CARBOHYDRATES Flashcards
what are the examples of compounds of carbohydrates
- starch
- sugars
- cellulose
- chitin
what are the general functions of carbohydrates
- structural components of DNA and RNA
- Serves as sources of energy e.g glucose
- serves are energy of storage e.g glycogen and satrch
- sparing the use of fats and proteins
what does the classification of carbohydrates based upon
- based on the size of base carbon chain
- based on the location of the C=O function group
- based on the number of sugar units
- based on the stereochemistry of the compound
how do we classify carbons accordding to the number of carbon in the molecule (Generic classification)
- Trioses (3 carbons)
- Tetroses( 4 carbons)
- Pentoses(5 carbons)
- Hexoses (6 carbons)
What distinguishes aldose from ketose in terms of their carbonyl group location?
Aldose derivatives have a terminal carbonyl group (O=CH-) at the end of their carbon chain, while ketose derivatives have a middle carbonyl group (O=C) linked to two other carbon atoms.
Describe the structure of the carbonyl group in aldose.
A carbonyl group is a functional group in organic chemistry characterize
The carbonyl group in aldose is an aldehyde functional group (O=CH-) located at the terminal carbon.
Where is the carbonyl group located in ketose?
In ketose, the carbonyl group is positioned between two other carbon atoms, forming a ketone group (O=C).
How does the position of the carbonyl group affect the classification of aldose and ketose
The location of the carbonyl group determines whether a sugar is classified as an aldose or a ketose. Aldoses have the carbonyl group at the end, while ketoses have it in the middle of their carbon backbone.
what are 3 major classes of carbohydrates
- monosaccharides
- disaccharides
- Polysaccharides
what are monosaccharides
simplest carbohydrates that cannot be further hydrolyzed and can contain 3 to 6 or more carbon atoms
what are the examples monosaccharides
- glucose
- fructose
- galactose
what are disaccharides
A disaccharide is a carbohydrate composed of two monosaccharides joined together by a glycosidic bond.
Which disaccharide is most abundant in blood?
sucrose
How can sucrose be hydrolyzed, and what products are obtained
Sucrose can be hydrolyzed into glucose and fructose
What disaccharide is present in milk, and what monosaccharides constitute it?
Lactose, composed of galactose and glucose, is the disaccharide present in milk
What are the products when maltose breaks down?
Maltose breaks down into two glucose molecules.
What are polysaccharides?
Polysaccharides are complex carbohydrates composed of many monosaccharides, typically ranging from 200 to 2500.
How do polysaccharides serve as energy storage components?
Polysaccharides, such as starch and glycogen, function as energy storage molecules in organisms
Provide an example of a structural polysaccharide and describe its role.
Cellulose is a structural polysaccharide and serves as an integral component of plant cell membranes.
How are CHO (carbohydrates) ingested in the form of starch and glycogen?
CHO are ingested as polymers, specifically starch and glycogen.
Which enzymes break down CHO during digestion, and what simpler sugars do they produce?
Salivary amylase breaks down CHO into dextrines and maltose, while pancreatic secretions break it down into glucose, lactose, galactose, and fructose.
Where are monosaccharides absorbed in the digestive tract, and how
Monosaccharides are absorbed across the walls of the duodenum and ileum through an active, energy-dependent, carrier-mediated transport system.
Which monosaccharides are absorbed at a greater rate: glucose, galactose, or fructose?
Glucose and galactose are absorbed at a greater rate than fructose.
How are monosaccharides transported to the liver after absorption?
Monosaccharides are transported by the portal vein to the live
What is the fate of glucose in the body?
Glucose is the only carbohydrate that can be directly used for energy or stored as glycogen
What must happen to galactose and fructose before they can be utilized?
Galactose and fructose must be converted to glucose before they can be used.
: Which carbohydrate is an integral component of plant cell membranes?
Cellulose is a structural polysaccharide found in plant cell walls
What is the primary site of monosaccharide absorption in the small intestine
The primary site of monosaccharide absorption is the duodenum and ileum
Why is glucose essential for energy metabolism?
Glucose is directly used for energy production and can be stored as glycogen for future use
What are the different fates of glucose in the body?
- Metabolized completely into carbon dioxide and water: This occurs during cellular respiration in the mitochondria, where glucose is broken down into carbon dioxide (CO₂) and water (H₂O) to produce energy (ATP).
