replaced by foods containing added sugar

o dental caries- related to eating concentrated sweets and sticky CHO; sugar supports bacterial growth leading to plaque and tooth decay

o obesity/DM

SUGAR- A Special Disaccharide

other sweeteners sugar alcohols or sugar

replacers- are nutritive sweeteners because they provide 2 to 3 kcalories/gram

SUGAR- A Special Disaccharide

alternative sweeteners or artificial sweeteners- non-nutritive sweeteners, provide no nutrients and few, if any, kcalories; main function is to replace naturally sweet kcaloric substances such as sugar or honey

o ex. Aspartame(Nutrasweet/Equal) - formed by bonding of the amino acids phenylalanine and aspartic acid; 180 to 200 times sweeter than sucrose; contraindicated for persons with phenylketonuria(PKU)

SUGAR- A Special Disaccharide

Starch- the storage form of plant CHO -food sources: grains, legumes, vegetables and

fruits Fibers- consist of substances in plant foods

including CHO and lignin that cannot be digested by humans; its texture provides bulk that thickens chyme and eases the work of the GIT muscles that regulate movement of the food mass

Primary Prevention: obesity, constipation, colon cancer

COMPLEX CARBOHYDRATES/POLYSACCHARIDES

low blood glucose level is not a disease but a symptom of an

underlying disorderpossible causes:o fasting, intestinal malabsorption of glucoseo anti-DM drugs, overproduction of insulin by

the pancreas

HYPOGLYCEMIA

is a disorder of CHO metabolism characterized by hyperglycemia caused by insulin that is either defective or deficient

DIABETES MELLITUS

TYPE 1 DMo a form of DM in which the pancreas

produces NO insulin at allo characterized by Beta cell destruction with

severe insulin deficiency, is caused by autoimmune destruction of pancreatic B cells

o age of onset: < 30 years old NOT risk related

DIABETES MELLITUS

TYPE 2 DMo a form of DM in which the pancreas produces

some insulin that is defective and unable to serve the complete needs of the body

o insulin resistance is the hallmark of this disorder, this means there’s a decreased response to insulin by target tissues

o age of onset: > 30 years oldo risk related: the risk increases with family history,

age, weight and caloric intake

DIABETES MELLITUS

o a fasting plasma glucose ≥ 126 mg/dlo symptoms of DM plus a random

plasma glucose ≥ 200 mg/dlo a plasma glucose level ≥ 200 mg/dl

after an oral dose of 75 grams of glucose (oral glucose tolerance test)

DIAGNOSTIC CRITERIA OF DM

opolydipsia, polyuria (glucosuria), polyphagia, weight loss

Gestational DM- a form of DM occurring after the 20th month of gestation

S/SX