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FUNDAMENTALS OF MEDICINE > SUGARS AND POLYSACCHARIDES > Flashcards

SUGARS AND POLYSACCHARIDES Flashcards

1
Q

What are carbohydrates?

A
  • Consists of carbon, hydrogen and oxygen in a ratio of 1:2:1
  • Major source of energy from diets
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2
Q

What are proteins?

A
  • Coded by precise DNA sequences
  • Approx 20 amino acids (building blocks)
  • Standard peptide link (except for proline)
  • Tightly folded structures
  • Well defined
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3
Q

What are polysaccharides?

A

A large molecule made of many smaller monosaccharides. Monosaccharides are simple sugars, like glucose. Special enzymes bind these small monomers together creating large sugar polymers, or polysaccharides. A polysaccharide is also called a glycan.

  • Synthesized by enzymes without a template
  • Various links (alpha 1,4/1,6, beta 1.4)
  • Range of structures: rod, coil, amorphous
  • Poorly defined
  • Starch, glycogen and cellulose
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4
Q

What are monosaccharides?

A

A monosaccharide is the most basic form of carbohydrates. Monosaccharides can by combined through glycosidic bonds to form larger carbohydrates, known as oligosaccharides or polysaccharides.

  • Contains 3 (trisose) to 7 (heptose) carbon atoms (CH2O)n
  • Aldehydes (HC=O) or ketoses (C=0)
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5
Q

What are enantiomers?

A

They are mirror images of a chiral molecule

  • AKA optical isomers
  • Glucose can be found in nature as either D-Glucose or L-Glucose. The main difference between D and L Glucose is that D-Glucose rotates plane polarized light clockwise whereas L-Glucose rotates plane polarized light anticlockwise
  • D-glucose can be digested
  • L-glucose cannot be digested
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6
Q

Why is L-glucose a laxative?

A

The sugar is not digested so it remains in the gut lumen. The sugar, because of osmosis, draws water in from the surrounding tissue. This extra water then causes the laxative effect.

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7
Q

How are cyclic structures formed?

A

Monosaccharides with 5-6 carbon atoms form cyclic structures

  • The hydroxyl group on C5 reacts with the aldehyde or ketose group
  • Cyclization of glucose produces a new asymmetric centre at C1: Anomeric carbon (C1)
  • The 2 stereo-isomers are called anomers α and β
  • Different anomers of the same sugar are recognised by different enzymes
  • Important for glycosidic bond formation and hydrolysis
  • In solution, equilibrium exists between straight chain and two cyclic forms, cyclic forms are locked and less amenable to modifications
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8
Q

What is a glycosidic bond?

A

A glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group which may or may not be another carbohydrate

  • Bonds formed between 2 OH groups on different sugars leads to a loss of water
  • Catalyzed by specific glycosyltransferases
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9
Q

What are oligosaccharides?

A

Contains 3-10 monosaccharides

-Heparin, blood group antigens

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10
Q

What does a 1,4 link mean?

A

The bond connects carbon atom number 1 in one glucose to carbon atom number 4 in another glucose

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11
Q

Difference between alpha and beta glycosidic bonds

A

ALPHA: GLYCOGEN
-The hydroxyl group attached to carbon number 1 is below the plane of the cyclic ring

BETA: CELLULOSE

  • The hydroxyl group attached to carbon number 1 is above the lane of the ring
  • Hydrogen molecules between adjacent cellulose molecules allow them to form strong fibres

*Amylase in the digestive tract hydrolyses the ALPHA glycosidic bond but is inactive against BETA glycosidic bonds

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12
Q

Where are 1,6 links present?

A

At branching points

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13
Q

What is glycogen?

A

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria.

  • Main storage form of glucose in the body
  • A core protein of glycogenin surrounded by branches of glucose units
  • Insulin acts on hepatocytes to stimulate glycogen synthase
  • Glucose molecules are added to the chains of glycogen as long as both insulin and glucose levels remain high
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14
Q

What breaks down glycogen when it is needed for energy?