- Stored in the liver as glycogen: Excess glucose is converted into glycogen and stored primarily in the liver and skeletal muscles. Glycogen serves as a readily available energy reserve.
- Conversion to keto acids, amino acids, or protein: Glucose can be used for biosynthesis, contributing to the production of molecules like amino acids, proteins, and keto acids
What is glycolysis, and what does it involve?
Glycolysis is the metabolic pathway where glucose is broken down into smaller molecules. Key points:
~It occurs in the cytoplasm of cells.
~Glucose is converted into two molecules of pyruvate or lactate.
~ATP and NADH are produced during glycolysis.
What is glycogenesis, and where does it occur?
Glycogenesis is the process of converting glucose into glycogen for storage.
~It mainly occurs in the liver and skeletal muscles.
~Enzymes add glucose molecules to an existing glycogen chain.
~Glycogen serves as a short-term energy reserve
what is the difference between glycogenolysis and gluconeogenesis
glucogenolysis is a process by which glycogen breaks down into glucose while gluconeogenesis is a production of glucose from non-carbohydrate sources
what two major pancreatic hormones control blood glucose levels
- insulin
- glucagon
what glands plays a role in blood glucose control
adrenal grans and thyroid gland
What is the role of insulin in glucose metabolism?
Insulin, produced by the β-cells of the pancreatic islets of Langerhans, has several effects on glucose metabolism:Increases glycogenesis:
1. It promotes the conversion of glucose into glycogen for storage in the liver and muscles.
2. Enhances glycolysis: Insulin facilitates the breakdown of glucose into pyruvate or lactate.
3. Stimulates lipogenesis: It encourages the synthesis of fatty acids and triglycerides.
4. Decreases glycogenolysis: Insulin inhibits the breakdown of glycogen into glucose.
5.Reduces gluconeogenesis: It suppresses the production of new glucose from non-carbohydrate sources.
6. Inhibits proteolysis: Insulin prevents protein breakdown.
7. Suppresses lipolysis: It decreases the release of fatty acids from adipose tissue.
Where is insulin secreted, and what is its primary function?
Insulin is secreted by the β-cells of the pancreatic islets of Langerhans. Its primary function is to regulate blood glucose levels by promoting glucose uptake, storage, and utilization.
eplain glycogenesis and glycolysis: glucose →glycogen→pyruvate→ acetyl-CoA
Glycogenesis is the process of converting glucose into glycogen for storage.
Steps:
Glucose → Glycogen: Excess glucose is transformed into glycogen primarily in the liver and skeletal muscles.
Purpose: Glycogen serves as a readily available energy reserve.
Glycolysis is the breakdown of glucose into smaller molecules.
Steps:
Glucose → Pyruvate: Glucose is metabolized through a series of biochemical reactions, resulting in the production of pyruvate or lactate.
Energy Production: Glycolysis generates ATP and NADH.
Acetyl-CoA Connection: Pyruvate can further enter the citric acid cycle (Krebs cycle) to produce acetyl-CoA, a key molecule for energy production
what is lipogenesis
Lipogenesis is the process of producing lipid or fat to store biochemical energy for later metabolic use
What is the source of glucagon in the body?
Glucagon is secreted by the alpha cells of the islets of Langerhans in the pancreas.
When is glucagon released
Glucagon is released during stress and fasting states.
What is the primary function of glucagon?
Glucagon acts as a hyperglycemic agent, meaning it increases blood glucose levels.
How does glucagon affect glycogenolysis?
Glucagon stimulates glycogenolysis, leading to the breakdown of stored glycogen into glucose.
Describe the role of glucagon in gluconeogenesis
Glucagon promotes gluconeogenesis, where fatty acids are converted into acetyl-CoA, which can further form ketones, and proteins are broken down into amino acids that contribute to glucose production.
explain this in details “gluconeogenesis: fatty acids → acetyl-CoA → ketone, proteins → amino acids
Fatty Acids: These are primarily derived from stored triglycerides in adipose tissue
Fatty Acids → Acetyl-CoA:
Fatty acids undergo β-oxidation in mitochondria, producing acetyl-CoA.
Acetyl-CoA can enter the citric acid cycle (Krebs cycle) for energy production.
