Carbohydrates Overview and Classification

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Questions and Answers

What characteristic defines blood group O?

  • Presence of GalNAc
  • Absence of GalNAc and galactose (correct)
  • Presence of both GalNAc and galactose
  • Presence of galactose

Which enzyme is responsible for degrading glycosidic bonds during digestion?

  • α-amilase
  • Glucosidase (correct)
  • Amylase
  • Cellulase

What type of bonds does α-amilase disrupt?

  • β(1->2) bonds
  • α(1->2) bonds
  • β(1->4) bonds
  • α(1->4) bonds (correct)

Which transporter is responsible for the absorption of glucose and galactose in the intestine?

<p>SGLT-1 (D)</p> Signup and view all the answers

What blood glucose concentration is considered essential for normal cerebral function?

<p>About 5 mM (90 mg/dL) (C)</p> Signup and view all the answers

What is the general formula for carbohydrates?

<p>(C.H2O)n (A)</p> Signup and view all the answers

Which of the following is a classification of carbohydrates based on the number of units?

<p>Monosaccharides (D)</p> Signup and view all the answers

What type of sugar is classified as an aldopentose?

<p>Ribose (D)</p> Signup and view all the answers

What is formed when two monosaccharides undergo a glycosidic bond?

<p>Disaccharide (D)</p> Signup and view all the answers

Which of the following carbohydrates is a structural polysaccharide?

<p>Cellulose (C)</p> Signup and view all the answers

Which type of carbonyl group is present in ketoses?

<p>Ketone group (D)</p> Signup and view all the answers

What type of saccharide is formed from glucose and fructose?

<p>Sucrose (D)</p> Signup and view all the answers

Which of the following sugars is a ketohexose?

<p>Fructose (C)</p> Signup and view all the answers

What is the main function of glycogen in living organisms?

<p>Energy storage (B)</p> Signup and view all the answers

Which suffix is commonly added to the names of carbohydrates?

<p>-ose (D)</p> Signup and view all the answers

What is the main significance of branching in polysaccharides like amylopectin?

<p>More ends allow for faster energy production. (D)</p> Signup and view all the answers

What role do glycosaminoglycans (GAGs) play in the extracellular matrix?

<p>Bind large amounts of water and create a gel-like matrix. (B)</p> Signup and view all the answers

Which of the following best distinguishes glycoproteins from proteoglycans?

<p>Glycoproteins have a higher protein content. (A)</p> Signup and view all the answers

What is the most common posttranslational modification of proteins?

<p>Glycosylation (C)</p> Signup and view all the answers

How do glycoproteins function in cell-surface recognition?

<p>They serve as receptors for hormones and viruses. (A)</p> Signup and view all the answers

What happens if the terminal sugar on the glycan is galactose?

<p>The blood group type becomes B. (D)</p> Signup and view all the answers

Which electrolyte property is associated with the composition of proteoglycans?

<p>Negatively charged (A)</p> Signup and view all the answers

What is one of the primary functions of mucins in the gastrointestinal tract?

<p>Provide lubrication and protect epithelial surfaces. (C)</p> Signup and view all the answers

Flashcards

Carbohydrates

A group of organic compounds containing a carbonyl group (either an aldehyde or a ketone) and multiple hydroxyl groups.

Monosaccharides

The simplest form of carbohydrates. They cannot be broken down into smaller carbohydrate units.

Aldoses

Monosaccharides with an aldehyde group.

Ketoses

Monosaccharides with a ketone group.

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Disaccharides

Two monosaccharides joined together by a glycosidic bond.

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Polysaccharides

Long chains of monosaccharides linked together by glycosidic bonds.

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Glycogen

A type of polysaccharide that is the primary storage form of glucose in animals. It is highly branched.

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Cellulose

A structural polysaccharide found in plants. It is a straight chain of glucose units and forms the cell walls of plants.

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Starch

A type of polysaccharide that is the primary storage form of glucose in plants. It is less branched than glycogen.

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Chitin

A structural polysaccharide found in the exoskeletons of insects and crustaceans. It is a modified form of glucose.

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Alpha Glycosidic Bond

A type of glycosidic bond found in starch, where the glucose monomers are linked in a linear chain. It's easily broken down by human enzymes like α-amylases.