A

Glycogen phosphorylase

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15
Q

What are modified sugars?

A

Monosaccharides can be modified to acquire new characteristics and properties
-Modifications are made by replacing the OH group with Phosphates (PO4) to give phosphorylated sugars for energy, amine (NH2) groups to produce amino sugars, sulphate (SO4) groups to give sulfated sugars, lipid groups to give glycolipids and the removal of O to give deoxy sugars

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16
Q

What are phosphorylated sugars?

A

Formed by the transfer of a phosphate group from ATP

  • Important in the metabolism of sugars
  • Eg. Glucose to Glucose-6-phosphate with the use of Hexokinase in the first step of glycolysis to enable metabolism of glucose to pyruvate
17
Q

What are amino sugars?

A

Replacement of a hydroxyl group with an amine (NH2) group to produce amino sugars

  • It is a precursor in lipid biosynthesis, glycoprotein formation
  • Forms part of the structure of chitin (insects) and bacterial cell wall
18
Q

What is protein glycosylation?

A

The addition of a carbohydrate to a protein molecule is referred to as protein glycosylation. It is a common post translational modification for protein molecules involved in cell membrane formation.

  • Glycoproteins formed serve a variety of structural and functional roles in membrane and secreted proteins
  • Majority of proteins synthesized in the rough ER undergo glycosylation
19
Q

What is the function of glycosyl transferases?

A

Enzymes that establish natural glycosidic linkages

  • Activity of different glycosyl transferases leads to the generation of different end group sugars containing amino sugars
  • The different endings determines blood type (Antigen)
  • Response to antigen in blood group tests (Agglutination)
20
Q

What is agglutination?

A

Agglutination is the clumping of particles.

  • It is the process that occurs if an antigen is mixed with its corresponding antibody called isoagglutinin
  • Commonly used in blood grouping
21
Q

What are sulfated sugars?

A

Replacement of hydroxyl group with a sulfate group

  • Common constituents of glycosaminoglycans (GAG’s) in the extracellular matrix
  • Sulphate groups on the GAG’s make them highly negatively charged which makes them bind water and hence caan withstand pressure (eg. cartilage)
22
Q

What are GAG’s?

A

Glycosaminoglycans (GAGs) or mucopolysaccharides are long linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units).
-Because GAGs are highly polar and attract water, they are used in the body as a lubricant or shock absorber.

23
Q

What is heparin?

A

A naturally occurring GAG that acts as anticoagulant

  • Consists of variably-sulphated repeating disaccharide units joined together in a chain
  • Produced by mast cells at sites of damage to blood vessels
24
Q

What are glycolipids?

A

Lipids with a carbohydrate attached by a glycosidic bond

  • Maintains the stability of the cell membrane
  • Facilitates cellular recognition which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues
25
Q

What are bacterial lipopolysaccharides?

A

Bacterial lipopolysaccharides (LPS) are the major outer surface membrane components present in almost all Gram-negative bacteria and act as extremely strong stimulators of innate immunity

  • Microbial pattern recognition receptors of the innate response (TOLL-like receptors. TLR4) responds to LPS from microbes and activates an inflammatory and immune response
  • Anti-LPS antibodies that are bactericidal are produced
  • Present in bone marrow mesenchymal stem cells
26
Q

What are mesenchymal stem cells?

A

Multipotent adult stem cells that are present in multiple tissues, including umbilical cord, bone marrow and fat tissue. Mesenchymal stem cells can self-renew by dividing and can differentiate into multiple tissues including bone, cartilage, muscle and fat cells, and connective tissue.

27
Q

What are deoxy sugars?

A

Sugars that have had a hydroxyl group replaced with a hydrogen atom
-Eg. Deoxyribose, a constituent of DNA, the backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group

FUNDAMENTALS OF MEDICINE (8 decks)

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