Acetyl-CoA → Ketone Bodies:
In the liver, excess acetyl-CoA can lead to ketogenesis.
Ketone bodies (such as β-hydroxybutyrate and acetoacetate) are produced.
These ketones serve as an alternative fuel source during prolonged fasting or starvation
Proteins → Amino Acids:
Proteins are broken down into amino acids.
mention the hormones that affect glucose levels in the human body
- Epinephrine (stress hormone) inhibits insulin secretion, increasing glycogenolysis, and promoting lipolysis.
- Cortisol, decreases intestinal cell uptake and increases gluconeogenesis, glycogenolysis, and lipolysis so as to increase blood glucose levels
- Growth hormone: decreases the entry of glucose into the cells and increases glycolysis
- ACTH: stimulates cortisol release from the adrenal cortex
- Thyroxine that stimulates glycogenolysis, gluconeogenesis, and intestinal absorption of glucose
- Somatostatin produced by the δ-cells of the islets of Langerhans of the pancreas
~inhibits insulin, glucagon, growth hormone, and other endocrine hormones.
How do tubes containing sodium fluoride and potassium oxalate affect glycolysis?
These tubes inhibit glycolysis, preventing the breakdown of glucose, and can preserve blood samples for up to 3 days at room temperature.
What are the three measurement methods for glucose testing?
- Hexokinase Method: This enzymatic method measures glucose by using hexokinase to convert glucose to glucose-6-phosphate.
- Glucose Oxidase Method: Glucose oxidase reacts with glucose to produce gluconic acid and hydrogen peroxide, which is then detected.
- Glucose Dehydrogenase Method: Glucose dehydrogenase converts glucose to gluconolactone, and the resulting NADH is measured.
expain the working principle of a glucometer
Glucose meters employ enzymes such as glucose oxidase, hexokinase, or glucose dehydrogenase. These devices predominantly utilize pyrroloquinoline quinone (PQQ) or a combination of glucose oxidase and NAD for accurate glucose measurement. The final reading can be obtained through reflectance photometry or electrochemical methods
What is the purpose of the glucose tolerance test?
The glucose tolerance test assesses how effectively cells can utilize glucose
Which types of diabetes can be diagnosed using glucose clearance test?
gestational diabetes, type 1 diabetes, and type 2 diabetes
What are the three versions of glucose clearance test
1-hour, 2-hour, and 3-hour tests.
How much glucose is administered during each version glucose clearance test
50g, 75g, and 100g
What is the dosage of glucose given to children during glucose clearance test?
1.75 g/kg of glucose, up to a maximum dose of 75 g
Explain patient preparation for glucose clearance test
- patient should be ambulatory and on a normal to high carbohydrate intake for 3 days before the test.
- Patient dhould fast for 8 to atleast 10 hours
why should patient clearance be done in the morning
because of hormonal diurnal effect
in glucose clearance test what will basal fasting glucose indicate
type 1 and type 2 diabetes
what are the factors that affect the glucose tolerance results
- Medications e.g salicylates, anticonvulsants
- Gastrointestinal problems, including malabsorption problems, gastrointestinal surgery, endocrine dysfunction,
what is glycosylated hemoglobin
is a compund of glucose and hemoglobin (ketoamine)
what is the significance of glycosylated hemoglobin test
Provides time averaged picture of patients blood glucose levels over the past 3 months
what is the importance of glycosylated hemoglobin (ketoamine) test
it is reliable for monitoring long term diabetes control
what are the normal ranges glycosylated hemoglobin test
4% - 6%
What is the recomended test interval for patients with stable glucose levels and those with unstable glucose levels for keto amine test
- For patients with unstable glucose levels, quarterly HbA1c test is recommended
- For patients with unstable glucose levels, quarterly HbA1c test is recommended
explain 2 test categories for glycosylated hemoglobin test (HbA1c)
- Based on charge difference between glycosylated and no-glycosylated hemoglobin
- Based on structural characteristics of glycogroups on hemoglobin
What is the preferred method for glycosylated hemoglobin testing in a clinical laboratory
The preferred method is affinity chromatography.
How does cation exchange chromatography work in this context?
In cation exchange chromatography, negatively charged hemoglobins attach to the positively charged resin bed.
Which type of hemoglobins elute first from the column during cation exchange chromatography?
The glycohemoglobins, which are the most negatively charged, elute first.
