Carbohydrates and Lipids Flashcards by Fahcina Lawson

Galactose

Galactose is a monosaccharide similar to glucose, fructose, and mannose. They are compounds structurally known as isomers since they share the same chemical formula, C6H12O6. In addition, galactose is known to be a C-4 epimer of glucose since their structures differ only in the hydroxyl positioned at carbon 4. Galactose and glucose combine to form the disaccharide lactose, through a beta (1-4) linkage.
TAKEAWAY: Disaccharides are carbohydrates made up of two monomeric sugar moieties. Lactose is composed of glucose and galactose, joined by a beta (1-4) linkage.

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____carbohydrates made up of two monomeric sugar moieties. Lactose is composed of glucose and galactose, joined by a beta (1-4) linkage.

Disaccharides

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Fructose

Fructose is a monosaccharide similar to glucose, galactose, and mannose. They are compounds structurally known as isomers since they share the same chemical formula, C6H12O6. Fructose and glucose combine to form the disaccharide sucrose, or table sugar.

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_____ combine to form the disaccharide sucrose, or table sugar.

Fructose and glucose

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Maltose

Maltose is a disaccharide similar to lactose. Maltase is an intestinal brush border enzyme that cleaves the alpha (14)bond in maltose, producing two glucose monomers.

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______ an intestinal brush border enzyme that cleaves the alpha (14)bond in maltose, producing two glucose monomers.

Maltase

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_____ is a monosaccharide similar to glucose, galactose, and fructose. They are compounds structurally known as isomers since they share the same chemical formula, C6H12O6.

Mannose is a monosaccharide similar to glucose, galactose, and fructose. They are compounds structurally known as isomers since they share the same chemical formula, C6H12O6.

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Sucrose

Sucrose is a disaccharide similar to lactose. Sucrase is an intestinal brush border enzyme that cleaves the alpha (1-2)bond in sucrose, producing glucose and fructose.

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______ are not normal constituents of membranes, formed during periods of hyperglycemia and oxidative stress which transform normal constitutive membrane sugars into sugar alcohols that damage membranes of all cells including sensory neurons.

Sugar alcohols are not normal constituents of membranes, formed during periods of hyperglycemia and oxidative stress which transform normal constitutive membrane sugars into sugar alcohols that damage membranes of all cells including sensory neurons.
TAKEAWAY – Sorbitol is the main sugar alcohol that is formed from the hyperglycemia and oxidative stress associated with diabetes. Endothelial cells making up the inner lining of blood vessels is one of the initial targets of sorbitol, thereby decreasing the blood supply to various tissues, the most sensitive being the lower extremities causing diabetic foot ulceration, retina causing diabetic retinopathy and penis causing erectile dysfunction, among other sites.

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is the main sugar alcohol that is formed from the hyperglycemia and oxidative stress associated with diabetes. Endothelial cells making up the inner lining of blood vessels is one of the initial targets of _____, thereby decreasing the blood supply to various tissues, the most sensitive being the lower extremities causing diabetic foot ulceration, retina causing diabetic retinopathy and penis causing erectile dysfunction, among other sites.

Sorbitol

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Monosaccharides are normal constituents of membranes but during periods of hyperglycemia can become “glycated” and as glycated ____they are referred to as advanced glycation end products (AGEs) which can damage membranes of all cells including sensory neurons. losses.

Monosaccharides, amino acids, lipids and protiens

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28-year-old African American male visits his primary care physician for digestive problems. The patient states that he feels bloated and has flatulence whenever he eats foods containing milk products.
Which of the following chemical bonds is not being split due to his condition?

A glycosidic bond – This is the correct answer. The patient is exhibiting the classic signs of lactose intolerance, in which intestinal lactase levels are low, and the major dietary component of milk products (lactose) cannot be digested. Lactase will split the β-1,4 linkage between galactose and glucose in lactose. The lactose thus passes unmetabolized to the bacteria inhabiting the gut, and their metabolism of the disaccharide leads to the observed symptoms. Combining two sugars in a dehydration reaction creates a glycosidic bond. Adding a sugar to the nitrogen of a nitrogenous base also creates an N-glycosidic bond.
TAKEAWAY: Lactose intolerance is a common condition caused by a decreased ability to digest lactose, a sugar found in dairy products.

