Minnesota State University Moorhead

Carbohydrates:

• Carbohydrates are hydrates of carbon.  They have the empirical formula CH20.  CH0 are always found in a 1:2:1 ratio.  

• Examples you are familiar with them as sugars and starches.  

• Functions: 

  • Fuel:  Organisms either take carbohydrates in as food or manufacture them and then break them down ---> energy.

  • Structural--Cellulose is the structural component of the plant cell.  It is the most abundant organic molecule on earth.  

• Carbohydrate Structure:

  • The basic building block of the carbohydrate family are short carbon chains from 3-10 carbon atoms long.  These are called monosaccharides.  They are the monomers of more complex carbohydrates.

    • Draw glucose, a typical monosaccharide

      • It is a hexose--A 6 carbon compound.  sugar, there are also trioses (3), pentoses (5) and others which are common

      • It is an aldose because it has an aldehydo group.  Other sugars such as fructose are ketoses because they have a keto group.  

      • In water glucose forms a ring structure

    • Disaccharides:

      • Monosaccharides linked together to form disaccharides.  This is called a dehydration (condensation) reaction.  

      • The reverse, when disaccharides are broken down are called hydrolytic (the name makes sense--lysis or breakdown with the addition of water.  

    • Polysaccharides:

      • Several polysaccharides can be linked together to form polysaccharides.

      • Examples:

        • Starch-- a 1-4 glucose linkage with branching found in plants only.  No branches in one type of starch and few (one every 24-36 glucose units)

        • Glycogen--as above but with more branching (every 16-24 units)  Molecules are perfectly adapted for their functions.  Animals are more active and need more energy and glycogen is the reserve that is broken down.  The more loose ends which result from the more highly branched structure permit more rapid utilization.

        •  Cellulose--a b 1-4 linkage.  We can't break it down, but the bacteria in the stomach's of ruminant animals can.  That is why cattle can get along on grass but we can't.  

Lipids:  A diverse group of molecules characterized by water insolubility  and solubility in non-polar solvents.  

• Examples--Fats (solid at room temperature) and oils (liquid at room temp)

• Functions:  

  • Structural --Important component of membranes.  Lipids are nonpolar.  They are important in setting up barriers to water in the cell. 

  • Energy source--Lipids have a high energy content.

• Lipid structure:  Hard to generalize because there are several kinds of lipids.  

  • Tri glycerides:--have 2 parts

    • Glycerol--a 3 carbon alcohol

    • Fatty acids--long unbranched carbon chain with a carboxyl group at the end (C00H).  The chain is usually 16-18 C atoms in length.  May be either saturated or unsaturated.  Unsaturated are more fluid.  The fatty acid has hydrophilic and hydrophobic components.  

    • Diagram of the arrangement 

• Phospho lipids--Substitute a phosphate group for a FA.  

  • Phospholipids are found in membranes.  They also have hydrophilic and hydrophobic portions.  

• Steroids-- have complicated interconnected ring structures.  

Proteins:  The most abundant organic molecule within the cell ~ 50 % of the dry weight in many cells.  

• Functions: structural, catalytic (enzymes), carriers hormones, antibodies.  We may still not know the structure of many.  

• Structure:  Proteins are large, complex macromolecules of endless variety and diversity but basically very similar structure.  

  • The repeating unit is the amino acid.  There are 20 different naturally occurring amino acids.  All have an amino group and a carboxyl group connected to a carbon atom.  

  • Amino acids are connected by a peptide bond

• With 20 different repeating units the possible combinations are endless. 

  • A "protein" with 1 AA could have 20 possible structures

  • 2 = 400 (20²)

  • The smallest protein has 50 AA ---(20⁵⁰) combinations.

• We consider protein structure on 4 levels.  

  • Primary structure--The amino acid sequence

  • Secondary Structure (2)

    • a helix--most proteins

      • a spiral 3.6 AA/turn.

      • R groups stick out.

      • Helix is stabilized by H bonds between H and O.  

      • Some aa have R groups whose shapes make the helix impossible.  Then the protein goes on in another configuration until aa are present which permit the helix

    • b form--pleated sheet

      • a zigzag arrangement of chains parallel to each other.  

      • Structure stabilized by H bonds.

      • Like a paper fan 

      • example--silk, collagen

  • Tertiary structure--The characteristic shape which the protein assumes in space as it folds in 3D.  Bonds stabilizing the 3 D structure include:

    • Hydrophobic bonds

    • Disulfide bonds S-S

    • Ionic Bonds

    • H bonds

    • The tertiary structure of a protein is very important.  If it is altered (denaturation of a protein) the characteristic biological activity of a protein is lost.  Denaturing agents include heat, pH, high salt and solvent concentration.  

  • Quartinary Structure:  Association of several chains--Not all proteins have a tertiary structure.

• Protein combinations

  • Metals---> enzymes

  • Vitamins---->cofactors

  • Carbohydrates--->surface materials

  • Lipids-----> lipo proteins.

  • NA ---->nucleoproteins of which chromosomes are composed.

Nucleic Acids:  

• There are two kinds DNA (deoxyribonucleic acid and ribonucleic acid.)

• These are large macro molecules with a repeating unit called the nucleotide.

• Function:  They are informational molecules.  The nucleotide sequence determines the aa sequence of proteins

• Nucleotide structure

  Part	DNA	RNA
  Phosphate Group	+	+
  5 C sugar	deoxyribose	ribose
  N bases (2 types)
  Purines	Adenine (A)	Adenine (A)
  	Guanine (G)	Guanine (G)
  Pyrmindines	Cytosine (C)	Cytosine (C)
  	Thymine	Uracil

• The purine bases are 

• How are they connected ? BSP

• Several are connected via a SP backbone

• The structure of RNA is variable.  There are several kinds of RNA.  We will consider it later.

• Structure of DNA

  • DNA is a double helix.  

  • The two nucleotide strands are held together by H bonding between complementary purine and pyrimidine base pairs.  

  • The sugar phosphate backbone is on the outside.

  • The resulting structure is twisted.

Summary:

There are 4 major groups of organic molecules.

General Roles of these molecules

• Structural

• Energy rich Fuels

• Information that controls growth and development

• Catalysts.

Repeating monomers are linked together by condensation reactions with the removal of water to form macromolecules.  Macromolecules are broken down by hydrolysis reactions with the addition of water.  This what goes on during digestion. 

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