How does the presence of hemoglobin F affect test results?
It yields false increased levels of HbA1c
What effect do hemoglobins S and C have on test results?
They yield false decreased levels of HbA1c.
What is the basis of a point-of-care instrument HbA1c assay?
It is based on a latex immunoagglutination inhibition methodology
What two concentrations are measured in the HbA1c assay?
Both the concentration of HbA1c and the concentration of total hemoglobin are measured
How is the result reported in the HbA1c assay?
The result is reported as percent HbA1c
Does affinity chromatography involve a resin bed
The text doesn’t specify that affinity chromatography involves a resin bed; it mentions a resin bed in relation to cation exchange chromatography.
What is the primary purpose of measuring HbA1c?
HbA1c measurement provides an indication of long-term blood glucose control in individuals with diabetes.
What is the principle of the Molisch’s test?
The principle of the Molisch’s test involves the dehydration of pentoses and hexoses by Sulphuric acid and Hydrochloric acid. This forms furfural or hydroxymethylfurfural.
How does cation exchange chromatography work in this context?
In the Molisch’s test, the products of dehydration condense with alpha-naphthol or other phenols to form a purple condensate.
what is molisch test
is a general test for the presence of carbohydrates, which is perfomed before a more specific test
the test is positive for all types of carbohydrates
explain the fehlings principle
Fehling’s solution containing blue alkaline cupuric hydroxide solution, heated with reducing sugars gets reduced to yellow or red cupric oxide (brick red)and is precipitated.
explain the procedure of fehling’s test
In a test tube, add 2 ml of the test carbohydrate solution
Add equal volumes of Fehling A & Fehling B and place it in a boiling water bath for few minutes.
When thecontentsof the test tube comesto boiling, mixthem together and observe any change in color or precipitate formation.
The production of yellow ‘or brownish-red precipitate of cuprous oxide indicates the presence of reducing sugars in the given sample
what is the clinical significance of fehlings test
The test is used to differentiate between water-solube aldehyde and ketone functional groups
It is used as a generic test for monosaccharides
It will give a positive result with aldose monosaccharides
Fehling’s test man be used to screen glucose in urine (diabetes
what is the principle of benedicts test
The free aldehyde or keto groups in the reducing sugars reduces copper (II) ions in the Benedict’s solution are reduced to Copper (I) ions, which causes the color change.
Depending on the concentration of sugars the increased sugar concentration the nearer the final color is to brick red
What is the procedure of benedicts test
In the test tube with 2 ml of Benedict’s reagent, add 5-6 drops (1 ml) of the test carbohydrate solution and mix well.
Place the test tube in a boiling water bath for 3-5 minutes and observe any change in color or precipitate formation. Cool the solution.
Observe the colour change from blue to green, yellow, orange or red depending upon the amount of reducing sugar present in the test sample
explain 3 clinical significances of benedicts test
- If the color change into green, then there would be 0.1 to 0.5 percent sugar in solution., yellow, then 0.5 to 1 percent sugar is present, orange, then it means that 1 to 1.5 percent sugar is present, red, then 1.5 to 2.0 percent sugar is present., red to brick red it means that more than 2 percent sugar is present in solution.
- All monosaccharides will give a positive reaction, disaccharides like maltose may give a weak positive reaction
- This test may be used to detect glucose in urine and galactosemia
What is barfoed test
is a specific test for monosaccharides
what is the test principle for barfoed test
Reducing sugars in the presence of copper (II) and ethanoic acid, reduces coper to form a carboxylic acid and reddish precipitate of copper (I)
what is the test procedure for barfoed test
- To 2 mL of the test solution add about 2-3 mL of Barfoed’s reagent.
- Mix it well and boil it for 1-3 minutes in the water bath and allow to stand for a few minutes.
- Formation of a red precipitate of cuprous oxide in the bottom and along the sides of the test tube immediately,
clinical signiicance of barfoed test
A specific test for monosaccharides
Disaccharides are weak reducing agents and the test will be negative
What is the test principle for seliwanoff’s test
- concentrated HCL is added to ketoses yielding furfural more rapidly than aldoses
2.furfural forms complexes with recorcital to yield a deep red colour
explain the procedure for seliwanoff test
To 2 mL of Seliwanoff ’s reagent, Add two drops of test solution, heat the mixtureto just boiling.