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A phosphodiester bond

A phosphodiester bond is a phosphate in two ester linkages with two different compounds (such as the 3′–5′ link in the sugar phosphate backbone of DNA and RNA).

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is the joining of an amino group with a carboxylic acid with the loss of water.

An amide bond

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An ester linkage

Ester linkages contain an oxygen linked to a carbonyl group

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A man diagnosed with diabetes 10 years ago presents to his primary care physician for a routine physical. He is obese and admits to noncompliance with his antidiabetic medications. His non-fasting blood glucose level is 300 mg/dl (normal fasting 80-100 mg/dl). He has hypercholesterolemia and his plasma triglycerides are high. Urinalysis shows 3+ protein (normal 0, negative to trace on a scale of 0-4+) in his urine.
Dysfunction of which of the following biomolecules is mostly responsible for this man’s abnormal urinalysis?

The membrane proteoglycan (glycoprotein) heparan sulfate is the main component of the kidney’s basement membrane responsible for keeping proteins out of normal urine. The kidney’s glomerular basement membrane consists of a meshwork of type IV collagen, laminin, proteoglycans and glycosaminoglycans, also known as mucopolysaccharides. The glomerular membrane regulates renal filtration of blood plasma. The reflection coefficient of the membrane is such that it does not filter proteins the size of albumin and larger (> ellipsoid 15 x 4 nm, molecular weight > 69 kDa); therefore, albumin should not be found in normal urine or if it does, only in trace amounts. The net negative charge on the glomerular membrane proteins plays a major role in “reflecting” albumin (also negatively charged). Proteins smaller than albumin are filtered but are reabsorbed back into the blood plasma mainly in the kidney’s proximal tubules by the mechanism of endocytosis; therefore, there should be either no or only trace amounts of protein in the urine of a person with normal kidney function.

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The proteoglycan ____is an important component of the glomerular basement membrane that helps maintain the membrane’s net negative charge that reflects albumin and smaller plasma proteins which are also negatively charged. The basement membrane of the kidney’s glomerular filter, formed by fusion of basement membranes secreted by epithelial cells Bowman’s capsule and endothelial cells of glomerular capillaries. Proteins the size of albumin and larger are reflected off the kidney’s glomerular membrane, thereby keeping albumin in the blood plasma and out of urine. Proteins smaller than albumin are reabsorbed by endocytosis.

Heparan sulfate

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-___ is an amino sugar, abundant monosaccharide in tissues, and a precursor for synthesis of glycosylated proteins and sugars. -___also has anti-inflammatory properties but does not play a prominent role in filtration of the glomerular membrane.

Glucosamine

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The kidney’s glomerular basement membrane consists of a meshwork of type IV collagen, laminin, proteoglycans and ____, also known as mucopolysaccharides; however, a component other than ____ is mainly responsible for guarding against filtration of proteins and their presence in urine.

glycosaminoglycans

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-___ also known as phosphatidyl choline, is the most abundant phospholipid in cell plasma membranes, is also present in the glomerular membrane but not in the basement membrane the properties of which are mainly responsible for glomerular filtration of proteins and guarding against their appearance in urine.

Lecithin, also known as phosphatidyl choline, is the most abundant phospholipid in cell plasma membranes, is also present in the glomerular membrane but not in the basement membrane the properties of which are mainly responsible for glomerular filtration of proteins and guarding against their appearance in urine.

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Lecithin, also known as ____, is the most abundant phospholipid in cell plasma membranes, is also present in the glomerular membrane but not in the basement membrane the properties of which are mainly responsible for glomerular filtration of proteins and guarding against their appearance in urine.

phosphatidyl choline

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Compounds that have the same chemical formula but have different structures are called

isomers… For example, fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C₆H₁₂O₆

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Carbohydrate isomers that differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon, are defined as

epimers… For example, glucose and galactose are C-4 epimers because their structures differ only in the position of the –OH (hydroxyl) group at carbon 4.