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Beta Glycosidic Bond

A type of glycosidic bond found in cellulose, where the glucose monomers are linked with a flip in orientation. Humans lack the necessary enzymes to break these bonds.

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Intestinal Disaccharidases

Enzymes present in the small intestine that break down disaccharides into monosaccharides. This allows for absorption of simple sugars.

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Sodium-dependent glucose cotransporter 1 (SGLT-1)

A protein that transports glucose and galactose from the intestine into the bloodstream, using sodium as a co-transporter.

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Blood Glucose Concentration

The normal blood glucose concentration is maintained at about 5mM (90mg/dL), providing crucial energy for the brain.

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Amylose

A linear, unbranched polymer of glucose. It is a component of starch, and its structure makes it easier for enzymes to break down and release glucose.

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Amylopectin

A branched polymer of glucose. It is a component of starch, and its branched structure allows for faster breakdown and energy release due to more ends for enzymes to work on.

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Proteoglycan

A large molecule composed of a core protein with attached glycosaminoglycans (GAGs). Found in connective tissue and other bodily fluids.

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Glycosaminoglycans (GAGs)

Long, unbranched polysaccharide chains composed of repeating disaccharide units. They are negatively charged, and are found in proteoglycans and the extracellular matrix.

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Glycoprotein

A protein to which short, branched oligosaccharides (glycans) are attached. They play a role in cell signaling, recognition, and other cell functions.

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Glycosylation

The process of adding sugar chains to a protein. It is a common way to modify proteins after they are made.

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Blood Group Antigen

A type of glycoprotein responsible for blood type. The terminal sugar on the glycan determines the blood group.

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Study Notes

Carbohydrates Overview

  • Carbohydrates are a group of carbonyl compounds (aldehydes or ketones) also containing several hydroxyl groups.
  • They have a general formula of (CH₂O)ₙ.
  • Isomers have the same formula but different structures.
  • Fructose and glucose have the formula C₆H₁₂O₆.

Carbohydrate Classification

  • Classification is based on the number of units: monosaccharides, disaccharides, oligosaccharides, polysaccharides.
  • A "-ose" suffix is added to the name.
  • Monosaccharides are further categorized by the type of carbonyl group (aldose or ketose) and the number of carbons (triose, tetrose, etc.).
  • Examples of monosaccharides include trioses (3 carbons), tetroses (4 carbons), pentoses (5 carbons), hexoses (6 carbons), and nonoses (9 carbons).

Monosaccharides

  • Aldoses have an aldehyde group on the first carbon.
  • Ketoses have a ketone group on a carbon other than the first or last.
  • Examples: D-ribose, D-xylose, D-arabinose, D-glucose, D-galactose, D-fructose, D-ribulose.

Disaccharides

  • Formed when two monosaccharides are joined by a glycosidic bond.
  • Examples: Maltose (glucose + glucose), lactose (galactose + glucose), sucrose (glucose + fructose).

Polysaccharides

  • Large polymers of monosaccharides linked by glycosidic bonds.
  • Main energy storage polysaccharides in animals and plants are glycogen and starch.
  • Cellulose is a structural polysaccharide in plants.
  • Chitin is a structural polysaccharide in insects and fungi.

Protein-Carbohydrate Structures

  • Carbohydrates can combine with proteins to form glycoproteins and proteoglycans.
  • Glycoproteins are rich in protein, while proteoglycans are rich in carbohydrate, specifically glycosaminoglycans (GAGs).

Digestion

  • Enzymes called glycosidases break down glycosidic bonds.
  • Humans cannot digest cellulose due to the beta glycosidic bonds.
  • Starch is broken down to glucose by amylase.
  • Disaccharides like sucrose and lactose are broken down further into their monosaccharides.

Absorption

  • Monosaccharides are absorbed into the intestinal mucosa.
  • Sodium-dependent glucose cotransporter (SGLT1) and GLUT transporters are involved.
  • Fructose is absorbed primarily via GLUT-2.

Carbohydrate Metabolism

  • Blood glucose is tightly regulated (maintained around 5 mM or 90 mg/dL).
  • Low or high levels can lead to health issues.
  • Glycolysis breaks down glucose to produce ATP for energy.

Glycoprotein Functions

  • Involved in cell-cell communication, blood type, immune responses, and interactions between cells and hormones.
  • Essential parts of the extracellular matrix.

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