A cherry red condensation product will be observed indicating the presence of ketoses in the test sample.
There will be no significant change in colour produced for aldose sugar.
what is the principle of bails test
Pentoses and hexoses react with react s with Bail’s reagent and converted to furfural.
Orcinal and furfural condenses in the presence of ferric ions to form a colored product
what is the procedure of bails test
- To 5 mL of Bial’s reagent add 2–3 mL of test solution
- Warm gently in a hot water bath for 2minutes .
- The formation of a bluish green product is indicative of pentoses.
- Hexoses generally react to form muddy brown products
explain the principle of iodine test
Based on the formation od a blue-black starch-iodine complex.
Starch contain polymer of alpha-amylose and amylopectin which forms a complex with iodine
what is the test procedure for iodine test
Add 2 drops of iodine solution to about 2 mL of the carbohydrate containing test solution.
A blue-black colour is observed which is indicative of presence of polysaccharides
what is the test principle of osazone test
Aldoses and Ketoses react with phenylhydrazine to produce a phenylhydrazone which reacts with another two molecules of phenylhydrazine to yield osazone forming yellow colored crystals
what is the principle of osazone test
To 0.5 g of phenylhydrazine hydrochloride, add 0.1 gram of sodium acetate and ten drops of glacial acetic acid.
Add 5 mL of test solution to this mixture and heat under boiling water bath for about half an hour.
Observe the solution slowly and examine the crystals under a microscope.
what are the expected results in osazone test
Needle-shaped yellow osazone crystals will be observed for glucose and fructose, whereas lactosazone shows mushroom shaped and maltose produces flower-shaped crystals
define diabetes mellitus
A cluster of metabolic diseases resulting from defects in insulin secretion, insulin action or both
Differentiate between primary and secondary diabetes mellitus.
~Primary diabetes mellitus: Can be either monogenic or polygenic.
~Secondary diabetes mellitus: Occurs due to other underlying conditions or factors.
What is monogenic diabetes mellitus
Monogenic diabetes mellitus: Caused by a single gene mutation.
how is monogenic diabetes mellitus characterized
it is characterized by impared insulin secretion by beta cells of the pancreas
What are the characteristic features of type 1 diabetes mellitus?
Type 1 diabetes is caused by an absolute deficiency of insulin.
It is associated with the autoimmune destruction of beta cells.
Patients with uncontrolled type 1 diabetes present with diabetic ketoacidosis
Which serum measurements are used for the diagnosis of diabetes mellitus?
Fasting blood glucose, postprandial blood glucose, and glycated hemoglobin (HbA1c).
What criteria are used for diagnosing diabetes?
- Fasting blood glucose >126 mg/dL.
- 2-hour postprandial glucose >140 mg/dL.
HbA1C >6.5%. - Random blood glucose >200 mg/dL with classical symptoms.
Which auto-antibodies serve as biomarkers for type 1 diabetes?
Antibodies to GAD65 and antibodies to tyrosine phosphatase IA-2 and IA-2 beta.
What are 3 classifications of diabetes mellitus
- type 1 diabetes (insulin dependent)
- type 2 diabetes (non insulin dependent)
- Gestational diabetes
What percentage of all diabetes is accounted for by monogenic diabetes?
Monogenic diabetes accounts for 25% of all diabetes
Name three examples of monogenic diabetes
- Maturity onset diabetes of the young (MODY), 2.mitochondrial diabetes,
- neonatal diabetes.
What characterizes MODY
- Young age onset.
- Family history due to autosomal inheritance.
- Absence of obesity and insulin resistance.
- Negative autoantibodies.
- Mild hyperglycemia.
Which genes are most commonly mutated in MODY?
Genes encoding Glucokinase (GCK) and hepatocyte nuclear factors (HNF).
At what age does neonatal diabetes mellitus typically occur
Up to the age of six months
What causes neonatal diabetes mellitus?
Mutation of genes involved in organogenesis, formation of beta cells, and insulin synthesis.
Which gene is associated with Neonatal Diabetes Mellitus
Kir6.2 (ATP-sensitive inward rectifier potassium channel)
At what mean age does Mitochondrial DM typically onset?
35 YEARS
What causes Mitochondrial DM?
Mutation of mitochondrial DNA
Why do most patients with Diabetes Mellitus eventually require insulin therapy?