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Creation of an _____ carbon (the former carbonyl carbon) generates a new pair of isomers, the α and β

anomers (anomeric)

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The α and β forms of anomeric carbons are _not mirror images_, and they are referred to as \_\_\_

diastereomers

\_\_\_\_ are able to distinguish between The α and β forms of anomeric carbon structures and use one or the other preferentially

Enzymes… For example, glycogen is synthesized from α-d-glucopyranose, whereas cellulose is synthesized from β-d-glucopyranose.

\_\_\_\_can react with chromogenic agents (for example, **the Benedict reagent)** causing the reagent to be reduced and colored as the aldehyde group of the acyclic sugar is oxidized to a carboxyl group.

Reducing Sugars

If the hydroxyl group on the anomeric carbon of a cyclized sugar is not linked to another compound by a glycosidic bond, the ring can open. The sugar can act as a reducing agent and is termed a \_\_\_

reducing sugar.

All monosaccharides, but not all disaccharides, are ____ sugars.

reducing sugars

## Footnote A ___ test can detect a reducing sugar in urine. A positive result is indicative of an underlying pathology (because sugars are not normally present in urine) and can be followed up by more specific tests to identify the reducing sugar.

colorimetric

Carbohydrates can be attached by glycosidic bonds to noncarbohydrate structures, including purine and pyrimidine bases (found in nucleic acids), aromatic rings (such as those found in steroids and bilirubin), proteins (found in glycoproteins and proteoglycans), and lipids (found in glycolipids). If the group on the noncarbohydrate molecule to which the sugar is attached is an –NH₂ group, then the bond is called an N-glycosidic link. If the group is an –OH, then the bond is an O-glycosidic link [Note: All sugar-sugar glycosidic bonds are O-type linkages.]

Draw out the key concept map for the classification and structure of monosaccharides and the digestion of dietary carbohydrates

The _____ absorbs the bulk of the monosaccharide products of digestion. However, different sugars have different mechanisms of absorption

The upper jejunum

The _____ absorbs the bulk of the monosaccharide products of digestion. However, different sugars have different mechanisms of absorption

The upper jejunum

galactose and glucose are taken into enterocytes by secondary active transport that requires a concurrent uptake (symport) of sodium (Na⁺) ions. The transport protein is the sodium-dependent glucose cotransporter

1 (SGLT-1). [Note: Sugar transport is driven by the Na⁺ gradient created by the *Na⁺-potassium* (*K⁺*) *ATPase* that moves Na⁺ out of the enterocyte and K⁺ in

Fructose absorption utilizes an energy- and Na⁺-independent monosaccharide transporter

Fructose absorption utilizes an energy- and Na⁺-independent monosaccharide transporter **(GLUT-5).**

All three monosaccharides *(glucose, fructose and galactose)* are transported from the enterocytes into the portal circulation by yet another transporter

**GLUT-2**

Identification of a specific enzyme deficiency can be obtained by performing oral tolerance tests with the individual \_\_\_\_\_.

disaccharides

Measurement of _{___}in the breath is a reliable test for determining the amount of ingested carbohydrate **not** absorbed by the body, but which is _metabolized instead by the intestinal flora_

**H****₂**

**Monosaccharide** containing an aldehyde group are called \_\_\_\_, and those with a keto group are called \_\_\_\_

**aldoses and ketoses**

**Disaccharides**, **oligosaccharides**, and **polysaccharides** consist of monosaccharides linked by **glycosidic bonds**.

**glycosidic bonds**.

Compounds with the same chemical formula but different structures are called **isomers**.

**isomers**.

Two monosaccharide isomers differing in configuration around one specific carbon atom (not the carbonyl carbon) are defined as

**epimers**.

In ___ (mirror images), the members of the sugar pair are designated as \_\_\_\_\_. When the aldehyde group on an acyclic sugar gets oxidized as a chromogenic agent gets reduced, that sugar is a \_\_\_\_\_\_

In **enantiomers** (mirror images), the members of the sugar pair are designated as **d-** and **l-isomers**. When the aldehyde group on an acyclic sugar gets oxidized as a chromogenic agent gets reduced, that sugar is a **reducing sugar**.

When a sugar cyclizes, an _____ is created from the carbonyl carbon of the aldehyde or keto group.

When a sugar cyclizes, an **anomeric carbon** is created from the carbonyl carbon of the aldehyde or keto group.

anomeric carbon sugars can have two configurations, forming

anomeric carbon sugars can have two configurations, forming **α** or **β anomers**.

A sugar can have its anomeric carbon linked to an –NH₂ or an –OH group on another structure through **N-** and \_\_\_\_\_

A sugar can have its anomeric carbon linked to an –NH₂ or an –OH group on another structure through **N-** and **O-glycosidic bonds** respectfully

\_\_\_\_\_ initiates digestion of _____ (for example, starch or glycogen), producing oligosaccharides.

***Salivary α-amylase*** initiates digestion of **dietary polysaccharides** (for example, starch or glycogen), producing oligosaccharides.

\_\_\_\_\_continues the carbohydrate digestion process. The final digestive processes occur at the ______ of the \_\_\_\_\_.

***Pancreatic α-amylase*** continues the process. The final digestive processes occur at the **mucosal lining** of the **small intestine**.

Several *disaccharidases* (for example, ***lactase*** [***β-galactosidase***], ***sucrase***, ***isomaltase***, and ***maltase***) produce monosaccharides (glucose, galactose, and fructose).

These enzymes are **transmembrane proteins** of the luminal **brush border** of **intestinal mucosal cells** (**enterocytes**).

***lactase*** [***β-galactosidase***], ***sucrase***, ***isomaltase***, and ***maltase***

Absorption of the monosaccharides requires specific \_\_\_\_\_. If carbohydrate degradation is deficient (as a result of heredity, disease, or drugs that injure the intestinal mucosa), undigested carbohydrate will pass into the large intestine, where it can cause \_\_\_\_\_\_\_\_.

Absorption of the monosaccharides requires specific **transporters**. If carbohydrate degradation is deficient (as a result of heredity, disease, or drugs that injure the intestinal mucosa), undigested carbohydrate will pass into the large intestine, where it can cause **osmotic diarrhea**.

**Which of the following statements best describes glucose?** A. It is a C-4 epimer of galactose. B. It is a ketose and usually exists as a furanose ring in solution. C. It is produced from dietary starch by the action of α-amylase. D. It is utilized in biological systems only in the l-isomeric form.

Correct answer = A. Because glucose and galactose differ only in configuration around carbon 4, they are C-4 epimers that are interconvertible by the action of an epimerase. Glucose is an aldose sugar that typically exists as a pyranose ring in solution. Fructose, however, is a ketose with a furanose ring. α-Amylase does not produce monosaccharides. The d-isomeric form of carbohydrates is the form typically found in biologic systems, in contrast to amino acids that typically are found in the l-isomeric form.

**Routine examination of the urine of an asymptomatic pediatric patient showed a positive reaction with Clinitest (a copper reduction method of detecting reducing sugars) but a negative reaction with the glucose oxidase test for detecting glucose. Using these data, show on the chart below which of the sugars could (YES) or could not (NO) be present in the urine of this individual.**

Clinitest is a nonspecific test that produces a change in color if urine is positive for reducing substances such as reducing sugars (fructose, galactose, glucose, lactose, xylulose).