Because the disease develops due to failure of insulin secretion.
What is a characteristic feature distinguishing MODY from other types of Diabetes Mellitus?
Young age onset
What genetic mutation is associated with Neonatal Diabetes Mellitus?
Mutation in genes that encode Kir6.2.
What are the characteristic symptoms of Type 1 diabetes mellitus
Inappropriate hyperglycemia, polydipsia, polyuria, and rapid weight loss.
What is the primary cause of Type 1 diabetes mellitus?
Cell-mediated autoimmune destruction of pancreatic β-cells
Which autoantibodies are associated with Type 1 diabetes mellitus?
Islet cell autoantibodies, insulin autoantibodies, glutamate decarboxylase autoantibodies (GAD), and tyrosine phosphatase IA-2 and IA2 autoantibodies.
Which genes contribute to the genetic susceptibility of Type 1 diabetes mellitus?
HLA gene (HLA-DR3-DQ2 and HLA-DR4-DQ8).
What environmental factors may influence the development of Type 1 diabetes mellitus
Dietary constituents, Coxsackie viruses, and vaccinations
What is the consequence of cell-mediated auto immune destruction in Type 1 diabetes mellitus?
An absolute deficiency of insulin secretion
what is diabetes insipidus
Diabetes insipidus is a rare condition characterized by excessive urination and extreme thirst. It occurs due to problems with the hormone antidiuretic hormone (ADH), which regulates water balance in the body
What percentage of all diabetes cases does type 2 diabetes mellitus account for?
Type 2 diabetes mellitus accounts for more than 90% of all cases.
How is type 2 diabetes mellitus characterized?
It is characterized by adult onset, insulin resistance, and it may be accompanied by obesity and beta cell dysfunction.
What are the factors contributing to insulin resistance in type 2 diabetes mellitus?
Insulin resistance results from:
1. Down regulation of insulin receptor.
2. Abnormalities in the signaling pathway.
3. Impairment of fusion of GLUT-4 (glucose transporter 4) on cell membranes.
What was the former term used to refer to type 2 diabetes mellitus?
It was formerly referred to as NIDDM (Non-Insulin Dependent Diabetes Mellitus).
What is the genetic basis for type 2 diabetes mellitus?
It is polygenic, meaning multiple genes contribute to its development
What is gestational diabetes mellitus (GDM)
Gestational diabetes mellitus is a type of diabetes that occurs during pregnancy due to increased hormones (estrogen, progesterone) affecting insulin function.
When is gestational diabetes typically seen during pregnancy?
It is typically seen during the second or third trimester of pregnancy.
What are the risk factors for developing gestational diabetes
- Increased maternal age
- Obesity
- Family history of diabetes
- Previous history of gestational diabetes
- Polycystic ovary syndrome (PCOS)
What hormonal changes contribute to gestational diabetes?
Increased hormones (estrogen, progesterone) can lead to insulin resistance. Cortisol counteracts the effects of insulin
What other conditions or factors may result in gestational diabetes?
- Pancreatic conditions (e.g., cystic fibrosis, chronic pancreatitis, hemochromatosis)
- Endocrine diseases (e.g., Cushing’s syndrome, acromegaly, pheochromocytoma)
- Use of certain drugs (e.g., thiazide diuretics, glucocorticoids, thyroid hormones)
what are the indications of diabetes mellitus
- fasting plasma glucose concentration of 126 mg/dl or greater
- Glycosylated hemoglobin of greater than 6.5%
- Random blood sugar of greater than 200 mg/dl
- 2 hour post- grandial plasm glucose of greater than 200 mg/dl
what are the complications of diabetes mellitus
acute:
1.diabetic ketoacidosis
2. hyperosmolar non- ketosis
3. lactic acidosis
chronic:
1. macrovascular disorders (stroke, myocardial infarction,, gangrene)
2. microvascular disorders ( diabetic retinopathy, diabetic eye disese)
define hypoglycemia
means decreased plasma glucose levels
what are thw results of hypoglycemia
causes brain fuel deprivation which may lead to impared judgement and seizures, comas, seizures, functional brain failure, death.
outline the 2 classes of hypogycemia
- postabsorptive (fasting) hypoglycemia- 4 hours after meal
- postprandial (reactive) hypoglycemia