**Why are α-glucosidase inhibitors that are taken with meals, such as acarbose and miglitol, used in the treatment of diabetes? What effect should these drugs have on the digestion of lactose?**

α-Glucosidase inhibitors slow the production of glucose from dietary carbohydrates, thereby reducing the postprandial rise in blood glucose and facilitating better blood glucose control in diabetic patients. These drugs have no effect on lactose digestion because the disaccharide lactose contains a β-glycosidic bond, not an α-glycosidic bond

**Why are α-glucosidase inhibitors that are taken with meals, such as acarbose and miglitol, used in the treatment of diabetes? What effect should these drugs have on the digestion of lactose?**

Blood glucose can be obtained from three primary sources: \_\_\_, ___ , and \_\_\_\_.

Blood glucose can be obtained from three primary sources: **the diet**, **glycogen degradation**, and **gluconeogenesis**.

The main stores of **glycogen** in the body are found in \_\_\_, where they serve as a fuel reserve for the synthesis of ____ during muscle **contraction**, and in the **liver**, where they are used to maintain the _____ concentration, particularly during the early stages of a **fast**.

The main stores of **glycogen** in the body are found in **skeletal muscle**, where they serve as a fuel reserve for the synthesis of **ATP** during muscle **contraction**, and in the **liver**, where they are used to maintain the **blood glucose** concentration, particularly during the early stages of a **fast**.

Draw out Glycogen metabolism in the liver

Glycosaminoglycans (GAG) have the ability to bind large amounts of water, thereby producing the gel-like matrix that forms the basis of the body's ground substance, which, along with fibrous structural proteins such as collagen, elastin, and fibrillin-1, and adhesive proteins such as fibronectin, makes up the \_\_\_\_

extracellular matrix (ECM)

Because of the high concentration of negative charges GAG extends in solution, but repel each other and are surrounded by water molecules. When brought together, they slide past each other, like magnets with the same polarity. **This produces the slippery consistency of mucous** **secretions and synovial fluid and the vitreous fluid of the eye**. When a solution of GAG is compressed, the water is squeezed out, and the GAG are forced to occupy a smaller volume. When the compression is released, the GAG spring back to their original, hydrated volume because of the repulsion of their negative charges.

All (six major types) GAG, except for hyaluronic acid, are sulfated and are found covalently attached to protein, forming proteoglycan monomers.

GAG are synthesized in the\_\_\_\_

**Golgi**.

Draw out the key concept map for GAG and proteoglycans and glycoprotiens

**glycoproteins vs. proteoglycans**

Glycoproteins are proteins to which short, branched, structurally diverse oligosaccharide chains (glycans) are attached. Proteoglycans consist of a core protein to which long, unbranched, glycosaminoglycan (GAG) chains are attached. GAG are large complexes of negatively charged heteropolysaccharides composed of repeating [acidic sugar-amino sugar]_n disaccharide units.

Structures of some common classes of lipids

In humans, the majority of fatty acids are saturated or monounsaturated. When double bonds are present, they are nearly always in the cis rather than in the trans configuration. The introduction of a cis double bond causes the fatty acid to bend or kink at that position

The number before the colon indicates the number of carbons in the chain, and those after the colon indicate the numbers and positions (relative to the carboxyl end) of double bonds.

There are two classes of phospholipids: those that have \_\_\_\_\_l (from glucose) as a backbone and those that have _____ (from serine and palmitate). Both classes are found as structural components of membranes, and both play a role in the generation of lipid signaling molecules.

There are two classes of phospholipids: those that have **glycerol** (from glucose) as a backbone and those that have **sphingosine** (from serine and palmitate). Both classes are found as structural components of membranes, and both play a role in the generation of lipid signaling molecules.

Phospholipids that contain glycerol are called glycerophospholipids (or phosphoglycerides). Glycerophospholipids constitute the major class of phospholipids and are the predominant lipids in membranes.

All contain (or are derivatives of) phosphatidic acid (PA), which is DAG with a phosphate group on carbon 3

Cardiolipin is antigenic and is recognized by antibodies (Ab) raised against _Treponema pallidum_, the bacterium that causes syphilis. The Wasserman test for syphilis detects these Ab.]